Ecology of a corallivorous gastropod, Coralliophila abbreviata, on two scleractinian hosts. II. Feeding, respiration and growth

Coralliophila abbreviata is a corallivorous gastropod that has been observed to cause large feeding scars on reef-building corals on Floridian and Caribbean reefs. We detected differences in the population structure (length-frequency distribution and sex ratios) of C. abbreviata populations living on two coral host taxa, Acropora palmata and Montastraea spp., in the Florida Keys in a previous study. We hypothesize that diet (host) has a major influence on snail population structure and, thus, we characterize metabolism, feeding and growth for snails residing on these coral taxa. Here, we present results of a reciprocal transplant experiment demonstrating that the taxon of the host influences snail growth rates, as indicated by changes in shell and body tissue weight. Regardless of the host from which they were drawn, snails resident on A. palmata grew faster than those resident on Montastraea spp. Thus, diet influences snail population structure. However, the tissue of Montastraea spp. provides more N and C per area of tissue than that of A. palmata. Respiration rates and tissue composition of snails collected from the two host taxa did not differ. Therefore, snails feeding on Montastraea spp. should have to consume less tissue per day to satisfy their metabolic requirements compared to snails feeding on A. palmata. Feeding rates for snails on A. palmata were measured in the laboratory over 48 h (1-9 [cm.sup.2] coral tissue [snail.sup.-1] [day.sup.-1]) and estimated from feeding scars observed in the field (weekly mean rate of 1.07 [cm.sup.2] coral tissue [snail.sup.-1] [day.sup.-1]). The lack of definition of snail feeding scars on Montastraea spp. required the calculation of coral tissue consumption rates based on estimated minimum carbon requirements. Calculated feeding rates for C. abbreviata were 0.13-0.88 [cm.sup.2] coral tissue [day.sup.-1] [snail.sup.-1], when feeding on Montastraea spp., and 0.44-3.28 [cm.sup.2] coral tissue [day.sup.-1] [snail.sup.-1], when feeding on A. palmata. The calculated range for the latter is consistent with measured rates. Thus, C. abbreviata exhibits high variation in growth parameters in response to environmental variability and/or food source. At mean levels of snail density on reefs off Key Largo, Fla., 20% of A. palmata colonies lose between 1.32 and 9.84 [cm.sup.2] tissue day-1, while 50% of Montastraea spp. colonies lose between 1.04 and 7.04 [cm.sup.2] tissue [day.sup.-1]. Together with published coral tissue regeneration rates, these results suggest that if sustained, such rates of predation could have a serious effect on the viability of these coral populations on Florida's reefs.