Ocean heat waves are threatening marine life, biodiversity
Ocean heat waves are defined as periods of extreme temperatures lasting five days or more. They have become increasingly common in recent decades. In fact, the Earth’s number of annual ocean heat wave days spiked by around 54 percent between 1987 and 2016. That's according to a study published in Nature Climate Change. Abnormally high temperatures are occurring more frequently and are also lasting for longer periods of time.
According to Damian Carrington explaining for the Guardian, underwater heat waves pose a significant threat to marine ecosystems. The ecosystems are already at risk due to several issues. These include overfishing and rampant plastic pollution.
Extreme temperatures exact damage on foundational organisms, including kelp forests, seagrass meadows and coral reefs. These framework species provide shelter and food to many other ocean creatures. The temperatures sweep through oceans much like wildfires blaze through forests on land. Such destruction will likely have cascading consequences for marine biodiversity. The study’s authors make this warning.
Researchers were led by Daniel Smale. He is an ecologist and belongs to Great Britain’s Marine Biological Association. He turned to 116 previously published academic studies to assess the effects of ocean heat waves. The papers yielded data from more than 1,000 ecological records, enabling the team to hone in on multiple recorded instances of unusually high temperatures.
The scientists identified regions and species deemed most vulnerable to temperature surges and reflected on eight specific heat waves.
Areas of the Pacific, Atlantic and Indian Oceans topped the list. The Caribbean’s coral reefs, Australia’s seagrass and California’s kelp forests emerging as particular concerns. That's according to Mary Papenfuss writing for the Huffington Post.
In terms of species, the team notes that stationary plants and animals were the hardest hit, that's according to the Pacific Standard’s Kate Wheeling. Tropical fish and mobile invertebrates were able to cope with the heat by moving to different habitats.
Interestingly, the researchers actually observed heightened levels of fish diversity during periods of above-average temperatures, likely due to the animals’ mass migration toward friendlier waters. The same trend did not prove true for sea-dwelling birds. Shifting habitats limited the avian creatures’ access to prey, according to John Timmer reporting for Ars Technica.
According to Reuters’ Alister Doyle, marine heat waves are triggered by heat from the sun and shifting warm currents. Wheeling further explains that because the phenomenon is measured relative to average ocean temperature, it can occur in any region at any point during the year. El Nin?o is a regularly occurring climate pattern that makes the waters of the central and eastern Pacific warmer than normal. It appears to exacerbate incidents of extreme heat. But, according to The New York Times’ Kendra Pierre-Louis and Nadja Popovich, heat waves can (and do) occur without the presence of El Nin?o.
Although the researchers’ findings are most consequential for marine ecosystems, Pierre-Louis and Popovich explain that damage to ocean habitats will also affect humans who rely on fishing and fish farming.
“Certainly there’s going to be changes with climate change to marine communities, but still the sun is going to shine, and plankton is going to grow, and things are going to eat that plankton, so it's not like the oceans are going to become the dead sea," Nick Bond, a climatologist at the University of Washington tells Pacific Standard. He was not involved in the study.
“It's just that, as a consequence of what we're doing to the oceans, there's going to be different marine communities in different places than what we're used to,” Bond concludes. “Obviously that is a problem because we're sort of set up for what the climate is now rather than what it is going to be in the future."