January 2023

A SEM image of part of a calcified colony showing the individual functional units called zooids with brood chambers (ovicells) and defensive structures (avicularia) of the Antarctic bryozoan Astochoporella cassidula, which was one of the 549 species of bryozoans used in our study. Here, we provided the largest carbonate mineralogical dataset to date for Southern Ocean bryozoans, which are diverse, abundant and important as carbonate producers, thus making them excellent for monitoring the effects of ocean warming and acidification. We then assessed latitudinal and seafloor temperature patterns of skeletal mineralogy using bryozoan species occurrences together with temperature data for the first time. We found that the proportions of high- Mg calcite and bimineralic species increased significantly towards lower latitudes and with increasing seawater temperature. These patterns are consistent with the hypothesis that seawater temperature is likely a significant driver of variations in bryozoan mineralogy at a global scale. Our findings suggest that the combined effects of ocean warming and acidification may be seen first in high-Mg calcite species inhabiting in Antarctic coastal areas that have rapidly warmed in recent years such as the Western Antarctic Peninsula. Credit: Blanca Figuerola.

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