Spatial and Temporal Distributions of Live and Dead Copepods in the Lower Chesapeake Bay (Virginia, USA)

Hydrography and copepod abundances (Acartia tonsa, Eurytemora affinis, and nauplii) were regularly monitored for 2 years in sub-estuaries of the lower Chesapeake Bay. Copepod vital status was determined using neutral red. Abundances of A. tonsa copepodites and nauplii peaked in late summer and were related to water temperature. E. affinis was present in early fall and winter-spring. Copepod carcasses were a persistent feature in the plankton from 2007 to 2009, with similar annual patterns of occurrence during both years. The relative abundance of carcasses varied among species and developmental stages, with means of 30% dead for stages NI-NIII copepod nauplii, 12-15% for stages NIV-NVI nauplii and A. tonsa copepodites, and 4-8% for E. affinis copepodites. Percent dead was also higher for adult male than female A. tonsa. No strong relationships were found between measured hydrographic variables and percent dead, but the higher percent dead in young nauplii and adult male A. tonsa may indicate greater susceptibility of these stages to death from environmental stressors.