Abstract
Periphyton is a complex assemblage of micro- and meiofauna embedded in the organic matrix that coats most submerged substrate in the littoral of lakes. The aim of this study was to better understand the consequences of depth-level fluctuation on a periphytic community. The effects of light and wave disturbance on the development of littoral periphyton were evaluated in Lake Erken (Sweden) using an experimental design that combined in situ shading with periphyton depth transfers. Free-living nematodes were a major contributor to the meiofaunal community. Their species composition was therefore used as a proxy to distinguish the contributions of light- and wave-related effects. The periphyton layer was much thicker at a depth of 30 cm than at 200 cm, as indicated by differences in the amounts of organic and phototrophic biomass and meiofaunal and nematode densities. A reduction of the depth-level of periphyton via a transfer from a deep to a shallow location induced rapid positive responses by its algal, meiofaunal, and nematode communities. The slower and weaker negative responses to the reverse transfer were attributed to the potentially higher resilience of periphytic communities to increases in the water level. In the shallow littoral of the lake, shading magnified the effects of phototrophic biomass erosion by waves, as the increased exposure to wave shear stress was not compensated for by an increase in photosynthesis. This finding suggests that benthic primary production will be strongly impeded in the shallow littoral zones of lakes artificially shaded by construction or embankments. However, regardless of the light constraints, an increased exposure to wave action had a generally positive short-term effect on meiofaunal density, by favoring the predominance of species able to anchor themselves to the substrate, especially the Chromadorid nematode Punctodora ratzeburgensis.
Highlights
The littoral zones of lakes are highly dynamic regions subject to important physicochemical fluctuations along horizontal and vertical gradients
The amount of periphytic Chlorophyll a (Chl a) was significantly higher in the shallow than in the deep treatments and differed over time (F3,21 = 3.6, p< 0.05), whereas the interaction between depth and time was not significant
The Chl a concentration was three- to four-times higher at a depth of 30 cm than at a depth of 200 cm, with significant depth-dependent differences recorded at T0, T6, and T12
Summary
The littoral zones of lakes are highly dynamic regions subject to important physicochemical fluctuations along horizontal and vertical gradients. Almost every hard submerged substrate, including stones, woody debris, and macrophytes, is coated by periphyton, defined. Depth Constraints on Periphytic Meiofauna as a complex community comprising bacteria, fungi, algae, protozoa, and meiofauna embedded in a matrix of exopolymeric substances [1]. The importance of the periphyton community in the functioning of lake ecosystems has been increasingly recognized; for example, periphytic algae have a significant impact on whole-lake primary production [2,3]. Periphyton is an important mediator of nutrient cycling in lakes [10,11]
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