Date Awarded

2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

Kam W. Tang

Abstract

Several studies have documented the occurrence of substantial numbers of zooplankton carcasses in marine field samples. However, the potential effect of carcasses on conclusions resting on zooplankton abundance estimates, and the reasons for carcass occurrence have been largely disregarded. Many field studies do not account for the presence of carcasses in their sampling methodology. Zooplankton carcasses in situ are significant for several reasons. as concentrated particles of organic matter in the water column, zooplankton carcasses can be important vehicles for organic matter transport and hotspots of microbial abundance and activity. If dead animals are treated alive, carcasses could bias the ecological conclusions of field studies. Finally, naturally occurring carcasses lacking injuries likely represent instances of non-predatory mortality, a poorly studied phenomenon in marine zooplankton ecology. The goal of my research was to resolve the importance of naturally occurring zooplankton carcasses with regard to the roles described above. A detailed evaluation was made of the neutral red vital staining method, to resolve method limitations for quantifying zooplankton carcasses in situ. The method gave reliable results for common copepods in the lower Chesapeake Bay, and artifact collection mortality was negligible. Thus, neutral red is a valuable method for quantifying naturally occurring copepod carcasses in the lower Chesapeake Bay. A two year study was then done to quantify carcasses in the lower Chesapeake Bay. Carcasses were a persistent feature in the water column throughout the study, with a repeating pattern of higher carcass abundance during the summer and fall in each year. The fate of carcass organic matter was then determined using a combined laboratory, field, and mathematical modeling approach to quantify removal by sinking, necrophagy (consumption of carcasses), and microbial decomposition. Carcass removal due to sinking was impeded by turbulent mixing in the estuary, and the rate of removal depended on the magnitude of ingestion by necrophages and the effects of water temperature on microbial decomposition. The resulting carcass abundances and removal rates were then used to determine errors resulting from counting carcasses as alive in ecological field studies, and also to determine the contribution of non-predatory factors to zooplankton mortality in the lower Chesapeake Bay. When carcasses were treated as alive, there were substantial errors in mortality rates derived from field abundances. This demonstrated the importance of identifying carcasses in zooplankton field samples. Non- predatory mortality accounted for 8% to 42% of total zooplankton mortality. The importance of non-predatory factors (e.g. disease, starvation, environmental stress) deserves more attention in ecological studies of marine zooplankton mortality and population dynamics.

DOI

https://dx.doi.org/doi:10.25773/v5-wdgq-dt15

Rights

© The Author

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