Performing Department
Population Health & Reproduction
Non Technical Summary
Tomales Bay and Humboldt Bay are two of California's premier commercial fisheries for Pacific oyster (Crassostrea gigas), accounting for nearly 90% of all commercial shellfish production in California. In 2011, National Shellfish Initiative was created by NOAA to encourage expansion of coastal shellfish aquaculture and increase the benefits shellfish populations provide, including water quality improvement, habitat restoration, and shoreline protection. Suspension-feeding animals such as oysters are capable of filtering large volumes of nutrient and sediment laden water (15-60 gal/day). Deposition of feces and pseudo-feces from dense oyster production adds organic material, including bacteria, and locally reduces sediment grain size. This net loading of organic particles may create reservoirs of pathogens shed in the feces and capable of infecting nearby oyster beds and newly placed brood stock following disturbance events. Moreover, eelgrass beds adjacent to oyster production areas may act as vegetated buffer strips, capable of trapping fine particulates and pathogens entering and exiting oyster beds. Along the Pacific coast, eelgrass beds are nurseries for many common and commercially important fishes, including rockfish (Sebastes sp.), and kelp bass (Paralabrax clathratus), as well as supporting migrating shore birds and salmon smolts as they exit their natal streams. In California, Z. marina and its habitat are protected under the Magnuson-Stevens Act and the California Coastal Act, and oyster growers are required to mitigate any damage caused to eelgrass during the course of operations.Microbial water quality and preharvest food safety are a central focus for California public health, agricultural, and water quality agencies, yet aquaculture is a poorly addressed and under-represented segment of food animal agriculture. Despite rigid regulatory testing, incidents of shellfish-associated human illness have been on the rise over the last decade, and little research has been conducted to address the reduction in pathogen transfer between shellfish growing areas and the surrounding environment. Terrestrial vegetated buffer strips are effective at reducing overland transport of microbial pathogens from livestock operations to nearby waters, but this intervention strategy has not been evaluated for seagrasses near aquaculture operations.We will evaluate the ability of the eelgrass, Zostera marina, to reduce the transfer of pathogens from commercial shellfish operations by capturing and retaining bacterial indicators and pathogens being release from shellfish growing areas during tidal exchange. This will be accomplished through a systematic sampling effort to collect water and sediment samples from shellfish growing areas and adjacent Z. marina beds across seasons and tidal cycles. A wide range of environmental (physical, chemical, meteorological, and geospatial) information will collected in tandem with biological samples, enabling us to generate predictive models for the conditions that lead to increased pathogen release as well as improved capture and retention of pathogens by Z. marina.Understanding the utility of native eelgrasses for reduction of bacterial indicators and pathogens in commercial oyster beds may better inform the development of policy for California aquaculture. Better understanding of coastal microbial dynamics through science will help foster dialogue between terrestrial and marine-based beneficial uses of Tomales and Humboldt Bays. To ensure transparency and foster collaboration, we will work with local oyster growers to gain access to shellfish production areas and engage them on issues of water quality and food safety. At the completion of this project we will organize and conduct a series of workshops meant to convey the information gained through the project and inspire discussion on ways stakeholders can work together to improve water quality and increase sustainable food production in coastal systems.
Animal Health Component
100%
Research Effort Categories
Basic
75%
Applied
25%
Developmental
(N/A)
Goals / Objectives
Understanding the utility of native eelgrasses for reduction of bacterial indicators and pathogens in commercial oyster beds may better inform the development of policy for California aquaculture. Better understanding of coastal microbial dynamics through science will help foster dialogue between terrestrial and marine-based beneficial uses of Tomales and Humboldt Bays.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.
Project Methods
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.