Effects of diet on dimensions, density and sinking rates of fecal pellets of the copepod Acartia tonsa

Abstract

ABSTRACT. The effects of food type and concentration on fecal pellet characteristics of the calanoid copepod Acartia tonsa were examined in the laboratory. Copepods were fed several autotrophic and heterotrophic diets, including the diatoms Thalassiosira weissflogii and Chaetoceros neogracile, the photosynthetic flagellates Rhodomonas lens and Tetraselmis sp., the heterotrophic dinoflagellate Oxyrrhis marina, the heterotrophic flagellates Cafeteria sp. and Oikomonas sp., and the scuticociliate Uronema sp. Copepods were fed both a low (-100-300 pg C l-l) and a high (-500-1500 pg C l") concentration of these diets. Length. width and density of the resulting fecal pellets were measured. Sinking rates were calculated from a semi-empincal model based on these parameters. In general, diets that resulted in large pellets also resulted in the least dense pellets. Ciliate and diatom diets produced the largest pellets and resulted in the fastest estimated sinking rates. Heterotrophic flagellate and heterotrophic dinoflagellate diets resulted in the most dense and slowest sinking pellets Within a diet, significant differences in pellet characteristics were often found between food concentrations, but there was no consistent pattern of increasing or decreasing pellet size or density with an increase in food concentration. The coefficient of variation of pellet sinking rates across all diets in this study was nearly 40%. This indicates the uncertainty in estimated sinking rates if dlet is not considered. Combining the sinking rates from this study with published diet-specific fecal pellet degradation rates, we define an L-ratio, the fraction of pellet degradation per unit length of sinklng. The L-ratio may be useful in predicting the degree of recycling of pellets within the mixed layer. Diatoms show the lowest L-rat~os and photosynthetic fldgellates the highest L-ratios.

Modeling sinking rate of zooplankton carcasses: Effects of stratification and mixing

“…for copepod fecal pellets is , 150 kg m 23 (Feinberg and Dam 1998), which is 3 times higher than that for zooplankton carcasses. Consequently, environmental factors, such as temperature-driven variations in the water density and viscosity, affect their sinking rates to a much smaller degree than that of zooplankton carcasses.…”

Diatom-associated bacteria are required for aggregation of Thalassiosira weissflogii

“…The solid hydrated density (r s , gcm À3 ) of the particles inside the aggregates was determined in a density gradient using a modified version of previously reported methods (Schwinghamer, 1991;Feinberg and Dam, 1998). Seven dilutions were made using Ludox TM colloidal silica (SigmaAldrich, Munich, Germany), sucrose and distilled water ranging in density from 1.05 to 1.43 g cm À3 .…”

Testing for resistance of pelagic marine copepods to a toxic dinoflagellate

“…Both copepod populations were reared in these cultures under identical conditions (12-15°C and 12 h : 12 h light-dark regime) for over 11 generations (Colin and Dam, 2002a). Animals in the cultures were fed, what we term, their 'standard diet' ($ 500 lg CL )1 ) consisting of a mixture of equal proportions of Thalassiosira weissflogii, Isochrysis galbana and Rhodomonas lens (Feinberg and Dam, 1998). Rearing all of the copepod populations at the same temperature, light and food regimes for several generations eliminated both maternal effects and environmental variance.…”