Chemical micro-environments, ventilation behaviour and microbial processes in sponges

The oxygen dynamics and ventilation behaviour in Dysidea avara and Chondrosia reniformis (Porifera) were investigated using oxygen micro-electrodes and hot-bead thermistors. Both field and laboratory experiments proved the common occurrences of anoxia in the sponge tissue that lasted up to approximately 1 h. Strong temporal and spatial heterogeneity of oxygen concentrations was observed with replicate oxygen profile series across the sponge surface, though tissue close to an osculum was generally better oxygenated. The microbial processes of sponge-associated microbes were investigated in D. avara and C. reniformis. Their presence and rates were established through microsensor measurements of product accumulation and isotope tracer experiments. Total net nitrification occurred at 8.8 and 14.7 nmol cm-3 sponge h-1 for C. reniformis and D. avara, respectively. Rates of denitrification, an anaerobic microbial process, were 10 nmol N consumed cm-3 wet weight sponge h-1 in C. reniformis and 14.9 nmol N cm-3 wet weight sponge h-1 in D. avara while anaerobic ammonium oxidation (anammox) and sulfate reduction were below detectable limits in both species.