Zooplankton adaptation strategies against fish predation in Turkish shallow lakes

Publication Type:

Thesis

Source:

Department of Biology, Middle East Technical University, Ankara, p.181 (2012)

Abstract:

In this PhD study, the factors influencing zooplankton community structure in Turkish shallow lakes were elucidated with four main approaches: (i) space-for-time substitution for shallow lakes using snap-shot sampling in 31 lakes along a latitudinal gradient; (ii) in-situ mesocosm experiments in eleven lakes along a latitudinal gradient using three sets of artificial plants systems; (iii)‘Habitat Choice’ laboratory experiments mimicking a ‘shallow littoral’ zone with plants and a ‘deeper pelagic’ zone with sediments testing the response of Daphnia magna to predation cues; and (iv) long-term monitoring data (1997-2011) from two interconnected lakes. Snap-shot and long-term monitoring showed that eutrophication has a strong influence on the zooplankton community via increased fish predation, nutrient loading and salinization. Here too the zooplankton community shifted towards a smaller sized profile, especially in lakes located at lower latitudes. Moreover, The laboratory and in-situ mesocosm experiments revealed that under predation risk Daphnia preferred to hide near sediment instead of using submerged plants as a refuge. Accordingly, in-situ mesocosm experiments revealed a predation pressure induced size structure shift towards small-medium sized zooplankton and calanoid copepods. The long-term monitored lakes experienced (i) drought-induced water level drop, leading to increased salinity and eutrophication, and consequent anoxic conditions and fish kill; as well as (ii) biomanipulation in the downstream lake. Both conditions resulted in major reduction in the top-down control of fish and ultimate predomination by large sized Daphnia spp. Nevertheless, the excessive exploitation of lakes and ongoing warming entail Turkish shallow lakes to become more eutrophic, making this study indicative for the Mediterranean region.