Grazing rates of freshwater copepod Thermocyclops decipiens (Kiefer, 1929) on Chlorella vulgaris under different light intensities

Abstract

Light is one of the most important structuring factors for life in aquactic biology. For zooplankton grazers, including copepods, light offers a behavioral dilemma that is potentially present at both small and large scales. We investigated the grazing rate, clearance rate, fecal pellet production rate, egg production rate, percertage of egg hatching and survival percentage of the freshwater copepod Thermocyclops deceipiens under different light intensities (0 lx, 500 lx, 1500 lx) over periods of 15 days. For the grazing experiment the fresh water microalgae Chlorella vulgaris was used at concentrations 2–6 × 106 cells / mL−1. The grazing rates of the copepod decreased at higher light intensities when compared to other treatments. Maximum grazing rate and the clearance rate occurred in the treatment with 500 lx (70,490 cells copepod−1 h−1, 0.23 mL copepod−1 h−1). Egg production rate and hatching rate percentage (17.4 eggs female−1 day −1, 99 ± 0.98 %) were also higher at the algae fed with 500 lx light intensity. Copepods survived well and continuously produced fecal pellets on a 500 lx light intensity diet of Chlorella vulgaris. The results suggest that low light intensity influenced the grazing rate, fecundity and survival of copepod T.decipiens.