Effect of macroalgae, microbial films, and conspecifics on the induction of metamorphosis of the green sea urchin Strongylocentrotus droebachiensis (Müller)

Various macroalgae, microbial films, and conspecifics were tested for their potential to induce metamorphosis of larvae of the green sea urchin Strongylocentrotus droebachiensis (Müller) in the laboratory. The percentage of larvae that metamorphosed varied with macroalgal species: coralline and noncoralline red algae induced the greatest percent metamorphosis, fucoid and laminarian algae the lowest. Percent metamorphosis in response to acrylic plastic plates with marine microbial films was higher when films were developed in light than in dark and increased with the age of the film. Filmed substrata taken from the intertidal zone of a rocky shore induced a high percentage of larvae to metamorphose, sand collected subtidally did not. Adult urchins, adult-conditioned seawater, adult faecal matter, and recently settled juveniles did not induce metamophosis of larvae, suggesting that a conspecific cue was not involved. These laboratory findings suggest that settlement of S. droebachiensis in the field may not be very selective, although other factors influencing larval supply and transport in the water column and along the boundary layer may result in differential settlement among different micro- and macrohabitats.