Multivariate analyses of the role of environmental factors in seasonal and site-related growth variation in the Pacific oyster Crassostrea gigas

Monthly increases in shell height were measured for 2 age classes (Years 0 and 1) of a common broodstock of oysters Crassostrea gigas in 10 locations in British Columbia, Canada, over 14 mo.Measurements were also taken of several environmental variables known to affect oyster growth.Based on comparisons of shell height growth curves, sites were grouped into low, medium and high growth categories which were similar for both age classes of oysters.According to discriminant function analysis, differences in salinity and particulate organic matter (POM) concentration distinguished low growth sites from medium and high growth areas.Medium and high growth areas were segregated solely on the basis of food-related var~ables: POM, carotenoid concentration and Secchi depth.In multiple regression analysis, chlorophyll b concentration and water temperature were significantly correlated (for both age classes; l2 = 0.34, p < 0.001) to 109,~-transformed monthly instantaneous growth rate (G30) with chlorophyll b being the more important variable.Inclusion of monthly initial shell height in the regression analysis increased to 0.62 and 0.44 for Year 0 and Year 1 equations (p <0.001), respectively.Correlation of chlorophyll b to G.30 may b e indicative of the role of small nanoplankton in oyster diets.Monthly oyster growth rates were primarily regulated by food supply with temperature a secondary factor.Growth rates were highly site-specific depending on food supply and salinity conditions.