Does the invasive macro-algae Sargassum muticum (Yendo) Fensholt, 1955 offer an appropriate temporary habitat for mobile fauna including non indigenous species?

Abstract

The fauna inhabiting the brown seaweed Sargassum muticum was studied on a spatial scale along the Normandy coast from the Normand-Breton Gulf to the Bay of Seine (English Channel) in both shallow sandy and rocky tidal pools during the springs 2018 and 2019. In this paper, we test the following hypothesis: do the areas with dense populations of S. muticum represent an appropriate habitat for dense motile fauna including other Non-Indigenous Species (NIS)? The ALEX (ALien biotic indEX) is used to ascertain whether or not S. muticum favours the establishment of other NIS in this new habitat. Results show that the epifaunal assemblage associated with S. muticum differs between the five sampling sites. However, the fauna at all five sites is dominated by arthropoda, especially the amphipods and isopods. In addition, five non indigenous species are observed inhabiting the brown seaweed (four amphipods: Aoroides longimerus, Aoroides semicurvatus, Monocorophium acherusicum, Monocorophium sextonae and one decapod: Hemigrapsus sanguineus). In spite of the presence of Non-Indigenous Species (NIS) associated with the invasive Sargassum, the ALEX yields a high Ecological Quality Status for all the sites. Nevertheless, the results suggest that S. muticum is a suitable habitat for many invertebrates especially amphipods and isopods, while also representing a potential source of food for several local fish and cephalopod species.