The influence of variations in reedswamp structure and extent upon macroinvertebrates and associated ecological processes within the littoral zone of lakes

Reedswamps are a key feature of the shallows of many lakes, influencing biodiversity and functioning, but are in decline in lakes throughout Europe for reasons that are unclear. Metadata analysis of data extending over 100 years suggested that multiple stressors were implicated in reedbed decline within Windermere (UK), and that the influences of individual stressors should be investigated by comparing genetic diversity and environmental factors across lakes within the same catchment or region. Furthermore, the consequences of changes in reedswamp structure and coverage for whole lake functioning is an important gap in knowledge for Windermere and many other lakes. Macroinvertebrate data from two lakes in the Windermere catchment were used to investigate the influence of reedswamp habitat upon biodiversity, and key ecological processes such as decomposition. A semi-quantitative survey highlighted the importance of reedswamp size, shape, and structure in determining the ways in which macroinvertebrates influence lake functioning. Collection of macroinvertebrates from a wide range of niches along vertical and horizontal axes using a hand-net was a unique approach, and provided novel insights into key ecological processes. For example, seasonal influences were modified by structural heterogeneity, and position within reedswamps. This was supported by the findings of a field-based litter bag experiment; differences in macroinvertebrate seasonal dynamics were associated with differences in litter structure from two species of reed. Furthermore, there were interspecific differences in seasonal patterns of litter deposition. Both macroinvertebrate methods were efficient and effective, and should form the basis of a standardised sampling protocol for the shallows of lakes. This body of research on local variations (~8 m) demonstrates the need for a detailed understanding of how structural heterogeneity influences whole lake functioning. This should include comprehensive food webs that include vertebrates, macroinvertebrates, macrophytes, algae, and microbes for reedswamp and other key habitats.