Life cycle of Calanus finmarchicus in the lower St. Lawrence Estuary: the imprint of circulation and late timing of the spring phytoplankton bloom

Abstract

The life cycle of Calanus finmarchicus in the lower St. Lawrence estuary is described based on observations of female egg production rate, population stage abundance, and chlorophyll a biomass collected over 7 years (1991)(1992)(1993)(1994)(1995)(1996)(1997) at a centrally located monitoring station. The mean seasonal pattern shows maximum abundance of females in May, but peak population egg production rate and naupliar (N3-N6) abundance occur in early July just after onset of the late spring -early summer phytoplankton bloom. The population stage structure is characterized by low summer abundance of early copepodite stages C1-C3 and high stage C5 abundance in autumn. Between 1994 and 1997, there was important interannual variation in both timing (up to 1 month) and amplitude (five-to eight-fold) of population reproduction. Patterns of seasonal increase of C5 abundance in autumn suggest interannual variations of both timing and magnitude of deep upstream advection of this overwintering stage. Thus, the main features of C. finmarchicus population dynamics in the central lower St. Lawrence Estuary are (i) late reproduction resulting from food limitation prior to the onset of the summer phytoplankton bloom, (ii) probable export of early developmental stages during summer, and (iii) advection into the central lower St. Lawrence Estuary of overwintering stage C5 in autumn from downstream regions. These results support the hypothesis that circulation, mainly driven by discharge from the St. Lawrence River and its tributaries, is a key factor governing population dynamics of C. finmarchicus in this region.

Turbulent nitrate fluxes in the Lower St. Lawrence Estuary, Canada

“…About 75% of the surface nutrients found in the LSLE may therefore originate from the CIL because of this upwelling/mixing mechanism [Greisman and Ingram, 1977;Savenkoff et al, 2001], the remaining part being attributed to the St. Lawrence and Saguenay rivers discharge. These vertical nutrient fluxes at the HLC sustain a high primary productivity in the LSLE, with daily production rates during the summer nearly equivalent to those during spring blooms [Levasseur et al, 1984;Therriault and Levasseur, 1985;Plourde and Runge, 1993;Plourde et al, 2001]. This high primary productivity sustains high levels of secondary production that is then exported to the Gulf, mostly via the Gaspe Current Plourde and Runge, 1993].…”

Phenology and fitness of Calanus glacialis, C. finmarchicus (Copepoda), and their hybrids in the St. Lawrence Estuary

“…Environmental conditions were assessed and zooplankton was sampled every second week from early March to the end of July 2010 at Rimouski Station in the lower St. Lawrence Estuary (48°40' N, 68°35' W, Plourde et al 2001) (Table 1). This temporal sampling series was especially fruitful because of an exceptionally early start of sampling in late winter due to favourable (low) ice conditions (Galbraith et al 2012).…”

“…In sympa-try, the reproductive phenology of C. glacialis precedes that of C. finmarchicus (Madsen et al 2001, Plourde et al 2001. For instance, in the St. Lawrence Estuary, C. glacialis and C. finmarchicus lay eggs near the surface in late winter and late spring, respectively (Plourde et al 2001, S. Plourde unpubl.…”

Macrozooplankton community patterns driven by water circulation in the St. Lawrence marine system, Canada

“…For the NW GSL region, Stn U2 (49°43' N, 66°15' W) was sampled during each cruise (Fig. 1) Magdelan shelf L a u re n ti a n ch a n n e l , and the general surface circulation pattern in early summer (arrows) (adapted from Plourde et al 2001) temperature and salinity was obtained at each station using a Sea-Bird SBE 911plus CTD. Immediately following the CTD cast, zooplankton samples were collected using a 1 m 2 BIONESS sampler (Sameoto et al 1980) equipped with 9 opening/closing nets having a 250 µm mesh size (except in fall 1998 and 2001 when the mesh size used was 333 µm).…”

“…A number of integrated oceanographic and/or biological approaches have recently been used to examine the variable distribution and abundance of both krill and mesozooplankton in the LSLE (see Simard et al 1986a,b, Runge & Simard 1990, Plourde & Runge 1993, Simard 1996, Simard & Lavoie 1999, Zakardjian et al 1999, Lavoie et al 2000, Plourde et al 2001. A conclusion common to all these studies is that the abundance and distribution of krill in the upper part of the LSLE and the horizontal distribution of the common pelagic copepods Calanus finmarchicus and C. hyperboreus in the LSLE are controlled by the 2-layer estuarine circulation, the strong vertical currents at the head of the Laurentian Channel (LC), and the stage-specific vertical distribution of the various species.…”