Were it not for the oceans, climate change would have already made Earth uninhabitable. The world’s oceans have absorbed more than 90% of the warming created by humans since the 1970s. Had that heat gone into the atmosphere, global average temperatures would have jumped by almost 56 degrees Celsius. However, our oceans have their limits. Persistently rising temperatures are having destructive impacts on marine life.
Previous studies have shown that warmer waters have been threatening to cause mass migration of marine species in search of the right conditions for feeding and spawning. Change in water temperatures directly impacts the development and growth of most fish and cephalopods. The survival of coral reefs, mangroves, seagrasses, and other critical habitat-forming species are also at risk due to the rise of sea-levels.
Environmental Protection Agency’s Climate Change in the US: Benefits of Global Action report revealed that dramatic loss of shallow coral cover is predicted to occur without action on climate change. For instance, coral cover in Hawaii is projected to decline from 38% to about 5% by 2050. Corals, which provide vital fish spawning habitat and support for thousands of marine species, are having a hard time creating and maintaining the skeletal structures needed for their support and protection.
One-Sixth of Marine Life Could Disappear By 2100
A 2019 report conducted by Australian climate experts warned that human civilization could end by 2050 due to the destabilizing societal and environmental factors caused by a rapidly warming planet. The findings also showed that we will see a large decrease in the biomass of the oceans if the world doesn’t slow climate change. "Healthy oceans are required for planetary stability. Aggressive global action to slow climate change is a moral imperative,” University of Georgia marine biologist Samantha Joye said.
According to CBSNews, the news division of American television and radio service CBS, the researchers discovered that for every degree Celsius that the world’s oceans warm, the total mass of sea animals is projected to drop by 5%. Thus, if the world's greenhouse gas emissions stay at the present rate, there would be a 17% loss of biomass by the year 2100. Unfortunately, the biggest animals in the oceans are going to be hit hardest, according to study co-author Derek Tittensor, a marine ecologist at the United Nations World Conservation Monitoring Center in England.
"The good news here is that the main building blocks of marine life, plankton and bacteria may decline less heavily, the bad news is that those marine animals that we use directly, and care about most deeply, are predicted to suffer the most as climate change is working its way up the food chain," co-author Boris Worm, a marine biologist at Dalhousie University in Canada, said.
Another 2019 study found that local populations of marine animals are disappearing at double the rate of land-based species because they are more likely to be living near the threshold of life-threatening temperatures. At the same time, there are fewer places in the ocean where marine animals can hide from extreme heat. According to Inside Climate News, a non-profit news organization, focusing on environmental journalism, the findings were based on global research across more than 500 species. The researchers calculated safe temperatures for 88 marine and 294 land species, found the coolest temperatures available to each species during the hottest parts of the year, and identified whether warming had driven population loss for 159 species.
They found out that 56% of the marine species they studied experienced a range contraction due to global warming, compared to 27% of the land species. "These results are stunning, in part because the impacts of climate change on ocean life were virtually ignored just a decade ago," said Malin Pinsky, an ocean researcher at Rutgers University.
Additionally, several recent intense ocean heatwaves have already affected ocean systems, killing coral reefs, seabirds, and seagrass and leading to harmful invasions by non-native species. Denmark-based ocean researcher Mark Payne explained that even if the temperatures return to normal, the damage is done for the next 10 years. "Many of the changes will happen quickly and suddenly in response to marine heatwaves, and you just don't come back from these things quickly, especially long-lived species,” he said.
Marine Species Are Relocating
Marine species are hardly coping with the continuous increase of temperatures, but they are doing everything they can to survive. A recent study conducted by researchers from the University of Bristol and Exeter found out that marine species are changing as oceans warms. For instance, populations of Atlantic herring and Adélie penguins are declining in the warmer areas of their habitat and increasing in abundance at the cooler areas.
The team analyzed over 300 marine species spanning more than 100 years and reviewed 540 published records of species abundance to investigate how they are responding to warmer climates. The findings published in Current Biology showed a general pattern of species having increasing numbers on their poleward sides and losses toward the equator. According to Science Daily, an American website that aggregates press releases and publishes lightly edited press releases about science, the researchers found out that marine species are now more abundant at the poleward side of species ranges compared at the equatorward side of species ranges.
Senior author Martin Genner, an evolutionary ecologist at the University of Bristol, explained that the findings not only show the large-scale changes in the abundance of species but also suggests that climate change is affecting marine species in a highly consistent and non-trivial way. "This matters because it means that climate change is not only leading to abundance changes, but intrinsically affecting the performance of species locally. We see species such as Emperor penguin becoming less abundant as water becomes too warm at their equatorward edge, and we see some fish such as European seabass thriving at their poleward edge where historically they were uncommon,” Genner said.
While some marine species appear to benefit from climate change, some suffer as they are not able to adapt fast enough to survive warming. Unfortunately, both of these could be alarming. According to Environmental Journal, an online site that aims to highlight cutting edge practice from across the globe, champion innovation and lead debate, both increasing and decreasing abundances may have harmful knock-on effects for the wider ecosystem.
“We anticipate that marine species will be increasingly affected by climate change. This may lead to opportunity, such as greater catches of warm-water fishes that were previously uncommon. However, there could be negative effects for coastal livelihoods, for example, if warming seas enable harmful warm-water parasites to thrive in aquaculture systems where previously they were rare,” author Louise Rutterford said.