During bleaching events corals may avoid mortality by changing endosymbiotic algal partners during high thermal maximas. This is called shuffling, when changes are due only to changes in the relative abundance of the symbiotic partners and not to the uptake of new symbionts. Shuffling can allow the coral from losing their obligatory endosymbionts. To better understand the population dynamics of multiple endosymbionts within a single cnidarian host, we use a clonal, temperate sea anemone (Anthopleura elegantissima) commonly found intertidally along the Eastern Pacific coast. Two endosymbionts, called zoochlorellae and zooxanthellae, live within the cells of A. elegantissima. Changes in environmental conditions can produce shuffling of the dominant endosymbiont. Anemones were put into environmental conditions of normal or increased temperature and irradiance. Over the course of 5 weeks, symbiont populations were examined weekly to determine how 1) symbiont density and 2) relative abundances of the two symbionts effect bleaching and shuffling.
Results/Conclusions
We found symbiont densities to affect symbiont shuffling. Symbiont complements dominated by a single symbiont remained stable, but mixed populations shifted to zooxanthellae. This suggests that anemone symbionts exist in alternative stable states conditions with near 50:50 mixed complements, which is a temporary, unstable state. The absence of symbiont expulsion in high stress environments suggests that expulsion may not occur without long-term exposures of stress.