Marine Biodiversity Faces Double-Barreled Blast of Human Trouble

Climate change and industrial-scale fishing should be tackled simultaneously in order to prevent potentially catastrophic ecosystem collapse in the world's most diverse marine environments, according to new research.

Six marine biodiversity hotspots in the Atlantic, Indian and Pacific Oceans are being severely impacted by climate change and overfishing, according to the paper published in Science Advances.

"We have critical areas, where you have a long-term anomaly in the environment and those areas are also of high biodiversity," said André Chiaradia, a penguin biologist and one of the study's co-authors. "In some cases these places have extra pressure from commercial fisheries."

The study is the first to overlap global species distribution in oceans with marine areas most at risk from climate change and aimed to identify areas of marine conservation priority around the globe.

In order to do so, researchers compiled a database of 2,183 marine animals and more than three decades worth of information on sea surface temperatures, ocean currents and marine productivity.

They also evaluated industrial fishing data from the Food and Agriculture Organization from the last 60 years.

The environmental data showed an uneven distribution of changes to the Earth's oceans between 1979 and 2014, with the most striking shifts at the poles and the tropics.

Due to global warming, scientists found significant changes to water temperatures, current circulation and nutrient availability.

As the global average temperature has increased, the majority of extra heat has been absorbed by the oceans, leading to changes in the ocean's density, or stratification, the study said.

Increased stratification prevents water and nutrients mixing, which can hamper primary production that forms the basis of the food chain.

Water from melting ice sheets and glaciers, meanwhile, can influence the behavior of ocean currents, changing the marine ecosystem.

To get an idea about how these environmental changes could impact marine life, the researchers identified six marine biodiversity hotspots, all concentrated in the Southern Hemisphere.

They included the Pacific waters off Peru and the Galápagos Islands, stretches of the Atlantic Ocean around Argentina and Uruguay, the coastline stretching from South Africa to Kenya, the central western Pacific Ocean, the waters around New Zealand and eastern and southern Australia, and marine areas in Oceania and the central Pacific Ocean.

Global distribution of marine biodiversity with colors indicating the number of species — red indicating areas with the highest biodiversity.

When the global hotspots were overlaid with fisheries data "a worrying coincidence" was revealed where the world's richest areas for marine biodiversity were those mostly affected by overfishing and climate change, the study said.

"We knew about the fishery impact and high biodiversity. But guess what? These areas have seen a lot of environmental change as well," Chiaradia said.

Although it is unclear on what scale environmental stressors will impact these hotspots, it is unlikely to be beneficial in most cases, according to the study.

Warming oceans may affect production of nutrients essential for bigger animals, while changes to ocean currents could affect food availability.

Combined with the impacts of overfishing, which the authors said had decimated about 70 percent of world fish stocks since World War II, biodiversity hotspots will be put under even greater pressure in the future.

"Accordingly, climate and fishing impacts should not be treated in isolation from each other when it comes to conservation of marine biodiversity," the authors argue.

Read more at Discovery News