BLANQUEAMIENTO CORALINO DE 1990 EN EL PARQUE NACIONAL NATURAL CORALES DEL ROSARIO (CARIBE, COLOMBIANO

At the beginning of June 1990 a coral-bleaching event was detected in the Islas del Rosario reefs, Colombian Caribbean. A preliminary survey of the Isla Grande northern barrier, and of the Caño Ratón and Isla Pavitos south reefs slopes resulted in a list of 19 affected species, which includes scleractinians, zoantideans and milleporins. Bleached colonies accounted for less than 10% of the total observed. The species most affected were Montastrea annularis and Porites astreoides. The recovery process was followed during a five month period in 20 Montastrea annularis, 3 Acropora palmata and 3 Acropora cervicornis colonies . The bleached patches (injuries) of each colony were meassured, demarked with steel nails and their evolution monitored at monthly intervals. Total mortality was observed in 52% of the injures, incomplete recovery in 40%, and no apparent change in the remaining 8% of the colonies. The coral- bleaching event was coincident with an unusual rise in water temperature (31°C to 32°C) between May and June 1990. As the high temperatures lasted until October of the same year (>30°C), these arÿpressumed to be the main cause of the bleaching phenomenon. The possible role of light as a concomitant factor is-also discussed.

INTERACCIONES ENTRE CORALES Y MACROALGAS: DEPENDENCIA DE LAS ESPECIES INVOLUCRADAS

Macroalgae proliferation on coral reefs has been a recognized phenomenon for the past two decades and is generally entitled to the human activities on the coasts. Even thought, the role of competition in this process is not clear and it has been assumed that algae are competitively superior to corals, even when it has been demonstrated that this is not always the case. It is probable that the result of coral-macroalgae depends upon the species involved. The goal of this study was to demonstrate that there is a dependence relation between interaction category and interacting species. In order to resolve this, quantifications of interactions per category along 20 m transects were done on three representative localities at the Archipielago de San Bernardo. The results show a significant dependency between interaction category and coral-macroalgae combinations. The highest percentage of encounters at the R (overgrowth) category was that one between Halimeda opuntia, and the coral species Montastrea annularis, Porites astreoides and Porites porites, as well as this last coral with the alga Lobophora variegta. Halimeda discoidea was the macroalgae with the highest percentage of interactions on the categories CP (peripheral contact), CT (tissue contact) and NC (no contact). At the CP category, it was common to find the interactions between the coral M. annularis and the algae H. opuntia and Dictyota bartayresiana besides the interactions with the red calcareous algae group. All this have led us to conclude that the intrinsic factors, those inherent to the coral and macroalga species involved in interactions, have the potential to determine the category of interaction or the way these two benthic components relate to each other.