SPATIAL VARIABILITY IN THE DISTRIBUTION OF SPONGES AND CNIDARIANS IN A SUBLITTORAL MARINE CAVE WITH SULFUR-WATER SPRINGS

The distribution of sponges (Aplysilla sulfurea, Geodia cydonium and P etrosia ficiformis) and cnidarians (Astroides calycularis, Caryophylli a inornata and Leptosammia pruvoti) was investigated in a sublittoral cave with sulphur water springs from May 1993 to February 1994 at Capo Palinuro, on the south-western coast of Italy. Multi-factorial sampli ng designs were used to address: (1) the distribution and abundance of sponges and cnidarians on the vault and the sides of the cave at diff erent distances from the entrance; (2) the distribution of cnidarians on the vault of the cave with respect to the type of substratum (spong es vs others) and distance from the entrance; and (3) whether abundanc es were correlated with the distance from the sulphur boundary and how this relationships changed moving from the outer to the inner part of the cave. All the sources of variation included in the study affected to some degree the distribution of organisms but patterns were not co nsistent among species. The abundance of A. calycularis decreased proc eeding from the outer to the inner part of the cave, while the reverse was observed for L. pruvoti. Differences also occurred between the va ult and the sides, A. calycularis and G. cydonium being completely abs ent on the vertical walls. Both A. calycularis and L. pruvoti were les s abundant on sponges than on other types of substratum, but patterns changed in relation to the distance from the entrance. The abundance o f L. pruvoti decreased close to the sulphur boundary, while the percen tage cover of A. calycularis increased, but only at outer positions. S trong variability also occurred at the spatial scale of a few metres ( between replicated areas) often overriding other patterns of distribut ion. Results have been discussed in terms of variability in the physic o-chemical environment and in the outcome of interspecific interaction s.