The sponge community of a semi-submerged Mediterranean cave

The sponge fauna of a semi-submerged cave from the Tremiti Archipelago (Adr iatic Sea) was studied, and its distribution was analyzed in relation, to a biotic (water-movement and light gradients) and biotic (algae and anthozoan substrate cover) ecological factors. Fifty-five species of sponges were re corded. The number of species and the abundance values of sponges increase in the first part of the cave, then progressively decrease, with a sharp fa ll 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 su bsequent, progressive decrement of sponges could be the result of food depl etion phenomena due to a long persistence of the water body in this long ca vity. A high water-turbulence, due to the peculiar morphology of the cave a nd 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 i nner portion of the cave. This turbulence may also explain the absence of t ypical still-water cave species and probably affects the type of developmen t (shape, overgrowth) of the sponges in the community.