Species composition of drifting seaweeds and associated juvenile fishes in the Seto Inland Sea, Japan

Abstract

　Drifting seaweeds are utilized by some species of juvenile fishes. We collected drifting seaweeds and associated fishes off Kagawa Prefecture, Seto Inland Sea, monthly from June 2017 to June 2019. A total of 206 clumps of drifting seaweeds, comprised of 15 species, were collected. Average clump weight in each month ranged from 0.05 to 5.97 kg/clump, increasing from winter, reaching a peak in spring, and decreasing in summer and autumn. Sargassum horneri, S. muticum and S. fulvellum dominated in winter and spring, and Zostera marina did in summer and autumn. A total of 6,053 individual fish, belonging to 24 species, were collected. The density (number of individuals per kg of drifting seaweed) ranged from 0.1 to 209.0 and generally was low in winter and high in autumn. The numerically dominant species were Rudarius ercodes (54.7%), Sebastes cheni (21.7%), S. ventricosus (11.0%), Petroscirtes breviceps (4.4%) and S. schlegelii (2.8%). Rudarius ercodes was predominant between summer and autumn. Sebastes cheni and S. ventricosus were predominant species in spring, but the peak of their appearance in number was two months earlier in S. cheni than in S. ventricosus.