Award: OCE-1760465

The overall objective of this project was to examine how planktonic systems in the northern Gulf of Mexico (nGOM) respond to large, seasonally anomalous floodwater plumes generated by events like Hurricane Harvey. Our specific objectives were to: 1) Document how planktonic assemblages and food web interactions in the coastal and shelf waters were influenced by flood waters comparing data collected preceding Hurricane Harvey and in its aftermath. 2) Examining the extent of variability in community dynamics - from primary producers to ichthyoplankton – in relation to available historical records and trends. 3) Investigate the potential implications of storm events such as Harvey for system productivity and longer-term fisheries recruitment. We completed 3 research cruises on the Texas/Louisiana shelf during 2017-2018. A collaborative team from the University of Louisiana Lafayette, Texas A&M and North Carolina State University collected samples to characterize the plankton communities ranging from picoplankton to larval fish. Spatiotemporal analyses of plankton abundances and community composition (on-offshore transects, depth profiles) were combined with a series of grazing experiments (microzooplankton dilution series alongside copepod addition/exclusion experiments) to quantify growth and grazing and carbon transfer at low to mid-trophic levels. Preliminary data indicated an increase in primary producers within 3 weeks of the storm event relative to late July 2017, a month before Harvey made landfall. A subsequent decrease in chlorophyll biomass 6 weeks following the storm seemed more dramatic than typically seen in this region during Sept/Fall, based on samples analyzed from a long-term dataset (SEAMAP). These changes were most prevalent with the smallest phytoplankton, which also showed the highest rates of mortality by small, single-celled consumers (microzooplankton). These results suggest that the changes in phytoplankton biomass and community that we observed were likely due to a combination of both bottom-up and top-down (i.e. grazing) control on those organisms. Ongoing analyses of copepod grazing experiments will allow to contrast which grazers (microzooplankton versus mesozooplankton) were the main drivers of biomass and composition changes within the microbial communities during each of the cruise periods. The completion of all datasets will provide comprehensive snapshots of how planktonic communities (pico-to ichtyoplankton) were impacted by the large floodwater plume generated by Hurricane Harvey. This project supported the research of two female graduate students at North Carolina State University. These students participated in the cruises and graduated in fall of 2019. Also involved were two female undergraduate students who were trained in several research methods and data analyses. The project, so far, has resulted in 2 presentations at scientific conferences, 1 graduate thesis and 1 manuscripts close to submission. The entire project team (all universities) also engaged with K-12 classes in five states before, during, and after the research cruises through a Styrofoam cup activity and class visits. Last Modified: 04/15/2020 Submitted by: Astrid Schnetzer