Reproductive characteristics of Montastrea annularjs and M. cavernosa, 2 important framework-building corals on Caribbean reefs, were studied by collecting samples for histology biweekly from November 1982 through November 1983 and weekly from July through September 1984 Additional samples were collected to determine colony size at which reproduction begins and intracolonial variability of reproductive activity. Reproductive effort of M. annularis was estimated from elemental analysis of whole

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... olyps and dissected gonads. M. annularis is hermaphroditic, with a n annual gametogenic cycle that begins in May and ends with spawning in August and/or September. M. cavernosa is dioecious, with a prolonged oogenic cycle that begins in November, a briefer spermatogenic cycle that begins in May, and spawning events during July, August and/or September. Spawning for both species appears to occur about 1 wk after the full moon. Both species delay reproduction until colony size reaches about 100 cm2 in surface area. In M , annulans, but not in M. cavernosa, polyps in the middle of the colony have greater reproductive activity than those near edges of the colony. Ripe gonads of M. annularis account for about 30 to 40 % of the biomass of sexually mature polyps. Assuming 10 to 50 % bottom cover by this species. spawning releases 8.4 to 44 g C m-' and 0.9 to 4.7 g N m-' to the reef water column on 1 to 2 nights yr-' The failure of sexual recruits of M. annularis to appear on Caribbean coral reefs cannot be attributed to lack of reproductive effort.