Predicting the range expansion of larger benthic foraminifera under earth's changing climate.

Larger benthic foraminifera (LBF) are major carbonate producers in shallow marine ecosystems and serve as sensitive indicators of environmental change on continental shelves. We developed and tested species distribution models for four peneroplid species (Peneroplis planatus, P. pertusus, P. arietinus, and Coscinospira hemprichii) using 355 occurrence records from the Arabian Gulf and 32 environmental variables to predict their range expansion under the current climate change and future scenarios. Beyond well-established temperature controls, our models identified iron concentration (68% of explained variance), light attenuation (21%), and dissolved oxygen (10%) as the primary environmental drivers of LBF distributions. The models achieved exceptional predictive accuracy with 92% Area Under the Receiver Operating Characteristic Curve (AUROC) for regional validation and 85% AUROC when extrapolated globally, demonstrating strong transferability across ocean basins. Climate change projections for 2100 predict significant westward range expansion, particularly into Atlantic Ocean regions previously unsuitable for these species. The projected expansion remains constrained within tropical and subtropical latitudes (50°N-50°S), indicating that temperature continues to impose fundamental limits to biogeographic dispersals. These findings reveal the importance of iron-supported symbiotic relationships in determining LBF distributions and suggest that climate-driven iron enrichment will increase LBF abundance and carbonate production in shallow marine systems worldwide, with significant implications for reef and shallow-water ecosystem structure, and global carbon cycling.