Export production and the distribution of fish larvae and their prey in a coastal jet frontal region

Abstract

Fine-scale spatial sampling series and vertical cross-sections were used to obtain quasisynoptic images of the distribution of fish larvae and their prey in the permanent frontal region formed by the Gaspe coastal jet current and the adjacent Anticosti gyre (NW Gulf of St. Lawrence, Canada). The accumulation of large diatoms triggered the reproduction of copepods in the Gasp6 current where eggs and nauplii (the main prey of first-feeding fish larvae) were 10 to 20 times more abundant than in the gyre. Estuarine circulation resulted in the coincidence of the small and abundant larvae of capelin Mallotus villosus and sand lance Ammodytes sp. with this intense production of their food in the jet current. The large and less abundant larvae of redfish Sebastes sp. and Arctic shanny Stichaeuspunctatus exploited the scarcer food resources of the Anticosti gyre. We conclude that opportunistic species producing large numbers of small offspring with limited foraging skills depend on massive export production at hydrographic singularities (i.e. salient hydrographic features) for reproduction. Species producing fewer but larger and more competent larvae can colonize less productive areas of the ocean. Plankton dynamics in the dispersal area of the early larval stages appear to be a pnmary constraint defining the life strategy of a fish species.

Cross-frontal variation in growth rate and prey availability of larval North Sea cod Gadus morhua

“…These areas are characterised by large spatial variability in key physical parameters such as temperature and salinity (Fortier et al 1992, Lochmann et al 1997, Lee et al 2005, and here we often observe enhanced primary production, due to upwelled nutrients, and enhanced concentrations of zooplankton and fish larvae, partly due to converging currents and concentration of non-passive organisms (LeFevre 1986, Franks 1992, Franks & Chen 1996, Aretxabaleta et al 2005. Specific physical and biological measures vary markedly within relatively short distances across frontal zones (< 5 km), and both field observations (e.g.…”

“…Differential growth and thereby differential mortality has implications for the interpretation of larval concentrations in frontal zones. The frequently observed aggregations of plankton organisms are mainly attributed to localised spawning behaviour of adults and accumulation due to an interplay of converging currents and vertically migrating behaviour of plankton organisms (Fortier et al 1992, Franks 1992. However, no firm conclusion has been reached on the influence of differential mortality (e.g.…”

Description du régime alimentaire et comparaison de la niche alimentaire des larves de trois espèces de poisson fourragères dans le nord du golfe du Saint-Laurent :

“…Les larves ont également une faible capacité natatoire et leurs déplacements sur de longues distances consistent principalement au transport passif des courants marins. Dans certains cas, on observe une migration verticale leur permettant d'accéder à des courants plus favorables (Grioche et al, 2000), mais en général les courants créent une dispersion spatiale des larves pouvant les éloigner des zones productives nécessaires à leur survie (Iles & Sinclair, 1982;Fortier et al, 1992).…”

“…However, that ecosystem has marked océanographie and biological differences compared with the northwest GSL, which shows a zooplankton community typical of the sub-arctic northwest Atlantic dominated by Calanus species both in abundance and biomass and high abundance of much smaller Oithona (De Lafontaine et al, 1991;Plourde et al, 2002;Harvey and Devine, 2009). In the GSL, Fortier et al (1992) partially described the larval diet of arctic shanny, but indicated developmental stages only, without giving prey species identification; hence, very little is known about the feeding ecology of arctic shanny and snakeblenny larvae. Furthermore, since many studies have indicated that larval feeding selectivity and copepod escape response are dependent on species and developmental stage (Fields and Yen, 1997;Buskey et al, 2002;Visser, 2007;Robert et al, 2008), the detailed identification of prey species should be considered in the evaluation of feeding selectivity by fish larvae.…”

“…The feeding habits of sandlance larvae have been studied (Fortier et al, 1992;Simonsen et al, 2006;Malzahn and Boersma, 2009), but except for the study by Monteleone's (1986), none has given special attention to discriminating between copepod species and developmental stages in the diet. Monteleone's (1986) study took place in Long Island Sound, where sandlance actively prey on Temora longicornis, the most abundant copepod species in this region (Kane and Prezioso, 2008).…”