THE CONSEQUENCE OF CLIMATE CHANGE ON OYSTER FARMING: COMBINED EFFECT OF SALINITY AND TEMPERATURE ON MORTALITY OF PORTUGUESE OYSTER Crassostrea angulata

R ecent severe  mortality  episodes of Crassostrea gigas led to the need to diversify oyster species production. The Portuguese oyster Crassostrea angulata,  appears as a promising species in European aquaculture.  Moreover, the conservation of pure populations of this species is also important in the context of biodiversity preservation.  The main production areas of this species are intertidal production areas in estuaries and lagoon systems . Therefore, climate changes can promote physiological stress of bivalves, resulting in changes in physiological responses and, in extreme cases, leading to high mortalities.

This study evaluated the combined effect of salinity and temperature on mortality of  C. angulata .  Juveniles and adults of  C. angulata were exposed to a combination of temperature (5-35°C) and salinity (0-35). Five individuals fed once a day (2% of dry weight) were used in each treatment. Each trial (3 per size class)  had a duration of 120 hours, with survival and feeding behavior (presence of faeces) being evaluated every 24 hours.  Survival and feeding behavior of juveniles and adults showed an optimal combination of salinity and temperature. For  both juveniles and adults, survival was optimal at salinities between 20 and 35 and temperatures below 29°C. Juveniles' feeding activity was optimal in salinities between 20 and 35 with temperatures between 15°C and 32°C. Adults' feeding activity was more intense in salinities higher than 15 and temperatures between 15°C and 35°C.

Climate changes in south of Portugal are expected to be characterized by heavy and sporadic rainfall and high temperatures that will contribute to a  drastic reduction  in salinity and an increase in seawater temperature. The results clearly indicate that abrupt reductions in salinity will lead to high mortality of  C. angulata (either in adults and juveniles). Adults may suffer higher mortalities from the combination of low salinity and high temperatures. In this way, the recruitment of this oyster may fail, compromising the exploitation of the species.