Selective predation by the mosshead sculpin Clinocottus globiceps on the sea anemone Anthopleura elegantissima and its two algal symbionts

The mosshead sculpin Clinocottus globiceps (Girard, 1857) feeds on the sea anemone Anthopleuru elegantissima that contains two different algal endosymbionts, zooxanthellae and zoochlorellae. During laboratory feeding experiments, the sculpin selectively fed on the tentacles of zooxanthellate anemones over those of zoochlorellate and algae‐free anemones. Zoochlorellae passed through the fish gut unharmed while zooxanthellae were degraded. The productivity of zooxanthellae in the fish feces (0.20 ± 0.13 pg C cell −1 h −1 ) was significantly lower (93% less) than that of zooxanthellae freshly isolated from anemones (3.14 ± 0.52 pg C cell −1 h −1 ), whereas the productivity of fecal zoochlorellae was the same as that of freshly isolated zoochlorellae (1.21 ± 0.15 pg C cell −1 h −1 ). The chlorophyll content (Chl a and c ) of zooxanthellae was reduced by 50% after passage through the fish gut while the chlorophyll content of zoochlorellae (Chl a and b ) did not change. Selective predation on zooxanthellate anemones confers several ecological advantages to zoochlorellate anemones and to zoochlorellae, most notably predator avoidance and dispersal of viable zoochlorellae that may serve as a source of symbionts for other anemones. By influencing the outcome of predator‐prey interactions involving their hosts, symbiotic algae may have broader ecological roles in benthic communities than previously described.