Together is Better : The Importance of Heterotrophy and Photoautotrophic Symbiosis for Growth of the Sea Anemone Aiptasia pallida

Scleractinian corals are important because they are the foundation species that build coral reefs, but they are in decline worldwide. The sea anemone Aiptasia pallida is a possible model system for studying the nutrition of reef-building corals because both have the same algal symbionts (Symbiodinium spp.). The relative importance of exogenous nutrition (NX) versus symbiont-derived nutrition (Ns) for A. pallida is largely unknown. When stressed, both anemones and corals bleach (expel symbionts) and have to rely solely on NX. I measured changes in wet mass after 60 days for anemones divided into four treatments that manipulated the presence and absence of NX and Ns. The treatments were: symbionts present and food provided (S+/F+), symbionts absent, but food provided (S-/F+), symbionts present, but no food provided (S+/F-), and neither symbionts present nor food provided (S-/F-). TetraMin flake food was used for exogenous food. Anemones were rendered aposymbiotic using a combination of cold shocks and treatments with a photosynthesis-inhibiting compound, and subsequently maintained in darkness. Anemones with S+/F+ gained significantly more mass than other treatments (p<0.001). All other treatments lost mass and there were no significant differences among them. Under the experimental conditions used in this study, A. pallida needed both NX and Ns to grow, suggesting that some component of each nutritional source is necessary for the health of this sea anemone.