Ammonia Flux, Physiological Parameters, and Symbiodinium Diversity in the Anemonefish Symbiosis on Red Sea Coral Reefs

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Despite the ecological importance of anemonefish symbioses, little is known about how nutritional contributions from anemonefish interact with sea anemone physiology and Symbiodinium (endosymbiotic dinoflagellate) genetic identity under field conditions. On Red Sea coral reefs, wemeasured variation in ammonia concentrations near anemones, excretion rates of anemonefish, physiological parameters of anemones and Symbiodinium, and genetic identity of Symbiodinium within anemones. Ammonia concentrationsamong anemone tentacles were up to 49% above background levels, and anemonefish excreted ammonia significantly more rapidly after diurnal feeding than they did afternocturnal rest, similar to their excretion patterns underlaboratory conditions. Levels of 4 physiological parameters (anemone protein content, and Symbiodinium abundance,chlorophyll a concentration, and division rate) were similarto those known for laboratory-cultured anemones, and in thefield did not depend on the number of anemonefish peranemone or depth below sea surface. Symbiodinium abundance varied significantly with irradiance in the shaded reefmicrohabitats occupied by anemones. Most anemones at alldepths harbored a novel Symbiodinium 18S rDNA variant within internal transcribed spacer region 2 (ITS2) type C1, while the rest hosted known ITS2 type C1. Association with Symbiodinium Clade C is consistent with the symbiotic pattern of these anemones on other Indo-Pacific reefs, but the C1 variant of Symbiodinium identified here has not been described previously. We conclude that in the field, anemonefish excrete ammonia at rapid rates that correlate with elevated concentrations among host anemone tentacles. Limited natural variation in anemonefish abundance may contribute to consistently high levels of physiological parameters in both anemones and Symbiodinium, incontrast to laboratory manipulations where removal of fish causes anemones to shrink and Symbiodinium to become less abundant.