Abstract
This dissertation examines an area of the eastern Pacific, Golfo Dulce, Costa Rica, to evaluate coral reef demise associated with natural and anthropogenic disturbances. The coral reefs of Golfo Dulce can be divided into two groups based on species composition, reef structure and state of decline. The inner Gulf reefs are composed of the massive coral Porites lobata, mainly on the fore-reef and slope, and Pocillopora damicornis and Psammocora stellata on the reef-flat. These fringing reefs have a high topographic relief and are mostly dead, with less than 2% live coral coverage. The outer Gulf reefs contain comparatively high percentages of the same live coral species, but the reefs have lower topographic relief.One of the inner Gulf reefs, Punta Islotes, started growing on a basaltic promontory about 5500 yr B.P. Initially a small Pocillopora fringing reef formed, spreading over the surrounding sediments and rocky outcrop, forming the substrate for other corals. After two thousand years, three reef facies were distinguishable: a reef-flat branching coral facies consisting mainly of Pocillopora damicornis; a fore-reef massive coral facies consisting of Porites lobata, and a fore-reef talus sediment facies consisting initially of sand, mud and branching coral fragments and more recently of mud and massive coral fragments.The demise of coral reefs in Golfo Dulce has primarily resulted from increased sediment loads caused by deforestation, slash-burn agriculture, road construction and mining. Other reasons for reef decline include increased freshwater input in the last 500 years, the most severe El Nino warming event in the present century (1982-83) and intense dinoflagellate blooms. While other eastern Pacific reefs show signs of recovery even after severe natural disturbances, e.g., the 1982-83 El Nino warming event, the Golfo Dulce reefs are in a steady state of decline. Because of poor coral health, combined with intense bioerosion, these reefs may be poorly preserved in the geological record.