Effect of Symbiotic State on the Fatty Acid Composition of Anthopleura elegantissima

Anthopleura elegantissima, the most abundant intertidal sea anemone on the Pacific coast of North America, naturally occurs in three distinct symbiotic states: zooxanthellate (hosting the dinoflagellate Symbiodinium muscatinei), zoochlorellate (hosting the chlorophyte Elliptochloris marina), and aposymbiotic (lacking symbionts). S. muscatinei is more productive during summer months and may translocate considerably more carbon to the sea anemone host than does E. marina. Quantitative and qualitative differences in the contribution of energy from the symbiont are believed to affect host lipid levels, influencing growth and reproductive output. To study the effect of symbiotic state on host lipids in A. elegantissima, we collected ten specimens in each symbiotic state from the same habitat, separated symbiont and host tissues, and compared the fatty acid profiles of the two symbionts themselves, compared the fatty acid profiles of anemones in the three symbiotic states, and compared the profiles of the symbionts to their host anemones. We found significant differences in the fatty acid profiles of S. muscatinei and E. marina, with docosahexaenoic acid (DHA), oleic acid, and α-linolenic acid contributing most to the differences. DHA was abundant in S. muscatinei, while E. marina contained high levels of oleic and α-linolenic acids. We found higher total fatty acid content in zooxanthellate hosts than in zoochlorellate hosts, supporting previous research suggesting that S. muscatinei is a more favorable symbiont. We also found that aposymbiotic sea anemones had significantly lower concentrations of total fatty acids than symbiotic hosts and overall lower levels of all fatty acids, including polyunsaturated fatty acids (PUFAs). Because all the anemones came from the same habitat and should have had similar diets, and because cnidarians cannot synthesize PUFAs de novo, the depressed levels of fatty acids in aposymbiotic A. elegantissima suggest that these anemones deplete fatty acids faster due to the lack of symbiont photosynthate input. PUFAs play an important role in invertebrate growth and reproduction, so we expect symbiotic anemones to have higher fitness than aposymbiotic ones. Finally, although previous research suggests that symbionts translocate specific fatty acids to their cnidarian hosts, we found no evidence for fatty acid translocation in A. elegantissima. Our results reinforce the idea that hosting either type of symbiont increases the fitness of A. elegantissima, that hosting S. muscatinei may be more advantageous to the anemone, but do not support the hypothesis of fatty acid translocation between symbiont and host in this species