PALEOENVIRONMENTAL IMPLICATIONS OF VERY LARGE CRASSOSTREA OYSTERS FROM CARACASBAAI, CURACAO: CONSIDERATIONS FOR MANAGEMENT AND RESTORATION POLICIES

The American oyster, Crassostrea virginica, is abundant in estuaries along the Gulf of Mexico coastline. Resource managers in this region often use oysters as indicators of estuarine health. The largest oysters and “healthiest” reefs are found where predation and disease intensity are minimized, which occurs in areas with salinities below 15 psu or in intertidal conditions. Oyster growth is influenced by environmental conditions such as temperature, salinity, time exposed to air, turbidity, and availability of food. In areas where the salinity fluctuates through its normal range, oysters are known to grow faster. Oysters exposed to subtidal conditions for longer time periods do not grow as quickly. Large crassostreids are found within Cenozoic deposits throughout the Caribbean and the Gulf of Mexico. Were these oysters growing under similar environmental conditions? If not, the use of modern Crassostrea sp. for management and restoration policy may be weakened.

An outcrop of massive Crassostrea sp., located within the Pliocene Seroe Domi Formation along the shores of Caracasbaai in Curacao, Netherland Antilles, was studied to infer their paleoenvironmental conditions. Individual oysters, the associated fauna, and lithologic samples were collected. The oysters are very large when compared to modern Crassostrea sp., ranging up to 28 cm in length. Large clusters of oysters in life position were observed; clusters ranged up to 35 cm in height and 60 cm in width. Hermatypic corals are present immediately above and below the oyster horizon, and ahermatypic corals are present within the oyster bed. The environmental conditions in which these oysters were deposited are being investigated by both analyzing the taphonomy of the oyster valves and the composition of associated fauna. Clionid sponges (Entobia) and polycheates (Trypanites) appear to be the primary agents of bioerosion. No encrusters were found on the oyster shells. The calcitic fauna is intact; however the aragonitic fauna is moldic. Mudcreepers (Family Potamididae) were found to be a common faunal component. It is unclear at present whether the oysters' large size was due to advanced age or a rapid rate of growth. Although the paleosalinity of this environment is presently unclear, these oysters most likely developed in nutrient-enriched waters of low clarity.