Research Article

Cultured eastern oysters (Crassostrea virginica): retention and assimilation of picophytoplankton using a multi-biomarker approach

¹ Fisheries and Oceans Canada, Gulf Fisheries Centre, P.O. Box 5030, Science Branch, Moncton, NB E1C 9B6, Canada
² Institut des Sciences de la Mer, Université du Québec à Rimouski, 310 allée des Ursulines, C.P. 3300, Rimouski, QC G5M 1L7, Canada
³ Unité Mixte de Recherche Biologie des organismes et écosystèmes aquatiques (BOREA UMR 7208), Sorbonne Université, Muséum National d'Histoire Naturelle, Université Pierre et Marie Curie, Institut de Recherche pour le Développement, Université de Caen-Normandie, Université des Antilles, 61 rue Buffon, 75005 Paris, France

^* Corresponding author: Remi.Sonier@dfo-mpo.gc.ca

Handling Editor: François Le Loc'h

Received: 6 April 2017
Accepted: 1 August 2017

Abstract

In this study, we investigated the food sources of eastern oysters Crassostrea virginica cultivated in Atlantic Canada. Stable isotopes (¹³C and ¹⁵N) and fatty acid biomarkers were used to identify these sources under in situ conditions for suspended (∼0.5 m below surface) and bottom (∼2 m) culture stocks. It was found that particulate organic matter represented the main food source, with major contributions from live phytoplankton. Higher lipid contents were detected in the digestive glands of suspended oysters compared to bottom oysters (p < 0.05). Bottom oysters did not show significant preference for detrital or bacterial organic matter. Near-surface waters contained an elevated picophytoplankton biomass (PPP, 0.2–2 μm, 1.93 ± 0.16 μg l⁻¹, mean ± SEM) compared to nanophytoplankton biomass (NPP, >2 μm, 1.05 ± 0.15 μg l⁻¹, mean ± SEM). To determine whether the small size PPP was captured and assimilated by C. virginica, feeding trials were conducted in the laboratory using three PPP/NPP diets (20%, 50%, and 80% PPP), consisting of isotopically-labelled (δ¹³C) PPP cells (Nannochloropsis oculata) and non-labelled NPP cells (Tisochrysis lutea). An isotopically-labelled fatty acids analysis indicated PPP assimilation in various tissues (digestive gland, gills, mantle, and abductor muscle), including from oysters fed the reduced (20%) PPP diet. Isotopic enrichment (¹³C) in the FA 22:2 (non-methylene-interrupted or NMI) showed that precursors of NMIs utilized PPP carbon in its biosynthesis process. In conclusion, C. virginica assimilated primarily particulate organic matter (POM), including PPP, which dominated the phytoplankton community in near surface waters. C. virginica can exploit PPP carbon during fatty acid production and further biosynthesis.