MEPS 139:205-217 (1996)  -  doi:10.3354/meps139205

Variability of fluxes of particulate material in a submarine cave with chemolithoautotrophic inputs of organic carbon

Airoldi L, Cinelli F

The composition and vertical fluxes of particulate material were studied in February, May and October 1994 and in February 1995 in a submarine cave (Grotta Azzurra, Capo Palinuro, southwestern coast of Italy) influenced by the presence in its innermost dark region (Snow Hall) of hot sulphurous springs supporting dense mats of chemolithoautotrophic bacteria. A multifactorial sampling design was used to specifically address whether there were differences in the quantity and quality of particles sedimenting at different sites within Snow Hall and in the outer non sulphurous region of the cave (Central Hall), and whether patterns were consistent over time. Material collected in sediment traps was analysed to quantify the content of coarse particles, total particulate material, particulate organic carbon, particulate organic nitrogen, chlorophyll a, phaeopigments, total carbohydrates, total proteins and total lipids. Microscopic analyses were also carried out in order to characterise coarse and particulate material. The most abundant recognisable particles in the traps were faecal pellets, Posidonia and algal debris and fragments of organisms living on the vault of the cave, while a great proportion of coarse material consisted of generally unidentifiable amorphous aggregates. Both the magnitude of flux and nature of the sedimented material were heterogeneous. Such variability was especially evident on a small spatial scale. Significant variation among sites sampled in each region was detected during each sampling period for the majority of the compounds that were analysed. Conversely, differences between the 2 regions were generally low and were not consistent through time. A clear spatial trend emerged only for chloropigments, whose sedimentation rates consistently decreased from Central Hall to Snow Hall. In contrast to the general paradigm of caves as simplified oligotrophic ecosystems driven by their proximity to an outside source of energy, the observed patterns suggest that vertical fluxes of particulate material in this peculiar environment are influenced by local processes acting on a small spatial scale within the cave. It is also indicated that bacterial chemosynthetic production supplies fresh organic material to the cave benthos in the form of sinking particles.

Spatial variability · Particulate material · Fluxes · Sources · Biochemical composition · Sediment traps · Submarine caves · Chemosynthesis

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