Habitat selection of Japanese top shell (Turbo cornutus) on articulated coralline algae; combination of preferences in settlement and post-settlement stage

摘要

Laboratory experiments were conducted to examine the habitat preferences of top shell, Turbo cornutus, in settlement and post-settlement stages. Competent larvae were strongly induced to settle by five species of articulated coralline algae, three species of gelidiacean algae and an unidentified crustose coralline alga, when the algae were provided separately. Although a clear difference in the settlement percentage was not found between an articulated coralline alga, Marginisporum crassissima, and the crustose coralline alga in the no-choice experiment, a significantly greater percentage of top shell larvae settled on M. crassissima than on the crustose coralline alga when larvae could select algal fragments to settle in the choice experiment. In contrast, larvae did not show a settlement preference among articulated coralline algae species in either the no-choice or choice experiments. Aggregation behavior of juveniles of two size classes were observed; the juveniles aggregated with all three algal fragments tested (M. crassissima, a crustose coralline alga, and the brown alga Dictoya dichtoma) when each algal fragment was provided separately. When the three algae were provided together, juveniles of both size classes preferred the articulated coralline alga M. crassissima over the other two algae. The experimental results indicated that the specific distribution of top shell juveniles in coralline algal turfs in their natural habitat is determined by a combined preference for articulated coralline algae in the settlement and post-settlement stages.