Sauriau, P. CREMA (CNRS-IFREMER), pgsauria@ifremer.fr
Kang, C. K. National Fisheries Research & Development Institute, ckkang@ifremer.fr
Richard, P. CREMA (CNRS-IFREMER), prichard@ifremer.fr
Blanchard, G. F. CREMA (CNRS-IFREMER), gblancha@ifremer.fr

 
ISOTOPIC EVIDENCE OF A BENTHIC MICROALGAE-BASED SECONDARY PRODUCTION IN CERASTODERMA EDULE (L.), A COMMON FILTER-FEEDER BIVALVE IN MARENNES-OLERON BAY, FRANCE.
 
Stable carbon and nitrogen analyses were used to quantitatively define the trophic base of the filter-feeder bivalve Cerastoderma edule (L.) living on intertidal sandflats in Marennes-Oléron Bay. d13C and d15N ratios of both juvenile and adult cockles together with their potential food sources i.e. suspended particulate organic matter (POM), microphytobenthos, macroalgae (Enteromorpha spp., Fucus spp. Ulva spp.) and marine plants (Zostera noltii) were analysed during one year. Results clearly indicated that carbon assimilated by C. edule is a mixture of carbon from microphytobenthos (d13C= -16.0 ± 0.6%) and POM (d13C = -22.2 ± 1.1%). The d13C values (-15.7 to -14.8%) of juveniles were less negative than those (-19.1 to -17.2%) of adult cockles. This isotopic shift shows that the difference in growth between juveniles and adults during each main growing season originates from the utilisation and/or assimilation of different food resources. Results made quantitative assessment of proportion of food sources to the annual secondary production of cockles possible by using a simple carbon isotope mixing model with POM and microphytobenthos as end-members. We calculated that about 72 % of the overall annual secondary production of cockle (range 7.3-32.5 g AFDW m-2 y-1) was found to originate from microphytobenthos, with a much higher contribution for juveniles (89 %) than for adults (63%).
 
Day: Thursday, Feb. 4
Time:
Location: Sweeney Center
 
Code: SS46TH1694S