Spatial demography of Calanus finmarchicus in the Irminger Sea

Abstract

Continuous Plankton Recorder data suggest that the Irminger Sea supports a major proportion of the surface living population of the copepod Calanus finmarchicus in the northern North Atlantic, but there have been few studies of its population dynamics in the region. In this paper, we document the seasonal changes in the demographic structure of C. finmarchicus in the Irminger Sea from a field programme during 2001/2002, and the associations between its developmental stages and various apparent bio physical zones. Overwintering stages were found widely at depth (>500 m) across the Irminger Sea, and surviving females were widely distributed in the surface waters the following spring. However, recruitment of the subsequent generation was concentrated around the fringes of the Irminger Sea basin, along the edges of the Irminger and East Greenland Currents, and not in the central basin. In late summer animals were found descending back to overwintering depths in the Central Irminger Sea. The key factors dictating this pattern of recruitment appear to be (a) the general circulation regime, (b) predation on eggs in the spring, possibly by the surviving G0 stock, and (c) mortality of first feeding naupliar stages in the central basin where food concentrations appear to be low throughout the year.We compared the demographic patterns in 2001/2002 with observations from the only previous major survey in 1963 and with data from the Continuous Plankton Recorder (CPR) surveys. In both previous data sets, the basic structure of G0 ascent from the central basin and G1 recruitment around the fringes was a robust feature, suggesting that it is a recurrent phenomenon. The Irminger Sea is a complex mixing zone between polar and Atlantic water masses, and it has also been identified as a site of sporadic deep convection. The physical oceanographic characteristics of the region are therefore potentially sensitive to climate fluctuations. Despite this, the abundance of C.finmarchicus in the region, as measured by the CPR surveys, appears not to have responded to climate factors linked to the North Atlantic Oscillation Index, in contrast with the stocks in eastern Atlantic areas. We speculate that this may because biological factors (production and mortality), rather than transport processes are the key factors affecting the population dynamics in the Irminger Sea

High dispersal potential has maintained long-term population stability in the North Atlantic copepodCalanus finmarchicus

“…Exchange of individuals between the Norwegian Sea Gyre and the Irminger/Labrador Gyres may occur during the reproductive season as a result of lateral advective and mixing processes in the surface layers (Ivers 1975). This process is assisted by an apparent tendency for the C. finmarchicus adult stages to be associated with the margins of the two gyres where mixing between populations is more likely (Heath et al 2008). Such potential range-wide connectivity of C. finmarchicus populations implied by our study would appear to confirm the findings of a recent modelling study by Speirs et al (2006).…”

Role of ciliates and other microzooplankton in the Irminger Sea (NW Atlantic Ocean)

“…These cruises did not capture the spring bloom. Temperature, salinity, and nutrient data (see Table 1) were also collected; for details see Waniek et al (2005), Sanders et al (2005), Holliday et al (2006), Ward & Waniek, (2007), and Heath et al (2008). Many of the data have been archived at the British Oceanographic Data Centre (BODC; Liverpool, UK).…”

“…Furthermore, coastal studies of summer waters off Greenland indicate that <11 µm phytoplankton often dominate , and other work in the Irminger Sea alludes to the dominance of small taxa (e.g. Irigoien et al 2003, Mayor et al 2006, Heath et al 2008). Although these and other studies that focus specifically on phytoplankton production across the Irminger Sea (e.g.…”

“…(3) the spatial demography of Calanus finmarchicus (Fielding et al 2004, Lindeque et al 2006, Heath et al 2008, indicating, among other factors, that most recruitment is on the margins of the Sea; (4) the feeding and production of mesozooplankton nauplii and adults (Irigoien et al 2003, Castellani et al 2008, Mayor et al 2006, which indicated the importance of phytoplankton blooms and possibly ciliates as food for metazooplankton; (5) the distribution, population structure, and growth of euphausids (Saunders et al 2007), which indicated some patterns in the distribution of euphausids, similar to the physical regions outlined above.…”

Spring mortality of the cyclopoid copepod Oithona similis in polar waters

“…Furthermore, there are only a few estimates of copepod mortality in high latitudes (e.g. Matthews et al 1978, Ohman & Hirche 2001, Heath et al 2008, and epi-pelagic values from polar waters are especially sparse (e.g. Thor et al 2008).…”