Carbonate mineralogy and geochemistry of bryozoans along the South African coast

Abstract The main aim of this study was to investigate whether environmental or biological factors predominantly influence bryozoan mineralization along the South African coast (spanning from 29.263°S; 16.87°E to 27.540°S; 32.677°E), a region known for its diverse oceanographic conditions. New data into the mineralogical (calcite vs. aragonite) and geochemical (Mg content in calcite) composition of bryozoans are provided thereby enhancing the global database and understanding of biomineralization patterns. To date, there has been a notable scarcity of data on bryozoan skeletal composition in tropical and subtropical regions, representing a significant gap in our knowledge and understanding of the impacts of climate change on marine, calcifying organisms. Our research reveals a diverse array of carbonate skeletons across nearly half of the known bryozoan species in the region, with calcitic forms dominating, followed by bimineralic and aragonite-based forms. The prevalence of aragonite-containing skeletons, particularly within the Cheilostomatida, mirrors global patterns, indicating a correlation with sea temperature gradients. Significant mineralogy and magnesium calcite variability exist within the Flustrina and Membraniporina suborders (Cheilostomatida). Despite exploring various environmental parameters such as temperature, salinity, or impact of currents (Agulhas, Benguela, or mixed), no clear correlation with mineralogical patterns emerged. Instead, the study underscores the substantial influence of biological factors (including specific chemical, biochemical, or genetic controls), on bryozoan skeletal carbonate mineralogy and geochemistry. These findings highlight the importance of comprehensive, multi-parametric analyses to unravel environmental signals in bryozoan biomineralization, contributing to a deeper understanding of the impacts of climate and local conditions on marine calcifiers.