HOLOCENE GROWTH HISTORY OF AN EASTERN PACIFIC FRINGING-REEF, PUNTA-ISLOTES, COSTA-RICA

Rock and sediment cores reveal that a well-developed fringing reef in Golfo Dulce, Pacific Costa Rica, up to 9 m thick was established on Cr etaceous basalt about 5500 y BP. It is presently being smothered with fine sediments and is almost completely dead. This reef is made up of three main facies that are represented by comparable extant reef zones : reef-flat branching coral, fore-reef slope massive coral, and fore-r eef talus sediment facies. Reef growth began with the establishment of small patch reefs dominantly formed by the branching coral Pocillopor a damicornis. P. damicornis spread across the basalt bench and massive colonies of Porites lobata grew on the outer slopes, eventually block ing the seaward transport of Pocillopora fragments to the fore-reef ta lus sediments. The reef flourished until 500 years ago. Lower accumula tion rates during the past 500 years may be due to deteriorating envir onmental conditions rather than slower growth after the reef reached s ea level. Present-day reef communities are severely degraded with less than 2% living coral cover. The increased turbidity associated with t he final stage of degradation of this reef is probably related to huma n activity on the adjacent shores, including deforestation, mining, an d road construction.