Effects of the environment and culture depth on growth and mortality in juvenile Pacific oysters in the Strait of Georgia, British Columbia

Abstract

The effects of environmental variables, culture depth, and phytoplankton abundance and composition on juvenile Pacific oyster Crassostrea gigas growth and mortality were studied between June and October of 2008 at 4 sites in the Strait of Georgia, British Columbia, Canada. In addition, the effects of temperature-triggered depth manipulation on growth and mortality of oysters were examined in order to assess potential control measures for mitigating high summer mortalities associated with high temperature, harmful algal blooms (HABs), and other environmental stressors. Control oysters were held at constant depths of 3, 10, and 15 m, while experimental oysters were kept at 3 m depth and lowered to 10 or 15 m when the surface water temperature reached 14, 16, or 18°C. Site and Depth significantly affected the growth and mortality of control oysters. At the site with the best growth, cumulative mortality was low (range: 6.4 to 19%) and negatively correlated with temperature and positively with transparency. At the high-mortality site (range: 64 to 98%), mortality was positively correlated with temperature, chlorophyll concentration, and the biomass of diatoms and potentially harmful algae. Cumulative mortality was generally higher at 3 m than at 15 m depth. Significantly larger oyster volume was obtained with the oyster controls at 3 m than with those held at 10 or 15 m at most sites. Temperature-trigger treatments did not significantly affect oyster volume or cumulative mortality, and oysters moved to 10 and 15 m had final volumes similar to the 10 and 15 m controls, independent of trigger temperature. Oyster growers could select their sites for maximal growth and minimal mortality based on temperature profile, freshwater input, and phytoplankton abundance and composition.

The effects of environmental factors on survival, growth and biochemical composition of transplanted oysters (OstreaedulisLinnaeus, 1758) from Aegean Sea to southern Black Sea

“…Food content in the seawater can interact with temperature and influence the energy storage and their spawning event (Dridi, Romdhane & Elcafsi ). Seasonal growth rate depended on temperature, salinity, total suspended matter (TSM), organic matter (OM), inorganic matter (IM) and chlorophyll a (Fleury, Goyard, Mazurié, Claude, Bouget, Langlade & Le Coguic ; Cassis, Pearce & Maldonado ). Survivorship curves depends on physical factors such as temperature, salinity, desiccation, excessive deposition of silt and biological factors such as predators, parasites, pathogens and competitors for food and space (Tomaru, Kawabata & Nakano ; Lodeiros, Pico, Prieto, Narváez & Guerra ; Chávez‐Villalba, Hernández‐Ibarra, López‐Tapia & Mazón‐Suástegui ).…”

A comparative appraisal of the resilience of marine social-ecological systems to mass mortalities of bivalves

“…It raises questions about the future of such monospecific culture systems facing new hazards. The recent degradation of natural conditions with increasing temperatures and ocean acidification has reduced the natural resilience of these coastal systems (Harvell et al 1999, Cassis et al 2011, Domeneghetti et al 2014, Ekstrom et al 2015. Ecosystems could deteriorate in the future because of increasing CO 2 and ocean acidification.…”

“…Organizational responses (e.g., state aid, mutual funds, diversification strategies, private insurance, inventories, and savings) occur at both individual and collective levels (Grizel 1983, Le Bihan et al 2013, Lupo et al 2014. These responses also take the form of changes in practices and management rules such as limiting effort, reducing bivalve density, going off the coast, changing the culture height in the water column, triage of dead oysters, and building cages against predation (Smith et al 2000, Cassis et al 2011, Pernet et al 2011, Soletchnik et al 2011.…”

Ecological impacts of non-native Pacific oysters (Crassostrea gigas) and management measures for protected areas in Europe

“…However contradictory findings were obtained in North Wales by King et al (2006) who found gonad development to be greater at high shore compared to low shore sites, though oysters showed little maturation and spawning. Experiments in British Columbia on the growth rate and mortality of oysters suspended at different depths within the water column (Cassis et al 2011) showed that these parameters were affected by depth, temperature, freshwater input, phytoplankton abundance and assemblage composition. On the west coast of Ireland differences in the condition of intertidal and subtidal oysters varied between sites and among months (R. Mag Aoidh, unpubl.data).…”