Coastal fisheries quickly bounce back from marine heat waves

In a new study led by Rutgers University, researchers have discovered that coastal fisheries are surprisingly resilient to marine heat waves. The experts report that prolonged periods of warm ocean temperatures have not had a lasting effect on the fish communities that feed most of the world.

Study lead author Alexa Fredston conducted the research as a postdoctoral associate in the Global Change Research Group, part of the Department of Ecology, Evolution and Natural Resources in the Rutgers School of Environmental and Biological Sciences (SEBS).

“There is an emerging sense that the oceans do have some resilience, and while they are changing in response to climate change, we don’t see evidence that marine heat waves are wiping out fisheries,” said Fredston.

How the research was conducted 

The researchers analyzed the impacts of 248 marine heat waves on commercially important fish such as flounder and rockfish. 

They used data from long-running trawl surveys of continental shelf ecosystems in North America and Europe between 1993 and 2019. 

What the researchers learned 

The study showed that, in general, the marine heat waves did not have destructive effects on regional fish communities. 

In some cases, the team found that prolonged periods of heat were linked to declines in biomass, which refers to the total quantity of fish in a given area.

Natural variability 

Overall, however, the effects of marine heat waves are not distinguishable from the natural variability in these ecosystems, said the researchers.

“The oceans are highly variable, and fish populations vary quite a lot,” said Fredston, who is now an assistant professor of ocean sciences at University of California, Santa Cruz. “Marine heat waves can drive local change, but there have been hundreds of marine heat waves with no lasting impacts.”

Fish species distribution 

In addition to looking at biomass, the researchers examined whether marine heat waves have altered the species found in various fish communities. This transition may include the loss of cold water fish and an increase in fish that are associated with warmer temperatures.

In a process ķnown as tropicalization, heat-seeking fish can expand their habitats into temperate waters as the oceans warm. 

The results showed that marine heatwaves were not consistently associated with tropicalization or the loss of cold-affiliated species in these ecosystems.

Resilient fisheries

The findings suggest that fish seek refuge by moving to areas with cooler water during marine heat waves, which the researchers defined as periods of more than five days with extreme sea bottom temperatures for that region and season.

On the other hand, the experts identified examples of marine heat waves that did have profound impacts on fish communities. The 2014-2016 marine heat wave in the Northeast Pacific known as “the Blob” is one of the largest on record.

The experts report that while The Blob led to a 22 percent loss of biomass in the Gulf of Alaska, a 2012 marine heat wave in the Northwest Atlantic led to a 70 percent biomass gain. 

According to the researchers, these changes were not substantial compared to natural variability in biomass, and similar effects were not seen after most other marine heat waves.

“We found that these negative impacts are unpredictable and that other heat waves had no strong impacts,” said study co-author Malin Pinsky, an associate professor in the Department of Ecology, Evolution and Natural Resources and director of the Global Change Research Group at SEBS. “This means that each heat wave that hits is like rolling the dice: Will it be a bad one or not? We don’t know until it happens.”

The study is published in the journal Nature.

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