The structure of the littoral: effects of waterlily density and perch predation on sediment and plant‐associated macroinvertebrate communities

Abstract

Summary Littoral zones are complex and important for mechanisms that maintain clear water and submerged plant dominance in lakes. Details of their structure are scarce, largely because sweep or grab sampling, the most commonly used approach, is unable to reveal much subtlety. Invertebrate communities of plankton and sedimentary benthos, and of those living on submerged and floating leaves and their petioles of Nuphar lutea, were separately sampled from 2‐m2 mesocosms in a shallow lake, with different lily densities in the absence or presence of perch (Perca fluviatilis). Increasing plant density led to reduced sedimentary benthos populations other than those of tubificids. This was ascribed to greater shading of algal producers on the surface sediment by the increasing leaf canopy. Increasing leaf canopy increased the populations of several plant‐associated taxa, suggesting that habitat availability was potentially limiting for these. Submerged leaves supported more invertebrates per unit area than submerged petioles or the undersides of floating leaves. Greater periphyton production on leaf surfaces that had thinner cuticles and less waxy surfaces was probably responsible. Perch predation had unexpectedly little effect, although the perch fed widely among the subhabitats, and fish population densities were relatively high. Predation was most intense on the planktonic and sedimentary benthos communities, especially on actively motile invertebrates such as isopods and amphipods. Macroinvertebrates associated with plant surfaces, not least the predominant Acroloxus lacustris, were relatively immune. There were more predator effects on submerged leaves than on floating leaves and their petioles. Perch fed less effectively on some taxa at naturally high plant densities than at low and medium densities, and overall, the littoral communities showed resilience to fish predation, probably through the complexity of the plant structure.