Eastern Pacific Coral Reef Ecosystems

Abstract

Although not as common as coastal soft bottom, estuarine and mangrove ecosystems, reef-building coral communities and coral reefs occur in the eastern tropical Pacific region, ranging from northern Mexico to southern Ecuador, and are present on all offshore islands as well. Coral reefs are wave-resistant limestone structures built dominantly by the vertical accumulation of coral skeletons. In contrast, coral communities are loosely spaced to dense aggregations of coral colonies that veneer underlying substrates whose origin is other than the actively growing corals they support. This distinction is especially important in the eastern Pacific where coral communities can be easily confused with true structural coral reefs. Both coral reefs and coral communities consist of coral colonies that host zooxanthellae (endosymbiotic dinoflagellates), which are dependent on solar energy, and are thus confined to relatively shallow depths. Eastern Pacific coral reefs do not dominate coastal seascapes because they are relatively small and patchy in distribution, their presence depending upon a combination of requisite hydrographic and geomorphologic conditions. Also, eastern Pacific coral reefs are seldom visible to non-divers because they rarely build islands or possess emergent algal ridges, and are exposed for only brief periods during extreme low tides. However, where reefs are present they boost local biodiversity, provide habitats for a variety of fishes and shellfish, and offer attractive vistas for diver-oriented ecotourism. With the increasing attention and scientific interest directed toward eastern Pacific coral reefs since about the 1970s, our knowledge of this ecosystem has grown immeasurably (Cortés 1997) but the scope of new information is highly imbalanced. While much new understanding has been reached in the areas of systematics, population and community ecology, biogeography and reef growth history, no progress has been made at the ecosystem level focusing on trophic structure, nutrient cycling or productivity. Of necessity, therefore, the following essay will emphasize our level of understanding in the former disciplines. This bias is not meant to diminish the significance of organic production and related topics, but hopefully will serve to alert workers of this deficiency.