Motility of freshwater zooplankton from a temperate lagoon from Patagonia (Chubut, Argentina) throughout a year cycle: Influence of solar radiation.

J GONCALVES, RODRIGO; S BARBIERI, ELENA; VIRGINIA ESTELA VILLAFAÑE; WALTER HELBLING, E

Puerto Rico

Congreso; 33rd Annual Meeting of the American Society for Photobiology; 2006

We investigated the impact of solar ultraviolet radiation (UVR, 280-400 nm) on motility (i.e.,swimming speed) of dominating zooplankton species (cladocerans and copepods) from a freshwaterlagoon of Patagonia, Argentina, during a yearly cycle (February 2005 to February 2006). Zooplanktonsamples were collected with a net (200 m mesh size) from surface waters every 2-3 weeks;samples were put in UVR-transparent containers and exposed to solar radiation, insidetemperature-controlled water bath under three radiation treatments: 1) PAB (280-700 nm), 2) PA(320-700 nm), and 3) P (400-700 nm), and a control (no radiation). Swimming speed of free motileindividuals was measured every 2 h of exposure with an image-analysis system from videorecordings. Optical characteristics of the water body, i.e., the attenuation coefficient of PAR (400-700nm) (KdPAR) and mean irradiance (Im) in the upper mixed layer, were estimated from the measuredirradiance and published models taking into account the concentration of chlorophyll-a (Chl-a) andchromophoric dissolved organic matter (CDOM). Chl-a was variable between 4 and 800 g l-1, and itwas found to be the most important variable controlling KdPAR (range: 2-17 m-1).Carnivorous-cyclopoid copepods (Metacyclops sp) and herbivorous cladocerans (Daphnia sp.)dominated the zooplankton community at different times showing a negative relationship in theirabundance. Additionally, the abundance of cladocerans was negatively correlated with Chl-aconcentration, suggesting a top-down control of the phytoplankton population. Swimming speed ofboth zooplankton groups increased relatively when KdPAR was low (autumn / winter) and it decreasedwhen KdPAR was high. Solar ultraviolet radiation had relatively little impact on swimming speed andthese changes in motility seem to be more related to factors such as the underwater radiation field /KdPAR and prey concentration, than to the incident solar radiation.