The suspension-feeder communities of a Mediterranean sea cave

Abstract

The zonation pattern of suspension-feeder communities in a 80 m long cave of the Gulf of Naples has been evaluated by standard, visually oriented. and photographic samplings. Light and water movement intensities have been measured and their gradients have been compared with the distribution of the considered taxa (Porifera, Hydroida, Bivalvia, Serpuloidea, and Bryozoa). The so-called biocoenosis of semi-dark caves (GSO) is restricted to the entrance and its presence seems mainly related to light values. On the contrary, the biocoenosis of dark caves (GO) occupies the rest of the cave, where light is almost absent, and is likely to be mainly influenced by water movement. The individuality of cave communities is discussed, stressing that also other habitats are colonized by species assemblages which are referable to GSO and GO. The evolution of species retained as typical of shallow water marine caves of the Mediterranean is hypothesized as having occurred mainly in cryptic or bathyal environments. The colonization of caves possibly occurred as a event and therefore can be defined as secondary troglobiosis. As a consequence, the denomination of cave-inhabiting communities should be reformulated.