Should I stay or should I go? The diurnal behaviour of plant-attached zooplankton in lakes with different water transparency

<p>The role of transparency on the diurnal distribution of plant-attached cladocerans was studied in two similar-sized lakes with contrasting water colour. The diurnal attachment behaviour of <em>Sida crystallina</em> (O.F. Müller, 1776) was more pronounced in the less humic lake where the animals remained fixed on plants, indicating that staying attached was a more profitable option. In the highly humic lake, the pattern was opposite, and regardless of time the highest density observed was in the free-swimming individuals, with only few animals attached to the floating-leaves for refuge, indicating that low transparency provided sufficient protection against predation. The attached <em>S. crystallina</em> were larger compared to free-swimming individuals in the more transparent lake, suggesting greater vulnerability of large-sized individuals to predation. The results indicate that increasing concentrations of humic substances affecting the light environment may alter the diurnal behaviour and habitat use of plant-attached zooplankton. </p>