Climate change effects on photosynthetic symbionts in the sea anemone Anthopleura xanthogrammica

The giant green sea anemone (Anthopleura xanthogrammica) inhabits the rocky intertidal zone in California and Oregon. Two photosynthetic algal symbionts, zooxanthellae and zoochlorellae, make these anemones important primary producers in the intertidal zone. This study investigated the effects of changes in temperature and pH on anemones and their symbionts over a natural environmental gradient along the coast of California and Oregon. Zoochlorellae responded negatively to warmer temperatures and positively to more acidic conditions, while zooxanthellae responded positively to warmer temperatures and lower pH. Temperature and pH did not significantly affect chlorophyll a concentrations or anemone protein biomass. Depending on the magnitude of future changes in ocean temperatures and acidity, changes in the ranges of the two types of symbionts and increased densities of sea anemones in the rocky intertidal could be expected to occur.