Effect of oyster mariculture on submerged aquatic vegetation: an experimental test in a Pacific Northwest estuary (original) (raw)
Related papers
Journal of Shellfish …, 2009
The presence of bivalves and bivalve aquaculture can have positive and negative impacts on seagrass and associated benthic communities. Some oyster (Crassostrea gigas) aquaculture methods recently have been restricted to reduce benthic disturbance and protect native eelgrass (Zostera marina) in West coast (USA) estuaries. We argue that aquaculture, like all food production systems, involves tradeoffs with natural systems, but that the magnitude of those tradeoffs depends on the ecological details of the production system. Capitalizing on oyster aquaculture farms as large scale ''manipulations'' in Willapa Bay, WA (USA), we explored three different oyster aquaculture methods (mechanical harvest or ''dredged'' on-bottom, hand picked on-bottom and long line off-bottom). We found that both the biological (oyster-eelgrass interactions) and physical (disturbance or structure) components of aquaculture led to changes in the eelgrass population. Eelgrass density declined with oyster density in all aquaculture areas, likely as a result of direct competition for space. Eelgrass relative growth rate, plant size, and production did not change with oyster density. However, all eelgrass measures were affected by aquaculture, and the type and magnitude of impacts varied among eelgrass measures and aquaculture methods. Throughout the bay, eelgrass in long line areas occurred at densities indistinguishable from nearby uncultivated areas, but in 2004, eelgrass in long line areas was smaller (32%) and had lower production per area (70%). Cultivating oysters in dredged or hand picked beds increased eelgrass growth rates slightly, but led to lower eelgrass density (70% and 30%, respectively), plant size (32%, both cases), and production (70%, both cases). In a large scale simulated mechanical harvest experiment, the temporal response of eelgrass density varied dramatically by site, ranging from 1 to >4 y. If eelgrass impact reduction, rather than avoidance, is identified as the management goal, the degree of tradeoff between eelgrass habitat and oyster production can be minimized by managing aquaculture methods or oyster planting densities, depending on the eelgrass measure of interest. Explicit management goals and appropriate eelgrass habitat indicators must be developed before our findings can be used to suggest best management practices for intertidal aquaculture in the Pacific Northwest.
Importance of eelgrass early life history stages in response to oyster aquaculture disturbance
… Ecology Progress Series, 2007
Seagrasses are a critical element in many estuaries and act as drivers of abiotic and biotic processes. One species, Zostera marina L., has been declining globally. A potential contributor to this decline is shellfish aquaculture, although we know little about its impacts. On the US west coast, shellfish aquaculture co-occurs with protected eelgrass habitats. Many aquaculture practices constitute a periodic disturbance, and a key concern is eelgrass recovery. We used observations and experiments to understand how oyster aquaculture practices (i.e. dredging [oysters grown on the bottom and harvested mechanically via dredging] and off-bottom longline culture [oysters suspended off the bottom on rope and harvested by hand]) influence eelgrass recovery. Studies of natural recruitment showed highest seedling densities in dredged beds (7 seedlings m -2 ) and lowest under longlines (0.1 seedlings m -2 ). Seed production was highest in dredged beds (295 seeds m -2 ) and lowest in longline beds (52 seeds m -2 ). Seed addition experiments were conducted to understand the effect of oyster aquaculture and adult eelgrass neighbors on seedling germination, growth, and survival. In March 2005, seedling germination was 146% higher in eelgrass removal treatments compared to control plots, with no difference among aquaculture and reference areas. By April 2005, there were no effects of neighbors, but reference areas had greater seed densities (11 seedlings m -2 ) compared to longline areas (3.2 seedlings m -2 ). By August 2005, seedling mortality in longline and reference control plots was 100%. In dredged areas, seedlings in removal plots had greater biomass (0.38 g) than seedlings in control plots (0.14 g). We propose that if eelgrass is to be disturbed by aquaculture, dredge beds may recover more successfully than longline beds.
Botanica Marina, 2000
We investigated effects of the introduced Pacific oyster (Crassostrea gigas) on native eelgrass (Zostera marina) health on Cortes Island, British Columbia, Canada. Oysters physically alter their environment by increasing habitat complexity and altering water flow, and possibly by causing sulphide to accumulate in the sediment. Sulphide is toxic to eelgrass, and the current decline of eelgrass around Cortes Island may be a consequence of oyster population growth. While oysters and eelgrass coexist at a regional scale, eelgrass is typically absent directly seaward of oyster beds (the ''below-oyster zone'') on Cortes Island. In a controlled experiment, we transplanted eelgrass plugs to below-oyster plots to determine whether this habitat is suitable for eelgrass growth. Shoot and leaf number were significantly greater over time in eelgrass-bed transplants than in below-oyster transplants. These results indicate that the below-oyster zone is unsuitable for eelgrass growth; if a causal link exists between oyster presence in the high intertidal zone and eelgrass absence directly seaward, then expansion of feral and farmed oyster beds will result in further eelgrass loss on Cortes Island.
Estuaries and Coasts, 2016
Oyster farming in estuaries and coastal lagoons frequently overlaps with the distribution of seagrass meadows, yet there are few studies on how it/this aquaculture practice affects seagrass physiology. We compared in situ nitrogen uptake and the productivity of Zostera marina shoots growing near/alongside off-bottom longlines and at a site not affected by oyster farming in San Quintín Bay, a coastal lagoon in Baja California, Mexico. We used benthic chambers to measure leaf NH4 + uptake capacities by pulselabeling with 15 NH4 + , and plant photosynthesis and respiration. The internal 15 N resorption/recycling was measured in shoots two weeks after incubations. The natural isotopic composition of eelgrass tissues and vegetative descriptors were also examined. Plants growing at the oyster farming site showed a higher leaf NH4 + uptake rate (33.1 mmol NH4 + m-2 day-1) relative to those not exposed to oyster cultures (25.6 mmol NH4 + m-2 day-1). We calculated that an eelgrass meadow of 15-16 ha (which represents only about 3-4% of the subtidal eelgrass meadow cover in the western arm of the lagoon) can potentially incorporate the total amount of NH4 + excreted by oysters (~5.2 × 10 6 mmol NH4 + day-1). This highlights the potential of eelgrass to act as a natural biofilter for the NH4 + produced by oyster farming. Shoots exposed to oysters were more efficient in re-utilizing the internal 15 N into the growth of new leaf tissues or to translocate it to belowground tissues. Photosynthetic rates were greater in shoots exposed to oysters, which is consistent with higher NH4 + uptake and more positive δ 13 C values. Vegetative production (shoot size, leaf growth) was also higher in these shoots. Aboveground:belowground biomass ratio was lower in eelgrass beds not directly influenced by oyster farms, likely related to the higher investment in belowground biomass to incorporate sedimentary nutrients.
Oyster reef enhancement utilizing gardened oysters in a subtropical estuary
Restoration Ecology, 2019
Crassostrea virginica, the eastern oyster, is a native foundational species that inhabits coastal and estuarine ecosystems along the western Atlantic seaboard. Introduction of C. virginica into estuarine areas with limited or no extant populations is gaining popularity as a pro-active approach for improving estuarine water quality and creating natural wave breaks for shoreline stabilization. Adult oysters, grown by 113 community members under their private docks, were collected and deployed at 3 county-owned sites along the Indian River Lagoon within Brevard County, Florida. In this shallow, warm-water estuary, replicate treatments deployed at each site included bagged adult oysters collected from gardeners in fall 2014, bagged adult oysters from spring 2015 gardeners, bagged blank (clean) shell, and empty plots (control). Prior to deployment, morphometric data (shell length, weight) were collected on all gardened oysters. Morphometric data were then collected quarterly for all surviving and recruited oysters for 18 months. Our monitoring timeframe was sufficient for assessing survival of gardened oysters, but likely not sufficient to understand recruitment patterns. In areas with no recruitment and limited gardened oyster survival, regular enhancement with live oysters would be needed for long-term success. In areas with natural recruitment, the blank shell treatment was most successful. Lessons learned from this study include: 1) need for better tracking of abiotic variables (e.g. salinity) where gardening occurred, 2) role of seasonality in initial post-deployment survival, even in a warm-water estuary, and 3) importance of pilot studies prior to large-scale gardened oyster deployments.
2018
To better quantify the ecological benefits and impacts of oyster aquaculture, we sampled water quality, sediment quality, benthic macrofaunal communities and oysters at four oyster aquaculture sites located on the western shore of Chesapeake Bay in Virginia, USA. At each site, we collected samples from within the footprint of the aquaculture cages and from nearby areas with similar physical and environmental conditions but far enough away to be minimally influenced by aquaculture operations. Data collected from the water column included chlorophyll concentrations, turbidity, pH, dissolved oxygen concentrations, light attenuation, particle concentration, median particle size, total suspended solids and their organic content, and dissolved nutrient concentrations. Sediment and macrofauna community data collected included sediment grain size and organic content and macrofauna identity, abundance, biomass and species richness. In addition to assessing the potential impacts of oyster aqu...