Salinity effects on the growth, mortality and shell strength of Balanus amphitrite from the Salton Sea, California

The Salton Sea, the largest lake in California, has a salinity of around 43 g l(-1) that is increasing by about 0.4 g l(-1) y(-1). A 15 month microcos m experiment was conducted to determined the effects of salinity (30, 39, 4 8, 57, and 65 g l(-1)) and tilapia (Oreochromis mossabmicus) on an assembla ge of benthic and planktonic Salton Sea algae and invertebrates, including the barnacle Balanus amphitrite. Eleven months after the microcosms were es tablished, acrylic plates containing newly settled B. amphitrite collected at the Salton Sea were placed in the microcosms to determine the effects of salinity on their growth and shell strength. The Brody-Bertalanffy growth model was fitted to the B. amphitrite growth data. Growth was fastest at 48 g l(-1) and slowest at 65 g l(-1). B. amphitrite grown at 39-48 g l(-1) we re the largest and required the greatest force to break, but the strength o f the barnacle shell material declined steadily as the salinity increased. However, B. amphitrite at the higher salinities were shorter and had thicke r walls relative to their diameters, which may have increased their structu ral stability. The effects of salinity on the mortality of adult B. amphitrite was determi ned in laboratory aquaria set up at 43, 60, 70, 75, 80, 90, and 100 g l(-1) . Salinities were achieved in two ways: by salt addition and by evaporation . Calculated 12-day LC50 values were 81 g l(-1) when salinities were achiev ed through salt addition and 89 g l(-1) when salinities were achieved throu gh evaporation. Differences in B. amphitrite mortality between the two meth ods illustrate the importance of producing experimental salinity levels car efully. B. amphitrite is expected to become extinct within the Salton Sea w hen the salinity reaches 70-80 g l(-1) and to show marked declines in abund ance at salinities as low as 50 g l(-1).