Grazing, differential size-class dynamics and survival of the Mediterranean sponge Corticium candelabrum

The growth dynamics and survival of the sponge Corticium candelabrum (Demospongiae: Homosclerophorida) were surveyed in the northwestern Mediterranean for more than 3 yr. Growth and regeneration rates, fission and fusion events and survival were monitored monthly. Moreover, in situ punctual clearance experiments were conducted seasonally searching for possible relationships between food uptake and sponge dynamics. The monthly growth rates (GR) of C. candelabrum were low (0.19 ± 0.02 mean [±SE] for the 3 yr of study), variable and seasonal, with the highest values in summer. The cumulative survival function followed a stepped profile with several consecutive months without mortality separated by shorter mortality events, which mainly occurred in cold months (winter–spring). However, an event of high mortality (76% of the monitored individuals died) took place in the particularly warm summer 2003. Fission events were frequent after previous damage (e.g. partial predation) and only one fusion event was recorded along the study period. The diet of C. candelabrum was highly heterogeneous. Differences in clearance rates (CR) among picoplankton types with season indicated that the sponge retained with different efficiency the several picoplankton types present in the water. Survival and GRs were significantly different for small, medium and large individuals (size-classes I, II and III), with the small sponges showing the lowest survival (56.6% cumulative mortality for the last 2 yr of study) and the highest GRs (0.18 ± 0.03 mo–1, mean ± SE). On the whole, the results indicate that C. candelabrum is a slow-growing but dynamic sponge.