Science Advisory Report  2011/083

Assessing potential benthic habitat impacts of small-scale, intertidal aquaculture of the geoduck clam (Panopea generosa)

Summary

• A small-scale (3 x 20 m) intertidal study was conducted in Nanoose Bay, British Columbia to assess the potential impacts of geoduck clam culture and harvest on the benthic environment.
• Sediment samples were collected within the harvest zone and at various distances (5, 10, 25, 50 m) along three transects from the area of culture/harvest at various times (ranging from 1 month prior to seed out-planting to 6 months post-harvest).
• Various sediment qualities (i.e. grain size, percent organics, total carbon, total nitrogen, sulphide concentration, and redox) as well as infaunal quantity and diversity were measured.
• There was a significant increase in the amount of silt and clay and a significant reduction in infaunal abundance and richness within the culture plot immediately after harvesting compared to immediately prior to harvest. There was also a significant decrease in the sulphide concentration after out-planting compared to before out-planting and a significant increase in total carbon content and redox potential after harvesting compared to prior to harvest. Significant changes in the silt and clay content and infaunal community were limited to the area within the harvest zone and recovery of the sediment size structure was rapid (within 123 days). There were no other significant effects of seeding or harvesting on any other measured variables.
• It is difficult to assess the rate of recovery of the infaunal community after harvesting, due to the seasonal decline in abundance and richness and lack of long-term sampling.
• The change in sulphide concentration, total carbon content, and redox potential was not great enough and/or in the right direction to have significant ecological implications.
• Although there were few ecologically significant, long-term impacts of small-scale, short-term intertidal geoduck culture/harvest in the present study, changes in habitat, size of the culture plot, frequency of culture, and seasonal timing of out-planting and harvest may alter the degree of impact on, and rate of recovery of, the marine environment.
• The interpretation of the results of the study should be used with caution until further research (currently underway) validates findings for larger-scale operations and over a broader range of potential ecological indicators.  

This Science Advisory Report is from the November 30 – December 2, 2010 Pacific Invertebrate SubCommittee Meeting: Pink and Spiny Scallop, Sea Cucumber, Central Coast Manila Clam, Geoduck Clam Aquaculture, and Shrimp Trawl..  Additional publications from this process will be posted as they become available on the Fisheries and Oceans Canada Science Advisory Schedule.

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