Which Marine Species Are Most at Risk From Climate Change?

We all know that the world is warming under the effects of climate change and even our deep oceans aren’t escaping the rise in temperature. Climate change poses a major challenge to many of our marine species as they struggle to adapt at the same rate the ecosystem around them is changing. Today, the link between mitigating climate change and conserving vulnerable habitats and species is clearer than ever before, yet what species are we most at risk of losing if we don’t cut down our emissions?

Our planet has been warming since the industrial revolution but do you know that in that time, one third of our greenhouse gas emissions have been absorbed by the ocean alongside an astonishing 90% of the excess heat created by humans? Whilst our terrestrial environments may seem to be taking the brunt of extreme weather, such as droughts, wildfires and tropical storms, our oceans are suffering from their own array of disasters. Sea ice is melting at a worrying rate whilst sea temperatures rise around the world, causing a mass migration of species towards the poles, leading to local disappearance. As carbon dioxide enters the ocean, it creates a more acidic environment in which creatures must live whilst additionally, as the sea warms, water molecules are no longer as good at holding onto dissolved oxygen and so it bubbles to the surface and escapes into the air. This means some patches of ocean now hold dangerously low levels of oxygen where few species can live. Unlike rising temperatures and increased acidification, low oxygen is not something the majority of our marine life can adapt to. A recent study has revealed that if our greenhouse gas emissions continue on the same trajectory, a terrifying one third of all our marine animals could disappear in the next 300 years as our planet faces its the sixth mass extinction event. Let’s look at the species most at risk if we fail to curb our consumption.

The most iconic species associated with climate change is, of course, the polar bear and with good reason too as scientists believe they could become extinct as soon as 2100. The polar bear capital of the world is Churchill, Canada, a town on the edge of the Hudson Bay where leaving your car unlocked so it can act as a safe escape for passers-by from polar bears is the norm. Yet the polar bear population here has dropped by almost 30% in only five years due to dwindling sea ice. These unique lumbering creatures are drawn to the area because of the frozen Hudson Bay which acts as the perfect platform from which to hunt seals. However over the last few decades, the sea ice has melted earlier in spring and formed later in the year, making the hunting window shorter than ever. Polar bears aren’t fussy and will often eat berries, eggs, rodents and even reindeer to top up their meals but nothing can equal seal blubber for its fat content which will keep the bears going through the long cold fasting months. If we reach ice free summers as is predicted by 2050, our polar bear populations will begin to decline as researchers have found that after fasting for 180 days, the reproductive success of these creatures is negatively impacted, leading to fewer and fewer cubs. If we reach this stage, some sub-populations are likely to collapse with only those living in the high Arctic surviving. This species really do show the inextricable link connecting conservation and climate change, for no matter how many national parks we create or how many captive breeding programmes we try, if the environment is too warm, they simply won’t survive. 

Tracking collars used on polar bears have already shown that over the last 40 years, these bears have gone from spending a couple of weeks on land in summer to two months as the lack of sea ice prevents them from hunting. Over the last year, our understanding of the bears living in the Russian Arctic has fallen as the war prevents scientists from entering the region but the small isolated population living in south east Greenland can offer some hope. These bears have been seen to adapt by using freshwater ice which breaks off from glaciers in the fjords and allows them to hunt during the eight months of the year when sea ice is non-existent in the area, giving us a sign that small pockets of species may survive the changing environment. 

Similarly, ringed seals are also suffering from the rapidly vanishing sea ice as they rely on it to provide a base for mating, giving birth and resting. As the level of snow cover decreases, these seals are finding it harder to build sturdy snow caves in which to raise their young and with the ice melting earlier, these cosy homes often collapse before the pups are fully grown, leaving them open to predation, hypothermia and losing their mum who is still essential for providing food at this stage. In addition, warmer waters are providing the perfect home for pathogens that lead to deadly diseases for this species.

Hawaiian monk seals are similarly losing their resting places although in the much more exotic climes of the tropics. These are one of the world’s rarest seal species with only 1,200 remaining, yet their habitat is at risk. These seals spend one third of their time resting on the beaches of low lying islands and atolls, however with sea levels rising, these beaches are being lost to the sea. Whilst Hawaii is full of beaches, many have been developed and are now on incredibly busy sections of coastline, leaving these rare seals with few options for important quiet resting spots.

The green sea turtle is facing a more unique problem, specifically the population which lives on the Great Barrier Reef in Australia. These turtles are highly sensitive to changes in temperature, particularly in the egg stage as the sex of baby turtles is determined by the temperature of the sand in which the eggs are buried. The threshold appears to be 29.1 degrees Celsius, above which eggs hatch as females and below which hatch as males. With temperatures rising, more and more females are being born and on one Australian island, males are now outnumbered 116 to 1! This is creating a large and looming reproductive issue which threatens the size of the next generation. Conservationists are currently trialling various methods of cooling the sand however, using natural and artificial shade as well as rainwater and seawater irrigation. So far this has proved successful, with more male turtles being born and those which develop in shaded nests are found to be faster hatchlings, giving them a greater chance of survival in the first 48 hours of life.

Whilst the fate of fish doesn’t often make conservation headlines in favour of more iconic species, the changing future of our fish is actually already impacting some of our ocean’s largest creatures. For example, schooling fish, such as sardines and anchovies, are now found to be diving deeper and further offshore, partly in order to reach cooler waters but also because the phytoplankton they feed on are no longer rising in such abundance from the deep to the surface as the mixing of ocean layers slows due to the complex effects of climate change. This means our larger species which feed on small fish are also heading further away from the coast and into the depths. In 2015, California saw a particularly warm summer and conservationists found that thousands of sea lions were lying ill on the beaches. It is thought that due to a lack of nearshore food, mothers headed out to sea earlier than normal to forage, leaving their pups too soon before they are able to survive on their own. Krill are another species which form an important layer of the food web but these are thought to be declining in the Arctic due to a lack of sea ice which they use as shelter. With blue whales eating up to four tonnes of krill a day, these tiny critters are incredibly important in the food chain and affect multiple species.

Finally, shell forming sea creatures, such as crabs, oysters and corals, are struggling with the increasingly acidic waters which are arising from carbon dioxide being absorbed by the ocean. In some areas of the Pacific, sea snails have already been seen to be unable to form their shells properly as the acid affects the delicate calcium carbonate which builds the shell. Scientists believe we will reach a point where the seawater is so corrosive that the whole shell may dissolve, proving fatal to species such as these. Similarly, corals around the world are becoming increasingly stressed due to rises in water temperature which is causing them to bleach. This is when the algae which live inside the coral, providing their colour and essential nutrients, are expelled, leaving corals more open to death and disease. Increasing ocean acidification also leads to slower growth rates amongst corals which massively impacts the entire ecosystem as whilst reefs only occupy 0.1% of the seafloor, they are home to 25% of all marine life; that means they hold more biodiversity than rainforests!

Whilst the future for some of our beloved species may appear bleak, it’s not too late for us to make a difference! In order to cut down on greenhouse gas emissions, each and every one of us needs to and is able to play our part, giving us the chance to help marine species on the other side of the planet to ourselves as well as the ones closer to home.

By Neve McCracken-Heywood