Ayşe İdil Çakıroğlu

Fish assemblage and diversity in lakes of western and central Turkey: role of geo-climatic and other environmental variables

Abstract We conducted a fish survey in 40 lakes in western and central Turkey. Fifty species (one to eleven per lake) were recorded, including eighteen endemic and seven alien species. We investigated which local geo-climatic and other environmental variables shaped the fish assemblages. Altitude and temperature turned out to be the most important factors for total species richness as well as richness of omnivorous and zooplanktivorous species and the Shannon–Wiener diversity index, with more species and higher diversity occurring in the warmer lowland lakes. Altitude may affect the fish assemblage directly through dispersal limitation or indirectly by creating a gradient in temperature with which it was strongly correlated. Cyprinidae was the most species-rich and widespread family. Atherinidae, Gobiidae, and Mugilidae (families of marine origin) were mainly found in the lowland regions, while Salmonidae exclusively appeared in the high-altitude lakes. The presence of widely distributed translocated native and alien species revealed a large human impact on the fish assemblages, potentially threatening the rich endemic fish fauna in lakes in this region.

Water level and fish-mediated cascading effects on the microbial community in eutrophic warm shallow lakes: a mesocosm experiment

Information on the effects of water level changes on microbial planktonic communities in lakes is limited but vital for understanding ecosystem dynamics in Mediterranean lakes subjected to major intra- and inter-annual variations in water level. We performed an in situ mesocosm experiment in an eutrophic Turkish lake at two different depths crossed with presence/absence of fish in order to explore the effects of water level variations and the role of top-down regulation at contrasting depths. Strong effects of fish were found on zooplankton, weakening through the food chain to ciliates, HNF and bacterioplankton, whereas the effect of water level variations was overall modest. Presence of fish resulted in lower biomass of zooplankton and higher biomasses of phytoplankton, ciliates and total plankton. The cascading effects of fish were strongest in the shallow mesocosms as evidenced by a lower zooplankton contribution to total plankton biomass and lower zooplankton:ciliate and HNF:bacteria biomass ratios. Our results suggest that a lowering of the water level in warm shallow lakes will enhance the contribution of bacteria, HNF and ciliates to the plankton biomass, likely due to increased density of submerged macrophytes (less phytoplankton); this effect will, however, be less pronounced in the presence of fish.

Effects of nutrient and water level changes on the composition and size structure of zooplankton communities in shallow lakes under different climatic conditions: a pan-European mesocosm experiment

Lentic ecosystems act as sentinels of climate change, and evidence exists that their sensitivity to warming varies along a latitudinal gradient. We assessed the effects of nutrient and water level variability on zooplankton community composition, taxonomic diversity and size structure in different climate zones by running a standardised controlled 6-months (May to November) experiment in six countries along a European north–south latitudinal temperature gradient. The mesocosms were established with two different depths and nutrient levels. We took monthly zooplankton samples during the study period and pooled a subsample from each sampling to obtain one composite sample per mesocosm. We found a significant effect of temperature on the community composition and size structure of the zooplankton, whereas no effects of water depth or nutrient availability could be traced. The normalised size spectrum became flatter with increasing temperature reflecting higher zooplankton size diversity due to higher abundance of calanoid copepods, but did not differ among depths or nutrient levels. Large-bodied cladocerans such as Daphnia decreased with temperature. Taxonomic diversity was positively related to size diversity, but neither of the two diversity measures demonstrated a clear pattern along the temperature gradient nor with nutrient and water levels. However, genus richness decreased at the warm side of the temperature gradient. Our experiment generally supports recent empirically based findings that a continuing temperature increase may result in lower genus richness and lower abundance of large-sized zooplankton grazers, the latter likely resulting in reduced control of phytoplankton.

Patterns of microbial food webs in Mediterranean shallow lakes with contrasting nutrient levels and predation pressures

Abstract To elucidate the specific and combined effects of bottom-up and top-down control on the microbial community in warm lakes, we sampled microbial community along with physical–chemical and biological variables and performed in situ food web experiments, in 14 Turkish shallow lakes with contrasting nutrient levels and predation pressures. Our field results revealed that differences in microbial communities correlated with differences in zooplankton community structure, temperature (increasing nutrient concentrations, change in zooplankton composition), nutrient concentrations (increasing bacteria and heterotrophic nanoflagellate abundances with increasing nitrogen concentrations and temperature) and macrophyte coverage (ciliates as potential consumers of bacteria and HNF was strongest in macrophyte-dominated lakes). Our in situ experimental study revealed that the zooplankton not only affect the biomass and composition of microbial communities but also alter the microbial structure and trophic relationships. Our results therefore indicate that both bottom-up factors and top-down effects were important for the efficiency of the carbon transfer from bacteria to higher trophic levels in the study lakes. Due to an anticipated increase in eutrophication, temperature and alteration of the classical food web with climate warming, major changes in the microbial community of lakes are, therefore, expected in a warmer future in semi-arid Mediterranean climatic regions.