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Dartmouth, Canada

Comeau L.A.,Gulf | Mayrand E.,University of Moncton | Mallet A.,Mallet Research Services Ltd.
Marine Biology

To test the hypothesis that oysters, Crassostrea virginica, from the northernmost part of the species range in the Gulf of St. Lawrence (48°N) open their valves at lower temperatures than those reported for more southern oysters, Hall element sensors were used to monitor their gaping behaviour. These observations were made in a flow-through system and the temperature, salinity and relative fluorescence of unfiltered seawater were monitored. Photoperiod was controlled (15 h dark:9 h light) and light levels were measured but not closely controlled. Gaping behaviour was followed from February to June 2010 (113 days) and from April to May 2011 (34 days) and was classified into three successive phases: quiescent, awakening and active. Although valves were either closed or slightly open during the quiescent phase (maximum gape angle = 0. 49°, SE = 0. 04), they abruptly opened to maximum angles of about 5. 88° (SE = 0. 29) during the awakening phase. Moreover, there was noticeable synchrony amongst individuals, since approximately one-half of the monitored population awoke within a 6. 6-h period in both study years. Correlative analyses identified temperature as a factor influencing valve movement, and oysters awakened when temperatures were 0. 2-4. 0 °C (mean = 2. 2, SE = 0. 2). Oysters exerted their maximal gape angle as soon as temperatures reached 2. 8-6. 6 °C (mean = 4. 8, SE = 0. 2). During the active phase, valves remained open 68. 6 % (2010) and 79. 7 % (2011) of the time. An unexpected result was the observation of a diurnal rhythm in valve openness whereby the openness was greatest near the end of the afternoon and least in the early morning. © 2012 Her Majesty the Queen in Rights of Canada. Source

Filgueira R.,Dalhousie University | Filgueira R.,Gulf | Comeau L.A.,Gulf | Landry T.,Gulf | And 3 more authors.
Ecological Indicators

Shellfish aquaculture implies the placement of artificial structures in the coastal environment and the alteration of natural bivalve populations, which calls for the establishment of legislative regulatory frameworks based on an ecosystem approach. One of the challenges for policy makers is the need to monitor the effectiveness of management actions. In this study, a meta-analysis across different bays, covering a large spatial scale in Atlantic Canada, was performed to test the response of two potential indicators of aquaculture intensity: (1) the bivalve growth using both Dynamic Energy Budget (DEB) and Scope For Growth (SFG) approaches, and (2) the bivalve condition index (CI = (meat weight/shell weight) × 100). Our underlying premise was that overstocking of bivalves leads to increased competition for food resources, which might ultimately have a significant effect on bivalve growth performance and the CI. Bivalve growth performance for cohorts of Mytilus edulis and Crassostrea virginica were simulated by combining satellite remote sensing (temperature and chlorophyll) with individual based models using both DEB and SFG approaches. These models were calibrated for each cohort, by adjusting the half-saturation coefficient of the food ingestion function term (XK), which is a common parameter related to feeding behavior in both approaches. A significant correlation between XK and lease coverage (lease area/bay area, dimensionless) was found for M. edulis. However, because of unrealistic XK values in some M. edulis cohorts and the lack of consistent simulations for C. virginica precluded using XK as a reliable indicator of aquaculture intensity. By contrast, according to the observed results CI emerged as a good indicator of aquaculture intensity for both species. A General Additive Model (GAM) for C. virginica provided a regression that included the initial dry meat weight as a linear term and the lease area as a non-linear term, explaining a total deviance of 59.9% in describing final CI values. The GAM for M. edulis included only non-linear terms, lease coverage, and lease area, explaining a total deviance of 61.0%. Since the CI theoretically integrates the effects of changing trophic conditions over time, the good relationship between the CI and lease/bay characteristics provides a scientific framework for its use as a reliable ecological indicator of aquaculture intensity. From an applied perspective, this finding is of relevance because the CI is easy to measure and is widely available in government and industry datasets. © 2012 Elsevier Ltd. Source

Mallet A.L.,Mallet Research Services Ltd. | Carver C.E.,Mallet Research Services Ltd. | Doiron S.,Aquaculture and Fisheries | Theriault M.-H.,Gulf

Size groups of Eastern oysters Crassostrea virginica (20-30. mm, 30-40. mm, 40-50. mm, and 50-60. mm) were individually labeled, randomly assigned to two types of floating culture gears (horizontal ropes and Vexar bags) and deployed at various locations in northern New Brunswick, Canada. Results indicated that the rope-grown oysters substantially outperformed those deployed in floating bags; after one growing season, shell growth was 60% higher and weight gain was nearly double. More than 95% of the variance in shell or weight growth could be explained by the culture gear. The difference in oyster performance between the two culture gears was greater at certain sites, or a significant culture gear by site effect. In particular, it appeared that growth in the floating bags was relatively depressed at the more dynamic sites with higher wave action. Based on the rope-grown oyster performance, we would suggest that the environmental conditions at the various locations tested in this study would support similar levels of commercial oyster production. The prediction would be quite different, however, if the site productivity assessment were based on performance data from floating oyster bags. © 2013 Elsevier B.V. Source

Skinner M.A.,University of New Brunswick | Courtenay S.C.,University of New Brunswick | McKindsey C.W.,Maurice Lamontagne Institute | Carver C.E.,Mallet Research Services Ltd. | Mallet A.L.,Mallet Research Services Ltd.
Journal of Experimental Marine Biology and Ecology

Recent studies have hypothesized reduced eelgrass distribution in areas exposed to suspended bag oyster aquaculture of Crassostrea virginica in Eastern Canada is related to shading from aquaculture stock and equipment. The results of a 359-day manipulative field experiment support this hypothesis. Reductions in underwater light, at levels comparable to those found at suspended oyster operations, caused reduced eelgrass structure, morphometrics, and photosynthesis. Increased organic matter deposition under suspended bags neither led to biologically relevant declines in eelgrass metrics, nor mitigated the effects of light limitation. Shoot density, above-ground biomass, below-ground biomass, canopy height, leaf area index, leaf width, and photosynthetic capacity were all significantly reduced. These variables declined along a gradient of increased shading, with significant responses detected in as few as 67. days after exposure to 26% subsurface irradiance. Subsequent sampling 253. days after the removal of experimental treatments documented the potential for recovery in the form of seedling recruitment to the plots of heaviest impact. However, eelgrass response variables remained significantly reduced relative to controls, indicating previous assumptions of a rapid recovery potential for eelgrass exposed to suspended bag oyster aquaculture were incorrect. © 2014. Source

Comeau L.A.,Gulf | Mallet A.L.,Mallet Research Services Ltd. | Carver C.E.,Mallet Research Services Ltd. | Guyondet T.,Gulf
Aquacultural Engineering

Benthic impacts that may ultimately result from further intensification of suspended oyster culture in eastern Canada were proactively investigated. Eastern oysters (Crassostrea virginica) were placed in experimental floating rafts (12.1m2) designed to hold densities 2-3 times higher than those presently found in floating bag operations. Experimental rafts were moored in shallow water (1-2m) at fixed positions where no aquaculture had been practiced. A biodeposition model predicted that the majority of feces released by suspended oysters would fall onto the seabed area directly beneath the rafts. However, field measurements over a 132d period indicated that the fecal deposition from the highly aggregated oysters was not reflected in higher organic sedimentation rates or seabed sulfide levels. Rather, the proportion of organic matter in the top sediment layer was significantly lower in samples collected underneath rafts (5.1±1.5%) than in samples taken at reference sites (10.5±3.2%). This same pattern was observed for control rafts holding shells only. It is suggested that the floating raft impacted local hydrodynamic processes, forcing water to move underneath the structure, thereby amplifying turbulence and resuspending low shear strength particles such as biodeposits. © 2013. Source

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