The copepod Acartia tonsa dominates the mesozooplankton in the Chesapeake Bay at certain times of the year, providing a link between primary producers and higher trophic levels, including commercially important fish species. We evaluated the use of a DNA stain (DAPI) to measure egg development and explore the effects of low dissolved oxygen (hypoxia) on A. tonsa eggs. Stage distributions were determined from vertically stratified samples. Larger amounts of late stage eggs were observed in deeper water. Incubated samples also showed shifts in development distributions. Low staining success was observed, ranging from 19.6% to 37%. Possible reasons for the low staining success could be due to methodological or biological reasons, but these were not evaluated. The vital stain neutral red was tested to determine if non-viable eggs weren't staining, but the eggs did not take up the neutral red stain efficiently. Overall we found that the use of DAPI was effective in staining the eggs and allowed for the distribution of eggs in a particular site to be quantified. This technique could be used, along with controlled lab experiments, to determine egg development rates for A. tonsa in the future, and look at the variation of egg distributions and rates in different environmental conditions in the Bay.

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