Pacific oyster outplants and benthic surveys on intertidal aquaculture beds (Washington state, USA)

Description

Hypothesis: Pacific oyster (Magallana = Crassostrea gigas) performance and yield differ between ground culture and off-bottom culture methods and depending on the level of co-occurring eelgrass (Zostera marina). Benthic surveys were carried out on aquaculture beds at 10 sites around Washington state, USA, at tidal elevations of -0.4 to +0.4 m relative to mean lower low water. Beds consisted of ground culture or off-bottom culture (longlines or flip bags). Measurements on each bed included density of eelgrass, size and density of oysters, and sediment grain size. On each bed, Pacific oysters (initially ~25 mm) were outplanted in June and collected for measurements of survival, shell height, and dry meat weight in September (3 months) and March (9 months). Half of the sites were studied in 2020-21, and the remainder in 2021-22. Survival was better for oysters grown off-bottom in longlines or flip bags relative to ground culture. In ground culture, survival declined in finer sediments. Shell growth did not respond strongly to grow-out method, but condition (dry meat mass per shell height) was better in off-bottom than ground culture. After 3 summer months, no performance traits differed across amounts of co-located eelgrass, and performance also did not consistently improve with eelgrass after 9 months over winter. Relative to ground culture, off-bottom culture produced higher densities of oysters per footprint of area and/or increased yield due to shorter crop cycles.

Steps to reproduce

Overall design: 10 intertidal mudflat sites, within which several habitat types were selected. "Culture" was no shellfish culture, ground culture, or off-bottom culture (longlines or flip bags). Each culture type was crossed with three levels of eelgrass: none, sparse, dense. Benthic surveys were carried out within each habitat type at each site: 20 quadrats (0.25 m2) for cover of shell, counts of live oysters, shell height of up to 10 live oysters, counts of eelgrass vegetative and flowering shoots. Benthic.archive.csv: Reports data from 20 quadrats at each bed, for 9-11 beds per site, at each of 10 sites measured at low tide. A row represents a quadrat. Columns include site name, Culture type, Eelgrass level, Date, GPS in WGS84 datum (for some quadrats ), shell cover, oyster counts and shell heights (maximum dimension) on and off-bottom, eelgrass counts. Sediment.Elev.Archive.csv: Contains georeferenced sediment sample data from each bed at each site, usually 2 sediment samples. Samples were dried, and organic content determined by loss-on-ignition, followed by processing through a sieve series for grain size, reported as proportions caught on 1, 0.5, 0.25 etc mm mesh. Outplant.survival.archive.csv: Pacific oysters were outplanted in June of 2020 or 2021 and collected 3 or 9 months later. Live and dead individuals were counted from each outplant, providing a survival calculation based on live per total. Bed locations can be found from GPS points provided in associated archived data. Oyster.Outplants.Archive.csv: Measurements are for surviving oysters, with counts provided in Outplant.survival.archive.csv. Pacific oysters were outplanted in June of 2020 or 2021 and collected 3 or 9 months later. At collection, shells were measured for height, length, and width, and meat was removed and dried. Mass measurements are in g, and dimensions in mm.

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