Turbidity effects on feeding by larvae of the endemic Ambystoma mexicanum and the introduced Oreochromis niloticus in Lake Xochimilco, Mexico

Abstract

We tested the effects of turbidity on the prey consumption by larvae of an endemic predator (Ambystoma mexicanum) and an introduced predator (Oreochromis niloticus). Prey visibility is influenced by turbidity due to organic (algae, detritus) or inorganic (sediment) matter. We hypothesized that the axolotl would be more adversely influenced by high turbidity as compared to Tilapia, resulting in a decrease in the population of the former under natural conditions. In order to test this, we conducted prey preference experiments and tested the reactive distance of both predators at different turbidity levels. Prey species used were the cladocerans Alona glabra, Moina macrocopa, Macrothrix triserialis and Simocephalus vetulus and the ostracod Heterocypris incongruens. In both, clear and turbid waters, the fish consumed about 17.5% and 2.5%, respectively, more prey. The axolotl had a greater preference for H. incongruens and M. triserialis, and the fish for S. vetulus and M. triserialis. These results indicate that turbidity decreases the visual ability during the larval stages of A. mexicanum which in turn influences its capacity to compete against the invasive fish. Implications of these results on conservation efforts for the highly endangered Ambystoma mexicanum are discussed.