When carbon dioxide dissolves in seawater it lowers pH and causes ocean acidification.

Acidification reduces the availability of calcium minerals that corals need to build and repair their skeletons, contributing to bleaching and reef decline.

Shelled pteropods (sea butterflies) have more difficulty building and maintaining shells in more acidic water, and declines in their populations could cascade through the food web and carbon cycle.

Pteropod larvae and life stages present during winter are especially vulnerable because colder water holds more dissolved CO2 and acidification events can overlap with spawning, threatening future cohorts.

Fish can physiologically buffer increased acidity in their blood but doing so carries an energetic cost, and eggs and larvae are generally the most sensitive life stages to warming and acidification.

Laboratory experiments on Pacific cod larvae showed that warming was the dominant stressor while acidification effects were more modest and inconsistent across temperatures.

The provided documents do not report cephalopod-specific results for acidification.

Marine mammals are not described as being affected by acidification in these sources, but they are shown to suffer from other human-caused stressors such as acoustic noise, chemical pollutants (for example PCBs), and microplastics that can impair senses, immunity, and reproduction.

Responses vary by species and life stage and multiple stressors (warming, acidification, pollution) can interact, so species-level and stage-specific data are needed for effective outreach and management.

Conclusion: Ocean acidification most strongly threatens calcifying organisms (corals, pteropods) and stresses early life stages of fish, while the provided documents show marine mammals are mainly harmed by noise, chemical pollution, and plastics; no cephalopod-specific acidification findings appear in these sources.

When carbon dioxide dissolves in seawater it lowers pH and causes ocean acidification.

Title:

Content: Newswise — When carbon dioxide (CO2) enters the oceans, it can make the water more acidic, which is called ocean acidification. This can make it harder for some ocean creatures, like pteropods, to build and keep their shells. Pteropods are important for the ocean environment.

Pteropods are small sea creatures, including shelled sea butterflies. Not much is known about them because of their size, and they don't survive well in captivity. A team of marine scientists studied the life cycles, abundance, and seasonal changes of shelled sea butterflies in the north-east Scotia Sea, where climate change is happening quickly.

Dr Clara Manno, a researcher at the British Antarctic Survey and the corresponding author of the study published in Frontiers in Marine Science, said that the decrease in pteropod populations in the Antarctic Ocean could have significant consequences for the food web and carbon cycle. She also said that understanding the life cycle of this important organism could help to predict the impact of ocean acidification on the Antarctic ecosystem.

Population stability essential for species survival

To study the life cycle, abundance, and seasonal variability of shelled sea butterflies in the north-east Scotia Sea, a team of marine scientists collected sea butterflies in a sediment trap, a sampling device that was anchored at a depth of 400 meters. Since observing the entire life cycle of sea butterflies in a laboratory setting is impossible, the researchers had to gather information about their spawning, growth rate, and population structure. They were able to reconstruct the sea butterflies' life cycle for a year using the samples from the sediment trap.

The scientists found that the two most commonly collected species, Limacina rangii and Limacina retroversa, have different life cycles and therefore have different levels of vulnerability to changes in the ocean. During the winter months, L. rangii, which is a polar species, can be found as both adults and juveniles, while L. retroversa, a subpolar species, is only found as adults during the winter.

Sea butterflies that exist during the coldest season are more vulnerable to increased levels of ocean acidification. This is because ocean water is more acidic during this season than during other times of the year due to cooler temperatures that increase CO2 dissolution in the ocean. The researchers explained that the life stages of sea butterflies during this time are more exposed and vulnerable to the effects of ocean acidification.

L. rangii has a survival advantage over L. retroversa because both adults and juveniles coexist during winter, which reduces the risk of population instability if one cohort is vulnerable. In contrast, if one cohort is removed from L. retroversa, the entire population could be at risk.

Prolonged exposure is a survival challenge

The researchers pointed out that although the two species are affected differently, both are likely to suffer harm if they are exposed to unfavorable conditions for prolonged periods.

The scientists cautioned that the intensifying and prolonged events of ocean acidification overlap with the spring spawning period, posing a threat to the most vulnerable life stage, the larvae. This could endanger the future populations of sea butterflies.

The research team plans to further study the sea butterflies in the Scotia Sea to see how they would be affected by the increase in the intensity and duration of ocean acidification events. They will study multiyear sediment trap samples to identify potential changes in the life cycle that may occur due to environmental changes. Dr Jessie Gardner of the British Antarctic Survey, lead author of the study, said this will be the next step in their research.

Journal Link: Frontiers in Marine Science

What factors lead to damage of coral reefs?

What is the main cause of ocean acidification?

water absorbs carbon dioxide from the atmosphere

Acidification reduces the availability of calcium minerals that corals need to build and repair their skeletons, contributing to bleaching and reef decline.

Title:

Content: Can ‘good sounds’ help coral islands recover from bleaching?

Many coral islands like India’s Lakshadweep are inhabited by people

March 25, 2024 05:30 am | Updated 05:30 am IST

Staghorn corals seen in the waters off Man Nai Island, near Rayong province, Thailand, February 28, 2024. | Photo Credit: Reuters

Climate change is the most serious environmental problem facing the world today. One of the main reasons for this is the global warming caused by the extraction of coal and oil, which have been underground for millennia, and burning them for industrial and non-industrial purposes to generate energy. The effects of these activities were exacerbated by other causes of global warming, such as deforestation.

Global warming has many consequences, including rising sea levels and changes in the frequency of extreme weather. Another is the destruction of coral reefs. India’s Lakshadweep islands for instance are islands formed on such reefs.

Coral reefs have started to die

Coral reefs are built by a type of organism that, when it accumulates, forms reefs and islands. They live in large colonies. Corals have a symbiotic relationship with microscopic algae called zooxanthellae, which live in the corals’ tissues. Life becomes tough when the temperature of the water around them rises. When it does, the corals expel the zooxanthellae. An important visual symptom of these effects is that the colour of the coral reef changes, and subsequently they die off in droves. This event is called bleaching.

However, not all coral bleaching events are due to warm water. Ocean acidification – which is when the pH of the water drops as more carbon dioxide dissolves in it – is another well-known cause. More acidic water reduces the availability of calcium minerals that the corals need to build and repair their exoskeletons.

In many parts of the world, coral reefs have started to die due to global warming experienced over the years. The U.S. lost half of its coral reefs in the Caribbean in one year in 2005 due to a large-scale bleaching event after warm waters around the Virgin Islands and Puerto Rico expanded southward. When scientists collated satellite data of the region from the previous 20 years, they were able to confirm that the 2005 event exerted more thermal stress than those in the previous 20 years combined.

A source of hope

The Great Barrier Reef in Australia is the largest coral reef in the world. Recently many people there protested strongly against a plan to open a new coal mine because they were worried about the survival of the reef – not because the mine would directly affect the reef but because of the effects of burning fossil fuels at large.

Many coral islands like our Lakshadweep are inhabited by people. The destruction of these coral reefs will naturally affect the people there. A rising sea level due to climate change is another problem for them. Many small island countries like Tuvalu and Vanuatu are facing the threat of submergence and have articulated that at international climate conferences. Their submergence is a certainty now; the only question is when it will happen. Therefore, it is very scary that the coral reefs themselves are being destroyed and, axiomatically, any chance of saving the corals can and does become a source of hope.

It is against this background that about 5,000 scientists gathered in New Orleans, in the U.S., in February this year for the American Geophysical Union’s biennial ‘Ocean Sciences’ meeting. Here, Amy Apprill, a scientist at the Woods Hole Oceanographic Institute in Massachusetts and who studies coral reefs, provided information about a study she had been part of.

The coral polyps

To understand this study, we need to first understand what a coral reef is. Coral reefs are built by an organism called a polyp. A coral group is a colony of a large number of genetically identical polyps. Each polyp is a sac-like animal, usually a few millimeters wide and a few centimeters tall. It has a set of tentacles surrounding a mouth-like opening. Polyps are gregarious: they like to socialise.

Every polyp also sheds an exoskeleton at its bottom and over many generations this discarded substance accumulates to form a large structure up to several metres wide. The polyps organise their lives around this structure. A coral reef is formed when a large number of polyps collects in this way.

Polyps use sound to communicate with each other. Naturally, the sound of a healthy colony will differ from that of an unhealthy colony. Dr. Apprill and her team used this distinction in their new study.

The sound of a health colony

The investigators set about examining whether a degraded reef could be enriched by replaying healthy reef sounds, and increasing the rate at which polyps settled in it. They conducted a series of field studies in the Virgin Islands of the U.S., where they quantified the settlement rates of three species of corals with two different breeding strategies.

They found that in degraded coral reefs, the settlement rate increased when such sounds were played (using a novel underwater speaker system). They also reported that the settlement rate was higher closer to the speaker and reduced as one moved away from the speaker, indicating the impact of the sounds played.

Finally, it would be a mistake to think the researchers have solved the reef settlement problem posed by climate change. Their study was just an experiment. If what they did is tested repeatedly and at least a good fraction of instances are successful, then we can decide that their technique can help in practice. But we still don’t know what problems might arise when this project is implemented on a large scale to save coral reefs. We also need to find out the volume at which the sound has to be played and if there are any other parameters to be controlled.

In sum, the new study is just a pointer, even if also a positive one.

V. Sasi Kumar is a scientist formerly at the Centre for Earth Science Studies, Thiruvananthapuram.

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What factors lead to damage of coral reefs?

Shelled pteropods (sea butterflies) have more difficulty building and maintaining shells in more acidic water, and declines in their populations could cascade through the food web and carbon cycle.

Which marine organism is vulnerable to increased levels of ocean acidification?

Which ocean creatures have trouble forming shells due to ocean acidification?

Pteropod larvae and life stages present during winter are especially vulnerable because colder water holds more dissolved CO2 and acidification events can overlap with spawning, threatening future cohorts.

At what stage of life are calcium carbonate-based organisms most vulnerable to changes in water pH?

How do scientists expect ocean acidification to impact specific fish species?

Which marine organism is vulnerable to increased levels of ocean acidification?

Which ocean creatures have trouble forming shells due to ocean acidification?

Fish can physiologically buffer increased acidity in their blood but doing so carries an energetic cost, and eggs and larvae are generally the most sensitive life stages to warming and acidification.

Laboratory experiments on Pacific cod larvae showed that warming was the dominant stressor while acidification effects were more modest and inconsistent across temperatures.

The provided documents do not report cephalopod-specific results for acidification.

Marine mammals are not described as being affected by acidification in these sources, but they are shown to suffer from other human-caused stressors such as acoustic noise, chemical pollutants (for example PCBs), and microplastics that can impair senses, immunity, and reproduction.

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Q&A: Two ways researchers are studying marine microplastics

Tiny pieces of plastic in the ocean might seem innocuous on their own, but their growing presence is a frustrating issue facing marine ecosystems. The particles' small size makes them difficult to clean up, and it also allows them to easily burrow into marine environments or even get ingested by ocean organisms.

Two University of Washington researchers are using very different methods to investigate the issue of marine . Jacqueline Padilla-Gamiño, a UW associate professor of aquatic and fishery sciences, plans to study how microplastics are affecting coral reef ecosystems. Michelle DiBenedetto, a UW assistant professor of mechanical engineering, will study how microplastics move across the surface.

For Earth Day, UW News asked them to discuss their research.

Professor Padilla-Gamiño, your lab's experimental study in 2019 showed that corals are ingesting microplastics along with their typical food. Why are microplastics a problem for corals and other marine organisms?

Jacqueline Padilla-Gamiño: This material can prevent them from feeding, or damage their tissues. Plastics also contain plasticizers—chemicals used to provide flexibility and to reduce brittleness—which may cause hormone disruption and affect the ' reproduction.

What have you learned since then?

JPG: We have continued to explore the abundance and diversity of microplastics in coral reefs, including in water, sediments and other , such as sea cucumbers.

We are also doing other experiments to learn how different types of plastics can affect the performance of corals, because not all plastics are the same.

It's scary to think that corals and other marine organisms, which are already stressed by warming and acidifying oceans, are at the same time also consuming microplastics. How can research offer any hope?

JPG: Research can help us to understand what species are more sensitive to plastics. It can also help us to generate ecological baselines that can be used to assess impacts. Both can help us design strategies to reduce plastic pollution's impacts.

What motivated you to incorporate microplastics into your wider area of research on how climate change affects marine organisms?

JPG: Plastic pollution is a global problem and it is also a carbon dioxide problem. The process of plastic manufacturing creates more than a billion tons of per year. At least 14 million tons of plastic end up in the ocean every year. We need to understand the impacts of these plastics in marine ecosystems.

Professor DiBenedetto, what motivated you to study the movement of microplastics?

Michelle DiBenedetto: Plastic pollution is a relatively new issue and there is still a lot we do not know about what happens to plastic once it is in the ocean. For example, we do not know exactly how long it takes to degrade in the ocean, where it might settle out or at what rates it will be deposited on our beaches.

Many of these processes are influenced by the fluid dynamics in the ocean, such as waves, turbulence, wind and currents. How plastic behaves and is transported in the ocean is an interesting problem because plastic is different from traditionally studied ocean topics, such as bubbles, oil spills, sediment and biology. Thus, it leads to a lot of interesting physical questions that we can study in the lab.

Can you describe what those experiments look like?

MD: We turn on an adjustable wind tunnel that blows over the surface of a wave tank. This creates waves, turbulence and current in the water.

Next, we release particles upstream in the tank. In the middle of the tank, we have an area where we can take images of the particles. We use cameras and lighting to illuminate the particles so we can track their position and orientation (when using non-spherical particles). We either track the particle shadows, or we track the particles themselves.

How will tracking the particles in this way better inform our knowledge of microplastics transport in the ocean? Could this potentially help us design future cleanup methods?

MD: The goal of this research is to be able to develop a fundamental model for microplastics' vertical distribution at the ocean surface: How far below the surface do we expect buoyant microplastics to be mixed under different conditions?

This model would increase the accuracy of simulations of microplastics transport (ocean currents are typically faster at the surface) and degradation rates (sunlight degrades microplastics and is strongest at the surface). A model would also decrease uncertainty in measurements—we have many surface measurements of microplastics, but these need to be corrected for the number of microplastics mixed below the surface.

To design effective cleanup methods, we need to know how fast microplastics leave the ocean surface naturally, so that we can decide the value in designing cleanup methods—or focus our energies on polluting less plastic in the first place. This work's goal is to better our understanding of plastic's natural transport and fate in the ocean so we can decide how best to manage it.

Citation: Q&A: Two ways researchers are studying marine microplastics (2023, April 19) retrieved 19 April 2023 from https://phys.org/news/2023-04-qa-ways-marine-microplastics.html
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The hidden ocean pollution killing marine mammals
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Noise and chemical pollution in our oceans are affecting marine mammals' ability to navigate, communicate and detect danger.
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I've worn glasses since the age of five, my hearing isn't brilliant in busy environments and, like many others, I lost my sense of taste during Covid-19, which was incredibly disorientating. Perhaps once our senses are pushed to their limits, we begin appreciating them all the more. But we're certainly not the only ones relying on multiple senses: marine mammals depend on them to communicate, navigate, feed, hear and detect danger.

It's hard for us to imagine how marine creatures sense within their world. What's clear is that the picture is complex, and that human-induced impacts make that even more challenging.

Pollution is ubiquitous but not homogenous. There is oil and gas exploration on the seabed, military exercises, increasing shipping traffic and the relatively new threat of deep sea mining. Add to that sewage outflows, industrial discharge and agricultural run-off, the marine environment is getting busier, noisier and more polluted. So what are the hidden dangers to marine life?

As a marine strandings volunteer for the Devon Wildlife Trust in south-west England, I'm regularly asked to take photos and measurements of marine mammals stranded along my local coastline. Sometimes, there'll be noticeable injuries, rake marks from the teeth of bottlenose dolphin attacks perhaps, long straight cuts in the skin from a fishing line or occasionally a tail clean cut off as a result of bycatch. Usually though, the actual cause of death isn't simple to identify. A crack team of scientists are on a mission to discover more about how human-induced impacts affect UK populations of whales, dolphins and porpoises.

To find out more about their research, I visited Rob Deaville, a strandings scientist at the UK Cetacean Strandings Investigation Programme, this summer. Every year, he dissects about 150 stranded porpoises, dolphins and whales to find out what might have killed them. "In some cases, it can be very evident, for example bycatch, ship strike, grey seal predation, bottlenose dolphin attack, those causes of death are really obvious. But even a high level of pollution is not necessarily causal in an animal's death, it's more associated," says Deaville. "You're looking through a keyhole at one aspect, at what I call the terminal end, and then trying to look backwards at what that animal has experienced throughout their lifetime.

"High noise pollution or limited prey availability, climate change, chemical pollution all those things have an impact – it's hard to tease that apart for any single individual pressure," he says.

Marine mammals depend on their senses to communicate, navigate, feed, hear and detect danger

Watching Deaville deconstruct this porpoise was a fascinating biology lesson in itself. But more than that it highlighted just how much these creatures can reflect their marine environment and how they live within it. From the parasitic worms living in their lungs, guts and liver to the delicate fish bones found within one of porpoise's three stomachs, every insight is valuable.

But the most crucial of all, Deaville tells me, is the sample of blubber, that fatty layer just beneath the skin, that he cuts from just by the base of the dorsal fin. It's about an inch thick and acts as a ledger – Deaville will send it off for pollutant analysis by expert toxicologists. This helps build a picture of some of the less visible impacts that may be affecting marine life and potentially contribute to their death.

I set out to investigate how the less visible forms of human-induced pollution – both chemical and acoustic – could affect the senses and survival of porpoises, dolphins and whales, and discovered that there's a lot going on beneath the waves.

Super senses

"For whales and dolphins, 'listening' is as important as 'seeing' is for humans, as they live in a world of water and sound," says Danny Groves, communications manager at the non-profit Whale and Dolphin Conservation. He adds that the impacts of human-induced disturbance on cetaceans are "huge".

"Noise pollution threatens whale and dolphin populations, interrupting their normal behaviour, driving them away from areas important to their survival [for breeding, socialising and feeding] and at worst injuring them or sometimes even causing death," he says. Natural impacts such as earthquakes and lightning strikes also make big, sudden noises but tend to be more intermittent.

Toothed whales, a group that includes narwhals, dolphins and porpoises, hunt using echolocation or biosonar. They hear at high frequency ranges. Baleen whales hear at lower frequencies, and may be more affected by shipping noises as a result.

A porpoise autopsy revealed just how much these creatures can reflect their marine environment (Credit: Alamy)

There's more to sound than just noise though. Joy Reidenberg, a professor who studies whale anatomy at Mount Sinai in New York, explains that sound acts as a pressure wave. "Wherever in the body there are air-containing spaces, those can compress, then overexpand as a whale dives and ascends but if tissues can't deform accordingly, they'll rupture," she says. Seismic surveys – used to pinpoint deposits of oil and gas in the seabed – are incredibly intrusive, loud booms of sound. "I'm pretty sure the whale would feel that as a pressure wave moving through their body and also as a sound that they can hear. So there is a tactile aspect to hearing that we often overlook." How much of that pressure is felt by the skin is unknown.

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Chemoreception, that includes both smell and taste, could play a significant role too. Reidenberg explains that baleen whales can possibly smell, while some whales have taste receptors on their tongues but that it's not yet clear what exactly they are detecting. "They tend to swallow prey whole so maybe they are tasting the water to detect when they get close to prey or sensing salinity which may help them navigate," says Reidenberg. "It's even possible that narwhals could sense salinity through the sensitive pores in their tusk – that could be a really important sense."

DO WHALES HAVE WHISKERS?

Baby whales rely on whisker sensation "to help them figure out where the nipple is so they can nurse," says Reidenberg. Whiskers are usually lost by the time these animals become sexually mature, but in some toothed whales, 'pits' remain where the whiskers were.
In some species of dolphins, it has been shown that these pits have the anatomy of electrical sensors.

"So some dolphins plunge their faces into the sand of the seabed and do this spiral manoeuvre with their bodies, possibly detecting the electromagnetic field of a fish buried in the sand," says Reidenberg. Besides detecting prey, she says that hairs could be used to sense water currents flowing past, to indicate when an animal has reached the surface to breathe, or to detect friendly or aggressive encounters from other animals.

Whale vision is "much better than we'd expect it to be," says Reidenberg, though some species rely on it more than others. Indus and Ganges river dolphins are functionally blind because their murky habitat precludes them needing to see. Orcas, on the other hand,spy-hop out of the water when hunting seals and have relatively good eyesight.

An industrialised ocean

Research suggests that all these ways of sensing are being impaired by human activity.

For whales, dolphins and porpoises, both chemical and acoustic pollution affect the way their bodies can function in many ways. Some effects are immediate and acute while others are more long-term and chronic. Besides impacting their senses and ability to communicate, marine pollution can impair their fertility and immune systems.

Thomas Goetz, an expert in bioacoustics at the University of St Andrews in Scotland, studies how marine mammals are affected by human-generated noise and how sound can be used to keep animals away from harm. He explains why context is key: "To really understand the effects of a pollutant, you really need to understand the physiology of this animal, of the sensory systems for each species." Each pollutant in a cetacean's habitat can have different effects. "There's unfortunately no way around looking in real detail and accepting the complexity of it…because they have all evolved very different sensory organs and their perceptual worlds differ," says Goetz.

Acoustic pollution can hinder communication and echolocation sounds, change an animal's behaviour and elevate stress levels. For North Atlantic right whales, low-frequency noise from big ships can result in an increase in stress-related chemicals linked to growth suppression, reduced fertility and poor immune system function. That chronic stress is having a physiological impact.

Sudden and acute impulsive noise in the marine environment might lead to ear trauma haemorrhage, while more chronic exposure from the constant low-level whirr of a shipping lane nearby could perhaps shift its behaviour patterns and make communication or feeding more difficult. Deep-diving whales and dolphins can also suffer from decompression sickness or 'the bends' when they surface too quickly. Over time legions or tears in the internal tissue form due to nitrogen bubble formation, but it's hard to conclude whether that happened due to natural causes or human-induced noise.

"Different species are more sensitive to sound than others," says Deaville, who motions towards the Cuvier's beaked whale tooth on the desk in front of him. "That's the deepest diving cetacean species, it holds its breath for nearly three hours, dives down to 3000m (9843ft) in some instances and is really operating at the edge of what is physiologically possible," he says. "That's perhaps why they are more sensitive to noise disturbance - most of these mid-frequency sonar navy-related mass strandings involved beaked whales, particularly Cuvier's. So I suspect if they dive down as deep as they possibly can they're more at risk of coming to the surface too quickly and getting into conditions that might be problematic."

Scientist Maria Morrel at the University of Veterinary Medicine in Hanover, Germany, is studying the ears and ear bones from stranded toothed whales such as pilot whales and developing a protocol to assess loss of hearing in whales. Once stabilised in formalin to preserve the sample, she analyses the ear using a scanning electron microscope and has noticed that the loss of the tiny hair cells and membrane scarring within the inner ear may indicate loss of auditory function. But when that hearing loss happened exactly and what caused it remains unknown.

SENSORY OVERLOAD

From the microplastics sprayed on farmland to the noxious odours released by sewage plants and the noise harming marine life, pollutants are seeping into every aspect of our existence. Sensory Overload explores the impact of pollution on all our senses and the long-term harm it is inflicting on humans and the natural world.

According to Reidenberg, military sonar pulses act like a sound bomb and certain frequencies could result in decompression sickness. The US Navy, she adds, does its best to protect marine wildlife: "Sonar is well-regulated but in wartime those regulations are lifted – the navy is making extraordinary efforts to tag, track and monitor whales to protect them from sonar exercises."

That said, military operations in Europe have been implicated in mass cetacean deaths. When 85 harbour porpoises stranded along 100km (62 miles) of Danish coastline within one week of each other during April 2005, bycatch was initially established as the cause of death for most, due to net markings on their skin and the loss of tail flukes. Local fishermen confirmed that porpoise bycatch was much higher than usual in nets that had been set to catch lumpfish. Further investigation revealed military ships in the area that week, en route to a huge naval exercise.

In a study, Andrew Wright, a marine mammal researcher from Aarhus University in Denmark, concluded that while the use of sonar cannot be confirmed, it certainly cannot be ruled out as a contributing factor to increased bycatch rates. Perhaps sonar resulted in more porpoises being driven away from the noise towards nets, or perhaps disturbance masked their ability to detect the static fishing gear, he said. As Deaville states, "these things stack up in combination".

That highlights the problem – it's impossible to disentangle every effect.

Besides impacting their senses, marine pollution can impair mammals' fertility and immune systems

Deep-sea mining could also cause severe disturbance, according to new research. Marine researchers estimated that noise from just one mine on the seabed could travel approximately 500km (311 miles) through the water column in gentle weather conditions. In places where multiple mines might operate, the cumulative effect of acoustic pollution could be far greater. Because seabed mining companies have not yet shared their data on noise pollution, this study used noise levels from well-studied industries such as oil and gas industry ships and coastal dredges to model 'conservative' estimates.

The actual seabed mining equipment is far larger and more powerful than the proxies, the experts say. One of the study co-authors, Christine Erbe, a professor in underwater acoustics at Australia's Curtin University, says: "Estimating the noise of future equipment and installations is a challenge, but we don't have to wait until the first mines are operational to discover the noise they make. By identifying the level of noise in the engineering design phase, we can better prepare for how this might impact marine life."

In the Arctic, narwhals – deep-diving whales with the long, protruding unicorn-like tooth – live relatively far from human activity. But as the ice melts, more shipping routes are opening up through this region and oil and gas exploration is increasing. Scientists from the University of California have recently found that when narwhals in Greenland were exposed to seismic air guns (oil and gas survey instruments which produce high-intensity sound bursts), they immediately began diving quickly down from the surface. Normally, they'd glide down to conserve energy, but this speedy escape tactic is affecting how much blood and oxygen circulates in their body. It also distracts from other behaviours such as feeding, according to data collected using monitoring tags.

Rather than having to cope with one threat a time, marine mammals experience the combined pressures of multiple forms of pollution (Credit: Francois Gohier / Getty Images)

All of these invisible pollutants need to be taken into account. Hanna Nuutila, a marine ecology researcher at Swansea University, Wales, says it's vital to appreciate the cumulative effect of different stressors and pathways to disturbance. "Disturbance is both physical such as in-water structures (that includes every single coastal and offshore construction from oil and gas platforms to windfarm piles, harbours and marinas, and renewable energy structures) but also mobile in terms of ships, ferries, tankers and luxury cruisers," she says. She adds that all marine renewables are having to undergo much more detailed scrutiny in terms of impacts on wildlife than oil, gas and nuclear ever did.

"Obviously fishing too causes not just entanglement but also decreasing prey availability. All these tend to have a noise effect as well while most also leak oil, organic waste or chemicals into the sea." Nuutila emphasises the need to create designated safe zones free from human disturbance and the Marine Mammal Protected Areas Task Force runs a global initiative to create just that, in the form of Important to Marine Mammal Areas.

Swimming in a toxic soup

Toxic, synthetic chemicals are perhaps one of the most insidious forms of pollution entering the ocean. The worst culprits are persistent organic pollutants (POPs) that don't break down easily and are lipophilic or fat-loving; they end up in the blubber of porpoises, dolphins and whales. One particularly toxic legacy contaminant – so-called because it's still causing problems decades after being banned – is a class of 209 industrial chemicals known as polychlorinated biphenyls or PCBs. Invented in the 1920s, they  were used in machinery coolant, electrical goods, flame retardants, paints and building sealants. Although banned globally more than 40 years ago, they linger in landfills and escape into the marine environment.

Deaville explains why PCBs are so concerning: "They work in two ways, they affect the immune system, so [animals] might have lots of secondary diseases because [their] immune system is basically knackered and more insidiously they also affect reproduction so in highly PCB-exposed populations there'll be a drop-off in young animals being born.

"A population of whales might not have a calf for a long time even though they should be reproductively active – that to us would be a red flag and indicate potential PCB exposure."

In 2016, an orca known as Lulu was found dead on the coast of the Isle of Tiree, the most westerly island of the Inner Hebrides in Scotland, after becoming entangled in fishing gear. A post-mortem of her body found that her body contained extremely high levels of PCBs (100 times the toxicity threshold for PCBs in marine mammal blubber) and scientists concluded that she was one of the most contaminated animals on the planet in terms of PCB burden. On examination of her ovaries, the scientists at the Scottish marine animal stranding scheme found no evidence of her ever having been reproductively active.

Industrial chemicals known as PCBs linger in landfills and escape into the marine environment, damaging mammals' reproductive systems (Credit: Robertus Pudyanto / Getty Images)

Throughout any animal's lifetime, exposure to pollutants changes from place to place and from time to time. Exposure impacts different species to varying degrees too. Orcas tend to live for longer than porpoises, for example, so they have more time to accumulate chemical pollutants in their bodies. They also feed at a higher level within the food chain, so they are eating bigger fish and other marine mammals which themselves contain contaminants. Deaville explains that POPs are stored within the blubber. When an animal's nutritional state deteriorates, either seasonally or as a result of illness perhaps, those toxic contaminants are released into the blood as the fat layer thins. Toxic chemicals are also passed on to calves via breast milk and so a mother can unwittingly offload toxic pollution onto a firstborn calf, sometimes resulting in death.

Rosie Williams, a toxicologist who works alongside Deaville, found in a 2021 study that high levels of PCBs in blubber samples from 267 stranded harbour porpoises are associated with reduced testicle size in male harbour porpoises. These pollutants are having a direct impact on fertility and potentially affecting the future breeding success of the species. PCBs are also known to suppress the immune system so porpoises with higher contaminant levels are more likely to die from infectious disease

Of course, marine mammals are not experiencing just one chemical at a time. Since it began in 1990, the UK Cetacean Strandings Investigation Programme has carried out more than 4000 necropsies on porpoises, dolphins and whales and tested for a wide range of pollutants, from the widely known banned pesticide DDT to anti-foul paint residues and flame retardants added to textiles. "An animal may be living in a heavily fished area, with lots of bycatch, less prey, heavily contaminated, lots of noise, all those things are happening in tandem all at once – that's how the animal lives its life," Deaville says. "There's a cumulative impact. It's a complex thing to get a handle on."

In the case of the stranded porpoise being dissected in the lab, chemical pollution may well have played a part. In a few months' time, toxicology reports will show more about its specific chemical burden. Ultimately, for Deaville and Williams, it's about noticing changing trends, which could then inform policy and change how pollutants are managed. Plastics are high up on the agenda too – a 2019 study by the University of Exeter found microplastics within all 50 marine mammals sampled that had stranded on UK shores. As yet, the actual impacts of those plastic particles on cetacean survival remains inconclusive.

Experts say that rather than having to cope with threats one at a time, animals experience the combined pressures of multiple forms of pollution within the marine environment. Marine mammals are living in a "soup" of pollution issues, says Deaville. The effects change depending on location or depth, and the animals' season or stage of life, he adds.

So much of the damage and disturbance human activity causes is accidental and preventable, says Tom Mustill, filmmaker and author of a new book called How to Speak Whale. By designing things differently and considering how something might affect other animals, especially whales and dolphins that use such sophisticated communication, we can drastically reduce those negative consequences, he says. Enforcing speed limits on shipping vessels could drastically reduce collisions, for example – on the east coast of the US, proposals to introduce 'dynamic speed zones' could help protect endangered North Atlantic right whales in areas where these marine mammals are detected.

Slower ship speeds give the animals more time to adapt their navigation accordingly and reduce the risk of ship strikes. "This science of discovering what the sensory lives of these animals are like, how they perceive the world and how they communicate within it, allows us to understand how we might impact that and modify our impacts to that. That could be transformative," says Mustill.

As stomach-wrenching as this porpoise post mortem was to witness, it's clear that each stranding provides scientists with invaluable insight into how these cetaceans live and die, and how our actions are impacting them. The next step is to adapt strategies and policies accordingly so that by reducing pollution, marine wildlife and ocean health are better protected.

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Responses vary by species and life stage and multiple stressors (warming, acidification, pollution) can interact, so species-level and stage-specific data are needed for effective outreach and management.

Conclusion: Ocean acidification most strongly threatens calcifying organisms (corals, pteropods) and stresses early life stages of fish, while the provided documents show marine mammals are mainly harmed by noise, chemical pollution, and plastics; no cephalopod-specific acidification findings appear in these sources.


Ocean acidification occurs when carbon dioxide from the atmosphere dissolves into seawater and lowers its pH.

More acidic water reduces the availability of calcium minerals and makes it harder for corals to build and repair their skeletons.

Acidification makes it harder for shelled plankton such as pteropods to form and keep their shells.

Researchers warn that declines in pteropod populations could have major consequences for food webs and the ocean carbon cycle.

Seasonal and regional variation matters because colder water dissolves more CO2, making polar and winter conditions more acidic and exposing vulnerable life stages.

Laboratory experiments on Pacific cod eggs and larvae show that very young fish are sensitive to environmental stressors and that temperature often has larger effects than acidification.

The Pacific cod study reported that acidification effects were modest and inconsistent, and that warming was usually the dominant stressor driving growth, condition, and mortality.

Fish can partially buffer acidity in the bloodstream but doing so requires energy and can reduce growth or condition.

Prolonged or intensified acidification events that overlap with spawning or larval periods increase the risk to early life stages and future populations.

The provided documents describe impacts on corals, shelled plankton (pteropods), and Pacific cod, and they outline other threats to marine mammals such as noise and chemical pollution, but they do not report experimental results or detailed findings for cephalopods or octopuses in relation to acidification.

Summary: Based on the provided documents, ocean acidification directly harms calcifying organisms (for example corals and pteropods), can threaten fish early life stages especially when events overlap with spawning, and interacts with warming and seasonal cold conditions; the supplied context does not include specific findings for cephalopods or octopuses.

Ocean acidification occurs when carbon dioxide from the atmosphere dissolves into seawater and lowers its pH.

Title:

Content: There were 734 press releases posted in the last 24 hours and 394,615 in the last 365 days.

Study explores combined impacts of ocean warming and acidification on pacific cod

Newly hatched Pacific cod larva. (Image credit: NOAA Fisheries/Emily Slesinger)

As the climate changes, the ocean is simultaneously warming and acidifying. Both have been shown to adversely affect the vulnerable early life stages of Pacific cod. But until now, the interplay of these two environmental stressors was unknown.

new NOAA Fisheries study takes a look into the future by replicating predicted Alaska ocean conditions in the laboratory. The study is the first to look at the interactive effects of ocean warming and acidification on Pacific cod. Researchers evaluated the growth and survival of eggs and larvae at combinations of temperature and acidity representing current and future ocean environments. The findings can help improve predictions to ensure climate-ready Alaska fisheries and communities in the future.

Alaska Fish Face Multiple Climate-Driven Stressors

Ocean warming and acidification are escalating faster in Alaska and other high latitude regions than anywhere else on the planet. Alaska produces more than half of the nation’s wild-caught seafood. Local communities depend on the ecosystem for their livelihoods. Understanding how climate-driven stressors will affect these valuable resources is critical to ensuring resilient Alaska communities and a strong blue economy in the future.

Because fish are cold-blooded, temperature profoundly affects their growth and behavior. The effects of acidification are more nuanced. Fish can buffer acidity in the bloodstream but at an energetic cost.

Very young fish—eggs and larvae—tend to be the most sensitive stages of the fish life cycle to both warming and acidification. Unlike adult fish that can move to cooler waters, these tiny creatures are incapable of migrating to more favorable conditions. Subtle differences in their growth and condition can make a big difference to the number of young fish that make it to the adult population.

Laboratory set up for ocean acidification and ocean warming experiments with early stages of Pacific cod. Large tanks in the background provide chilled and ambient seawater that are mixed to temperature. Small round tanks house eggs and larvae at different temperatures and acidification levels. Acidification is controlled by bubbling carbon dioxide into the seawater: more carbon dioxide causes higher acidity (lower pH). (Image credit: NOAA Fisheries/Emily Slesinger)

Pacific cod is an important subsistence food, a key species in the food web, and the second-largest commercial groundfish catch in Alaska. Understanding how warming and acidification together may affect this ecologically, culturally, and commercially valuable species is key to predicting future climate impacts.

“Knowing how individual species will respond to multiple climate stressors helps us put together this puzzle to figure out what species are more vulnerable than others,” Emily Slesinger said. “And that will help guide ecosystem-based fisheries management to ensure their sustainability.”

Partnerships and Unique Laboratory Capabilities Expand Possibilities for Studying Alaska Species

Finding answers posed some hurdles. “It’s really challenging to study these fish that are found in remote and cold environments,” Slesinger said.

They met those challenges through partnerships and a specially equipped laboratory facility.

Fishermen played a key role. To obtain eggs and larvae for experiments, they first needed live adults, ready to spawn. Commercial fishermen used baited fishing pots to catch adults off Kodiak Island during the spawning season.

Fertilized eggs were shipped to the NOAA Fisheries Alaska Fisheries Science Center Laboratory in Newport, Oregon. The eggs and larvae were reared at six combinations of temperature (3°C, 6°C, 10°C) and acidification (ambient and high acidity). Scientists measured their hatch success, growth, nutritional condition, and mortality throughout the nine-week experiment.

“The Newport lab is very special,” Slesinger said. “What is most unique is our seawater system that can chill water to Arctic temperatures. The lab has the capacity to house many fish at all life stages and the expertise to keep them thriving. And it has the facilities to run these complicated experiments on the younger life stages.”

Experiments Reveal a Dominant Stressor

The study found that overall, Pacific cod’s early life stages were more sensitive to warming than to acidification:

  • Temperature affected all measured traits: growth, condition, and mortality
  • Mortality of both eggs and larvae was highest at the warmest temperature
  • 6°C was the optimal temperature for hatching, condition, and survival
  • At the warmest temperature (10°C), Pacific cod grew the fastest but were in poor condition with high mortality rates
  • At the coldest temperature (3°C), mortality rates were lower, but both growth and condition were also low
  • Acidification effects were more modest and inconsistent
  • The single instance of a negative effect of acidification was at the optimal 6°C temperature

“We’re seeing that either temperature or acidification drove the response—they were not additive. At optimal temperatures, Pacific cod may be impaired by acidification. At the warm temperature, they were overwhelmingly negatively impacted, but there was pretty much no effect of acidification,” Slesinger said. “Our findings suggest that temperature is the dominant stressor and ocean warming is likely the greater threat.”

The research highlights the complexity of species- and stage-specific responses to multiple climatic stressors and the importance of understanding them.

“This work is exciting because we are able to provide information about these fish that can be useful for future management. It is really important to me that my research can be directly helpful to societies, economies, and communities,” Slesinger said. “This research contributes to our common goal of ensuring productive, sustainable fishing into the future.”

Ecomagazine, 30 April 2024. Press release.

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Content: Newswise — When carbon dioxide (CO2) enters the oceans, it can make the water more acidic, which is called ocean acidification. This can make it harder for some ocean creatures, like pteropods, to build and keep their shells. Pteropods are important for the ocean environment.

Pteropods are small sea creatures, including shelled sea butterflies. Not much is known about them because of their size, and they don't survive well in captivity. A team of marine scientists studied the life cycles, abundance, and seasonal changes of shelled sea butterflies in the north-east Scotia Sea, where climate change is happening quickly.

Dr Clara Manno, a researcher at the British Antarctic Survey and the corresponding author of the study published in Frontiers in Marine Science, said that the decrease in pteropod populations in the Antarctic Ocean could have significant consequences for the food web and carbon cycle. She also said that understanding the life cycle of this important organism could help to predict the impact of ocean acidification on the Antarctic ecosystem.

Population stability essential for species survival

To study the life cycle, abundance, and seasonal variability of shelled sea butterflies in the north-east Scotia Sea, a team of marine scientists collected sea butterflies in a sediment trap, a sampling device that was anchored at a depth of 400 meters. Since observing the entire life cycle of sea butterflies in a laboratory setting is impossible, the researchers had to gather information about their spawning, growth rate, and population structure. They were able to reconstruct the sea butterflies' life cycle for a year using the samples from the sediment trap.

The scientists found that the two most commonly collected species, Limacina rangii and Limacina retroversa, have different life cycles and therefore have different levels of vulnerability to changes in the ocean. During the winter months, L. rangii, which is a polar species, can be found as both adults and juveniles, while L. retroversa, a subpolar species, is only found as adults during the winter.

Sea butterflies that exist during the coldest season are more vulnerable to increased levels of ocean acidification. This is because ocean water is more acidic during this season than during other times of the year due to cooler temperatures that increase CO2 dissolution in the ocean. The researchers explained that the life stages of sea butterflies during this time are more exposed and vulnerable to the effects of ocean acidification.

L. rangii has a survival advantage over L. retroversa because both adults and juveniles coexist during winter, which reduces the risk of population instability if one cohort is vulnerable. In contrast, if one cohort is removed from L. retroversa, the entire population could be at risk.

Prolonged exposure is a survival challenge

The researchers pointed out that although the two species are affected differently, both are likely to suffer harm if they are exposed to unfavorable conditions for prolonged periods.

The scientists cautioned that the intensifying and prolonged events of ocean acidification overlap with the spring spawning period, posing a threat to the most vulnerable life stage, the larvae. This could endanger the future populations of sea butterflies.

The research team plans to further study the sea butterflies in the Scotia Sea to see how they would be affected by the increase in the intensity and duration of ocean acidification events. They will study multiyear sediment trap samples to identify potential changes in the life cycle that may occur due to environmental changes. Dr Jessie Gardner of the British Antarctic Survey, lead author of the study, said this will be the next step in their research.

Journal Link: Frontiers in Marine Science

What is the main cause of ocean acidification?

water absorbs carbon dioxide from the atmosphere

What is the main cause of ocean acidification?

water absorbs carbon dioxide from the atmosphere

More acidic water reduces the availability of calcium minerals and makes it harder for corals to build and repair their skeletons.

Title:

Content: Can ‘good sounds’ help coral islands recover from bleaching?

Many coral islands like India’s Lakshadweep are inhabited by people

March 25, 2024 05:30 am | Updated 05:30 am IST

Staghorn corals seen in the waters off Man Nai Island, near Rayong province, Thailand, February 28, 2024. | Photo Credit: Reuters

Climate change is the most serious environmental problem facing the world today. One of the main reasons for this is the global warming caused by the extraction of coal and oil, which have been underground for millennia, and burning them for industrial and non-industrial purposes to generate energy. The effects of these activities were exacerbated by other causes of global warming, such as deforestation.

Global warming has many consequences, including rising sea levels and changes in the frequency of extreme weather. Another is the destruction of coral reefs. India’s Lakshadweep islands for instance are islands formed on such reefs.

Coral reefs have started to die

Coral reefs are built by a type of organism that, when it accumulates, forms reefs and islands. They live in large colonies. Corals have a symbiotic relationship with microscopic algae called zooxanthellae, which live in the corals’ tissues. Life becomes tough when the temperature of the water around them rises. When it does, the corals expel the zooxanthellae. An important visual symptom of these effects is that the colour of the coral reef changes, and subsequently they die off in droves. This event is called bleaching.

However, not all coral bleaching events are due to warm water. Ocean acidification – which is when the pH of the water drops as more carbon dioxide dissolves in it – is another well-known cause. More acidic water reduces the availability of calcium minerals that the corals need to build and repair their exoskeletons.

In many parts of the world, coral reefs have started to die due to global warming experienced over the years. The U.S. lost half of its coral reefs in the Caribbean in one year in 2005 due to a large-scale bleaching event after warm waters around the Virgin Islands and Puerto Rico expanded southward. When scientists collated satellite data of the region from the previous 20 years, they were able to confirm that the 2005 event exerted more thermal stress than those in the previous 20 years combined.

A source of hope

The Great Barrier Reef in Australia is the largest coral reef in the world. Recently many people there protested strongly against a plan to open a new coal mine because they were worried about the survival of the reef – not because the mine would directly affect the reef but because of the effects of burning fossil fuels at large.

Many coral islands like our Lakshadweep are inhabited by people. The destruction of these coral reefs will naturally affect the people there. A rising sea level due to climate change is another problem for them. Many small island countries like Tuvalu and Vanuatu are facing the threat of submergence and have articulated that at international climate conferences. Their submergence is a certainty now; the only question is when it will happen. Therefore, it is very scary that the coral reefs themselves are being destroyed and, axiomatically, any chance of saving the corals can and does become a source of hope.

It is against this background that about 5,000 scientists gathered in New Orleans, in the U.S., in February this year for the American Geophysical Union’s biennial ‘Ocean Sciences’ meeting. Here, Amy Apprill, a scientist at the Woods Hole Oceanographic Institute in Massachusetts and who studies coral reefs, provided information about a study she had been part of.

The coral polyps

To understand this study, we need to first understand what a coral reef is. Coral reefs are built by an organism called a polyp. A coral group is a colony of a large number of genetically identical polyps. Each polyp is a sac-like animal, usually a few millimeters wide and a few centimeters tall. It has a set of tentacles surrounding a mouth-like opening. Polyps are gregarious: they like to socialise.

Every polyp also sheds an exoskeleton at its bottom and over many generations this discarded substance accumulates to form a large structure up to several metres wide. The polyps organise their lives around this structure. A coral reef is formed when a large number of polyps collects in this way.

Polyps use sound to communicate with each other. Naturally, the sound of a healthy colony will differ from that of an unhealthy colony. Dr. Apprill and her team used this distinction in their new study.

The sound of a health colony

The investigators set about examining whether a degraded reef could be enriched by replaying healthy reef sounds, and increasing the rate at which polyps settled in it. They conducted a series of field studies in the Virgin Islands of the U.S., where they quantified the settlement rates of three species of corals with two different breeding strategies.

They found that in degraded coral reefs, the settlement rate increased when such sounds were played (using a novel underwater speaker system). They also reported that the settlement rate was higher closer to the speaker and reduced as one moved away from the speaker, indicating the impact of the sounds played.

Finally, it would be a mistake to think the researchers have solved the reef settlement problem posed by climate change. Their study was just an experiment. If what they did is tested repeatedly and at least a good fraction of instances are successful, then we can decide that their technique can help in practice. But we still don’t know what problems might arise when this project is implemented on a large scale to save coral reefs. We also need to find out the volume at which the sound has to be played and if there are any other parameters to be controlled.

In sum, the new study is just a pointer, even if also a positive one.

V. Sasi Kumar is a scientist formerly at the Centre for Earth Science Studies, Thiruvananthapuram.

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What factors lead to damage of coral reefs?

Acidification makes it harder for shelled plankton such as pteropods to form and keep their shells.

Which ocean creatures have trouble forming shells due to ocean acidification?

Researchers warn that declines in pteropod populations could have major consequences for food webs and the ocean carbon cycle.

Which marine organism is vulnerable to increased levels of ocean acidification?

Seasonal and regional variation matters because colder water dissolves more CO2, making polar and winter conditions more acidic and exposing vulnerable life stages.

At what stage of life are calcium carbonate-based organisms most vulnerable to changes in water pH?

What is the main cause of ocean acidification?

water absorbs carbon dioxide from the atmosphere

Which regions are most affected by ocean acidification?

Laboratory experiments on Pacific cod eggs and larvae show that very young fish are sensitive to environmental stressors and that temperature often has larger effects than acidification.

At what stage of life are calcium carbonate-based organisms most vulnerable to changes in water pH?

How do scientists expect ocean acidification to impact specific fish species?

it will affect their physiology and growth

The Pacific cod study reported that acidification effects were modest and inconsistent, and that warming was usually the dominant stressor driving growth, condition, and mortality.

Fish can partially buffer acidity in the bloodstream but doing so requires energy and can reduce growth or condition.

How do scientists expect ocean acidification to impact specific fish species?

it will affect their physiology and growth

Prolonged or intensified acidification events that overlap with spawning or larval periods increase the risk to early life stages and future populations.

At what stage of life are calcium carbonate-based organisms most vulnerable to changes in water pH?

How do scientists expect ocean acidification to impact specific fish species?

How does elevated water acidity affect fish ability to survive?

What factors lead to damage of coral reefs?

The provided documents describe impacts on corals, shelled plankton (pteropods), and Pacific cod, and they outline other threats to marine mammals such as noise and chemical pollution, but they do not report experimental results or detailed findings for cephalopods or octopuses in relation to acidification.

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Content: Loading
The hidden ocean pollution killing marine mammals
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Noise and chemical pollution in our oceans are affecting marine mammals' ability to navigate, communicate and detect danger.
I

I've worn glasses since the age of five, my hearing isn't brilliant in busy environments and, like many others, I lost my sense of taste during Covid-19, which was incredibly disorientating. Perhaps once our senses are pushed to their limits, we begin appreciating them all the more. But we're certainly not the only ones relying on multiple senses: marine mammals depend on them to communicate, navigate, feed, hear and detect danger.

It's hard for us to imagine how marine creatures sense within their world. What's clear is that the picture is complex, and that human-induced impacts make that even more challenging.

Pollution is ubiquitous but not homogenous. There is oil and gas exploration on the seabed, military exercises, increasing shipping traffic and the relatively new threat of deep sea mining. Add to that sewage outflows, industrial discharge and agricultural run-off, the marine environment is getting busier, noisier and more polluted. So what are the hidden dangers to marine life?

As a marine strandings volunteer for the Devon Wildlife Trust in south-west England, I'm regularly asked to take photos and measurements of marine mammals stranded along my local coastline. Sometimes, there'll be noticeable injuries, rake marks from the teeth of bottlenose dolphin attacks perhaps, long straight cuts in the skin from a fishing line or occasionally a tail clean cut off as a result of bycatch. Usually though, the actual cause of death isn't simple to identify. A crack team of scientists are on a mission to discover more about how human-induced impacts affect UK populations of whales, dolphins and porpoises.

To find out more about their research, I visited Rob Deaville, a strandings scientist at the UK Cetacean Strandings Investigation Programme, this summer. Every year, he dissects about 150 stranded porpoises, dolphins and whales to find out what might have killed them. "In some cases, it can be very evident, for example bycatch, ship strike, grey seal predation, bottlenose dolphin attack, those causes of death are really obvious. But even a high level of pollution is not necessarily causal in an animal's death, it's more associated," says Deaville. "You're looking through a keyhole at one aspect, at what I call the terminal end, and then trying to look backwards at what that animal has experienced throughout their lifetime.

"High noise pollution or limited prey availability, climate change, chemical pollution all those things have an impact – it's hard to tease that apart for any single individual pressure," he says.

Marine mammals depend on their senses to communicate, navigate, feed, hear and detect danger

Watching Deaville deconstruct this porpoise was a fascinating biology lesson in itself. But more than that it highlighted just how much these creatures can reflect their marine environment and how they live within it. From the parasitic worms living in their lungs, guts and liver to the delicate fish bones found within one of porpoise's three stomachs, every insight is valuable.

But the most crucial of all, Deaville tells me, is the sample of blubber, that fatty layer just beneath the skin, that he cuts from just by the base of the dorsal fin. It's about an inch thick and acts as a ledger – Deaville will send it off for pollutant analysis by expert toxicologists. This helps build a picture of some of the less visible impacts that may be affecting marine life and potentially contribute to their death.

I set out to investigate how the less visible forms of human-induced pollution – both chemical and acoustic – could affect the senses and survival of porpoises, dolphins and whales, and discovered that there's a lot going on beneath the waves.

Super senses

"For whales and dolphins, 'listening' is as important as 'seeing' is for humans, as they live in a world of water and sound," says Danny Groves, communications manager at the non-profit Whale and Dolphin Conservation. He adds that the impacts of human-induced disturbance on cetaceans are "huge".

"Noise pollution threatens whale and dolphin populations, interrupting their normal behaviour, driving them away from areas important to their survival [for breeding, socialising and feeding] and at worst injuring them or sometimes even causing death," he says. Natural impacts such as earthquakes and lightning strikes also make big, sudden noises but tend to be more intermittent.

Toothed whales, a group that includes narwhals, dolphins and porpoises, hunt using echolocation or biosonar. They hear at high frequency ranges. Baleen whales hear at lower frequencies, and may be more affected by shipping noises as a result.

A porpoise autopsy revealed just how much these creatures can reflect their marine environment (Credit: Alamy)

There's more to sound than just noise though. Joy Reidenberg, a professor who studies whale anatomy at Mount Sinai in New York, explains that sound acts as a pressure wave. "Wherever in the body there are air-containing spaces, those can compress, then overexpand as a whale dives and ascends but if tissues can't deform accordingly, they'll rupture," she says. Seismic surveys – used to pinpoint deposits of oil and gas in the seabed – are incredibly intrusive, loud booms of sound. "I'm pretty sure the whale would feel that as a pressure wave moving through their body and also as a sound that they can hear. So there is a tactile aspect to hearing that we often overlook." How much of that pressure is felt by the skin is unknown.

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Chemoreception, that includes both smell and taste, could play a significant role too. Reidenberg explains that baleen whales can possibly smell, while some whales have taste receptors on their tongues but that it's not yet clear what exactly they are detecting. "They tend to swallow prey whole so maybe they are tasting the water to detect when they get close to prey or sensing salinity which may help them navigate," says Reidenberg. "It's even possible that narwhals could sense salinity through the sensitive pores in their tusk – that could be a really important sense."

DO WHALES HAVE WHISKERS?

Baby whales rely on whisker sensation "to help them figure out where the nipple is so they can nurse," says Reidenberg. Whiskers are usually lost by the time these animals become sexually mature, but in some toothed whales, 'pits' remain where the whiskers were.
In some species of dolphins, it has been shown that these pits have the anatomy of electrical sensors.

"So some dolphins plunge their faces into the sand of the seabed and do this spiral manoeuvre with their bodies, possibly detecting the electromagnetic field of a fish buried in the sand," says Reidenberg. Besides detecting prey, she says that hairs could be used to sense water currents flowing past, to indicate when an animal has reached the surface to breathe, or to detect friendly or aggressive encounters from other animals.

Whale vision is "much better than we'd expect it to be," says Reidenberg, though some species rely on it more than others. Indus and Ganges river dolphins are functionally blind because their murky habitat precludes them needing to see. Orcas, on the other hand,spy-hop out of the water when hunting seals and have relatively good eyesight.

An industrialised ocean

Research suggests that all these ways of sensing are being impaired by human activity.

For whales, dolphins and porpoises, both chemical and acoustic pollution affect the way their bodies can function in many ways. Some effects are immediate and acute while others are more long-term and chronic. Besides impacting their senses and ability to communicate, marine pollution can impair their fertility and immune systems.

Thomas Goetz, an expert in bioacoustics at the University of St Andrews in Scotland, studies how marine mammals are affected by human-generated noise and how sound can be used to keep animals away from harm. He explains why context is key: "To really understand the effects of a pollutant, you really need to understand the physiology of this animal, of the sensory systems for each species." Each pollutant in a cetacean's habitat can have different effects. "There's unfortunately no way around looking in real detail and accepting the complexity of it…because they have all evolved very different sensory organs and their perceptual worlds differ," says Goetz.

Acoustic pollution can hinder communication and echolocation sounds, change an animal's behaviour and elevate stress levels. For North Atlantic right whales, low-frequency noise from big ships can result in an increase in stress-related chemicals linked to growth suppression, reduced fertility and poor immune system function. That chronic stress is having a physiological impact.

Sudden and acute impulsive noise in the marine environment might lead to ear trauma haemorrhage, while more chronic exposure from the constant low-level whirr of a shipping lane nearby could perhaps shift its behaviour patterns and make communication or feeding more difficult. Deep-diving whales and dolphins can also suffer from decompression sickness or 'the bends' when they surface too quickly. Over time legions or tears in the internal tissue form due to nitrogen bubble formation, but it's hard to conclude whether that happened due to natural causes or human-induced noise.

"Different species are more sensitive to sound than others," says Deaville, who motions towards the Cuvier's beaked whale tooth on the desk in front of him. "That's the deepest diving cetacean species, it holds its breath for nearly three hours, dives down to 3000m (9843ft) in some instances and is really operating at the edge of what is physiologically possible," he says. "That's perhaps why they are more sensitive to noise disturbance - most of these mid-frequency sonar navy-related mass strandings involved beaked whales, particularly Cuvier's. So I suspect if they dive down as deep as they possibly can they're more at risk of coming to the surface too quickly and getting into conditions that might be problematic."

Scientist Maria Morrel at the University of Veterinary Medicine in Hanover, Germany, is studying the ears and ear bones from stranded toothed whales such as pilot whales and developing a protocol to assess loss of hearing in whales. Once stabilised in formalin to preserve the sample, she analyses the ear using a scanning electron microscope and has noticed that the loss of the tiny hair cells and membrane scarring within the inner ear may indicate loss of auditory function. But when that hearing loss happened exactly and what caused it remains unknown.

SENSORY OVERLOAD

From the microplastics sprayed on farmland to the noxious odours released by sewage plants and the noise harming marine life, pollutants are seeping into every aspect of our existence. Sensory Overload explores the impact of pollution on all our senses and the long-term harm it is inflicting on humans and the natural world.

According to Reidenberg, military sonar pulses act like a sound bomb and certain frequencies could result in decompression sickness. The US Navy, she adds, does its best to protect marine wildlife: "Sonar is well-regulated but in wartime those regulations are lifted – the navy is making extraordinary efforts to tag, track and monitor whales to protect them from sonar exercises."

That said, military operations in Europe have been implicated in mass cetacean deaths. When 85 harbour porpoises stranded along 100km (62 miles) of Danish coastline within one week of each other during April 2005, bycatch was initially established as the cause of death for most, due to net markings on their skin and the loss of tail flukes. Local fishermen confirmed that porpoise bycatch was much higher than usual in nets that had been set to catch lumpfish. Further investigation revealed military ships in the area that week, en route to a huge naval exercise.

In a study, Andrew Wright, a marine mammal researcher from Aarhus University in Denmark, concluded that while the use of sonar cannot be confirmed, it certainly cannot be ruled out as a contributing factor to increased bycatch rates. Perhaps sonar resulted in more porpoises being driven away from the noise towards nets, or perhaps disturbance masked their ability to detect the static fishing gear, he said. As Deaville states, "these things stack up in combination".

That highlights the problem – it's impossible to disentangle every effect.

Besides impacting their senses, marine pollution can impair mammals' fertility and immune systems

Deep-sea mining could also cause severe disturbance, according to new research. Marine researchers estimated that noise from just one mine on the seabed could travel approximately 500km (311 miles) through the water column in gentle weather conditions. In places where multiple mines might operate, the cumulative effect of acoustic pollution could be far greater. Because seabed mining companies have not yet shared their data on noise pollution, this study used noise levels from well-studied industries such as oil and gas industry ships and coastal dredges to model 'conservative' estimates.

The actual seabed mining equipment is far larger and more powerful than the proxies, the experts say. One of the study co-authors, Christine Erbe, a professor in underwater acoustics at Australia's Curtin University, says: "Estimating the noise of future equipment and installations is a challenge, but we don't have to wait until the first mines are operational to discover the noise they make. By identifying the level of noise in the engineering design phase, we can better prepare for how this might impact marine life."

In the Arctic, narwhals – deep-diving whales with the long, protruding unicorn-like tooth – live relatively far from human activity. But as the ice melts, more shipping routes are opening up through this region and oil and gas exploration is increasing. Scientists from the University of California have recently found that when narwhals in Greenland were exposed to seismic air guns (oil and gas survey instruments which produce high-intensity sound bursts), they immediately began diving quickly down from the surface. Normally, they'd glide down to conserve energy, but this speedy escape tactic is affecting how much blood and oxygen circulates in their body. It also distracts from other behaviours such as feeding, according to data collected using monitoring tags.

Rather than having to cope with one threat a time, marine mammals experience the combined pressures of multiple forms of pollution (Credit: Francois Gohier / Getty Images)

All of these invisible pollutants need to be taken into account. Hanna Nuutila, a marine ecology researcher at Swansea University, Wales, says it's vital to appreciate the cumulative effect of different stressors and pathways to disturbance. "Disturbance is both physical such as in-water structures (that includes every single coastal and offshore construction from oil and gas platforms to windfarm piles, harbours and marinas, and renewable energy structures) but also mobile in terms of ships, ferries, tankers and luxury cruisers," she says. She adds that all marine renewables are having to undergo much more detailed scrutiny in terms of impacts on wildlife than oil, gas and nuclear ever did.

"Obviously fishing too causes not just entanglement but also decreasing prey availability. All these tend to have a noise effect as well while most also leak oil, organic waste or chemicals into the sea." Nuutila emphasises the need to create designated safe zones free from human disturbance and the Marine Mammal Protected Areas Task Force runs a global initiative to create just that, in the form of Important to Marine Mammal Areas.

Swimming in a toxic soup

Toxic, synthetic chemicals are perhaps one of the most insidious forms of pollution entering the ocean. The worst culprits are persistent organic pollutants (POPs) that don't break down easily and are lipophilic or fat-loving; they end up in the blubber of porpoises, dolphins and whales. One particularly toxic legacy contaminant – so-called because it's still causing problems decades after being banned – is a class of 209 industrial chemicals known as polychlorinated biphenyls or PCBs. Invented in the 1920s, they  were used in machinery coolant, electrical goods, flame retardants, paints and building sealants. Although banned globally more than 40 years ago, they linger in landfills and escape into the marine environment.

Deaville explains why PCBs are so concerning: "They work in two ways, they affect the immune system, so [animals] might have lots of secondary diseases because [their] immune system is basically knackered and more insidiously they also affect reproduction so in highly PCB-exposed populations there'll be a drop-off in young animals being born.

"A population of whales might not have a calf for a long time even though they should be reproductively active – that to us would be a red flag and indicate potential PCB exposure."

In 2016, an orca known as Lulu was found dead on the coast of the Isle of Tiree, the most westerly island of the Inner Hebrides in Scotland, after becoming entangled in fishing gear. A post-mortem of her body found that her body contained extremely high levels of PCBs (100 times the toxicity threshold for PCBs in marine mammal blubber) and scientists concluded that she was one of the most contaminated animals on the planet in terms of PCB burden. On examination of her ovaries, the scientists at the Scottish marine animal stranding scheme found no evidence of her ever having been reproductively active.

Industrial chemicals known as PCBs linger in landfills and escape into the marine environment, damaging mammals' reproductive systems (Credit: Robertus Pudyanto / Getty Images)

Throughout any animal's lifetime, exposure to pollutants changes from place to place and from time to time. Exposure impacts different species to varying degrees too. Orcas tend to live for longer than porpoises, for example, so they have more time to accumulate chemical pollutants in their bodies. They also feed at a higher level within the food chain, so they are eating bigger fish and other marine mammals which themselves contain contaminants. Deaville explains that POPs are stored within the blubber. When an animal's nutritional state deteriorates, either seasonally or as a result of illness perhaps, those toxic contaminants are released into the blood as the fat layer thins. Toxic chemicals are also passed on to calves via breast milk and so a mother can unwittingly offload toxic pollution onto a firstborn calf, sometimes resulting in death.

Rosie Williams, a toxicologist who works alongside Deaville, found in a 2021 study that high levels of PCBs in blubber samples from 267 stranded harbour porpoises are associated with reduced testicle size in male harbour porpoises. These pollutants are having a direct impact on fertility and potentially affecting the future breeding success of the species. PCBs are also known to suppress the immune system so porpoises with higher contaminant levels are more likely to die from infectious disease

Of course, marine mammals are not experiencing just one chemical at a time. Since it began in 1990, the UK Cetacean Strandings Investigation Programme has carried out more than 4000 necropsies on porpoises, dolphins and whales and tested for a wide range of pollutants, from the widely known banned pesticide DDT to anti-foul paint residues and flame retardants added to textiles. "An animal may be living in a heavily fished area, with lots of bycatch, less prey, heavily contaminated, lots of noise, all those things are happening in tandem all at once – that's how the animal lives its life," Deaville says. "There's a cumulative impact. It's a complex thing to get a handle on."

In the case of the stranded porpoise being dissected in the lab, chemical pollution may well have played a part. In a few months' time, toxicology reports will show more about its specific chemical burden. Ultimately, for Deaville and Williams, it's about noticing changing trends, which could then inform policy and change how pollutants are managed. Plastics are high up on the agenda too – a 2019 study by the University of Exeter found microplastics within all 50 marine mammals sampled that had stranded on UK shores. As yet, the actual impacts of those plastic particles on cetacean survival remains inconclusive.

Experts say that rather than having to cope with threats one at a time, animals experience the combined pressures of multiple forms of pollution within the marine environment. Marine mammals are living in a "soup" of pollution issues, says Deaville. The effects change depending on location or depth, and the animals' season or stage of life, he adds.

So much of the damage and disturbance human activity causes is accidental and preventable, says Tom Mustill, filmmaker and author of a new book called How to Speak Whale. By designing things differently and considering how something might affect other animals, especially whales and dolphins that use such sophisticated communication, we can drastically reduce those negative consequences, he says. Enforcing speed limits on shipping vessels could drastically reduce collisions, for example – on the east coast of the US, proposals to introduce 'dynamic speed zones' could help protect endangered North Atlantic right whales in areas where these marine mammals are detected.

Slower ship speeds give the animals more time to adapt their navigation accordingly and reduce the risk of ship strikes. "This science of discovering what the sensory lives of these animals are like, how they perceive the world and how they communicate within it, allows us to understand how we might impact that and modify our impacts to that. That could be transformative," says Mustill.

As stomach-wrenching as this porpoise post mortem was to witness, it's clear that each stranding provides scientists with invaluable insight into how these cetaceans live and die, and how our actions are impacting them. The next step is to adapt strategies and policies accordingly so that by reducing pollution, marine wildlife and ocean health are better protected.

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Which ocean creatures have trouble forming shells due to ocean acidification?

Which ocean creatures have trouble forming shells due to ocean acidification?

Which ocean creatures have trouble forming shells due to ocean acidification?

Which ocean creatures have trouble forming shells due to ocean acidification?

Summary: Based on the provided documents, ocean acidification directly harms calcifying organisms (for example corals and pteropods), can threaten fish early life stages especially when events overlap with spawning, and interacts with warming and seasonal cold conditions; the supplied context does not include specific findings for cephalopods or octopuses.