SEXUAL REPRODUCTION OF THE REEF CORAL MONTASTREA-CAVERNOSA (SCLERACTINIA, FAVIIDAE) IN THE SANTA-MARTA AREA, CARIBBEAN COAST OF COLOMBIA

Sexual reproduction of the reef-building coral Montastrea cavernosa wa s studied in the Santa Marta area, Caribbean coast of Colombia, from O ctober 1990 to October 1991. The area is subjected to a seasonal upwel ling-outwelling regime. From microscopical analysis of tissue sections sampled each lunar month around the full moon, it was confirmed that this is a gonochoric, broadcasting species, with a single gametogenic cycle per year, and a 1:1 sex ratio. Oogenesis began a few weeks after spawning, and extended for 11 mo. The onset of spermatogenesis occurr ed just before the full moon of June, later than at other localities w here sea-water temperatures during the first half of the year are not as low. The amount of reproductive tissue strongly increased in both s exes after July, in association with an increase in sea-water temperat ure and a decrease in photoperiod. The gonad index of fully mature fem ale colonies was about four times lower than at other localities, perh aps due to the stressful seasonal regime. The male gonad index was low er than that of the female, indicating sex-related differences in the rates of biomass allocation to reproduction. As in other Caribbean loc alities, spawning occurred after the full moons of August and Septembe r. However, there was some evidence of a third spawning episode after the full moon of October, possibly associated with a delay in the occu rrence of maximum sea-water temperatures in near-equatorial localities compared to higher latitudes. The probability of cross-fertilization in this species with a gonochoric breeding system and a broadcasting m ode of reproduction is favored by its balanced sex ratio, its usually high within-reef zone abundance, and by localized and repeated spawnin g episodes, synchronized by lunar phase.