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

Abstract

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 ecosystems.

Is Recovery of Large-Bodied Zooplankton after Nutrient Loading Reduction Hampered by Climate Warming? A Long-Term Study of Shallow Hypertrophic Lake Søbygaard, Denmark

“…Accordingly, we found that summer air temperatures, especially in April where fish are spawning, have become warmer in the region during the study period, and the changes were significantly correlated with the abundances of small (positive) and large fish (negative). Concurrently, field research undertaken in numerous European lakes has shown a significant decline in fish body size with decreasing latitude and thus higher temperatures [20,21,25,61]. The change in fish body size might be a result of improved recruitment of fish due to higher temperatures in spring and likely also as a result of increasing survival of young fish during winter due to a shorter ice cover period [29].…”

Ecological impacts of global warming and water abstraction on lakes and reservoirs due to changes in water level and related changes in salinity

“…Global warming reinforces the eutrophication of already eutrophic lakes (Moss et al, 2011), with significant changes in lake food web structure and community composition Meerhoff et al, 2007;Brucet et al, 2010;Jeppesen et al, 2010a, b;Brucet et al, 2012;Meerhoff et al, 2012), and causes higher proportions of cyanobacteria in summer (Wagner & Adrian, 2009;Kosten et al, 2012). In the Mediterranean climate zone and other areas with semi-arid desert climates, changes in water level, hydraulic retention time and salinity associated with warming may have considerable further effects on lake ecosystem structure and dynamics (reviews by Wantzen et al, 2008, andBrucet et al, 2010;Zohary & Ostrovsky, 2011;Brucet et al, 2012).…”

“…In the Mediterranean climate zone and other areas with semi-arid desert climates, changes in water level, hydraulic retention time and salinity associated with warming may have considerable further effects on lake ecosystem structure and dynamics (reviews by Wantzen et al, 2008, andBrucet et al, 2010;Zohary & Ostrovsky, 2011;Brucet et al, 2012). Besides nutrient loading, evaporative up-concentration of nutrients in reduced water volumes becomes an additional factor enhancing eutrophication under warmer conditions (Ö zen et al, 2010), and longer water residence time may favour the rowth and blooming of cyanobacteria, especially the toxin-producing ones such as Microcystis spp.…”

Effects of salinity tolerances on survival and life history of 2 cladocerans

“…In addition, with the increase in concentrations an increase in BL and BW was observed. These results suggest that changes in the body structure of zooplankton are caused by increases in salinity (Brucet et al, 2010).…”