Ammonia flux,physiological parameters,and <Emphasis Type="Italic">Symbiodinium</Emphasis> diversity in the anemonefish symbiosis on Red Sea coral reefs |
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Authors: | Modi Roopin Daniel J Thornhill Scott R Santos Nanette E Chadwick |
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Institution: | (1) Department of Biological Sciences, Auburn University, 101 Rouse Life Sciences Building, Auburn, AL 36849, USA; |
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Abstract: | 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, we measured variation in
ammonia concentrations near anemones, excretion rates of anemonefish, physiological parameters of anemones and Symbiodinium, and genetic identity of Symbiodinium within anemones. Ammonia concentrations among anemone tentacles were up to 49% above background levels, and anemonefish excreted
ammonia significantly more rapidly after diurnal feeding than they did after nocturnal rest, similar to their excretion patterns
under laboratory conditions. Levels of 4 physiological parameters (anemone protein content, and Symbiodinium abundance, chlorophyll a concentration, and division rate) were similar to those known for laboratory-cultured anemones, and in the field did not
depend on the number of anemonefish per anemone or depth below sea surface. Symbiodinium abundance varied significantly with irradiance in the shaded reef microhabitats occupied by anemones. Most anemones at all
depths 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, in contrast to laboratory manipulations where removal of fish causes anemones to shrink and Symbiodinium to become less abundant. |
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