Effect of mesozooplankton feeding selectivity on the dynamics of algae in the presence of intermediate grazers-a laboratory simulation

摘要

An indirect increase in algal abundance that is induced by mesozooplankton preda-tion on intermediate trophic level grazers (microzooplankton) is among the factors that shape the structure of a marine planktonic food web (copepods/cladocerans-ciliates-algae). Marine mesozooplankton include species with diverse feeding strategies, and hence they play different roles in trophic interactions. In this study, we simulated a simple pelagic food web in the laboratory using 3 copepod species and 1 cladoceran as top predators to test the hypothesis that different species with different feeding behaviors will cause different impacts on prey communities. Our results showed that among the 3 crustacean mesozooplankton species, Parvocalanus crassirostris was the most carnivorous species that caused the strongest cascading effect, which led to an increase in algal density as the rate of the cascading effect exceeded the direct consumption of algal prey by intermediate consumers. In contrast, the marine cladoceran Penilia avirostris generally caused a decline in algal density because it created no indirect positive effect on algae since it was incapable of capturing the intermediate grazers. Temora turbinata fed on ciliates and algal prey at similar rates so that the direct consumption of the algal prey was balanced by the indirect trophic cascade effect. The strength of the cascade effect induced by Acartia erythiaea was significantly enhanced by increasing the densities of ciliates. The mechanism was due to a switch in preying behavior from suspension feeding to ambush feeding. Our results imply that mesozooplankton omnivory is important in maintaining the stability of the community structure of microplankton because the effects of direct consumption and the cascading effect balanced each other due to the broad feeding strategies of predators.