INVASION, EXPANSION AND PROLIFERATION OF AMPHISTEGINA SPP. IN TIMES OF GLOBAL CHANGE

Climate-related shifts in biogeographic patterns have been observed for terrestrial and marine organisms. Among marine taxa, benthic foraminifera of the genus Amphistegina exhibit a particularly detailed biogeographic record to study and prognosticate past, present and potential future range changes. Latitudinal expansions of amphisteginids in times of global warming are well documented in the fossil record (e.g., during the Eocene or Miocene).

Range expansions of larger foraminifera and other tropical organisms were recently documented in the Mediterranean Sea and the Western Indian Ocean (WIO). Both ecosystems have undergone significant warming within the last decades. However, temperature increases in the Mediterranean have been faster than in the WIO. Here we compare rates of range shifts in amphisteginid foraminifers in two oceanic systems that experienced differential rates of warming.

Large-scale analyses of distributional data reveals that amphisteginid foraminifera in the Mediterranean Sea and the Western Indian Ocean display diverging rates of range expansion: While amphisteginids from the Mediterranean Sea reveal an average spread rate of 12.5 km per year, ranges in the WIO expand with a reduced rate of 8 km per year. Moreover, species distribution models show that potentially suitable habitats within the central Mediterranean are less exploited in comparison to the WIO. Modeled projections for the upcoming century predict continued range extensions within both systems with a potentially larger dimension in the Mediterranean Sea.

Observations from recently invaded areas in the Mediterranean show that Amphistegina spp. is a very prolific newcomer, which locally exhibits relative abundances of 70 % and more (e.g., Israel and Cyprus). Because amphisteginids act as ecosystem engineers, their ongoing proliferation may substantially impact native foraminiferal diversity as well as local sediment structures within their new distribution ranges. Our results also illustrate that the Mediterranean Sea is ideally suited as a natural laboratory to study implications of range-shifting organisms in the face of the climate change to come.