Mobile epifaunal community in marine caves in comparison to open habitats

Abstract

Mobile epifauna is an essential component of rocky reef ecosystems. In spite of this and the great scientific interest that the study of marine caves has aroused in the last decades, little research has been conducted on the macrofauna associated with animal substrates in submarine caves. This study explores the main differences between marine caves and open habitats in terms of species composition and diversity patterns of epifaunal communities in 4 different shallow marine caves in southern Spain. Colonies of Eudendrium sp., a marine hydroid widely distributed in the Mediterranean Sea, were taken from inside and outside each cave, and all associated mobile fauna were sorted and identified. More than 90% of organisms were crustaceans, with Amphipoda as the dominant group. Although the main species did not vary significantly in abundance between open and cave habitats, multivariate analysis carried out for the entire amphipod community showed significant differences between these 2 habitats. nMDS analysis showed that marine cave assemblages were also characterized by a higher degree of individuality, and univariate analysis showed a decrease in Shannon diversity and species richness with distance into the caves, a consistent pattern for all caves studied. Although the possible role of predation pressure in the structure of such assemblages was also discussed, we propose that the absence of plant substrates inside the caves, in conjunction with oligotrophic conditions and low siltation, are the main factors responsible for the impoverishment of the epifaunal community. The near lack of photosynthetic activity reduced the presence of herbivorous species, while the rich detritus-feeder community supported by the animal substrates was limited by the low rate of sedimentation.