Mediterranean marine caves: A synthesis of current knowledge

Abstract

Marine caves are biodiversity reservoirs and refuge habitats, harbouring rare species and living fossils. The Mediterranean Sea hosts more than 3000 caves, which are among the most studied in the world. This review aims to synthesize and update knowledge of Mediterranean marine caves. Their biota includes few obligate cave-dwelling organisms, but many cryptobiotic or crevicular (crevice-dwelling) and bathyphilic (preferring deep-water) species that secondarily colonize caves. A total of 2369 taxa have been reported from 404 caves in 15 countries, with several species new to science described in recent decades. Dramatic environmental gradients generate a zonation of the biota, with up to six faunal zones and two main biocoenoses. Biotic cover and biomass are strongly reduced inside caves, due to hydrological confinement and trophic depletion. The food web is based on suspension-feeders, but motile carnivores play a role in the importation of organic matter from outside. Lack of primary production, faunal affinities and microbial metabolism make marine caves readily accessible models of deep ocean ecosystems. Future research should focus on filling regional (e.g. south-eastern Mediterranean) and thematic (e.g. microbes, meiofauna, macro-infauna) gaps in fundamental knowledge, and on management measures. Marine caves have low ecological resilience and harbour many species of conservation interest, but are threatened by sea-water warming, local human impacts and non-indigenous species.