Gabi Sánchez Soler

It has been over 10 years since the phenomenon of extensive coral bleaching was first described. In most cases bleaching has been attributed to elevated temperature , but other instances involving high solar irradiance, and sometimes disease, have also been documented. It is timely, in view of our concern about worldwide reef condition , to review knowledge of physical and biological factors involved in bleaching, the mechanisms of zooxan-thellae and pigment loss, and the ecological consequences for coral communities. Here we evaluate recently acquired data on temperature and irradiance-induced bleaching, including long-term data sets which suggest that repeated bleaching events may be the consequence of a steadily rising background sea temperature that will in the future expose corals to an increasingly hostile environment. Cellular mechanisms of bleaching involve a variety of processes that include the degeneration of zooxanthellae in situ, release of zooxanthellae from mesenterial filaments and release of algae within host cells which become detached from the endoderm. Photo-protective defences (particularly carotenoid pigments) in zooxanthellae are likely to play an important role in limiting the bleaching response which is probably elicited by a combination of elevated temperature and irradiance in the field. The ability of corals to respond adaptively to recurrent bleaching episodes is not known, but preliminary evidence suggests that phenotypic responses of both corals and zooxanthellae may be significant.

This paper presents systematic and ecological remarks about three species of Mytilidae (Lithophaga aristata, L. plumula, and L. hancocki) and one of Gastrochaenidae (Gastrochaena ovata) found boring scleractinian corals of Gorgona lsland; Colombian Pacific coast. It includes a description of diagnostic characteristics of the shells, notes about habitat, bathymetríc range, sizes and geographical distribution. The dead bases of branched corals, and live parts of massive species, present more taxa and numbers of borers.

Abslrad: The coral reefs and coral cornmunities in Golfo Dulce, soulhem Pacific Coast of Costa Rica, are described. The Inner Gulf reefs are characterized by a high topographic relief, low coral diversily and live coral covegage, and high dead coral coverage. The reefs can be zoned into: l. A reef-flat zone, where dead Pocíllopora and Psammocora are predorninant, togetber witb live and dead rnicroatolls of Porí/es loba/a. 2. A reef-edge zone, where tbere is a mar ked change in physiognorny, from a relatively horizontal reef-flat to an a1rnost vertical reef-fronL Tbis is tbe zone witb highest live coral coverage and is for tbe most part Porí/es loba/a. 3. A reef-front, extending frorn 2 to 10 m deptb, made up mainly of dead Porí/es lobala. The Outer GuIf reeís are characterized by a low topograpbic relief, high live coral coverage and diversity, and low dead coral coverage. A total of nine sc1eractinian species were found in Golfo Dulce. Most abundant are PorÍJes lobala, Psammocora stella/a and Pocillo poro damicornis, which have also becn present tbere tbroughout tbe Holocene. Twenty four fish species were observed in two reefs. Most of them are impor tant for tbe artesanal fisheries of Golfo Dulce. Otber species are important recf herbivores or coralli vores. Intemal ro-ral bioerosion (chief1y boring bivalves: Lithophaga) is more important tban extemal bioerosion.. Enviromnental conditions at Golfo Dulce were conducive to reef growth in tbe recent past but are now deteriorating as a result of Íhcreased sediment loads. Deforestation, pemicioÍls agricultural practices and miniog in tbe Golfo Dulce watershed must be brought under control and erosion reduced. H tbese were possible a program of reef rehabilitation by transplanti ng corals could be started to recover sorne oí tbe reefs.