Award: OCE-1259691

Observations of zooplankton from the middle of Chesapeake Bay during summer show that abundance is generally lower in this region compared to regions up or down estuary. This region of low zooplankton abundance is also a region of low oxygen concentration in the bottom water during summer, a phenomenon known as hypoxia. The prevalence of hypoxia in coastal and estuarine systems is increasing worldwide, and evidence suggests that hypoxia can have a number negative direct and indirect impacts on zooplankton populations and individuals, including decreasing reproduction, reducing their vertical movement, and making them more susceptible to predators. Thus, the impacts of hypoxia have important implications on the food web in these systems. In the Chesapeake Bay, the hypoxia is generally most severe in the main channel that runs down the middle of the Bay. Few studies have looked at how currents in the estuary might affect the supply of zooplankton from areas where there is no hypoxia. In this study, we examined whether the zooplankton population in the shallow regions on either side of the deep channel might be supplying zooplankton to the deep channel region. This could be a means of maintaining the population in that deep channel region even during periods when hypoxia is having a strong negative impact on the populations. To examine this question, we conducted two one-week long and five one-day research cruises throughout the summer. During each cruise we collected zooplankton from across the channel region of the Chesapeake Bay to determine the abundance of zooplankton in the shallow and deep areas. We focused on the copepod Acartia tonsa, which is the dominant zooplankton in this region of the Chesapeake Bay and in the samples we collected, and they are important prey for larval and forage fish. At the same time as our sampling, a different team was collecting data on the speed and direction of currents across the region, which we were able to use to build a numerical model to estimate how the currents might be moving zooplankton within this region. Our findings suggest that the copepods on the western shore of the Chesapeake Bay had higher reproduction rates and were overall more concentrated than in the Channel region or the eastern part of the Chesapeake Bay. Overall water movement was also shown to be from the western shore towards the channel. These lines of evidence suggest that zooplankton could be supplied to the channel from the shallow areas, and from the western part in particular, and that this would be supported by the high reproduction in this region. As hypoxia begins to break down in the autumn, this could be a mechanism to quickly increase the population in the channel region, as has been observed in analysis of monitoring data. These findings have been presented at a variety of national and international meetings, and multiple manuscripts are being prepared for submission to peer-reviewed journals. In addition, all of our data collected on the cruises has been submitted to the Biological & Chemical Data Management Office (BCO-DMO) and is publicly available. In addition to research activities, during the course of the project a series of educational projects were conducted with local schools to provide opportunities for students to participated in guided research projects to learn about and collect zooplankton from local waters. Last Modified: 06/02/2018 Submitted by: James J Pierson