Ocean warming has been shrinking sea creatures for 450 million years

Marine animals do not just struggle when ocean temperatures spike, they actually shrink, and a massive new study shows this pattern has been repeating for nearly 450 million years.

Researchers built one of the largest collections of marine body size data ever assembled, drawing on almost 9,000 recorded changes and over 1.6 million individual measurements taken from fossils, historical records and living animals. Sea creatures shrank far more sharply during periods of intense global warming compared to crises caused by cooling or falling oxygen levels, suggesting the shrinking already being measured in today’s fish and shellfish is part of a pattern written deep into the planet’s history.

Paulina S Nätscher, a paleobiologist who led the study at Friedrich Alexander Universität Erlangen Nürnberg in Germany, and her team sorted thousands of records into three categories: calm background periods, sharp environmental crises and the recovery periods that followed. Cold-blooded sea creatures, including mussels, crustaceans and fish, consistently shrank whenever a crisis hit, but when researchers separated out warming-linked crises specifically, the shrinking effect was roughly twice as strong compared to other kinds of disasters.

Researchers are describing genuine dwarfing, meaning individual animals within a species actually grew to smaller adult sizes, rather than larger species simply dying out and leaving smaller ones behind. The findings have been published in the journal Proceedings of the National Academy of Sciences.

Image: Wikimedia Commons/by Xplore Dive