CHARACTERIZATION OF THE PELAGIC ECOSYSTEM IN SURFACE WATERS OF THE NORTHERN GULF OF ST-LAWRENCE IN EARLY SUMMER - THE LARVAL REDFISH CALANUS MICROPLANKTON INTERACTION

Citation
Ja. Runge et Y. Delafontaine, CHARACTERIZATION OF THE PELAGIC ECOSYSTEM IN SURFACE WATERS OF THE NORTHERN GULF OF ST-LAWRENCE IN EARLY SUMMER - THE LARVAL REDFISH CALANUS MICROPLANKTON INTERACTION, Fisheries oceanography, 5(1), 1996, pp. 21-37
Citations number
52
Categorie Soggetti
Fisheries,Oceanografhy
Journal title
ISSN journal
10546006
Volume
5
Issue
1
Year of publication
1996
Pages
21 - 37
Database
ISI
SICI code
1054-6006(1996)5:1<21:COTPEI>2.0.ZU;2-G
Abstract
In June 1989, the water column along a transect in the north-central G ulf of St Lawrence was thermally stratified (10-14 degrees C at the su rface; 0-1 degrees C at 30 m). In the surface layer, nitrate and chlor ophyll concentrations were very low; the mean concentration of chlorop hyll a > 5 mu m in the subsurface maximum was 0.26 mu g l(-1). Autotro phic and (presumably) heterotrophic flagellates and dinoflagellates we re the most abundant microplankton. In this system, redfish (Sebastes spp.) larvae and the planktonic copepod Calanus finmarchicus overwhelm ingly dominated the ichthyoplankton and zooplankton, respectively. Red fish larvae, Calanus females and Calanus eggs were most abundant in th e surface layer (0-25 m) day and night. Daily specific egg production rates of Calanus, calculated from shipboard incubations of females, ap proached the predicted maximal level for this species at the ambient t emperature of the surface layer, indicating no or little food limitati on. The redfish larvae were feeding almost exclusively on the Calanus eggs' and were found in greatest abundance along the transect where Ca lanus egg production rates (eggs m(-2) day(-1)), calculated from the p roduct of the specific egg production rate and female concentration, w ere highest. The monospecificity of the larval redfish diet and the co -dominance with Calanus Finmarchicus are consistent with the findings of previous research in regions of the North Atlantic, including the I rminger Sea and Flemish Cap. Contrary to predictions of the traditiona l view of the relationship between C. finmarchicus and phytoplankton b looms, however, Calanus was not dependent on high phytoplankton concen trations for egg production in this region, at least at this time of y ear. These observations lay the foundation for characterization of the surface layer of the north-central Gulf in late lune as a summer, pos t-bloom environment in which production of autotrophic and heterotroph ic microplankton supports the Calanus-larval redfish interaction.