Twenty-seven species of known or suspected coral skeletal borers were identified from shallow Hawaiian reefs. In comnarison to inventories of the borer communities collected from other tropical areas Hawaiian corals had an abundance of polychaetous annelids, fewer species of sipunculans,and acrothoracican barnacles, and far fewer boring sponges. Polychaetes were responsible for the majority of the bioerosion of dead coral in Kaneohe Bay, Oahu. Comparisons of living and dead sections of coral colonies indicated that the borer community was more diverse and abundant in areas of the skeletons lacking living tissue. Skeletal densities of three common coral species with branching growth form were found to influence the abundance of coral borers. The least dense skeletons had greater population densities of borers. It is suggested that these three species of corals can coexist in close proximity due, in part, to the development of varying abilities to withstand invasion by skeletal borers. In order to determine rates, si te preference and seasona.li.ty of settlement a series of settlement plates were cut from coral and placed in the field at ten sites in Kaneohe Bay, Oahu. Extrapolating from the surface area of the settlement plates, mean recruitment rates of coral borers were found to be 10,000 - 50,000 individuals m-2 month-1. The recruitment rates and species composition of epibiotic and borer faunas settling; on the dead coral plates differed dramatically between areas in Kaneohe Bay due to the effects of differences in physical and biological factors caused by sewage and slltation. The larvae of coral borers generally lacked clear seasonal settlement periods, suggesting that one or more mechanisms (e.g. continuous reproduction, long pelagic phase, etc.) functioned to assure the presence of larvae throughout the year. The ultimate cause for the development of such a strategy may be that the time and location of the production of suitable settlement sites on the reef surface is. unpredictable. Some of the larvae of both epibiotic and borer species exhibited settlement selectivity with respect to the position of the settlement surface. This finding indicates that the distribution of borers in coral skeletons might be due, in part, to active selection by the laryae for particular conditions. Development of the epibiotic and borer communities of dead coral was monitored using sequentially collected blocks cut from the coral Porites lobata. The abundance and species composition of these communities were found to differ between sites in Kaneohe Bay because of several biological and physical factors. In the south bay increased food supplies (in the form of plankton and plankton-derived detrital material). due to sewage enrichment, support extensive populations of filter and deposit-feeding invertebrates including coral borers. Sewage diversion did not appear to have had any dramatic effect on these communities by the end of the study period. In the north bay, where food availability is lower, fewer borers and epibiotic organisms were collected. The effects of fish grazing are considered to be another important factor determining the species composition and abundance of the coral borer community. Grazing fish were rare in south Kaneohe Bay during the study period, which may help to explain the abundance of sessile epifaunal species. In the north bay fish grazing is extensive and contributes to the growth of encrusting coralline algae on the test blocks and the benthos. Based on the results of the long term block study it was found that in Hawaii sessile filter-feeding invertebrates do not exclude coral borers from the substratum or inhibit their growth. In south Kaneohe Bay, where conditions caused increased abundances and growth rates of filter and depositfeeding invertebrates, bioerosion rates were accelerated. Encrusting coralline algae, which flourish on reefs exposed to fish grazing (eg. north Kaneohe Bay), inhibit settlement of borers and grow over burrow apertures, thus reducing the population of borers within the dead coral. Bioerosion rates of exposed, coralline algal covered, dead coral substrata are very low on pristine shallow Hawaiian reefs. / Bibliography: leaves 181-192.