Effects of Temperature, Salinity and Fish in Structuring the Macroinvertebrate Community in Shallow Lakes: Implications for Effects of Climate Change

Climate warming may lead to changes in the trophic structure and diversity of shallow lakes as a combined effect of increased temperature and salinity and likely increased strength of trophic interactions. We investigated the potential effects of temperature, salinity and fish on the plant-associated macroinvertebrate community by introducing artificial plants in eight comparable shallow brackish lakes located in two climatic regions of contrasting temperature: cold-temperate and Mediterranean. In both regions, lakes covered a salinity gradient from freshwater to oligohaline waters. We undertook day and night-time sampling of macroinvertebrates associated with the artificial plants and fish and free-swimming macroinvertebrate predators within artificial plants and in pelagic areas. Our results showed marked differences in the trophic structure between cold and warm shallow lakes. Plant-associated macroinvertebrates and free-swimming macroinvertebrate predators were more abundant and the communities richer in species in the cold compared to the warm climate, most probably as a result of differences in fish predation pressure. Submerged plants in warm brackish lakes did not seem to counteract the effect of fish predation on macroinvertebrates to the same extent as in temperate freshwater lakes, since small fish were abundant and tended to aggregate within the macrophytes. The richness and abundance of most plant-associated macroinvertebrate taxa decreased with salinity. Despite the lower densities of plant-associated macroinvertebrates in the Mediterranean lakes, periphyton biomass was lower than in cold temperate systems, a fact that was mainly attributed to grazing and disturbance by fish. Our results suggest that, if the current process of warming entails higher chances of shallow lakes becoming warmer and more saline, climatic change may result in a decrease in macroinvertebrate species richness and abundance in shallow lakes

Could artificial plant beds favour microcrustaceans during biomanipulation of eutrophic shallow lakes?

Introduction of artificial plants may facilitate the transition from a turbid to a clear-water state in shallow lakes, particularly when plant establishment is delayed. We investigated the usefulness of artificial plants as a restoration tool in an experimental setup mimicking open submerged plant beds with high plant density [80%, HPD] and low plant density [20%, LPD] in shallow Lake Vaeng, Denmark, having undergone biomanipulation in the form of extensive fish removal. Biological measures of the fish, and of both free-swimming (FSM) and plant-attached microcrustaceans (PAM) within the experimental beds and in the lake, were obtained from before, during and after biomanipulation. We found that microcrustacean measures (density, biomass and Cladocera:FSM) were significantly larger in the HPD beds, before and during fish removal, while the effect of plants was not significant after biomanipulation, with low fish biomass. On PAM, these effects were less pronounced and only significant after biomanipulation. Microcrustaceans were larger-bodied at HPD in all years, for both FSM and PAM. In conclusion, artificial plant beds acted as an effective microcrustacea refuge against fish, particularly for the FSM at HPD and in the years with high fish densities, providing further evidence that artificial plant beds could assist lake restoration efforts.Fil: Balayla, David. University Aarhus; DinamarcaFil: Boll, Thomas. University Aarhus; Dinamarca. University of Southern Denmark; DinamarcaFil: Trochine, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina. University Aarhus; DinamarcaFil: Jeppesen, Erik. University Aarhus; Dinamarca. Sino-Danish Centre for Education and Research; Chin

Effects of Temperature, Salinity and Fish in Structuring the Macroinvertebrate Community in Shallow Lakes: Implications for Effects of Climate Change

Climate warming may lead to changes in the trophic structure and diversity of shallow lakes as a combined effect of increased temperature and salinity and likely increased strength of trophic interactions. We investigated the potential effects of temperature, salinity and fish on the plant-associated macroinvertebrate community by introducing artificial plants in eight comparable shallow brackish lakes located in two climatic regions of contrasting temperature: cold-temperate and Mediterranean. In both regions, lakes covered a salinity gradient from freshwater to oligohaline waters. We undertook day and night-time sampling of macroinvertebrates associated with the artificial plants and fish and free-swimming macroinvertebrate predators within artificial plants and in pelagic areas. Our results showed marked differences in the trophic structure between cold and warm shallow lakes. Plant-associated macroinvertebrates and free-swimming macroinvertebrate predators were more abundant and the communities richer in species in the cold compared to the warm climate, most probably as a result of differences in fish predation pressure. Submerged plants in warm brackish lakes did not seem to counteract the effect of fish predation on macroinvertebrates to the same extent as in temperate freshwater lakes, since small fish were abundant and tended to aggregate within the macrophytes. The richness and abundance of most plant-associated macroinvertebrate taxa decreased with salinity. Despite the lower densities of plant-associated macroinvertebrates in the Mediterranean lakes, periphyton biomass was lower than in cold temperate systems, a fact that was mainly attributed to grazing and disturbance by fish. Our results suggest that, if the current process of warming entails higher chances of shallow lakes becoming warmer and more saline, climatic change may result in a decrease in macroinvertebrate species richness and abundance in shallow lake

Free-swimming potentially predatory macroinvertebrates and fish at different salinities.

<p>Mean densities (mean day and night densities, ±1SE) among submerged plants (S, black) and open sites (O, red) at different salinities.</p

Diel changes of fish and free-swimming potentially predatory macroinvertebrates at each lake.

<p>Diel changes in density of fish and free-swimming macroinvertebrate predators between submerged plants (S, black) and open sites (O, red).</p

Partial correlations from the stepwise multiple regression between the richness and density of plant-associated macroinvertebrates and the density of each taxonomic group with salinity and density of fish in that habitat (indicator of predation pressure).

<p>Significance levels as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030877#pone-0030877-t003" target="_blank">Table 3</a>. Degrees of freedom of the regression and the error are 2 and 62, respectively.</p

Density and richness of plant-associated macroinvertebrates, fish and large free-swimming potentially predatory macroinvertebrates and periphyton biomass in the Mediterranean and cold temperate region.

<p>Average (±SE) of density (ind. m⁻²) and richness of plant-associated macroinvertebrates (macroinv.), density of fish and large free-swimming potentially predatory macroinvertebrates (ind. m⁻²) and periphyton biomass (mg m⁻²) and <i>p</i>-values for the nested ANOVAs. Two-way nested ANOVA for density and richness of plant-associated macroinvertebrates and periphyton with factors ‘region’ (2 levels, cold temperate ‘T’ and Mediterranean ‘M’) and ‘lake’ (4 levels) nested inside region and three-way nested ANOVA for the density of fish and large free-swimming macroinvertebrate predators with ‘habitat’ (2 levels, open areas ‘O’ and submerged plants ‘S’) as an additional factor. The factor ‘lake’ nested inside region was significant for all variables (<i>p</i><0.01).</p

Densities of the different plant-associated macroinvertebrate taxa in the two regions.

<p>Mean density (ind. m⁻²) of the different plant-associated macroinvertebrate taxa and results of nested ANOVA (<i>F</i>-values) on the effects of ‘region’ (two levels, cold temperate and Mediterranean and ‘lake’ (four levels) nested inside ‘region’. Significance levels:</p>*<p><i>p</i><0.05,</p>**<p><i>p</i><0.01,</p>***<p><i>p</i><0.0001,</p><p>ns, non significant (p≥0.05).</p