Persistent shift of Calanus spp. in the south-western Norwegian Sea since 2003, linked to ocean climate

Abstract The southwestern Norwegian Sea is characterized by an inflow of warm and saline Atlantic water from the southwest and cold and less saline East Icelandic Water (EIW), of Arctic origin, from the northwest. These two water masses meet and form the Iceland-Faroe Front (IFF). In this region, the copepod Calanus finmarchicus plays a key role in the pelagic ecosystem. Time-series of C. finmarchicus and Calanus hyperboreus in May and September, extending back to the early 1990s, were studied in relation to phytoplankton bloom dynamics and hydrography. The main reproductive period of C. finmarchicus started consistently earlier south of the IFF, resulting in different life cycles and stage compositions in the two water masses. In 2003, a sudden shift occurred north of the IFF, resulting in a similar phenology pattern to south of the IFF. Before this, only one generation of C. finmarchicus was produced in the Arctic water, but the earlier reproduction enabled the species to produce two generations after 2003. Simultaneously, C. hyperboreus, an expatriate in the EIW, largely disappeared. Food availability is unlikely the reason for the phenological differences observed across the front, as the typical pattern of the phytoplankton spring bloom showed an earlier onset north of the IFF. Temperature and salinity peaked at record high values in 2003 and 2004, and therefore possible links to oceanography are discussed. The dominant role of Calanus spp. and the potential linkages to water mass exchanges may herald strong effects on the ecosystem and pelagic fish in this subpolar Atlantic region under expected climate change.</jats:p

The North Atlantic Ocean as habitat for Calanus finmarchicus : environmental factors and life history traits

This paper addresses relationships between the distribution and abundance of zooplankton and its habitat in the northern North Atlantic Ocean. Distributions of ten representative zooplankton taxa, from recent (2000-2009) Continuous Plankton Recorder data, are presented, along with basin-scale patterns of annual sea surface temperature and phytoplankton color. The distribution patterns represent the manifestation of very different physiological, life history and ecological interactions of each taxon with the North Atlantic habitat characteristics. The paper then focuses on a pan-Atlantic compilation of demographic and life history information for the planktonic copepod, Calanus finmarchicus, perhaps one of the most ecologically important and certainly the most studied zooplankton species in the North Atlantic. Abundance, dormancy, egg production and mortality in relation to temperature and phytoplankton biomass, using chlorophyll a as a proxy, are analyzed in the context of understanding factors involved in determining the distribution and abundance of C. finmarchicus across its range. Several themes emerge: (1) transport of C. finmarchicus is from the south to the north in the northeast Atlantic, but from the north to the south in the western North Atlantic, which has implications for understanding population responses to climate forcing on coastal shelves, , (2) recruitment to the youngest copepodite stages occurs during or just after the phytoplankton bloom in the east while it occurs after the bloom in many western sites, (3) while the deep basins in the Labrador Sea and Norwegian Sea are primary sources of C. finmarchicus production, the western North Atlantic marginal seas have an important role in sustaining high C. finmarchicus abundance on the western North Atlantic shelves, (4) differences in mean temperature and chlorophyll concentration between the western and eastern North Atlantic are reflected in regional differences in female body size and egg production responses, (5) differences in functional responses in egg production rate may reflect genetic differences between western and eastern populations, (6) dormancy duration is generally shorter in the deep waters adjacent to the lower latitude western North Atlantic shelves than in the east, and (7) differences in stage-specific mortality rates are related to bathymetry, temperature and potential predators, notably the abundance of congeners Calanus hyperboreus and C. glacialis, which likely feed on early life stages of C. finmarchicus. Two modeling approaches have previously been used to interpret the abundance and distribution of C. finmarchicus in relation to the North Atlantic habitat. A statistical approach based on ecological niche theory and a dynamical modeling approach, based on knowledge of spatial population dynamics and life history and implemented by recent developments in coupled physical-life cycle modeling. The strengths and weaknesses of each approach are discussed. A synthesis of the two modeling approaches to predict North Atlantic zooplankton species shifts, not only for C. finmarchicus, but also for other major taxa, is advocated. While the computational resource requirements and lack of species-specific life history information for physical-biological modeling hinder full application for many zooplankton taxa, use of the approach, where possible, to understand advective influences will provide insight for interpretation of statistical predictions from species distribution models

Biogeography of key mesozooplankton species in the North Atlantic and egg production of Calanus finmarchicus

-Here we present a new, pan-North-Atlantic compilation of data on key mesozooplankton species, including the most important copepod, Calanus finmarchicus. Distributional data of eight representative zooplankton taxa, from recent (2000–2009) Continuous Plankton Recorder data, are presented, along with basin-scale data of the phytoplankton colour index. Then we present a compilation of data on C. finmarchicus, including observations of abundance, demography, egg production and female size, with accompanying data on temperature and chlorophyll

Vertical distribution and population structure of copepods along the northern Mid-Atlantic Ridge

The Mid-Atlantic Ridge (MAR) between 40°N (Azores) and 63°N (Iceland) is the largest topographic feature in the North Atlantic Ocean. Despite generally limited surface production, there is evidence that the mid-ocean ridges are ecologically important for higher trophic levels relative to the surrounding open ocean. Vertical migrations of zooplankton are one of the primary mechanisms for the vertical transfer of carbon from surface waters to the deeper waters and sediments. The complicated topography of the MAR influences local and regional circulation patterns, which in turn are likely to affect the distribution of the zooplankton fauna. The crest of the MAR rises to 1000 m, thus intersecting the meso- and bathypelagic layers. In this paper we explore the vertical distribution and population structure of selected copepod species on the northern MAR, with the goal of better understanding the nature of the interactions between zooplankton and a mid-ocean ridge system. Zooplankton were sampled on the ridge from Iceland to the Azores (~60-41°N, 25-35°W) in June 2004. Depth stratified sampling revealed information on vertical distributions from surface down to 2500 m. The Subpolar Front (SPF) is the major biogeographic boundary in the studied area. Species with a wide vertical range also had a wide geographical distribution, occurring both north and south of the SPF. Several species were observed to change their vertical distributions along the transect, becoming deeper on the southern stations. Factors influencing vertical distributions are evaluated and relationships between zooplankton, water masses, and ridge topography are discusse

Abundance and productivity of the pelagic ecosystem along a transect across the northern Mid Atlantic Ridge in June 2003

A research cruise was conducted into the Irminger Sea west and southwest of Iceland on the Icelandic vessel Árni Friðriksson, from 4-30 June 2003, investigating redfish, Sebastes mentella, other pelagic fishes, zooplankton, phytoplankton and the hydrography of the area. Part of the cruise was devoted to a special study on the physical and chemical factors as well as the abundance of phytoplankton, meso- and macrozooplankton and planktivorous fish on a transect across the northern part of the Mid-Atlantic Ridge (MAR). This research is a part of the MAR-ECO project which aims to study the ecosystem associated with the northern MAR. In this paper we analyse the organisation of the pelagic ecosystem on the transect over the northern MAR, from phytoplankton to fish as apex predators. Keywords: MAR-ECO, Mid-Atlantic Ridge, environmental factors, phytoplankton, zooplankton, fish

Data collection of Calanus finmarchicus reproduction life history traits in the North Atlantic Ocean

Observations of egg production rates (EPR) for female Calanus finmarchicus were compared from different regions of the North Atlantic. The regions were diverse in size and sampling frequency, ranging from a fixed time series station in the Lower St Lawrence Estuary, off Rimouski, where nearly 200 experiments were carried out between May and December from 1994 to 2006, to a large-scale survey in the Northern Norwegian Sea, where about 50 experiments were carried out between April and June from 2002 to 2004. For this analysis the stations were grouped mostly along geographic lines, with only limited attention being paid to oceanographic features. There is some overlap between regions, however, where stations were sometimes kept together when they were sampled on the same cruise. As well some stations other than off Rimouski were occupied more than once during different years and/or in different seasons