Eelgrass and Oysters; an Evaluation Of Zostera Marina as A Vegetated Buffer for Marine Aquaculture

<p>Sampling: To quantify bacterial loading from oyster beds and bacterial removal by adjacent eelgrass beds, water and sediment samples will be collected from the two bays responsible for the majority of commercial oyster culture in the state, Tomales Bay and Humboldt Bay. To account for seasonal effects, samples will be collected during the peak oyster depositional periods of July to Sept and during the high rainfall periods of Nov to Feb. The sampling plan within each season will follow a pseudo-randomized block design, with bay as the primary block (n=2). Sub-blocks will consist of season (n=2), habitat type (isolated oyster beds, isolated eelgrass beds, oyster beds adjoined to eelgrass beds, n=6 with replicates), and tidal stage, with oyster or eel grass bed area (sqrm), and distance across the bed as factors. Sampling distances will be distance from the bed edge in the direction of predominant flow (n=3) (e.g. 20%, 60%, and 100% of bed length). Sampling will be conducted at 2 different points of the tidal cycle (ebb and flood, n=2), on 3 occasions per season (n=6) for fecal coliforms, Enterococcus spp., V. parahaemolyticus and V. vulnificus. Paired with water sampling, we will collect sediment samples for pathogen and organic content quantification. . For water samples, enumeration of fecal coliforms and Enterococcus will be performed according to USEPA accepted methods. Vibrio spp. will be enumerated as described by Di Pinto, et al. (2012), followed by biochemical and molecular confirmations of species. Preliminary data collected in Tomales Bay during the summer of 2014 detected V. parahaemolyticus in 42% of water and 37% in sediment samples. Therefore, we estimate a sample size necessary for detecting a 15% difference in prevalence from eelgrass buffered to unbuffered oyster beds (main effect) at n=222 per group, with α=0.05 and 90% power. The design we've outlined would include 288 samples per group (habitat) for water (n=576) and an equal number in sediments (n=576).Analysis: We will use multilevel generalized linear and logistic regression models to quantify the association between our covariates (e.g., eelgrass bed size, tidal oscillations, water quality, climate) and our outcome variables (FC log(1+cfu/100 mL), Enterococcus cfu/100 mL, Vibrio spp. cfu/100 mL) and positive/negative status for virulent V. parahaemolyticus, and V. vulnificus, while adjusting for nested random effects (site within Bay). This statistical design will allow us to test our hypothesis of biotic and abiotic factors that govern bacterial contamination of oyster beds and the surrounding water. Geospatial analyses will be utilized to determine bacterial hotspots within the Bay that warrant further research.Evaluation: The purpose of this study is to gain knowledge in an poorly understood area of a food animal production environment. Tide-based, serial sampling of water for bacterial indicators and pathogens will generate a rich longitudinal data set for identifying key processes (e.g., bacterial loads, climate, and tidal oscillations) that govern the influx, magnitude, and persistence of bacterial contamination of shellfish growing areas. By quantifying the ability of Z. marina to reduce pathogens released from oyster beds that are capable of impacting both human and oyster health, we will be better enabled to guide aquaculture policy development for a safe and sustainably harvestable commodity.Effort: We will work with stakeholder advocacy groups (e.g. Tomales Bay Watershed Council) to develop and give two workshops outlining our findings and recommedations for future action by commercial shellfish growers and resource managers and further research to better understand the interaction of commercial operations and the surrounding environment.</p>