Influence of environmental parameters on reproduction of the European flat oyster (Ostrea edulis L) in a coastal lagoon (Mar Menor, southeastern Spain)

The influence of environmental parameters (temperature, dissolved oxygen, suspended matter, chlorophyll a) on the condition indices and gametogenic cycle of the European flat oyster (Ostrea edulis L.) was analyzed in the Mar Menor (Murcia, Spain) between January 1990 and December 1992. The highest condition index values were recorded during the prespawning season at temperatures between 11-12 degrees C. Condition index values gradually decreased from 14 degrees C, coinciding with the appearance of the first larvae in the plankton. Condition index values were lowest in summer. Multiple regression analysis revealed that the condition indices were correlated mainly with temperature and to a lesser extent, with dissolved oxygen, chlorophyll a and suspended matter. Absolute chlorophyll concentrations were low and presented a negative correlation with the condition index values, though this correlation was less pronounced than that of temperature. Gametogenesis was continuous all year round, but spawning took place only at temperatures of 14 degrees C or higher, and larvae were present in the plankton to 28 degrees C. The low absolute values of chlorophyll a and suspended matter found in the oligotrophic Mar Menor did not seem to affect the gametogenesis, spawning or the larval development of the oysters, which feed on picoplankton, principally composed of dinoflagellates and bacteria.