Quartermaster Harbor Bivalve Mariculture Nutrient Mitigation Analysis and Outreach

Purpose or Scope:

Poor circulation and nutrient inputs have resulted in critically low dissolved oxygen levels in portions of Quartermaster Harbor (QMH) on Vashon Island, particularly in late summer/early fall. The negative impact on overall estuary health and function prompted King County to initiate the 2009-2012 QMH Nitrogen Loading Study. In concert with this work, Pacific Shellfish Institute (PSI) and project partners were awarded a subcontract from the Russel Family Foundation to culture native mussels on an experimental field station in QMH as an alternative form of nitrogen removal.

The project has several goals; 1) to work with the community of Vashon to build a creative strategy that mitigates for chronic nutrient inputs in QMH, 2) to engage residents in the recovery of healthy marine resources, and 3) to develop market-based mechanisms for cleaning Puget Sound. To reach these goals, the project will quantify the nitrogen removal services of mussels grown in QHM, evaluate mussel production and market potential of products grown in the Harbor, and foster project participation among the community. The study will also help develop a conceptual model for a nitrogen trading system that could potentially be applied to other parts of Puget Sound. Pilot mussel raft

This project addresses high priority 2015 goal 4.1.6, "Quantitatively document water quality improvements that result from shellfish aquaculture, i.e. nitrogen removal, benthic/pelagic coupling, nutrient recycling, reduced turbidity. It also addresses high priority goal 10.3.6, “Promote and educate the public, government agencies, and decision-makers on the ecological benefits shellfish culture is providing to the marine environment.”

Approach:

An 8 x 30 foot raft was installed in QMH to evaluate the use of mussels to mitigate nitrogen inputs in QMH. The raft was seeded with Mytilus trossilus from Penn Cove, WA and equipped with instrumentation for measuring water motion and quality.

Mussel biomass measurements were collected monthly in addition to information on fouling organisms and community assemblages. An underwater cylinder was positioned around the entire system to measure nutrient concentrations in seawater up-current and down-current from the raft. Mussels were sent to Taylor Shellfish Farms Quilcene Hatchery for dry weight and nitrogen analyses. Data will be used to quantify the amount of nutrient sequestration by mussels and associated marine biomass. Harvested mussels will be tested for safety and utility as a soil amendment and/or animal feed additive.

Community members and students assisted with raft construction, seeding, and data collection. Interactive presentations were offered to K-12 students.

Progress and Results:

In spring of 2011, the mussel raft was installed in northeast QMH. Data was collected for mussel growth, fouling, and community assemblages from May through October. Preliminary results indicate that growth rates were fastest in late May and early-mid June. Between July and August, barnacle fouling encased most of the mussel surface area restricting further growth. Large clusters of mussels, in addition to empty mussel shells, created protective structure for a number of marine organisms. Natural mussel set was also observed.Mussel line

In September, mortality was high among the original mussel set. Many clusters dropped off the lines or were consumed by seabirds and/or other predators. The additional space resulted in increased mussel weights in both the original and new set. Mussels were harvested in October and are being evaluated as a safe material for compost or animal feed. Further analyses are currently underway.

The raft engaged the community in hand-on science and promoted dialogue about nutrient loading in QMH. In March and April, community members assisted with raft construction and seeding. In May, Vashon High School students performed mussel biomass measurements while learning about nutrient sources and control measures. In June, seventy five 1st-3rd grade students from Chautauqua Elementary School attended a field trip to Fern Cove where they performed the process of Eutrophication, observed live phytoplankton under a microscope, and discussed the role of shellfish as a tool for reducing nutrient levels.

The study will be refined and repeated in 2012 with attention given to minimizing mussel losses due to predation, drop off, and material failure.

Oral presentations include:

Cool links:

Project Partners:

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