Effects of temperature and circulation on the population dynamics of Calanus finmarchicus in the Gulf of St. Lawrence and Scotian Shelf: Study with a coupled, three‐dimensional hydrodynamic, stage‐based life history model

Abstract

[1] We developed a physical-biological model for the Gulf of St. Lawrence (GSL) and Scotian Shelf (SS) by coupling a stage-based life-history model of the planktonic copepod Calanus finmarchicus to a three-dimensional ocean circulation model. The life-history model consists of 13 morphologically distinct life stages of C. finmarchicus, with stagespecific and temperature-dependent molting rates. The model also includes stage-specific vertical distribution and seasonally varying diapause, egg production, and stage-specific mortality rates. The model domain covers the eastern Canadian shelf from 55°W to 72°Wand from 39°N to 52°N, including the Gulf of St. Lawrence, Scotian Shelf, and Gulf of Maine. A comparison of a 1-year simulation with observations indicates that the physical-biological model reasonably describes the observed abundance and distribution of C. finmarchicus in this region. To determine the effects of ocean circulation in the C. finmarchicus population dynamics, we divided the GSL-SS region into eight sub-areas and compared the net fluxes of C. finmarchicus across lateral boundaries to the net production in each sub-area. We found that the annual cross-boundary exchange rates constitute from <1% to 39% of the local net production, indicating that the horizontal transport of C. finmarchicus by the ocean currents can play a very important role in the dynamics of local C. finmarchicus populations. The results provide insights into the mechanisms of exchange in the GSL-SS system, as put forward in recent hypotheses.

Ocean-scale modelling of the distribution, abundance, and seasonal dynamics of the copepod Calanus finmarchicus

“…The behavioural model of Fiksen (2000) cues diapause entry in a similar way to Carlotti & Wolf (1998), but only during the C5 stage. Tittensor et al (2003) allow individuals to enter diapause at a constant rate throughout the C5 stage, while Zakardjian et al (2003) had a similar approach but with a seasonally varying rate. It has also been suggested that the arrival of seasonally migrating fish can promote diapause entry (Kaartvedt 2000), although the difficulties of representing predator fields means this has never been included in a demographic model.…”

“…Recently, a number of authors have used Eulerian descriptions of Calanus finmarchicus in which the spatial domain is divided up into set of discrete cells (Bryant et al 1997, Tittensor et al 2003, Zakardjian et al 2003. These models are a more natural representation of the density of organisms continuously distributed over large areas, but the accurate characterization of both spatial and physiological structure by standard methods is computationally demanding.…”

Trapping migrating zooplankton

“…However, the necessary observations and understanding of depth selection and foraging behavior in marine zooplankton are extremely limited. Thus, for example, modeling studies of mesozooplankton population dynamics embedded in multidimensional ocean circulation schemes repeatedly identify controls of vertical distribution and migration behavior (that is, depth selection) by individual zooplankters as essential information that is usually unknown (Batchelder et al 2002;Hannah et al 1997;Miller et al 1998;Reiss et al 2003;Werner et al 1993;Wroblewski 1982;Zakardjian et al 2003). Recent modeling work suggests that small-scale behaviors such as foraging may indeed have a large impact on the transport of zooplankters (Woodson and McManus 2007).…”

Le Parc Marin Saguenay–Saint-Laurent : processus océanographiques à la base de ce site unique d’alimentation des baleines du Nord-Ouest Atlantique

“…C'est dans ce contexte écosystémique que s'inscrivent les processus responsables de l'existence et des variabilités spatiale et temporelle du site d'alimentation traditionnel des baleines du PMSSL (Figure 2). Le « bloom » printanier (prolifération massive du phytoplancton) qui démarre immédiatement après la fonte des glaces en avril dans le golfe du Saint-Laurent, en exploitant les éléments nutritifs remis en disponibilité dans la couche photique par le profond mélange vertical encouru depuis l'automne précédent, initie la ponte des espèces zooplanctoniques herbivores dominantes de copépodes et d'euphausides (krill) ayant complété leur diapause (baisse de l'intensité des activités métaboliques) hivernale (DE LAFONTAINE et al, 1991;LE FOUEST et al, 2005;MAUCHLINE, 1980;PLOURDE et RUNGE, 1993;PLOURDE et al, 2001;PLOURDE et THERRIAULT, 2004;ZAKARDJIAN et al, 2003). Ceci amorce le processus de production biologique conduisant à la formation des agrégations de zooplancton et, éventuellement, de leurs prédateurs, poissons pélagiques ou baleines planctivores et piscivores (DE LAFONTAINE et al, 1991;PLOURDE et al, 2001;RUNGE et SIMARD 1990;RUNGE et al, 1999;THERRIAULT, 1991).…”