The Chesapeake Bay has witnessed staggering losses to oyster populations over the past century, reported to be down by 97% when likened to early records (Chesapeake Bay Foundation 2016). Atrazine is commonly used in and around agricultural fields in the Chesapeake Bay watershed (USDA). For this reason, it was chosen to be the focus in this study examining the effects of herbicide-induced bacterial composition changes by running 16S sequencing in hatchery-reared spat. This study hopes to further our understanding of both oyster-prokaryote symbiosis and  herbicide-prokaryote effects.
 Methods
   
Oyster Acquisition and Stabilization
250 oyster (Crassostrea virginica) spat were purchased from Horn-Point Laboratory in April 2016. 50 oysters, of similar size, shell width, and age were chosen from >1000 juvenile diploid oysters.  The 250 chosen oysters were subsequently assigned into 4 color coded groups containing 50 oysters in each group (Green, Pink, Blue, Orange, and White). Each color group was then parted into 5 sub-groupings and were labeled as follows: “Group Color” - I, II, III, IV, or V” (ie. Green-I, Green-II, Pink-I, Pink-II, etc.). Each sub-group contained 10 diploid [TS1] oyster juveniles. 3.0 mm square mesh sieves were used to separate each sub-group. No oyster was smaller than 5.0 mm long x 4.0 mm wide when placed in the mesh sieves. A large holding tank, which served as the in-lab microcosm, was filled with 300L of pressure filtered water at a salinity of 25 parts per thousand (ppt). The oysters were allowed to grow in the lab within this microcosm for a stabilization period of three months prior to atrazine exposure. Frequent water changes (25% twice weekly) were used in order to minimize a buildup of both ammonium and nitrate levels within the closed water system[TS2] . In addition to frequent water changes, Kordon AmQuel Plus Ammonia Detoxifier/ Conditioner and TLC Saltwater aquarium conditioner were used in order to remove Nitrate, Nitrite and Ammonia as needed.  During the three-month stabilization period, oysters were fed 6 L of a concentrated phytoplankton mixture of (Tetraselmis Chuii, isochrysis galbana, and Nannochloropsis oculata) approximately ~ 400,000 cells/mL) 3 times per week on Mondays, Wednesdays and Fridays. Before adding 6L of the plankton mixture, 6L of water from the oyster microcosm were removed.
Relevant tank [TS3] water parameters were monitored and adjusted as needed by replacing old water with new water. The tank was consistently maintained to fit the following water quality parameters: