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

Abstract

The copepod Calanus finmarchicus is widely distributed over the sub-polar Atlantic and dominates the mesozooplanktonic biomass in that region. Despite this, all previous C. finmarchicus population modelling studies have been spatially and temporally limited. In this paper we present results from a fully stage-resolved model in a domain spanning the entire geographic range of the species (30 to 80°N and 80°W to 90°E. The model was driven by temperature and transport from the Ocean Circulation and Climate Advanced Modelling project (OCCAM) and phytoplankton food derived from satellite (SeaWiFS) sea-surface colour observations. The resulting quasi-stationary yearly cycle was assessed against seasonally resolved maps of continuous plankton recorder observations, winter cruise data on the distribution of diapausers, and time series from locations distributed over the North Atlantic. The model's high computational efficiency permitted its free parameters to be selected to yield a good correspondence with the field data. We were also able to explore the effects of changing the assumptions regarding diapause and mortality. By falsifying alternative models we conclude that (1) a fixed fraction of each surface generation enters diapause, (2) overwintering individuals enter diapause at the end of the fifth copepodite stage, and (3) mortality is an increasing function of temperature. Finally, we demonstrate that the demographic impact of transport is limited, except in shelf seas and at the edges of the distribution; nevertheless, there is a very high level of population connectivity over the whole domain.

CO2-induced acidification affects hatching success in Calanus finmarchicus

“…This is of particular importance for the 'epicentre' populations of C. finmarchicus, e.g. those in the Gulf of Maine and the Norwegian Sea (Speirs et al 2006 and references therein), where animals overwinter at depths between 500 and 1200 m (Miller et al 1991, Edvardsen et al 2006). The present study demonstrates that future risk/ environmental impact assessments of marine CO 2 disposal/storage options must look beyond adult mortality as an endpoint (e.g.…”

Environmental Impacts—Marine Ecosystems

“…It is generally accepted that the distribution of C. finmarchicus in the North Atlantic reflects its thermal niche, along with advection from deep-water overwintering areas onto continental shelves such as the North Sea (Speirs et al 2006;Helaouet and Beaugrand 2007). In accordance with recent warming, large declines in abundance of C. finmarchicus have occurred in the North Sea and low reproductive success of several forage-fishdependent seabird species has been linked to these declines (Frederiksen et al 2006).…”

Model-based estimates of Calanus finmarchicus abundance in the Gulf of Maine

“…Having mortality change with temperature provides seasonal variability, but tied to conditions in the water rather than to the calendar. Speirs et al (2006) inferred parameter values by comparing their model to Calanus finmarchicus abundance across the North Atlantic. For the present study, we assume that the functional form of their mortality function is correct but that the parameter values may need adjustment to simulate conditions in the Gulf of Maine.…”

“…Further increasing the number of substages did not lead to any noticeable changes in the population's seasonal development. The Campbell et al (2001) parameter values serve as the basis of most C. finmarchicus models , Zakardjian et al 2003, Speirs et al 2006, including ours (Table 1). At maximum temperature, development rate varies in proportion to chlorophyll (F in mg m -3 ) as an Ivlev function (Ivlev 1961), representing the proportion of maximum development rate: (4) where q is the carbon:chlorophyll ratio and b j is the food dependence.…”

“…The function should also incorporate an element of density dependence. Speirs et al (2006) developed a temperature and food-dependent mortality function that has many of these qualities. Having mortality change with temperature provides seasonal variability, but tied to conditions in the water rather than to the calendar.…”