Influence of carcass abundance on estimates of mortality and assessment of population dynamics in Acartia tonsa

Using 2 yr of field data on the abundances of live and dead planktonic copepod nauplii and Acartia tonsa copepodites from the lower Chesapeake Bay, we evaluated the accuracy of calculated mortality rates and modeled population dynamics. Copepod mortality rates were estimated from field data both before and after removal of carcasses from abundance values, resulting in significantly different mortality rates. After removing carcasses, instantaneous mortality rates for nauplii varied from \u3c0.01 d(-1) to a maximum of 0.35 d(-1) (in August 2009), and for A. tonsa copepodites from \u3c0.01 d(-1) in winter to 0.5 d(-1) or higher in summer. A simple model was used to evaluate the effect of both uncorrected and corrected mortality rate estimates on A. tonsa population dynamics. Model predictions more closely matched field observations when parameterized with corrected mortality rates, indicating the importance of the abundances of live and dead organisms for field studies in zooplankton ecology. We used the same field dataset to estimate the predatory and non-predatory components of mortality. Non-predatory mortality comprised an aver age of 25% of total mortality for nauplii, and 12% of total mortality for A. tonsa copepodites. Predatory mortality alone was insufficient to keep the A. tonsa population size under control during the growing season (from June to October), demonstrating the importance of non-predatory mortality for A. tonsa in the lower Chesapeake Bay