Heterotrophy is examined in the hydrocoral Millepora complanata Lamarck and compared with scleractinian corals. Natural zooplankton catch rates and digestion rates were determined from counts of prey items captured by the gastrozooids on surfaces of millepore colonies collected in the field. The mean catch rate or feeding rate (+ SD) was 7.1 ? 4.10 prey items cm-2 surface d-' and complete digestion of prey required about 24 h. Copepods comprised the bulk (63 %) of the diet. Based on the argument that measured catch rates of corals are highly variable because of plankton patchiness, and the assumption that millepore colonies with expanded zooids feed both day and night, a potential feeding or catch rate was derived from the mean number of gastrozooids on the colonies times the digestion rate. Daily food consumption estimated from the potential catch rates exceeded estimates of daily energy needed for respiration by a factor of 6.7. It was concluded that heterotrophic feeding in M. complanata can potentially supply more than the daily energy requirements of the hydrocoral and may exceed feeding rates of scleractinian corals.

ABSTRACT. The distribution of living colonies of the calcareous hydrozoan Millepora complanata and broken and reattached millepore fragments was examined in m* quadrats along line transects on fringing reefs at Barbados, West Indies. Of the broken fragments 35 % reattached, but survival was not found to be size-dependent, in contrast to reports of breakage in Scleractinia. The number of reattached fragments was positively correlated with the total number of fragments and with the number of quadrats containing mlllepore colonies. It is proposed that fragmentation has a selective advantage because of the high survival rate of fragments and that there should be an advantage to increasing colony size in the population because the risk of breakage increases with colony size.