Macrobioerosion of dead branching Porites, 4 and 6 years after coral mass mortality

Internal bioerosion by macroborers (polychaetes, sipunculans, bivalves, and sponges) was investigated in dead Porites branches collected from 8 coral reefs along the Kenyan coast, 4 and 6 yr after the 1998 mass mortality of corals.Levels of nutrients, benthic cover, and numbers of grazing and invertebrate-eating fish and sea urchins were measured and evaluated for their influence on macrobioerosion.The macroboring community composition was influenced by the grazer composition on each reef; worms were the major macroboring agent where sea urchin biomass was high, and sponges were the dominant agent where herbivorous fish biomass was high.Bivalves accounted for a small proportion of the internal bioerosion and were not measurably influenced by consumers or water quality.The total macrobioerosion rates in Porites branches ranged from 534 ± 70 to 1134 ± 44 g CaCO 3 m -2 (4 yr after the coral death) and 837 ± 111 to 2149 ± 314 g CaCO 3 m -2 (6 yr after the coral death).The macrobioerosion rates were linearly and positively correlated with chlorophyll a concentrations (chl a) in the water column 4 and 6 yr after the coral death.Sponge boring rates were also positively correlated to chl a 6 yr after coral death but not after the initial 4 yr.Consequently, the macrobioerosion rates responded to nutrient status, but the community of borers changed with the dominant grazers, which in turn were influenced by fisheries management.