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Global fisheries threatened by climate change

A team of researchers led by the Queensland University of Technology (QUT) has recently found that the diet quality of fish across the world’s oceans could decline by up to ten percent as climate change impacts critical parts of marine food chains. This could have major repercussions, threatening global fisheries and the livelihoods of billions of people worldwide.

The researchers investigated the possible impact of climate change on zooplankton, a highly abundant and diverse group of microscopic marine animals accounting for over 40 percent of the world’s marine biomass and representing the primary link between phytoplankton (which converts sunlight and nutrients into energy) and larger fish.

“Despite their abundance, diversity, and critical importance in transferring energy from phytoplankton to fish, knowledge about what shapes the composition of zooplankton communities across the world’s oceans is relatively limited,” said study lead author Ryan Heneghan, a lecturer in Mathematical Sciences at QUT.

“This is a challenge, since if zooplankton are affected by climate change, this could have important implications for the ocean’s ability to sequester carbon emissions, and the productivity of fisheries.”

The experts used a global marine ecosystem model to assess how the impact of climate change on all the major zooplankton groups – from single-cell zooplankton to krill and jellyfish – may affect the diet quality of larger fish feeding on zooplankton. The analysis revealed that future zooplankton communities will be increasingly dominated by carnivorous groups (such as chaetognaths) and gelatinous groups (like salps and larvaceans), at the expense of small crustacean omnivores such as copepods or krill.

Since gelatinous groups can directly access smaller phytoplankton for food, they may provide an effective shortcut for the transfer of energy from increasingly dominant phytoplankton to fish. 

“This shortcut partially offsets the increase in the number of steps from phytoplankton to fish from shrinking phytoplankton and increases in carnivorous zooplankton. But it comes at a cost: these groups are gelatinous, having about five percent of the carbon contained in omnivorous zooplankton such as krill and copepods. In terms of nutrition, this would be like replacing a rib-eye steak with a bowl of jelly,” Heneghan explained.

“As a result, our model projects that the diet quality of small fish could decline across large areas of the world’s oceans, which would exacerbate declines in fish biomass from climate change by up to 10 percent.”

“For human societies, this could have far-reaching implications globally, since according to the United Nations Food and Agriculture Organization fisheries are a key ecosystem service worth US$150 billion a year, providing more than 20 percent of dietary animal protein for 3.3 billion people, and supporting 60 million livelihoods,” he concluded.

The study is published in the journal Nature Climate Change.

By Andrei Ionescu, Staff Writer

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