Growth, morphometrics, and nutrient content of farmed eastern oysters, Crassostrea virginica (Gmelin), in New Hampshire, USA

Abstract

When harvested, oysters represent a removal from the ecosystem of nutrients such as nitrogen (N) and carbon (C). A number of factors potentially affect nutrient content, but a quantitative understanding across the geographic range of the eastern oysters is lacking. The present study was designed to quantify the relationships among various metrics of farmed eastern oysters near its northern geographic range focusing on nutrient content. Hatchery-reared oysters were deployed in polyethylene bags at six sites, and were measured on multiple occasions from 2010-2012. A quadratic polynomial fit to the combined datasets for shell height indicated that on average a 'cocktail' size oyster (63 mm shell height) would be reached after 2 yr, and 'regular' size (76 mm) would require 3 yr. There were significant differences in growth rates and oyster nutrient content among the sites; means for %N in soft tissue ranged from 6.9 to 8.6, and 0.07 to 0.18 in shell. Percent N in soft tissue and shell were highest at two sites at the mouths of rivers with elevated dissolved inorganic N concentrations in the water. Grand means (all sites, seasons and years combined) of soft tissue N and C for regular size oysters were 7.3% and 38.5%, respectively; and for shell N and C were 0.13% and 12.0%, respectively. Our study extends the range of data on nutrient content of the eastern oyster to northern New England, and indicates that oyster size, seasonality, and nutrient concentration in ambient water potentially affect %N and %C content of oysters.

Keywords: bioextraction; eutrophication; nutrient assimilation; shellfish aquaculture; water quality.

Fig.1

Six sites where oysters were deployed 2010-2012 (see text for details).

Fig. 2

Oyster growth as shell height using combined datasets from all sites, seasons, size classes. The gray shaded area around the fit line is 95% confidence interval. Open squares = small size class; Black inverted triangles = large size class.

Fig. 3

Final shell heights (2.3 yrs of growth) by size class for four sites (no final data were available for BMY and SQR) with complete datasets. P values shown for overall ANOVAs by size class and significance groups based on Tukey test (p<0.05) indicated with lower case letters (normal font for small size class, italicized for large class).

Fig. 4

Relationship between shell height and whole oyster wet (fresh) weight for overall dataset (all sites, seasons and size classes combined). Best-fit power regression model shown.

Fig. 5

Relationship between shell height and soft tissue DW for overall dataset (all sites, seasons and size classes combined). Best-fit power regression model shown.

Fig. 6

Relationship between shell height and shell DW for overall dataset (all sites, seasons and size classes combined Best-fit 2^nd order polynomial regression model shown.

Fig. 7

Relationship between shell height and soft tissue %N from overall dataset (all years, sites, seasons). Best-fit 2^nd order polynomial regression model shown.

Fig. 8

Relationship between soft tissue DW and soft tissue %N from overall dataset (all years, sites, seasons); linear model shown only for those individuals = or > 0.5 g DW.

Fig. 9

Soft tissue %N and %C by site using combined data from all years and seasons. P values shown are for an ANOVA testing the effect of site. Letters indicate significance among means (Tukeys).

Fig. 10

Shell %N and %C by site; note: shell data were only available for Nov 2012 sampling (see Table 1). P values shown for overall ANOVAs, etc. as in Fig. 9.