Original paper

At the front of expanding ranges: Shifting community structures at amphisteginid species range margins in the Mediterranean Sea

Mouanga, Gloria H.; Langer, Martin R.


Climate warming and the poleward widening of the tropical belt have induced range shifts in a variety of marine and terrestrial organisms. Among the key taxa that are rapidly expanding their latitudinal range are symbiont-bearing foraminifera of the genus Amphistegina. Analyses of foraminiferal faunas from new sites in the western Ionian Sea (Ithaka and Lefkada Islands) show that amphisteginid foraminifera continue to expand their biogeographic range, rapidly outcompete all native species and represent the most abundant taxon at almost every site colonized. The introduction and range expansion of Amphistegina puts significant pressure on local species, affects foraminiferal diversity and decreases species richness of associated biotas. Native species richness is reduced at all sites invaded by amphisteginids and correlates with the degree of infestation. Amphisteginids invasions specifically impact those species that share a similar microhabitat and include other larger symbiont-bearing foraminifera and numerous trochospiral species. The impact of Amphistegina on native biotas gradually increases from the range expansion front towards those sites where invasions commenced decades ago. High abundances may result in prolific monocultures of Amphistegina that modify the composition of sedimentary substrates and ultimately trigger changes in ecosystem functioning. Assemblage structures and patterns observed at the expansion front in recent examples resemble amphisteginid invasions recorded in Miocene foraminiferal communities from the Vienna Basin and Poland, these latter being indicative of shifts in biogeographic ranges at that time. The assemblages thus preserve environmental information that is useful in paleoecologic and paleobiogeographic interpretations to evaluate the extent and magnitude of shifts along the front of expanding species ranges.


biogeographyecosystem engineerforaminiferamediterranean seaprotistarange expansion