Ecosystem Concepts for Sustainable Bivalve Mariculture (2010) / Chapter Skim
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3 Ecological Effects of Bivalve Mariculture
3 Ecological Effects of Bivalve Mariculture
Pages 39-72
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From page 39... ...
the inci dental impacts of bivalve mariculture operations on multiple components of the ecosystem caused by mariculture structures and activities and by the biological activities of the molluscs; and (3) consequences of actions taken by culturists to alter ecological interactions purposely to manage the effects of pests, competitors, and predators on mariculture systems.
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From page 40... ...
reviews the effects of molluscan cultivation on the ecology of systems, identifying a similar set of mechanisms of influence, and concludes that such processes have a generally positive influence on the overall water quality of a system. Suspension-feeding bivalves also drive many other biogeochemical processes and cycles, which are well described for intertidal oysters by Dame (2005)
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From page 41... ...
Silicon is an important element for diatoms and can be limiting in systems dominated by diatoms. Bivalve molluscs contribute to recycling of silicate through transfer of this nutrient from the water column to the sediment with little being sourced from the bivalves (Prins and Smaal, 1994)
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From page 42... ...
Bivalves can reduce excessive growth of phytoplankton and, at high density, can counteract symptoms of eutrophication, thereby improving local, and in some cases downstream, water quality. Yet many bivalve molluscs have been depleted by overfishing, especially oysters (Jackson et al., 2001a; Kirby, 2004; Lotze et al., 2006; Beck et al.
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From page 43... ...
. The change in carbonate water chemistry and concomitant decrease in viability of bivalve molluscs potentially will reduce both the provisioning and persistence of shell in coastal and estuarine systems, particularly those in high-latitude areas with low alkalinity seawater (Feely et al., 2004; Lee et al., 2006)
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From page 44... ...
Mariculture of bivalve molluscs can contribute favorably to shell production and preservation in coastal ecosystems if the operators return the shell resource to the environment after harvest. However, regulations requiring the return of shells to the estuarine, lagoonal, or coastal bottom after shucking may be required to achieve this goal.
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From page 45... ...
. Both the reduction of turbidity and fertilizing effects of bivalve molluscs have been demonstrated experimentally for modest densities (16 per m2)
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From page 46... ...
Z marina distribution overlaps directly with the area where most bivalve culture occurs, extending to almost –10 m where water clarity is high on both coasts of the United States (Phillips, 1984; Moore et al., 1996; Thom et al., 2003; Kemp et al., 2004)
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From page 47... ...
As a result, scien tific studies demonstrate a broad range of responses of benthic infauna to mariculture, ranging from no or moderate negative effects to positive effects. In addition to the relatively complex nature of the impacts of bivalve culture on benthic invertebrate populations and communities, many of the studies have focused only on the grow-out phase of cultiva tion rather than assessing all aspects of the cultivation process (Kaiser et al., 1998)
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From page 48... ...
Structures used in some types of mariculture operations, such as racks, bags, and ropes, can increase biodiversity by providing more habitat for fouling species (e.g., Powers et al., 2007) but also can alter the hydrodynamics of an area to some degree (see review by Kaiser et al.
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From page 49... ...
can be affected, and the mopping activity can substantially alter the benthic epifaunal community structure. Fish and Mobile Crustaceans Studies of bivalve mariculture operations, mostly off-bottom, have shown higher abundances of some fish and crustaceans in areas with mariculture structures in comparison to nearby areas with unstructured open mudflats, eelgrasses, or even nearby oyster reefs and rocky substrates, although eelgrass generally harbors more unique species (DeAlteris et al., 2004; Clynick et al., 2008; Erbland and Ozbay, 2008)
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From page 50... ...
. Genetics of Bivalve Molluscs The following are three areas in which bivalve genetics are pertinent to the development of best practices for mariculture: (1)
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From page 51... ...
. Obvious candidates for concerted domestication efforts are the seven bivalve molluscs among the top-40 species of global aquaculture (C.
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From page 52... ...
; early experience with tetraploid Pacific oysters suggests that they are not robust enough, at present, to have a negative impact on reproduc tive success of diploid stocks. Even when native molluscs are used in mariculture, the natural genetic structure can be disrupted via interbreeding between wild and cultured
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From page 53... ...
and, ideally, also by quantitative analysis of local adaptation. The majority of marine bivalve molluscs share a suite of life-history traits -- relatively late maturation, high fecundity, small eggs, long-lived plankton-feeding larvae with relatively high-dispersal potential, and broad geographic ranges (Winemiller and Rose, 1992)
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From page 54... ...
, but public resistance to genetically modified organisms makes this a less attractive strategy. Introduced Species To augment or replace depleted natural stocks or to diversify the number of species used in mariculture operations, managers of molluscs in the past have employed translocations of native species and introductions of nonnative species.
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From page 55... ...
details the impacts and risks of nonnative species introductions, focusing on Pacific oysters. Several practices are used to reduce the risk of the establishment of naturalized populations from nonnative cultured bivalves, including the use of triploid seed or the culture of bivalves in areas with low potential for the establishment of a wild population.
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From page 56... ...
, bivalve mariculture industry practices have been adopted to reduce the potential spread of nonnative species. For instance, the use of hatchery-reared seed on the U.S.
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From page 57... ...
. The culture of native species is frequently recommended as an alternative to reduce or avoid harmful interactions among cultured nonnatives and wild species (e.g., Naylor et al., 2001)
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From page 58... ...
. Birds, Marine Mammals, and Marine Turtles Mariculture can have both positive and negative effects upon populations of large marine vertebrates, such as birds, marine mammals, and marine turtles.
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From page 59... ...
explored broader interactions between mariculture and marine mammals and marine turtles, and a discussion paper on the potential effects of mussel farming on marine mammals and seabirds was produced by the New Zealand Department of Conservation (Lloyd, 2003)
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From page 60... ...
. Alternatively, farm structures may increase food availability by providing a substrate for biofouling organisms suitable as prey, such as mussels.
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From page 61... ...
. In addition, limited understanding of the foraging distribution of birds, marine mammals, and marine turtles from spatially localized breeding colonies also makes it extremely challenging to assess population-level impacts of disturbance, entanglement, or habitat loss resulting from bivalve mariculture.
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From page 62... ...
. Although current international protocols, typically enforced at the state level in the United States, have reduced unintentional species introductions associated with culture of nonnative bivalve molluscs, fouled hulls and ballast water releases associated with global trade and marine transport have resulted in more introductions of nonnative fouling organisms, including various species of algae and tunicates (e.g., the algae Sargassum muticum, Undaria pinnatifida, and Codium fragile and the tunicates Didemnum spp.
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From page 63... ...
The general trend is to use techniques that reduce labor costs, ensure product quality, and minimize potential environmental impacts. Techniques include mechanical, chemical, and biological control methods with mechanical and chemical techniques being the most common methods used to remove fouling species from cultured bivalve molluscs and mariculture gear (Watson et al., 2009)
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From page 64... ...
. Removal of fouling organisms on mariculture gear is done almost univer sally over the water.
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From page 65... ...
In the United States, turtles and some marine mammals are protected TABLE 3.2 Techniques Attempted to Mitigate Sea Duck Predation on Bivalves Technique Challenge Effectiveness Cost Exclusion nets Fouling and Effective Relatively high predator mortality Loud sounds Habituation and Moderate Expensive battery life Chemical deterrents Effect duration Effective Unknown Boat patrol Habituation Effective Expensive, at large spatial scale Biological methods Habituation Minimal Unknown (e.g., falcons, eagles)
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From page 66... ...
. Protective structures modify water flow; affect sediment deposition; provide attachment sites for fouling organisms; and some structures, such as racks, create shaded spots that inhibit the growth of seagrasses (Everett et al., 1995; Rumrill and Poulton, 2004; Tallis et al., 2009)
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From page 67... ...
This section summarizes some of the areas in which additional research would help to address key questions about the ecological effects of molluscan mariculture to improve best management practices. Nutrient Cycling and Carrying Capacity The impact of a small mariculture operation (possibly defined by stocking density)
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From page 68... ...
; how plants respond to disturbance from bivalve mariculture operations relative to natural disturbances; and how response to disturbance varies by season (plant density varies naturally across seasons) , location, environment, and species.
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From page 69... ...
Culture of Nonnative Molluscs The use of nonnative species in bivalve mariculture is likely to persist in areas, such as the Pacific Northwest, where there is a long history of culturing nonnatives, such as the Pacific oyster and the Manila clam. In some cases, these nonnatives have become naturalized -- reproductive populations have become established in ecosystems well removed from the immediate vicinity of the shellfish farms.
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From page 70... ...
Recommendation: To prevent unintentional and probably irreversible establishment of breeding populations of introduced species, maricul ture operators should use sterile triploids as much as possible when they grow nonnative bivalves in areas where the cultured species either has not been introduced or has not established a reproductive population. More attention should be directed toward the eradica tion of undesirable nonnative species, and a greater emphasis should be placed on studies of ecosystem-level effects of nonnative bivalve introductions.
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From page 71... ...
Interactions with Wildlife Populations Information on the potential effects of mariculture outlined above is largely based upon a general understanding of wildlife ecology and the relationships of these species to the physical and biological environment rather than directed studies built around mariculture operations. In addition, limited understanding of the foraging distribution of birds, marine mammals, and marine turtles from spatially localized breeding colonies makes it extremely challenging to assess populationlevel impacts of disturbance, entanglement, or habitat loss resulting from bivalve mariculture.
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From page 72... ...
Focused studies should be done to identify management approaches that best minimize potential impacts upon birds, marine mammals, and turtles. Finding: While integrated pest management is the broader goal, it is rarely being implemented, and the ecology and effects of pests, predators, and control practices are rarely evaluated, especially at spatial scales larger than an individual farm or portion thereof (e.g., for burrowing shrimp in west coast oyster mariculture; Dumbauld et al., 2006)
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