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

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

Factors influencing zooplankton size structure at contrasting temperatures in coastal shallow lakes: Implications for effects of climate change

We assessed the importance of temperature, salinity, and predation for the size structure of zooplankton and provided insight into the future ecological structure and function of shallow lakes in a warmer climate. Artificial plants were introduced in eight comparable coastal shallow brackish lakes located at two contrasting temperatures: cold-temperate and Mediterranean climate region. Zooplankton, fish, and macroinvertebrates were sampled within the plants and at open-water habitats. The fish communities of these brackish lakes were characterized by small-sized individuals, highly associated with submerged plants. Overall, higher densities of small planktivorous fish were recorded in the Mediterranean compared to the cold-temperate region, likely reflecting temperature-related differences as have been observed in freshwater lakes. Our results suggest that fish predation is the major control of zooplankton size structure in brackish lakes, since fish density was related to a decrease in mean body size and density of zooplankton and this was reflected in a unimodal shaped biomass-size spectrum with dominance of small sizes and low size diversity. Salinity might play a more indirect role by shaping zooplankton communities toward more salt-tolerant species. In a global-warming perspective, these results suggest that changes in the trophic structure of shallow lakes in temperate regions might be expected as a result of the warmer temperatures and the potentially associated increases in salinity. The decrease in the density of largebodied zooplankton might reduce the grazing on phytoplankton and thus the chances of maintaining the clear water state in these ecosystem

Plant-associated macroinvertebrates along the salinity gradient.

<p>Plant-associated macroinvertebrates density in black and richness in red (±1SE).</p

Plant-associated and free-swimming macroinvertebrate species present in cold temperate and Mediterranean shallow lakes with indication of potentially predatory species (*).

<p>(P) macroinvertebrates sampled by removing the artificial plants and therefore considered plant-associated macroinvertebrates; (F) macroinvertebrates sampled by nets and therefore considered free-swimming macroinvertebrates; (P+F) macroinvertebrates sampled both by nets and removing the artificial plants and therefore considered both plant-associated and free-swimming macroinvertebrates. Note: only potentially predators were considered in the free-swimming macroinvertebrate community (see also methods for details). In brackets, number of species for each taxonomic group in each region.</p

Densities of plant-associated macroinvertebrates, free-swimming potentially predatory macroinvertebrates and fish, and taxon richness of plant-associated macroinvertebrates.

<p>The data are means (±1SE) of data collected at day and night-time in four lakes in the cold temperate region and four lakes in the Mediterranean region. Fish biomass in fresh weight.</p

Relative abundance of plant-associated macroinvertebrate taxa.

<p>Relative abundance of plant-associated macroinvertebrate taxa.</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

Main limnological characteristics of the eight study lakes at the time of the experiment. TP, total phosphorus; TN, total nitrogen.

<p>Main limnological characteristics of the eight study lakes at the time of the experiment. TP, total phosphorus; TN, total nitrogen.</p

Densities of fish species in the lakes.

<p>Mean abundance (ind. m⁻²) and biomass in fresh weight (g m⁻²), with standard error (SE) of each fish species captured in the eight studied lakes and with indication of typical consumption of macroinvertebrate prey (⁺) and periphyton (*) as indicated in the literature <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030877#pone.0030877-Monakov1" target="_blank">[32]</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030877#pone.0030877-Vizzini1" target="_blank">[39]</a>.</p