Effects of a grazing fish, Plecoglossus altivelis (Osmeridae), on the taxonomic composition of freshwater benthic algal assemblages
Abe, Shin-ichiro; Uchida, Kazuo; Nagumo, Tamotsu; Ioriya, Teru; Tanaka, Jiro
published: Feb 15, 2001
ArtNo. ESP141015004003, Price: 29.00 €
The effects of grazing fish, Plecoglossus altivelis (ayu), on freshwater benthic algal assemblages were investigated by experiments in outdoor water tanks with fish (2.2 indiv./m2) and without fish for 25 d. To simulate the condition of running water in each tank, a water current was generated with a water pump. In three replicate experiments, algal biomass and diatom biovolume were reduced in presence of the fish. The biovolume of the filamentous cyanophyte, Homoeothrix janthina increased in response to grazing, and finally predominated in presence of the fish. Observations of grazing scars by scanning electron microscopy verified the supposition that the basal cells of Homoeothrix janthina, which were the hormogones attached to the substrate, had relatively higher resistance to fish grazing. The grazing resistance of the basal cells would contribute to colonization of the filamentous cyanophytes under fish grazing. These results show that grazing fish regulated algal assemblages dominated by filamentous cyanophytes through their foraging activities.