Depth-Related Effects on a Meiofaunal Community Dwelling in the Periphyton of a Mesotrophic Lake

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.

Environmental factors regulate the fatty acid content of primary producers and consumers in a freshwater pond in a warming world

“…Abiotic factors (i.e., light, nutrients, and water temperature) have been shown to affect biofilm quantity and quality, both separately and interactively. Depth can have varying effects on biofilm biomass, depending on the growth substrate, however, artificial substrates have been used to show increased biofilm biomass at shallower depths (Liboriussen & Jeppesen 2006Yang & Flower 2012;Sánchez et al 2013;Schroeder et al 2013;Kreuzinger-Janik et al 2015). The effect of grazers and nutritional quality of biofilm has also been studied in relation to depth.…”

“…3.11) than shallower biofilm (25 and 50 cm). Greater algal biomass is typically observed near the water surface during summer months (Liboriussen & Jeppesen 2009;Kreuzinger-Janik et al 2015), where the high levels of PAR irradiance can stimulate algal growth. Chlorophyll samples were not analyzed for this experiment, however, higher UV (-R, -A, and -B) observed at shallower depths during both seasons may have also reduced biofilm biomass near the water surface, as UV radiation can reduce AFDW and densities of cellular biovolume (Vinebrooke & Leavitt 1996).…”

“…Thus, the increase in pelagic phytoplankton growth and biomass during summer months typically supresses the growth of biofilm (Hansson 1988(Hansson , 1992Sand-Jensen & Borum 1991;Havens et al 2001a;Vadeboncoeur et al 2001) and this suggests that pelagic phytoplankton play key role in determining light availability for underlying biofilm communities. Studies examining depthrelated effects of biofilm typically observe greater algal biomass (measured via chl a content) when biofilm is growing near the water surface, especially during spring/summer months (Liboriussen & Jeppesen 2009;Kreuzinger-Janik et al 2015) and relate it to greater PAR irradiance at shallower depths (Yang and Flower 2012;Schroeder et al 2013).…”

“…Artificial surfaces typically misrepresent natural communities as they can underestimate both biomass (Cattaneo & Amireault 1992) and species richness (Barbiero 2000) compared to natural surfaces. However, due to the high replicability of artificial surfaces (Barbiero 2000) they have been used to clearly demonstrate that lower biofilm biomass is typically observed at greater depths (Liboriussen & Jeppesen 2006Sánchez et al 2013;Kreuzinger-Janik et al 2015).…”

“…This decrease in biofilm biomass at greater depths is typically linked with the decreasing algal biomass (Liboriussen & Jeppesen 2009;Kreuzinger-Janik et al 2015) due to diminishing light availability vertically in the water column (Yang & Flower 2012;Schroeder et al 2013). The effect of depth on biofilm biomass has typically been studied in the context of grazers, however, limited work has examined the nutritional value (standardized for organic biomass) of depthdistributed biofilm, especially in terms of the physiologically-important PUFA.…”