Floating large-volume mesocosms as a simple, lowcost experimental design suitable for the variety of lakes and reservoirs

Mesocosms represent a helpful tool enabling in situ experiments within the pelagic zone of lakes and reservoirs. Experimental studies using mesocosms are widely used in shallow lakes. Here, we describe an improved method suitable for deep freshwater ecosystems. We use a metal supporting framework carrying four polyethylene bags (circular cross-section, diameter 1.5 m, length 9.5 m). The mesocosm dimensions allow us to test hypotheses covering whole pelagic assemblages including the entire food chain up to fish as the top consumers. The floating construction is light, reusable and inexpensive. The suggested mesocosm design maintains conditions close to those occurring in the adjacent lake water and thus effectively simulates the pelagic environment for various experimental studies.