Growth rates (skeletal linear extension) of columnar and lobate morphotypes of the reef-building coral Montastrea annularis were compared within and among seven fringing reefs along a previously described eutrophication gradient on the west coast of Barbados using X-ray radiography. Both morphotypes of M. annularis exhibit similar patterns of increasing average growth rates with improving environmental conditions. However, the average growth rates of the columnar morphotype are statistically higher (P<0.001) on all reefs in the study, when compared to the lobate morphotype. It is suggested that while environmental conditions exert a measurable effect on the growth rates of both morphotypes, the differences in the average growth rates between the two growth forms, under similar environmental conditions, may be related to genetic differences rather than to gross environmental conditions. Index master chronologies computed for a columnar morphotype of M. annularis indicate a general pattern of decreasing growth rates within the past 30 yr at each of the seven fringing reefs. It is postulated that this general pattern of decreasing growth rates may be directly related to the deterioration of water quality along the west coast of the island. © 1990.
