Meeting Abstract
The stability of nutrient exchange in a mutualistic symbiosis is highly dependent on the availability of resources to both partners. Thus, depending on resource availability, some conditions could be favorable for symbiosis while others could inhibit symbiosis or even result in a break-down in the interaction. Symbiotic sea anemones on California rocky shores obtain nitrogen and some carbon from prey that they capture. Some of the nitrogen from prey is translocated to algal symbionts living within the sea anemone tissue. Unlike some tropical symbioses with algal symbionts, nitrogen is plentiful and is frequently excreted as waste if it is not used by the symbionts. In exchange, the algal symbionts translocate fixed carbon to their host anemone. Algal symbionts are therefore highly advantageous when prey is scarce but may not be as useful when prey, and therefore dietary carbon, is plentiful. To test this hypothesis, we designed an in situ experiment where the diet of two closely related sea anemones, Anthopleura sola and A. xanthogrammica, was manipulated by either adding or removing prey daily for three weeks. Algal symbiont condition was measured using a pulse-amplitude modulated fluorometer and by taking tissue samples to quantify symbiont density and chlorophyll a concentrations. Even though both species interact with the same symbiont genotype, they responded to the treatments differently. Symbionts within A. xanthogrammica increased their photochemical efficiency (Fv/Fm) when prey were supplemented as compared to a control, whereas symbionts within A. sola did not change photochemical efficiency in any treatment. This suggests that A. xanthogrammica may be able to take advantage of an increase in prey availability and pass on benefits to its symbionts, whereas A. sola cannot.
