Nutritional Role of Two Algal Symbionts in the Temperate Sea AnemoneAnthopleura elegantissimaBrandt

Abstract

The intertidal sea anemone Anthopleura elegantissima in the Pacific Northwest may host a single type of algal symbiont or two different algal symbionts simultaneously: zooxanthellae (Symbiodinium muscatinei) and zoochlorellae (green algae; Trebouxiophyceae, Chlorophyta). A seasonal comparison of zooxanthellate and zoochlorellate anemones showed stable symbiont population densities in summer and winter, with densities of zoochlorellae about 4 times those of zooxanthellae. Photosynthesis-irradiance curves of freshly isolated symbionts show that the productivity (P(max) cell) of freshly isolated zooxanthellae was about 2.5 times that of zoochlorellae during July; comparable rates were obtained in other months. Models of algal carbon flux show that zoochlorellae may supply the host with more photosynthetic carbon per unit anemone biomass than zooxanthellae supply. Zooxanthellate anemone tissue was 2 per thousand ((13)C) and 5 per thousand ((15)N) enriched and zoochlorellate anemone tissue was 6 per thousand ((13)C) and 8 per thousand ((15)N) enriched over their respective symbionts, suggesting that zoochlorellate anemones receive less nutrition from their symbionts than do zooxanthellate individuals. The disparity between predicted contributions from the algal carbon budgets and the stable isotopic composition suggests that short-term measures of algal contributions may not reflect actual nutritional inputs to the host. Isotopic data support the hypothesis of substantial reliance on external food sources. This additional nutrition may allow both algae to persist in this temperate intertidal anemone in spite of differences in seasonal photosynthetic carbon contributions.

To What Extent Do Food Preferences Explain the Trophic Position of Heterotrophic and Mixotrophic Microbial Consumers in a Sphagnum Peatland?

“…The low availability of energetic resources probably led H. papilio to use its endosymbionts as complementary energy source and, thus, to receive more translocated carbon from the stimulated activity of its endosymbionts than from CA, explaining why the δ 13 C signature of H. papilio was so high. By analogy to our results, Bergschneider and Muller-Parker [61] showed that the δ 13 C signature of zoochlorellae increased from −25 to −20 ‰ when they were used as complementary energy source in Anthopleura elegantissima. These authors also showed that zoochlorellae anemone exhibited distinctly lower patterns of δ 15 N values than non-zoochlorellae anemone, indicating that symbiotic anemones received nutrition from both external (heterotrophic) and internal (translocated algal products) sources.…”

Summer autotrophy and winter heterotrophy in the temperate symbiotic coral Cladocora caespitosa

“…Such stability of the symbiosis has previously been observed in the same coral species (Rodolfo-Metalpa et al 2008c) and in other temperate corals and sea anemones (Farrant et al 1987;MullerParker and Davy 2001;Bergschneider and Muller-Parker 2008), and might result from different algal expulsion rates between summer and winter, or a balanced growth of zooxanthellae and host (Verde and McCloskey 2007). The fact that corals sampled in Bonassola, only 50 km away from Lerici, presented significantly lower zooxanthellae density in summer compared to the other locations suggests that algae are rather expulsed by the host when irradiance levels are high (Fitt et al 2000;Rodolfo-Metalpa et al 2008c).…”

“…In a previous experimental study performed on the same temperate coral, heterotrophy was found to function as an alternative source of carbon when corals were maintained in the dark, and was sufficient to maintain calcification rates at a basal value (Hoogenboom et al 2010). The same observation, that feeding sustains carbon requirements in winter, was also made for temperate anemones and zoanthids (Davy et al 1996;Bergschneider and Muller-Parker 2008). Also, in winter conditions, zooxanthellae d 13 C was more depleted than in summer, showing that they might have relied to a greater extent to host-derived carbon sources.…”

Symbiotic state influences life-history strategy of a clonal cnidarian

“…A Danner Mag Drive submersible pump (113 l min 21 ) ran continuously, increasing water circulation. When the tank was full, simulating high tide, the irradiance shields were submerged and the anemones were under 16 cm of seawater.…”

“…Symbiont counts were normalized to anemone protein content determined from replicate homogenate subsamples [30]. Anemones were considered aposymbiotic if symbiont densities were less than 8 Â 10 4 cells mg protein 21 (approx. 10% of a normal symbiont density for A. elegantissima in the nearby San Juan Islands, WA, USA [20]).…”