Do invasive macroalgae influence biodiversity and abundance of Amphipod Crustaceans ?

Amphipods are an essential element of the food web in marine coastal environments, and represent a good indicator of the health of the ecosystems. The composition of amphipod assemblage is often linked to algal coverage, in which the benthic species find refuge from predators and a great availability of food resources. Within the management and conservation of natural environments, one of the main problems is currently represented by the invasion of non-indigenous species, which modifies native communities. This research compares the amphipod fauna associated with Asparagopsis taxiformis (Delile) Trevisan de Saint-Léon, a non-indigenous red macroalga widely distributed along the west coast of Sicily (central Mediterranean), with the one associated with Cystoseira brachycarpa J. Agardh, 1896, a brown alga typical of the shallow rocky subtidal of the south-western Mediterranean. Samples were collected in shallow habitats with dominance of both macroalgae, in the period of the highest abundance of amphipods, in order to investigate the potential relation between the macroalgae and the crustacean dwellers. The main structural indices were calculated (i.e., number of species, S; number of individuals, N; eveness index, J; Shannon index, H'). An overall reduction in the number of species and abundance of amphipods was found to be associated with the invasive alga. This result highlights the problem linked to the expansion of non-indigenous populations and their capability to affect not only native species but also the composition and structure of the associated fauna.