Depth-related effects on a meiofaunal community dwelling in the periphyton of a mesotrophic lake

Kreuzinger B, Schroeder F, Majdi N, Traunspurger W. Depth-related effects on a meiofaunal community dwelling in the periphyton of a mesotrophic lake. PLoS One. 2015;10(9): e0137793.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

Analysis of the invertebrate community in moss with focus on trophic relationships

Kreuzinger-Janik B. Analysis of the invertebrate community in moss with focus on trophic relationships. Bielefeld: Universität Bielefeld; 2021

Population density, bottom-up and top-down control as an interactive triplet to trigger dispersal

Kreuzinger-Janik B, Gansfort B, Ptatscheck C. Population density, bottom-up and top-down control as an interactive triplet to trigger dispersal. Scientific Reports. 2022;12(1): 5578.**Abstract** Dispersal reflects the trade-offs between the cost of a change in habitat and the fitness benefits conferred by that change. Many factors trigger the dispersal of animals, but in field studies they are typically not controllable; consequently, they are mostly studied in the laboratory, where their single and interactive effects on dispersal can be investigated. We tested whether three fundamental factors, population density as well as bottom-up and top-down control, influence the emigration of the nematodeCaenorhabditis elegans. Nematode movement was observed in experiments conducted in two-chamber arenas in which these factors were manipulated. The results showed that both decreasing food availability and increasing population density had a positive influence on nematode dispersal. The presence of the predatory flatwormPolycelis tenuisdid not consistently affect dispersal but worked as an amplifier when linked with population density with respect to certain food-supply levels. Our study indicates that nematode dispersal on small scales is non-random; rather, the worms’ ability to perceive environmental information leads to a context-dependent decision by individuals to leave or stay in a patch. The further use of nematodes to gain insights into both the triggers that initiate dispersal, and the traits of dispersing individuals will improve the modeling of animal behavior in changing and spatial heterogenous landscapes

Who feeds on whom in semi-aquatic moss ecosystems?

Kreuzinger-Janik B, Traunspurger W, Majdi N. Who feeds on whom in semi-aquatic moss ecosystems? Food Webs . 2022;32: e00237.Moss patches growing at the interface between terrestrial and limnic ecosystems (in the splash-water zone) are colonized by terrestrial, semi-aquatic, and aquatic animals. Besides being a refuge, mosses provide food resources, such as micro-algae, particulate organic matter, and moss tissues themselves. In this study, the standing stocks and isotopic signatures of both resources and consumers were measured to analyze the trophic channels utilized by moss-dwelling consumers in two semi-aquatic moss ecosystems of a stream and a lake. The mean total invertebrate abundance (+/- SD) in the lake mosses was 1109.08 +/- 230.33 ind.10(gmoss)DW(- 1), which was ~4-fold higher than in the stream (265.37 +/- 184.62 ind.10(gmoss)DW(-1)). We found that moss tissues were a fairly minor contributor to the diets of the invertebrates; instead the most important resource for invertebrates was the epiphytic biofilms growing on them. The moss-dwelling community in the lake occupied a larger isotopic space than in the stream, suggesting a lower trophic redundancy of the community in the lake. This was especially the case for the delta C-13 range, which was 39% larger in the lake than in the stream, where delta C-13 signatures appeared more focused. In contrast, the delta N-15 range of the invertebrate community associated with mosses was rather large and did not differ substantially between stream and lake. Dorylaimid nematodes, predatory dipters and water mites showed enriched delta N-15 signatures suggesting they could occupy apex positions in moss food webs despite their small body sizes. Our results suggested that mosses were not an important food resource, but instead their textural complexity enabled a coherent and relatively large invertebrate food web composed of detritivores, algivores, omnivores, predators, and probably parasites

Distribution and diversity of meiofauna along an aquatic-terrestrial moss ecotone

Kreuzinger-Janik B, Majdi N, Traunspurger W. Distribution and diversity of meiofauna along an aquatic-terrestrial moss ecotone. Nematology. 2021;23(6):695-714.**Summary** This study provides first insights into the moss-dwelling meio-invertebrate community inhabiting mosses collected from underwater, splash-water and adjacent terrestrial habitats along a Swedish lake. Additionally, changes in both species and functional diversity of the nematode community were followed. Total meio-invertebrate mean densities and biomass peaked at 10 644.2 ± 2391.8 individuals (g dry weight (DW) moss)−1and 14 199.3 ± 5037.3 μg DW (g DW moss)−1underwater, 1 m away from the shoreline, where the community was strongly dominated by rotifers, followed by nematodes. Total invertebrate biomass in terrestrial mosses was much lower, indicative of a significantly higher carrying capacity of moss patches in aquatic environments, which provide a high level of resource turnover as well as a buffer against desiccation and extreme temperature fluctuations. We found a total of 74 nematode species and maximum diversity was attained 1 m away from the shoreline and at the splash-water zone. The underwater mosses at the shoreline thus housed the most diverse and abundant assemblages of meio-invertebrates, suggesting they may play an important ecological role at the land-water interface. Evidenced by the multiple shifts in dominance, our study clearly showed that feeding types differed between habitats. The taxonomic and functional segregation of the nematode community along the ecotone further indicated that the composition of nematode species assemblages has the potential to mirror the ecological changes of the study site, even at small scales

It's all about food: Environmental factors cause species‐specific dispersal

Kreuzinger-Janik B, Gansfort B, Traunspurger W, Ptatscheck C. It's all about food: Environmental factors cause species‐specific dispersal. Ecosphere. 2022;13(10).Abstract Dispersal is a vital component of the life history of nearly all organisms. Theability to disperse determines the distribution and abundance of a species andthus its community dynamic at different sites. The scientific challenge is todesign standardized laboratory experiments that not only record the effects ofsingle factors but also include the multicausal nature of dispersal. Here we testedthe effect of the environmental factorsdensity, food availability and predation,and the combinations thereof on the dispersal of five free-living nematode speciesby performing experiments in two-patched systems. We hypothesized thatemigration is generally positively correlated with the intrinsic rate of naturalincrease and would decrease with increasing food availability and increase bothwith the presence of a predator and at higher initial population densities.These predictions were tested both using single-species tests with laboratorycultures and using intact natural nematode communities to investigate whetherenvironmental factors determine the composition of dispersing species. Theresults of our study revealed a positive correlation between dispersal and intrinsicgrowth ability, whereas the studied nematode species differed in their dispersalpatterns, both under control conditions and in response to bottom-up, top-down,and density-dependent stimuli. Despite the species-specific differences indispersal behavior in response to the environmental factors, the availability offood appeared as the main driver. This was particularly pronounced regarding anatural nematode community. Our experiments emphasize the central role offood availability in spatial structuring nematode communities

Glossary of terms.

<p>Glossary of terms.</p

Survival, fecundity and egg production of <i>Pristionchus pacificus</i> (strain PS312).

<p>Nematodes were cultured at 20°C by means of the hanging drop method. The survival data fit a type I attenuation curve, which is typical in species with a low level of juvenile mortality [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0134105#pone.0134105.ref036" target="_blank">36</a>]. Values are reported as the means (N = 33, ±SD).</p

Hatching time (h) for <i>Caenorhaditis elegans</i> and <i>Pristionchus pacificus</i>.

<p>Values are means.</p><p>Hatching time (h) for <i>Caenorhaditis elegans</i> and <i>Pristionchus pacificus</i>.</p

Life table of <i>P</i>. <i>pacificus</i> (N = 33).

<p>D (h) = time interval; l_x = juvenile survival probability; m_x = mean number of juveniles produced.</p><p>Life table of <i>P</i>. <i>pacificus</i> (N = 33).</p