1Research Center for Subtropical Fisheries, Seikai National Fisheries Research Institute, Fisheries Research Agency, Ishigaki, Okinawa 907-0451, 2Institute for East China Sea Research, Nagasaki University, Taira-machi, Nagasaki 851-2213, Japan
The effects of artificial seaweed and water depth on vulnerability of juvenile black-spot tuskfish Choerodon schoenleinii to the carnivorous crab Ashtoret lunaris were examined in the laboratory. Ten hatchery-reared tuskfish were exposed to five crabs for 24 h in replicate 400 L tanks (N=8) for each of the six treatments. The predation rate was significantly lower in the tanks with artificial seaweed than in the tanks without it. There was no significant difference in predation rate between standing artificial seaweed and lying artificial seaweed. There was no significant effect of water depth on the predation rate, either. When the behavioral pattern of the tuskfish was examined in tanks without crabs, most of the tuskfish were associated with the artificial seaweed. However, the tuskfish showed a clear diurnal activity pattern, and were distributed on the bottom of the tank during the night when the artificial seaweed was removed, implying that the predation mainly occurred at night. These results suggest that the foliage of Sargassum plants is an important nursery as a predation refuge for the tuskfish because wild black-spot tuskfish settle mainly on the thalli of Sargassum polycystum distributed in the intertidal zone, in which A. lunaris occurs simultaneously.