Continuous behavioral observation reveals the function of drifting seaweeds for Seriola spp. juveniles

A large number of fish species are associated with drifting seaweeds; however, the ecological significance of such seaweeds for fishes remains unclear.Here, we developed a raft equipped with a seaweed clump, interval still/video cameras, and a GPS satellite buoy.This novel monitoring system was used to monitor the schooling and associative behavior with seaweeds by Seriola spp.juveniles for up to a week in the East China Sea.We observed diel behavioral patterns in the fish, which swam around the seaweeds during the day and remained attached to the seaweeds or conspecifics at night.This nighttime behavioral pattern suggests that the fish may utilize drifting seaweeds to maintain schools at night when vision is less effective.Solitary individuals and those in smaller schools tended to remain close to the seaweeds, whereas fish in larger schools were observed swimming actively around the seaweeds.Additionally, some of the solitary fish and small schools escaped into the seaweeds when potential predators appeared.As the school size of the fish increased over time, solitary individuals and small schools may utilize drifting seaweeds as a shelter from predators until the fish can gather to form larger schools.We suggest that drifting seaweeds have multiple ecological functions for Seriola and other seaweed-associated fishes, and the knowledge on the functions will be useful in designing the conservation and management measures of the associated fishes. KEY WARDS: Fish Aggregating Devices . Floating seaweed