Larger symbiont-bearing foraminifers of the genus Amphistegina are currently expanding their biogeographic range in the Mediterranean Sea. They are rapidly progressing northwestward, closely approaching the Adriatic and the Tyrrhenian seas. The shift in range locally leads to profound ecological changes where amphisteginids have become the dominant species along entire stretches of coastline. Mass deposits of amphisteginids reflect an increased carbonate production and reduced assemblage diversity, and these are likely to trigger major changes in ecosystem functioning. It is anticipated that the ongoing warming trend will convey the northwestward migration of amphisteginid foraminifers. To project future species distributions we applied a species-distribution model (SDM) that is based on ecological niche constraints of current distribution ranges. Our model indicates that further warming is likely to cause a northwest-ward range extension and predicts dispersal through the straits of Sicily, Messina, and Otranto into the Tyrrhenian and Adriatic seas. Our results corroborate reports that show a remarkable increase and range expansion of tropical species, indicating a continued meridionalization of the Mediterranean Sea.

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