August 4, 2022 — The future may be smaller for sea life, according to a new scientific model. Influenced by warming oceanic conditions, microbes and megafauna may not grow as large as they do now.
This shrinking effect, should it occur, could have wide repercussions: reduced food mass at the bottom of the food chain would affect fisheries, leaving less food for people, as well as mean less carbon sequestered in the sea, potentially making climate change worse.
Scientists say the ability to accurately predict these impacts could improve management of ocean resources. But researchers don’t agree on exactly why this sea life shrinkage is happening, and say a variety of factors may need to be considered to make accurate forecasts.
In the new study, researchers present a mathematical model that explains these size reductions as a response to lower oxygen levels in the ocean. Looking at rising temperature and reduced oxygen level forecasts for the next decades, researchers found that zooplankton and other microscopic species could be up to 30% smaller, with impacts reverberating higher up the food chain.
There is a “temperature-size rule,” that describes the tendency for ectotherms (animals whose body temperature regulation depends on external sources) to reach smaller adult sizes under warmer conditions. With climate change escalating, the implications for marine life — and humanity — could be dire.
But so far, direct experimental evidence for this rule mostly comes from organisms with a body mass of less than 1 gram, explained study lead author Curtis Deutsch, a climate scientist at Princeton University in the U.S.
“Our mechanistic model tries to quantify that effect and use it to understand how much smaller things might get in the future,” explained Deutsch, who collaborated with ocean biologists and a paleobiologist to formulate the model. The results “suggest that larger fish [further up the food chain] will also be subject to shrinkage.”