Spatial and vertical distribution of the genus Amphistegina and its relationship with the indigenous benthic foraminiferal assemblages in the Pelagian Archipelago (Central Mediterranean Sea)

A serious threat affecting the Mediterranean Sea is the migration of Indo-Pacific marine species through the Suez Canal following its opening in 1869. This phenomenon gives extreme causes for concern as many non-indigenous species are highly invasive and seriously threaten native biodiversity. Particularly insidious are small-size taxa such as benthic foraminifera, which are able to invade wide areas un-noticed. The objective of this study is to evaluate the stage of invasion of non-indigenous foraminifer Amphistegina lobifera and the re-colonization of Amphistegina lessonii in two islands of the Pelagian Archipelago (Central Mediterranean) where both species were first recorded in 2005. Absolute abundances quantified in seabed and algal samples collected in 2014 were compared with those detected in 2005 and 2009. Results show that, in the innermost part of the neritic environment, amphisteginids were so abundant and widespread as to have replaced native benthic foraminifera just a few years after earlier reports. On Lampedusa Island, Amphisteginids seem to compete mainly with other symbiont-bearing foraminifera, such as the milioliid Peneroplis pertusus and Peneroplis planatus; we hypothesize that the different algal symbionts housed by the invasive species could play an important role in the invasion success in the Mediterranean Sea. In the most severe case of amphisteginid invasion, as seen around the volcanic island of Linosa, the accumulation of their carbonatic remains is causing a sedimentation switch: increasing the content of white carbonatic sands and replacing the black volcanic substrates, as already observed in Indian Ocean atolls.