Soft-bottom diversity patterns in marine caves; Lessons from crustacean community

• We studied the soft bottom crustacean fauna in six different marine caves.
• Soft bottom communities from marine caves show a strong individuality.
• A significative decrease for diversity values was found inside all caves.
• Small scale variability is similar in cave and open habitats sediments.

Previous marine cave studies have been generally qualitative, focusing on hard benthic communities of single caves. The ecological patterns of marine cave assemblages, particularly those with soft-sediment bottoms, are poorly known. The aim of this study was to investigate ecological patterns of macroinfauna inhabiting marine caves. Using a multifactorial design, the soft-bottom crustacean fauna of six previously unsampled Mediterranean marine caves was studied. To investigate the influence of the marine cave habitat on local crustacean assemblage two stations were compared in each cave; one internal site from within the marine cave cavity and one external site, in sediments near the opening of the cave. The caves selected had a wide range of profundity in order to explore the influence of depth on the community. External sediments had higher species richness, and a significant decline in diversity values inside the caves was found at all marine cave locations studied. The abundance of organisms was strongly influenced by depth, with deeper internal cave sites having lower abundance than the external stations, while more shallow internal cave sites provide a more stable environment, which allows higher density of individuals. The results described here for soft-sediment marine cave bottoms are in contrast to previous observations in hard benthic marine cave communities, where small-scale variability was similar for interior and exterior cave habitats. The results of this study show that even in the absence of endemic cave taxa, the species assemblage at each cave was clearly different from that present in the exterior habitat and also from that present in other cave sediments. This high variability and strong individuality observed in soft-bottom marine caves suggest that there are many and complex factors controlling these communities.