The Sponge Community of a Semi-Submerged Mediterranean Cave

. The sponge fauna of a semi‐submerged cave from the Tremiti Archipelago (Adriatic Sea) was studied, and its distribution was analyzed in relation to abiotic (water‐movement and light gradients) and biotic (algae and anthozoan substrate cover) ecological factors. Fifty‐five species of sponges were recorded. The number of species and the abundance values of sponges increase in the first part of the cave, then progressively decrease, with a sharp fall at the end of the cave. The quick disappearance of algae along the light gradient allows sponges to thrive in the first portion of the cave. The subsequent, progressive decrement of sponges could be the result of food depletion phenomena due to a long persistence of the water body in this long cavity. A high water‐turbulence, due to the peculiar morphology of the cave and indicated by the recorded values of water‐movement, occurs at the end of the cavity and probably determines the sharp decrement of sponges in the inner portion of the cave. This turbulence may also explain the absence of typical still‐water cave species and probably affects the type of development (shape, overgrowth) of the sponges in the community.