Fish-mediated zooplankton community structure in shallow turbid waters: a mesocosm study

Abstract

Turbidity influences the success of fish feeding, but little is known about the difference in the effects of turbidity as a result of organic and inorganic matter. To assess the feeding behaviour of a native fish, Goodea atripinnis, under turbid conditions (up to 120 NTU) generated by Microcystis aeruginosa or silt, we conducted mesocosm experiments for 25 days using 40-L plastic mesocosms. Each tank received two G. atripinnis individuals (predators) with a mean total length 61 mm and cladoceran zooplankton (prey) (Alona glabra, Chydorus sphaericus, Moina macrocopa, Simocephalus vetulus, Ceriodaphnia dubia, and Daphnia pulex) of 100 ind. L−1. Filtered water from Xochimilco Lake was used to fill the mesocosms. Goodea atripinnis had a selective effect on the zooplankton community in the form of a decrease in the number of pelagic cladocerans. The zooplankton composition, which was least affected by the fish, included small-sized (400–480 µm) benthic cladocerans (e.g. Chydorus sphaericus) and copepods (both calanoids and cyclopoids). Prey consumption by the fish was highest under conditions with inorganic turbidity, while in the fishless treatments, small cladocerans (along with calanoids) had a high density. Organic turbidity offered refuge against fish predation to A. glabra, C. sphaericus, Daphnia pulex, M. alburquerquensis and A. americanus, whereas inorganic turbidity allowed only both test copepods to coexist in the presence of fish. The results suggest that fish predation is a powerful factor regulating zooplankton communities, even in highly turbid waters.