A recent study led by researchers at Rutgers University has revealed that marine heat waves, prolonged periods of abnormally warm ocean temperatures, have not had a significant and lasting impact on the fish communities that support much of the world’s food supply. This discovery stands in stark contrast to the devastating consequences observed in other marine ecosystems following similar warming events, including widespread coral bleaching and harmful algal blooms.
The study, published in the journal Nature, focused on the effects of marine heat waves on commercially important fish species such as flounder, pollock, and rockfish. Researchers analyzed data obtained from extensive scientific trawl surveys conducted between 1993 and 2019 in continental shelf ecosystems across North America and Europe. During this period, they identified 248 marine heat waves characterized by extreme sea bottom temperatures.
Surprisingly, the study found that, in general, marine heat waves did not result in major adverse effects on regional fish communities. While some declines in biomass were observed after certain marine heat waves, these instances were exceptions rather than the rule. Overall, the researchers concluded that the impacts of marine heat waves were indistinguishable from the natural variability in these ecosystems.
Alexa Fredston, the lead author of the study and an assistant professor of ocean sciences at the University of California, Santa Cruz, emphasized that the oceans exhibit high variability, and fish populations naturally fluctuate. While marine heat waves can trigger local changes, the study revealed that most marine heat waves had no lasting impacts on fish communities.
In addition to assessing changes in biomass, the researchers examined whether marine heat waves led to shifts in the composition of fish species within communities, potentially favoring warm-water species over cold-water ones, a phenomenon known as tropicalization.
The findings suggested that fish might be able to seek refuge in cooler waters during marine heat waves, mitigating their impacts. The study’s data included notable examples, such as “the Blob,” a massive marine heat wave in the Northeast Pacific from 2014 to 2016, which led to a 22 percent loss of biomass in the Gulf of Alaska. However, a 2012 marine heat wave in the Northwest Atlantic resulted in a 70 percent biomass gain. Despite these variations, the researchers emphasized that such changes were not large when compared to natural biomass fluctuations.
Malin Pinsky, an associate professor at Rutgers University and a co-author of the study, emphasized the unpredictability of the negative impacts of marine heat waves, noting that each event is akin to rolling the dice, with uncertainty about whether it will be detrimental or not.
The study’s co-authors included researchers from the University of British Columbia, the University of Bern in Switzerland, the National Oceanic and Atmospheric Administration (NOAA), the French Research Institute for Exploitation of the Sea, the University of Montpellier in France, the University of Tromsø in Norway, and Fisheries and Oceans Canada.