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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California Introduction to Drakes Estero Drakes Estero is located approximately 25 miles northwest of San Francisco, California, within the Point Reyes National Seashore, a unit of the National Park Service (NPS) that was established by Congress in 1962 (Point Reyes National Seashore Enabling Act, 16 U.S.C. § 459c–459c-7). In 1976, Drakes Estero was designated as “Potential Wilderness” by Congress (Point Reyes Wilderness Act, Public Law 95-544), one of eleven marine Wilderness areas in the United States (NPS, 2007c). There is also a designated Wilderness Area in Point Reyes National Seashore that includes Estero de Limantour and the mouth of Drakes Estero (Figure 1). Several agencies have jurisdiction over various aspects of the Point Reyes National Seashore and Drakes Estero, including NPS, the California Fish and Game Commission, the California Coastal Commission, the National Marine Fisheries Service, and the U.S. Fish and Wildlife Service (Figure 2). NPS holds primary management authority over the Point Reyes National Seashore, including its tidelands and submerged lands (DOI, 2008). The California Department of Fish and Game regulates use of state water bottoms, including two mariculture leases located in Drakes Estero and currently operated by the Drakes Bay Oyster Company (DBOC); however, the Point Reyes National Seashore is acknowledged to have primary management authority over the mariculture operation. The California Coastal Commission holds primary enforcement authority for coastal development, enforcement, and violations under the Coastal Act Sections (e.g., 30106, 30600, 30610, and 30810). Section 30810 delineates the Commission’s permitting jurisdiction over sea bottoms and submerged
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California FIGURE 1 Drakes Estero is located within the Point Reyes National Seashore in Marin County, California. Inset provides larger view of Drakes Estero and shows the location of Drakes Bay Oyster Company. Map provided by courtesy of David Press, NPS. areas and property (those below the mean high tide level). Marin County asked the California Coastal Commission in 2003 to assume primary enforcement authority for Coastal Act violations resulting from mariculture activities on the portion of the property above the mean high tide line. The coastal waters off the Point Reyes National Seashore, including Drakes Bay, are part of the Gulf of the Farallones National Marine Sanctu-
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California FIGURE 2 Jurisdictions that have a regulatory or advisory role in permitting for DBOC operations in Drakes Estero. Rectangles indicated federal agencies and authorities; ovals indicate state agencies and authorities, and rounded square indicates county authority. Responsibilities of the various entities are described in the text. ary, which encompasses 1,255 square miles of marine waters extending just north of San Francisco, west beyond the Farallon Islands and north to Bodega Head. The National Marine Fisheries Service’s Office of Protected Resources is responsible for protecting marine mammals and endangered marine life by working to conserve, protect, and recover species under the Marine Mammal Protection Act and the Endangered Species Act. The U.S. Fish and Wildlife Service is the primary federal agency tasked with protecting and enhancing the populations of and habitats for all types of water birds and migratory birds that spend some portion of their lives in the United States. Both Drakes Estero and Estero de Limantour are under consideration for designation as state marine conservation areas under California’s Marine Life Protection Act, in the Integrated Preferred Alternative from the Blue Ribbon Task Force for the North Central Coast. In its recommendations to the California Fish and Game Commission, the Task Force notes: “While the stakeholders generally preferred a state marine reserve designation for the entire estuary, accommodating the existing maricul-
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California ture lease required an additional state marine conservation area designation in part of the area” (California Marine Life Protection Act Initiative Blue Ribbon Task Force, 2008). Ocean waters bordering and flowing into Drakes Estero are characterized by local upwelling and are influenced by outflows from San Francisco Bay (John Largier, unpublished data), a highly modified ecosystem and urbanized area. Drakes Estero is a large, shallow coastal marine lagoon encompassing 2,270 acres or about 9 km2 at high tide. Water depth is typically less than 2 m with the exception of the mouth and a channel with a depth of up to 7–8 m in the central lagoon (Dixon, 2007; NPS, 2007). The lagoonal system encompassing Drakes Estero has five branches off a main 1,300-acre lagoon; four of these branches plus the central lagoon are considered part of Drakes Estero including Home, Schooner, Creamery, and Barries Bays (Figure 1, inset). A fifth branch constitutes Estero de Limantour. A single passage to the sea remains open year-round and allows tidal exchange between Drakes Estero and Drakes Bay. Freshwater input consists of perennial and ephemeral streams that provide the majority of the freshwater during the rainy season, which typically runs from October through April; the watershed covers approximately 31 square miles (Anima, 1991; Balton, 2006). Drakes Estero is considered a low-inflow marine lagoon in which all but the innermost branch (Schooner Bay) is marine-driven and thus possesses salinities and temperatures reflecting nearby oceanic conditions. Two tidal cycles exchange a volume of water equal to that contained within the estero, although the estimated residence time of water in the innermost branch, Schooner Bay, is 20 days. Tidal excursion is the major driver of circulation in Drakes Estero (Largier et al., 1997; Balton, 2006; John Largier, unpublished data). Like other marine lagoons with little freshwater input, hypersaline conditions may develop during a dry summer season (Harbin-Ireland, 2004). Drakes Estero is bordered by cattle grazing lands, all part of the Point Reyes National Seashore (Harbin-Ireland, 2004; Balton, 2006). In addition to cattle ranching, a single commercial oyster operation, DBOC, operates within the Point Reyes National Seashore. Oyster culture began in Drakes Estero in the early 1930s and has continued to the present under various owners. For most of that time, 1954 until 2005, the farm was operated by the Johnson Oyster Company (see Box 2 for details). DBOC took over the farm in 2005, which currently is composed of two leases administered by the California Department of Fish and Game. DBOC is the lease holder and operator of both leases in Drakes Estero. The on-land operations occur adjacent to Schooner Bay (Figure 1, inset) and house the shellfish hatchery, processing, and packing, and include boat docks and piers, two septic systems, a water well, worker housing, parking, interpretation for the visiting public, and retail sales.
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California BOX 2 History of Oyster Mariculture in Drakes Estero 1932: Initial test plants of imported Crassotrea gigas seed in Drakes Estero. 1934: Earliest state water bottom leases in Drakes Estero that led in the next year to the establishment of the original DBOC. 1962: Point Reyes National Seashore established (Point Reyes National Seashore Enabling Act, 16 U.S.C. § 459c–459c-7). 1965: California conveys the tidal and submerged lands within the boundaries of Point Reyes National Seashore to the United States and these areas, including Drakes Estero, become subject to the laws, regulations, and policies governing NPS property. 1972: Charles W. Johnson sells his property on Drakes Estero to NPS, subject to reservation of the right to use the property for 40 years “… for the purpose of processing and selling wholesale and retail oysters, seafood, and complimentary food items, the interpretations of oyster cultivation to the visiting public, and residential purposes reasonably incidental thereto.…” (DOI, 2004; see Appendix A). 1976: Point Reyes Wilderness Act of 1976 designates 25,370 acres as Wilderness and 8,003 acres as Potential Wilderness which includes Drakes Estero (P.L. 94-544, Oct. 18, 1976). 1992 Record of Agreement (ROA) restricts boat access to main and lateral channels during pupping season March 15–June 1 (ROA with NPS, the National Marine Fisheries Service, the California Department of Fish and Game, and the Johnson Oyster Company). 1997: Marin County Stipulated Court Order (Marin County Superior Court #165361) that orders Johnson Oyster Company to be in compliance with the law (Coastal Act, building code, and health and safety code violations) and meet conditions as specified. 2003: California Coastal Commission’s Cease and Desist Order No. CCC-03-CD-12 concerns onshore development by Johnson Oyster Company without the required coastal development permit. This followed the Marin County request that the Commission assume primary enforcement authority with regards to Coastal Act violations on the property (California Coastal Commission, 2007). 2004: California Fish and Game Commission issues a 25-year renewal of water bottom leases to Johnson Oyster Company contingent upon the term of the Reservation of Use and Occupancy agreement with NPS. 2005: Tom Johnson (son of Charles W.) sells oyster farm with remainder of Reservation of Use and Occupancy to Kevin Lunny. 2008: In April, DBOC and NPS reach agreement on the terms of a new Special Use Permit that authorizes operation of the oyster farm in Drakes Estero until November 2012.
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California DBOC holds a Reservation of Use and Occupancy (RUO) from the Point Reyes National Seashore for the use of 1.43 acres of land at the north end of Schooner Bay and operates in the estero waters under the conditions stipulated in an NPS Special Use Permit and the state lease from the California Fish and Game Commission (see Figure 2). The state lease is subject to the terms of the RUO and the conditions of the Special Use Permit: the present RUO expires in 2012. DBOC practices two types of oyster mariculture. The first is Japanese rack culture that is used to grow oysters on shell cultch predominantly for the shucked product. The second is cultchless culture, in which individual oysters are grown in bags for the half shell market. These methods are described below with specific reference to their application in Drakes Estero. DBOC imports Pacific oysters as eyed larvae from West Coast hatcheries. The larvae are cultured in tanks where they set on bagged cultch, consisting of cleaned oyster shells from the shucking operation, or on ground oyster shell fragments (250–300 μm in size) for cultchless culture, depending on the desired end product. At DBOC, oysters can be set successfully from April to October. While in the tanks, the young oysters feed on algae from the estero’s naturally productive water that is pumped into the shoreside facility. For rack culture, the bags of cultch with oyster spat are suspended in the water column in the nursery area (area 6 in Drakes Estero, see Figure 3), a site with high productivity that supports rapid growth. After about two months, the bags of seeded cultch are brought back onshore and strung onto wires. At DBOC, the stringing can take place from April to December or January. Boats then transfer the loaded wires from the shoreside facility to racks, which are located near the main channels of Drakes Estero. Wires are hung over the racks, such that at the lowest point the cultch is 0.5 m off the bottom and at the top of the rack the cultch is 2 m above the bottom. The racks are submerged at high tide and become partially exposed during low tide (Figure 4). Once the oysters have matured to market size, the wires are brought onshore, and workers use a pneumatic hammer to remove and separate the oysters. Oysters are sorted and graded to determine whether they will be sold in the shell or shucked; both occur onsite. DBOC is the last on-site shucking and packing facility in California (Kevin Lunny, during October 30, 2008 site visit). For cultchless culture, ground oyster shells are used to ensure settlement of a single larva per fragment. These seed oysters are put into a container with a mesh screen bottom and placed in another tank where an upwelling system pumps estero water through the screens to feed the young oysters. As the seed oysters grow, they are serially transferred into bags of increasing mesh size at lower densities for hanging bag culture
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California FIGURE 3 Map of Drakes Estero illustrating mariculture lease areas and oyster beds (sites used for growing oysters on racks or in bags). California Department of Health Services, 2007 (this map does not represent a legal description of the actual lease/bed locations).
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California FIGURE 4 Oyster cultch strung on wire with spacers and hung over racks. Eelgrass, Zostera marina, appears in the foreground (photograph courtesy of T. Moore). in the estero. When the oysters reach a size of 3 mm, they are bagged and placed in the intertidal area where they float during high tide and sit on the substrate during low tide. When the oysters are approximately 2 inches long, about 120 oysters are bagged and tethered to groundlines staked on the sand bars in the estero. The bags are flipped once every 2–3 weeks both to reduce fouling and also to ensure more uniform shell growth (Figure 5). The oysters stay in these bags for 1–4 months for “beach hardening time” or “finishing time” to induce shell growth. This process is necessary in order to condition the oysters for transport of live animals to be sold to the half-shell market. The production of single oysters requires more effort and a longer culture period, but results in a higher value product. Weekly oyster and water samples are provided to the Department of Health Services for monitoring of the presence and or levels of toxic phytoplankton. In Drakes Estero, biotoxins (e.g., saxitoxin, which is responsible for paralytic shellfish poisoning; domoic acid, which causes amnesic shellfish poisoning) are more of a problem towards the mouth of the bay and less of a problem in the upper reaches (Kevin Lunny, during October 30, 2008 site visit). During a biotoxin alert, it is possible that the water quality and/or harvested oysters will be sampled every day. However, after significant rainfall, automatic closures restrict harvesting to area 17, a 25 acre sand bar closer to the mouth of the estero approved for year-round
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California FIGURE 5 Oyster bags tethered to groundlines on a sand bar in Drakes Estero (photograph courtesy of T. Moore). harvest, the only fully approved shellfish growing area in California. Part of area 17 is inside the seal protection area, and therefore may not be used for oyster culture. Boat transit to area 17 is also directed away from the main channel to avoid disturbance of harbor seals. In periods of high rainfall, DBOC helps other growers keep their markets open by providing them with oysters from the approved area. According to Kevin Lunny (October 30, 2008 site visit), DBOC harvests oysters daily throughout the year. Between harvest and setting, DBOC boats may make more than one trip to the racks or bags per day. The typical work day is 8:00 a.m. to 4:30 p.m., Monday through Saturday and occasionally on Sunday when it coincides with a holiday. With the hanging rack culture, DBOC can work at more stages of the tidal cycle than most other oyster operations. In addition to oysters, DBOC also grows Manila clams. The technique is the same as for cultchless oyster culture, with the clams grown in mesh bags, but the clams require less tending than the oysters (Kevin Lunny, 3.4.09 communication). The State of California has production minima that oyster growers must meet in order to maintain a lease for the state water bottom. Growers must plant a minimum of 10,000 oysters per acre and harvest a minimum of 2,000 oysters per acre per year; therefore DBOC is required to harvest 180,200 lbs shucked weight to meet this minimum based on lease acreage
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California (Moore, 2008). According to the map produced by the California Department of Public Health, 147 acres of the total 1,059 acres available for oyster growing were under production in November 2007—this represents a snapshot in time because areas used for growing oysters will shift at different times of year depending on the planting schedule (Kevin Lunny, 3.4.09 communication). The actual footprint of the racks and bags on bottom in Drakes Estero in 2008 was less than 30 acres (Moore, 2008). Since 1960, the size of the oyster harvest has fluctuated from lows of 29,799 lb and 34,094 lb in 1960 and 2000, respectively, to a high of 769,590 lb in 1995 (Figure 6). Insufficient information is available to explain the steep decline in the oyster harvest from 1996 to 2000. A change in planting methods in the early 1990s may be responsible for the massive increase in the reported number of seed oysters planted as estimated by the owner of Johnson Oyster Company (Figure 6). The fate of DBOC after 2012 has become a matter of public controversy. Highly publicized disputes over the science addressing impacts of the oyster farm on Drakes Estero have erupted in the context of the continuing operation of a commercial shellfish farm within a designated Potential Wilderness area (DOI, 2004; see Appendix A) and an Office of the FIGURE 6 Drakes Estero Oyster Planting and Production 1950–2007. Shucked weight = 100 oysters per gallon × 8.5 pounds per gallon. Oyster shucked weight is calculated from Shellfish Harvest Tax Reports which are filed monthly for all state water bottom leases. Arrow indicates the year (2005) in which DBOC assumed operation of the oyster farm. (Oyster production and planting values were obtained from Tom Moore, Marine Region Aquaculture Coordinator, California Department of Fish and Game).
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California Inspector General investigative report (DOI, 2008) that was undertaken in response to complaints from the owners of DBOC with regard to the Point Reyes National Seashore actions. To resolve some of these issues, Senator Dianne Feinstein and the NPS requested that the National Research Council (NRC) of the National Academies conduct an independent assessment of the scientific basis for NPS presentations and reports on the ecological effects of DBOC operations on the Drakes Estero ecosystem. In addition to the review of the science on Drakes Estero, the committee will produce a second report, published separately, that will address in more general terms the elements of best management practices that could be employed to enhance the benefits of shellfish mariculture and minimize any negative ecological effects (see Appendix B for the NRC statement of task). The committee held its first meeting in Mill Valley, California, and spent the first day receiving oral and written input directly from key participants in the controversy over the impacts of DBOC and the second day visiting Drakes Estero with guidance from NPS and DBOC principals (see Appendix C for meeting agenda). To fulfill part one of the statement of task, the committee organized a framework to answer the ecological questions using information from local empirical studies, studies in comparable ecosystems, and a conceptual understanding based on a synthesis of scientific studies and ecological theory. This report is organized according to this framework and includes an introduction to the Drakes Estero environment and the controversy, followed by sections that address questions about the accuracy of the science presented by NPS, the effects on NPS decision making, and suggestions for future research. The committee relied on the published scientific literature, presentations at the first committee meeting, and the many documents provided to the committee both on Drakes Estero and other sites worldwide in which studies have been conducted that could provide insight into impacts of shellfish culture on the Drakes Estero ecosystem. HISTORICAL BASELINES AND HUMAN MODIFICATIONS Although relatively unmodified by human interventions, especially as compared to highly developed portions of San Francisco Bay, Drakes Estero is not a pristine coastal lagoon. The current status of the estero’s ecosystem reflects many influences of human populations both past and present. Modifications to the ecosystem include both local interventions and local manifestations of distant interventions operating on wider spatial scales. Perhaps the ecologically most significant modifications of coastal bays and estuaries, possibly including Drakes Estero, follow from the local human over-exploitation and functional extinction of the native
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California Olympia oyster population. The Olympia oyster, Ostrea lurida, was a former constituent of Drakes Estero of some unquantifiable abundance as evidenced by the mounds of its shells in the Coast Miwok midden near the on-land facilities of DBOC.1 Kirby (2004) describes a pattern of regional over-exploitation of the native oyster during the 1800s across every estuary of the western states for which historical fisheries landings data are available. These oysters were harvested to supply the growing San Francisco market during the Gold Rush period (Conte and Dupuy, 1982). Baker (1995) provides a personal communication from C. Johnson that Olympia oysters are “common but not abundant” in Drakes Estero, but it is unclear what information this comment was based upon and when such observations were made. There are no recent observations of the Olympia oyster in Drakes Estero. This oyster has been functionally removed by unsustainable exploitation from most of its natural range in California, Oregon, and Washington (Kirby, 2004), but a recent 2008 photograph of natural Olympia oyster populations in Nootka Sound in British Columbia (Figure 7) and descriptions of Olympia oyster populations at several sites throughout British Columbia (Gillespie, 2009) indicate conditions that may have prevailed in Drakes Estero before the mid-1800s. The natural Olympia oyster reefs form a nearly continuous band covering the low-intertidal surfaces of many tidal flats sheltered in lagoons, bays, and estuaries, where recent quantitative sampling of three such flats revealed densities of 109–360 per square meter (Gillespie, 2009). Before intense exploitation by fishermen, densities were described as far higher in locations in the Strait of Georgia, where populations now remain relatively low (Gillespie, 2009). The tidal flat in the Figure 7 photograph ends with a steep slope into the subtidal and the oysters do not extend below about mean low water, although the Olympia oyster typically extends into the subtidal where the slope is gradual (Couch and Hassler, 1989; Shaw, 1997; Gillespie, 2009). Although no fisheries data are available for Drakes Estero per se, the lack of effective management of the native oyster fishery in the late 1800s to the early 1900s that led to overfishing and functional extinction of the native oyster throughout the western states (Kirby, 2004) for transport to San Francisco markets suggests that a similar pattern of over-exploitation occurred in the nearby Drakes Estero. Limited sampling of the bottom benthos in Drakes Estero (Harbin-Ireland, 2004 [in eelgrass beds]; Press, 2005 [on intertidal flats]) did not detect evidence of this native oyster, implying little or no recovery during the recent decades. The loss of
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California FIGURE 7 Photograph of a natural Olympia oyster reef in Nootka Sound in British Columbia at low tide (taken in 2008 by Michael Beck, The Nature Conservancy). oysters from estuaries and coastal lagoons has cascading consequences on the functioning, resilience, and value of ecosystem services of these environments worldwide (Jackson, J.B.C. et al., 2001; Lotze et al., 2006). Oysters have been characterized as ecosystem engineers (term from Jones et al. ; application to oysters in Lenihan and Peterson ) and a foundation species (term from Dayton ; application to oysters in Bruno and Bertness ); these terms are used to imply the dramatic impacts that the presence and biological activities of oysters have on the composition and dynamics of an entire ecosystem. The Atlantic States Marine Fisheries Commission identifies oyster reef habitat as valuable, serving perhaps as essential fish habitat for some fish (Coen et al., 1999; Atlantic States Marine Fisheries Commission, 2007). Our report details the most important of these ecological consequences below. Drakes Estero has also been modified by introductions of nonnative species. The most evident and aggressively invasive of these is the clonal tunicate, Didemnum vexillum, which forms yellow blankets over many subtidal hard substrates, especially shells of cultured oysters and oyster racks. Although the Didemnum introduction cannot be attributed to local human importation, other nonnative species were introduced by the shellfish mariculture operations, including the intentionally imported shellfish—the Pacific oyster (Crassostrea gigas), the Kumamoto oyster (Crassostrea sicamea), and the Manila clam (Venerupis [Ruditapes] philippinarum); and two hitchhikers—a nonnative marsh snail (Batillaria attramentaria) (Byers, 1999) and a protozoan parasite of oysters (Burreson et al., 2000).
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California Other local and regional interventions of humans have also modified the ecosystem of Drakes Estero from its baseline conditions. Cattle ranching takes place on many of the lands abutting the estero, probably modifying the composition and appearance of terrestrial vegetation in the Point Reyes National Seashore but with little apparent contribution to nutrient run-off in streams that feed into Drakes Estero, as noted in Anima (1991) that “it seems unlikely that surface nutrient inputs to Drakes Estero are of concern.” Cattle typically destabilize stream banks, potentially enhancing erosion and sedimentation into Drakes Estero. Documented increases of sedimentation over the past 150 years in Drakes Estero (Anima, 1991) can be attributed to increased land use, such as “trail and road use, road building, increase in paved areas” as well as effects of cattle grazing (Anima, 1991). Kayakers and hikers make use of the lands surrounding Drakes Estero, and those who approach wildlife closely can cause seals and water birds to flush. Since 1900, California has lost over half of its coastal wetland habitat to development (Dahl, 1990, 2006) so these changes elsewhere in the state probably affect the numbers of shorebirds and wetland-dependent birds using Drakes Estero and elevate the value of Drakes Estero because of the comparatively high quality of its estuarine environment. Human activities and development have displaced harbor seals from traditional habitats in areas such as San Francisco Bay, highlighting the importance of Drakes Estero as a relatively unmodified habitat. Global climate change is modifying not only the distributions of individual species but also changing many communities as new mixes of species induce new dynamics in estuarine and lagoonal environments (Scavia et al., 2002; Parmesan and Yohe, 2003; Parmesan and Galbraith, 2004; Parmesan, 2006). The initiation of commercial mariculture of Crassostrea gigas in the 1930s and its perpetuation through present represents another human intervention of significance to the ecosystem of Drakes Estero. The oyster re-introduction and enhancement through mariculture (albeit not the native oyster) represents a form of restoration of historic functionality of the estero, although there may be differences in the habitat functions of the native oyster beds compared to nonnative oysters grown in mariculture. Effects of nonnative oyster presence and its biogeochemical processing can be viewed as contributions towards restoring an historic baseline ecosystem in Drakes Estero (e.g., Jackson et al., 2001; Lotze et al., 2006). Past oyster culture came at a cost—modifying the ecosystem state by leaving a legacy of nonnative species. In addition, continued culture of nonnative oysters and clams poses some risk of their eventual naturalization in Drakes Estero and larval spread to other coastal lagoons, a risk that could be minimized but not entirely eliminated by culturing triploids (NRC, 2004a). Given the proximity of the estero to a large urban area and the
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California influence of the highly modified San Francisco Bay, and the other activities in the Point Reyes National Seashore (ranches and recreational use), the ecosystem of Drakes Estero will be affected by both legacy effects of earlier human interventions and also ongoing human activities, even if the oyster farm were closed and all the associated equipment removed. Nevertheless, removal of the Pacific oysters and nonnative clams under culture and all the structures used in the culture process would carry the consequences of removing the direct and indirect influences of the biogeochemical processes now provided by the filtration, excretion, and biodeposition of the shellfish and the influences of structural substrates of the oysters and the racks and bags that now hold them. In addition, the activities of the oyster culturists would also cease so impacts of those activities would disappear, some immediately and others gradually over time. The committee describes these effects, positive and negative, of oyster and shellfish feeding and biodeposition, of hard structures, and of activities of culturists in detail below. ECOLOGICAL AND ENVIRONMENTAL RESPONSES The committee organized its synthesis of the assessment of impacts of culturing nonnative oysters and clams in Drakes Estero by first preparing Table 1, which breaks down the question of mariculture impacts into seven largely separate ecosystem responses and one response for human use values. Columns separate the synthesis into a series of questions about each potential response. Answers to each question are presented in the report by treating each of the eight potential responses and addressing four questions: (1) reviewing relevant background science of Drakes Estero, (2) identifying the body of relevant studies on mariculture impacts in Drakes Estero, (3) specifying the impacts of mariculture that can be directly demonstrated by studies of Drakes Estero, and (4) specifying the impacts of the Drakes Estero mariculture that can be reasonably inferred from research conducted in other systems. The committee was asked to address two additional questions: (5) identify conclusions that can be drawn from the body of scientific studies, how they compare with what the NPS presented to the public, and how these conclusions affected NPS decision making; and (6) what research is recommended to resolve important remaining uncertainties—the answers to these questions were combined across all eight types of ecological/environmental/human use value responses and are presented after the discussion of the individual responses.
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Shellfish Mariculture in Drakes Estero, Point Reyes National Seashore, California TABLE 1 Ecological, Environmental, and Human Use Values in Response to Mariculture Operations Potential ecological or environmental response or effect on human use value Background of relevant science in Drakes Estero Studies of relevant mariculture impacts in Drakes Estero Impacts directly demonstrated by studies of Drakes Estero Impacts reasonably inferred from research conducted in other systems Benthic/pelagic coupling—nutrients and particulates I. A I. B I. C I. D Eelgrass II. A II. B II. C II. D Fish III. A III. B III. C III. D Benthic invertebrates in soft sediments IV. A IV. B IV. C IV. D Harbor seals V. A V. B V. C V. D Nonnative species VI. A VI. B VI. C VI. D Birds VII. A VII. B VII. C VII. D Human-use values—economics, recreation, aesthetics VIII. A VIII. B VIII. C VIII. D NOTE: The column headings correspond to questions posed in the Statement of Task and the rows identify the various components of the Drakes Estero ecosystem that could be affected by mariculture. The table provides a guide (Roman numerals) to the presentation of the committee’s findings.