Bioerosion of coral heads: inner patch reefs, Florida reef tract

Eight small heads of several species of massive reef corals collected southwest of Tavernier, Florida, were slabbed in thin serial sections for X-ray radiography. From enlarged prints of the radiographs, borings by three groups of organisms could be distinguished: boring sponges, spionid polychaetes, and mytilid bivalves.Sponges and spionids were volumetrically the most important groups, reworking from 7.1% to 68.9% of the primary skeletal framework. Bioerosive activity was concentrated at the base and around the periphery of heads, decreasing their ability to withstand wave shock.Estimates on a slab of Pleistocene Key Largo Limestone cut from a Diploria labyrinthiformis head indicated long-term reworking by organisms of 40% of the primary skeletal framework. In contrast, an ahermatypic Solenastrea hyades head from North Carolina was 3.5% reworked. Calculated annual rates of bioerosion, although subject to error, exceeded estimated rates of skeletogenesis. Sediment production by boring sponges (lime silt) and mytilid bivalves (carbonate sands and silts) amounted to 15% of the volume of the primary skeletal framework.