Feeding of Copepodite and Adult Stages of Eudiaptomus Gracilis (G.O. Sars, 1863) (Copepoda, Calanoida) On Mixed Plastic Beads

Abstract

AbstractSize selection of Eudiaptomus gracilis copepodites (CI-CV) and adults was studied in feeding experiments with beads of 1-84 μm diameter. Concentration of particles ranged between 1.3-2.1 x 107 beads ml-1, i.e. it was similar to the natural particle concentration. Animals were collected in Lake Balaton and acclimated to laboratory conditions for a few days before the experiments. On average, 91% of the experimental animals ingested beads. Almost each of the bead-ingesting animals took in 1 μm beads. Young copepodites had a narrow size spectrum (1-12 μm), whereas old copepodites and adults had broader spectra (1-39 μm). The number of ingested beads varied widely in each stage and among the individuals of the same stages. Diameter of the largest ingested bead, average number of beads in the guts, and clearance rate increased linearly with dry weight of the different stages (p < 0.001). Clearance rates were different for various particle sizes. Relatively high clearance rates were obtained for 6 μm and 10-12 μm beads in each stage. Moreover, older copepodites had higher clearance rates for beads of 20 and 25 μm diameter, and clearance rates of adults increased for larger than 30 μm particles. CI copepodites selected for particles of 4-12 μm diameter, and their selectivity increased with the increasing bead size within this range. Older stages selected only for beads larger than 12 μm, whereas adults did only for beads larger than 22 μm.