SOURCES AND BIOCHEMICAL-COMPOSITION OF SUSPENDED PARTICULATE MATERIALIN A SUBMARINE CAVE WITH SULFUR WATER SPRINGS

Sources, biochemical composition and nutritional value of suspended pa rticulate material were investigated from February 1994 to February 19 95 in a submarine cave (Grotta Azzurra, Capo Palinuro, southwestern It aly) with hot sulphur springs and associated mats of chemolithoautotro phic bacteria in its innermost dark part (Snow Hall). Concentrations o f total suspended material (TSM), particulate inorganic material (PIM) , organic carbon (POC), organic nitrogen (PON), chlorophyll a (Chi a), phaeopigments (Phaeo), carbohydrates (TCH), proteins (TPR) and lipids (TLI) were measured at four stations along an outside-inside transect , in order to address whether the quantity and quality of suspended pa rticles varied over time with increasing distance from the entrance of the cave and estimate the relative contribution of chemosynthesis ver sus photosynthesis in supplying POC to cave heterotrophs. The abundanc e and biochemical composition of suspended material available to filte r-feeders varied over time, but no significant quantitative or qualita tive differences were detected along the outside-inside transect. Conc entrations of TSM and of its different compounds (PIM, POC, PON, Phaeo , TCH, TPR, TLI) were homogeneous among the four stations or fluctuate d without any consistent trend, with no apparent ageing and degradatio n of organic material in the innermost dark station. Conversely, conce ntrations of Ch1 a significantly decreased from outside to inside the cave at all sampling periods. It is suggested that suspended POC in Gr otta Azzurra consists of mixed assemblages of particles coming from ad vection of photosynthetic material from the open sea and local inputs of carbon by sulphur-oxidizing bacteria. Based on POC/Chi a ratios, th e relative contributions of chemosynthesis versus photosynthesis in su pplying POC to benthic heterotrophs was estimated to be 31 and 69%, re spectively.