Juveniles' Predation Refuge or Predators' Foraging Ground? Two Pathways of Contributions of Vegetated Habitats to Production of Coastal Fishery Resources

Nocturnal increase in predation risk was demonstrated in seagrass Zostera marina bed which has been referred as predation refuge for small fishes. Seasonal and day-night changes in fish community structures and predation rate on juvenile and small-sized fishes were examined in a seagrass bed in temperate waters in southwestern Japan. The number of piscivorous fish species, and their abundance and biomass during nighttime were significantly higher than those in daytime in all seasons. Analysis of stomach contents of 182 piscivorous fishes showed higher predation rate during nighttime. Visit of piscivorous fishes to the seagrass bed during nighttime was also confirmed by the use of a video camera. Size-selective predation on juveniles of a dominant fish species, black rockfish, was observed by comparison of body lengths between surviving and eaten juveniles. Since the piscivorous fishes which visit the seagrass bed during nighttime include important fisheries resource species, the evidence of nighttime predation indicates that these piscivorous fishes obtain energy in the seagrass bed through predation on small fishes. Function of seagrass bed as fish habitat should be evaluated considering two possible pathways in which seagrass beds contribute to fishery production: predation refuge for juvenile fishes and foraging ground of piscivorous fish.