Trophic Interactions among a Beetle Predator, a Chironomid Grazer, and Periphyton in a Seasonal Wetland

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Abstract
Trophic interactions among a predaceous hydrophilid beetle larva, Berosus ingeminatus d'Orchymont, a grazing chironomid midge larva, Cricotopus sylvestris (Fabr.), and algal periphyton were examined in 11 experimental ponds. Each pond was divided into two plant-cover treatments, 50% plant-cover and unmanipulated plant-cover (100%), to determine how differences in plant-cover influenced interactions. After the ponds were flooded in September, higher numbers of adult B. ingeminatus beetles colonized 50% plant-cover treatments than 100% plant-cover treatments; after these beetle adults reproduced, a similar pattern existed for their predaceous larvae from October until March, when the ponds were drained. In 50% plant-cover treatments, the abundant beetle larvae reduced autumn densities of midge larvae, which allowed periphyton to grow independently of midge density. When densities of beetle larvae declined in winter, midge populations increased. In the 100% plant-cover treatments, with low numbers of larval beetle predators, a close relationship existed between densities of C. sylvestris midge larvae and periphyton biomass. Grazing by midge larvae reduced periphyton biomass, which in some instances then resulted in insufficient periphyton reserves to further support high midge production. Although predation eliminated many midge larvae, seasonal production of midges was marginally higher in habitats with abundant beetle predators than in habitats with fewer predators.

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