Anchoring effects on faunal communities in Posidonia oceanica meadows

Abstract

[eng] Seagrasses, marine flowering plants, are considered among the most productive ecosystems on Earth. Posidonia oceanica is an endemic seagrass of the Mediterranean Sea that creates extensive underwater meadows, and, through its ecological functions provides fundamental benefits to society. Multiple stressors cause its decline, with potential knock-on effects to associated organisms. The effects of anchoring by recreational boats on Posidonia oceanica meadows and associated faunal communities were analysed in Mallorca during the summer of 2021. Two treatments were compared (control and impacted) and two sites of each treatment were examined. To assess the health of the meadows, measurements of density and cover were taken. The fauna assessed were the epifauna (small invertebrates associated with the seagrass canopy) and fish community. Epifauna were collected with a fine-meshed bag and fish counts were obtained by visual surveys. The results indicate that there was no difference between seagrass shoot density and cover between control and impacted meadows. A total of 17 taxonomic groups from 6340 epifaunal organisms and 1104 individuals of 20 species of fish were identified. The epifaunal community was dominated by Copepoda whereas the fish community by Atherina hepsetus. No differences in fish and epifauna communities were found between the impacted and control meadows. The distribution and diversity of species in a seagrass ecosystem can depend on various factors. Thus, the use of epifauna and fish community as an indicator of the effects of anchoring may not provide conclusive results.