THE determination of coral skeletal growth, from both a biological and a geological standpoint, has long presented difficulties in ease and accuracy of measurement. As a consequence, factors which limit growth are only beginning to be investigated. Radiometric methods using natural radioactive series nuclides have recently been used to determine the growth rate of certain corals1,2. In addition, X radiographs coupled with 90Sr-induced autoradiographs have demonstrated that at least some hermatypic corals record annual growth bands in their skeletons3,4. Once annual banding is confirmed, measurement of band widths allows precise determination of yearly growth increments. It is thus possible to compare inter- and intraspecific coral growth rates from different areas with pertinent environmental variables and to educe possible correlations. We describe here an investigation of the effects of resuspension of bottom sediments on the growth rate, as determined by a 228Ra technique and X radiography of Montastrea annularis in different parts of Discovery Bay, Jamaica. Such a study is unique both because the annual nature of growth bands is established for the most important reef-forming coral in the Caribbean5 and because radiometric and radiographic techniques are extended to measure growth rates as a function of environmental parameters.