Warming seas could lead to a decline in body size for most marine mollusks—such as clams, snails, and oysters—by 2100, according to a recent study led by scientists at the University of Louisiana at Lafayette. This research challenges the long-held belief that warmer oceans will uniformly shrink marine life. The study, titled "Nonuniform resizing of marine life under climate change," was published in the Proceedings of the National Academy of Sciences. Researchers examined over 23,000 species of marine mollusks and found that while most ocean regions are expected to see a reduction in body size by 2100, the effects are not uniform across all species or regions. To reach their conclusions, the scientists combined over 2.79 million records of species occurrences with body-size measurements. This data helped them analyze how factors like temperature, oxygen levels, and ocean productivity influence the size of five major groups of mollusks. The researchers then projected these trends across 10 major ocean basins under both high- and low-emissions climate scenarios. Their work relied on extensive historical data compiled in open biodiversity databases, including the Marine Organismal Body Sizes database, developed with the help of a postdoctoral researcher at the University of Helsinki. Under a high-emissions scenario, the study predicts that about two-thirds of the mollusk groups and ocean regions examined will experience significant decreases in body size. In some cases, average body length could drop by as much as 16% by 2100. These reductions in length can result in even greater losses in biomass. For instance, a 16.2% decrease in the average length of clams in the Baltic Sea could translate to a 41% drop in their average body mass. However, not all species are expected to shrink. In the Arctic Ocean, cephalopods—such as squid and octopuses—and tusk shells are projected to grow larger under high emissions, with average lengths increasing by 2.9% and 3.3%, respectively. The differences in how species respond to warming depend largely on both their biology and geographic location. Cephalopods, for example, have high oxygen needs but also efficient circulatory systems and fast life cycles, which may allow them to thrive or even grow larger in warmer conditions. In contrast, heavily shell-building groups like bivalves and gastropods seem more vulnerable to shrinking. The severity of these changes is also strongly influenced by future greenhouse gas emissions. Under a low-emissions scenario, significant declines in body size were projected for only 14 out of 50 group-and-ocean-basin combinations studied—less than half the number expected under high emissions. Meanwhile, the number of species projected to grow larger remained roughly the same. Mollusks play vital roles in ocean ecosystems, from filtering water and cycling nutrients to supporting fisheries and food security.