Abstract
The effects of shrimp (Palaemon paucidens) on water quality and the zooplankton community were investigated by using eight enclosures in a restoration experiment pond of the Inbanuma Fishermen Cooperative Association in Kitasuga, Narita, Chiba (Japan). In shrimp enclosures, NH4-N, total nitrogen (TN), and chlorophyll a (Chl a) concentrations increased soon after the start of the experiment, indicating shrimp excretion and bioturbation caused increased NH4-N, TN, and Chl a concentrations. Suspended solids (SS), TN, total phosphorus (TP), Chl a, and dissolved organic carbon (DOC) were significantly higher (P < 0.001) when shrimp were present. The total density of cladocerans and rotifers decreased significantly when shrimp were present but increased in the absence of shrimp. Among cladocerans, total densities of Daphnia, Diaphanosoma, and Scapholeberis decreased significantly (P < 0.05) when shrimp were present; however, the densities of Alona and Chydorus, which are small-sized benthic animals, did not differ significantly in the presence or absence of shrimp. The results of this study show that the presence of shrimp decreased water quality because nutrient recycling was accelerated by shrimp excretion and bioturbation, in addition to the trophic cascade effects, i.e. zooplankton community structure changes from shrimp through feeding on large cladocerans.
