Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California (2009) / Chapter Skim
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Recent public documents produced by NPS characterizing the impacts of shellfish culturing in Drakes Estero have stimulated public debate over the pending expiration of the RUO and the presentation of scientific information that appeared to justify closing the oyster farm. The increasingly contentious nature of the debate led to the request for this The term estero is used instead of estuary because Drakes Estero has more in common with coastal lagoons (low freshwater input and high salinity)
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From page 2... ...
The degree to which the presence and biogeochemical activities of the nonnative Pacific oysters in Drakes Estero reproduce the historic contributions of the original Olympia oysters to the ecological functioning of the estero depends on how closely historic oyster abundances, collective biomass, and thus filtering capacity plus hardsubstrate habitat are matched by the cultured nonnative oysters. The hard BOX 1 Statement of Task -- Part 1a An ad hoc committee will be formed to produce two reports on shellfish mariculture in coastal areas.
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From page 3... ...
First, NPS does not acknowledge the changing ecological baseline of Drakes Estero, in which native Olympia oysters probably played an important role in structuring the estuary's ecosystem for millennia until human exploitation eliminated them in the period from the mid 1800s to the early 1900s. Second, NPS selectively presents harbor seal survey data in Drakes Estero and over-interprets the disturbance data which are incomplete and non-representative of the full spectrum of disturbance activities in the estero.
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From page 4... ...
Limited observations of eelgrass in Drakes Estero demonstrate absence of eelgrass directly under oyster culture racks and from propeller scar damage attributable to boats operated by the oyster farm. Mariculture activities had an impact on about 8% of the eelgrass habitat in Drakes Estero in 2007: 1% of eelgrass acreage was displaced by oyster racks and 7% was partially scarred by boat transit through the eelgrass beds.
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From page 5... ...
This nonnative tunicate has become established in Drakes Estero, where it covers much of the subtidal hard surfaces provided by oyster shells, racks, and other structures. The cultured oysters together with wooden culture racks and plastic mesh bags increase the availability of hard surface for colonization by tunicates in Drakes Estero, which has few natural hard substrates such as rocky bottom, although shells of native Olympia oysters would have provided
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From page 6... ...
Visits to DBOC could be considered a form of recreation and the oyster farm represents part of the cultural history of the estero. Conversely, the low-tide appearance of culture racks holding oysters partially covered by the invasive, yellow tunicate and the sight of plastic mesh culture bags lying on some intertidal flats conflict with the aesthetics of the vistas expected in a National Park Wilderness Area.
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From page 7... ...
Because the likely beneficial functions of oysters in biogeochemical processes were not acknowledged, they did not appear to play a role in NPS decision making. Similarly, NPS did not mention that Olympia oysters were part of the historic ecological baseline condition of Drakes Estero and that, in the past, Olympia oysters could have played a significant role in the biogeochemical processes of the estero.
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From page 8... ...
Additional research could be directed at understanding the relative habitat value of eelgrass, mud flat, and mariculture structures for fish at a landscape scale in the estero and similar systems. Additional observational and experimental studies are needed for use in carrying capacity models to determine how many oysters can be cultured in Drakes Estero without depleting phytoplankton and organic matter also used by native species and to avoid sediment anoxia from excess production of feces and pseudofeces by oysters.
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