Temperature and Salinity Response Surface Analysis of a Subtropical Oyster Crassostrea virginica (Gmelin, 1791)

Anthropogenic modifications to' the St. Lucie River watershed have significantly altered
the patterns offreshwater flow, resulting in extreme changes of salinity and the subsequent
decline in the health ofthe estuary. While much is already reported for the response of
Crassostrea virginica to temperature and salinity, distinct differences exist along its distribution
range warranting site specific assessments for previously unstudied populations. A modified
Central Composite Inscribed response surface analysis was designed to describe the response of
the local C. virginica population to a range of endemic salinity and temperature combinations.
Controlled temperature and salinity studies were carried out at the Gumbo Limbo Marine Science
Center in a mesocosm facility specifically designed and constructed for this project.
Condition index and RNA:DNA ratio served as response measures. Minimum values for
condition index were observed at combinations of high temperatures(> 25 °C) and low salinities
(< 5 psu). The analysis of oyster RNA: DNA ratios showed a similar pattern of response,
although, in this case, its relationship with temperature and salinity was not as strong. The final
models for mean condition index and the RNA:DNA ratios explained 77.3% and 35.8% of the
respective variances.