Trophic interactions of meso- and macrozooplankton and fish in the Iceland Sea as evaluated by fatty acid and stable isotope analysis

A trophic study was carried out in August of 2007 and 2008 on the pelagic ecosystem in the Subarctic Iceland Sea. Carbon and nitrogen stable isotopes and fatty acid biomarkers were used to study trophic linkages and the trophic ecology of the most important pelagic species in this ecosystem, with emphasis on capelin (Mallotus villosus). According to 15N enrichment results, there are 3–4 trophic levels in this ecosystem excluding organisms of the microbial loop and birds and mammals. The primarily herbivorous copepod Calanus hyperboreus occupies the lowest trophic level of the animal species studied, and adult capelin and blue whiting (Micromesistius poutassou) occupy the highest level. Calanus spp. proved to be an important dietary component of most of the species studied, the euphausiid species Thysanoessa inermis and T. longicaudata being exceptions. The chaetognath Eukrohnia hamata is a pure carnivore, feeding heavily on Calanus spp., whereas most of the other zooplankton species studied practice an omnivorous–carnivorous feeding mode. The amphipod species Themisto libellula is important in the diet of adult capelin. Adult capelin and blue whiting share the same feeding habits and could therefore be competing for food

Lipid content in overwintering Calanus finmarchicus across the Subpolar Eastern North Atlantic Ocean

The boreal copepod Calanus finmarchicus accumulates lipid reserves during summer feeding in surface ocean waters, which enable it to stay at depth and survive famine during overwintering. Respiration of lipids during prolonged overwintering at ocean depths (> 1000 m in some areas) has been shown to result in a net sequestration of carbon into the deep ocean: the so-called “lipid pump.” Here, we provide a comprehensive synthesis of the geographic and vertical variations in lipid content of overwintering animals across the Subpolar Eastern North Atlantic and, on the basis of this, we revise the estimates of carbon sequestration. Wax ester content ranged from 40 to 190 μg individual −1 at > 250 m depths, with highest concentrations in the coldest ( 4°C) Irminger Sea and Rockall Basin. Our new analysis results in about 44% higher estimates of carbon sequestration at up to 11.5 g C m −2

Remote sensing of zooplankton swarms

Zooplankton provide the key link between primary production and higher levels of the marine food web and they play an important role in mediating carbon sequestration in the ocean. All commercially harvested fish species depend on zooplankton populations. However, spatio-temporal distributions of zooplankton are notoriously difficult to quantify from ships. We know that zooplankton can form large aggregations that visibly change the color of the sea, but the scale and mechanisms producing these features are poorly known. Here we show that large surface patches (>1000 km 2 ) of the red colored copepod Calanus finmarchicus can be identified from satellite observations of ocean color. Such observations provide the most comprehensive view of the distribution of a zooplankton species to date, and alter our understanding of the behavior of this key zooplankton species. Moreover, our findings suggest that high concentrations of astaxanthin-rich zooplankton can degrade the performance of standard blue-green reflectance ratio algorithms in operational use for retrieving chlorophyll concentrations from ocean color remote sensing.publishedVersio

Bridging the gap between marine biogeochemical and fisheries sciences; configuring the zooplankton link

Exploring climate and anthropogenic impacts on marine ecosystems requires an understanding of how trophic components interact. However, integrative end-to-end ecosystem studies (experimental and/or modelling) are rare. Experimental investigations often concentrate on a particular group or individual species within a trophic level, while tropho-dynamic field studies typically employ either a bottom-up approach concentrating on the phytoplankton community or a top-down approach concentrating on the fish community. Likewise the emphasis within modelling studies is usually placed upon phytoplankton-dominated biogeochemistry or on aspects of fisheries regulation. In consequence the roles of zooplankton communities (protists and metazoans) linking phytoplankton and fish communities are typically under-represented if not (especially in fisheries models) ignored. Where represented in ecosystem models, zooplankton are usually incorporated in an extremely simplistic fashion, using empirical descriptions merging various interacting physiological functions governing zooplankton growth and development, and thence ignoring physiological feedback mechanisms. Here we demonstrate, within a modelled plankton food-web system, how trophic dynamics are sensitive to small changes in parameter values describing zooplankton vital rates and thus the importance of using appropriate zooplankton descriptors. Through a comprehensive review, we reveal the mismatch between empirical understanding and modelling activities identifying important issues that warrant further experimental and modelling investigation. These include: food selectivity, kinetics of prey consumption and interactions with assimilation and growth, form of voided material, mortality rates at different age-stages relative to prior nutrient history. In particular there is a need for dynamic data series in which predator and prey of known nutrient history are studied interacting under varied pH and temperature regimes

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

Life-cycle strategies and seasonal migrations of oceanic copepods

Abstract Abundance and seasonal vertical distribution of dominant zooplankters in the Irminge

Distribution, maturity and population structure of Meganyctiphanes norvegica and Thysanoessa inermis around Iceland in spring.

This study aims to explain the distribution, maturity and population structure of Meganyctiphanes norvegica and Thysanoessa inermis in springtime in relation to main hydrographic regions around Iceland: Atlantic in the southwest, Atlantic-Arctic mixture in the north and Arctic in the east. Krill were collected 14-29 May 2013 using a macrozooplankton trawl. Biomass of both species combined was significantly higher in the southwest than in north and east. M. norvegica clearly dominated in Atlantic waters, whereas T. inermis was more evenly distributed around the island, while the highest values were also observed in the southwest for this species. Simple linear regressions showed that the abundance of M. norvegica was positively related to temperature, salinity and phytoplankton concentration, while the abundance of T. inermis was negatively related to bathymetry. Multiple linear regression analyses did not add to this information of a positive relationship between abundance and temperature for M. norvegica, while T. inermis was shown to be negatively related to both temperature and bathymetry. During the latter half of May, the main spawning of both species was confined to the regions off the southwest coast. Sex ratio (males/females) of M. norvegica was higher in the southwest than in the north and east, whereas T. inermis showed a similar sex ratio all around the island. In all regions, M. norvegica appears to have a lifespan of 2 years while T. inermis of 1 year in the southwest and possibly 2 years in north and east

Water chemistry, and isotopic ratios and fatty acids and alcohols in Calanus finmarchicus CV, norther Mid-Atlantic Ridge

Fatty acid and alcohol profiles and stable nitrogen and carbon isotope values, d15N and d13C, of Calanus finmarchicus CV were studied in June 2004 to estimate their trophic status along the northern Mid-Atlantic Ridge i.e. the Reykjanes Ridge (RR), extending from Iceland in the north to the productive region of the Sub-Polar Front (SPF) in the south. Two main groups of stations were defined in the study area based on fatty acid (FA) and fatty alcohol compositions, the stations in the RR area constituted one group and the stations in the frontal area constituted another. The sum of relative amounts of the dietary FAs was significantly higher in the RR area than in the frontal area. Conversely, the long-chained FAs, 20:1 and 22:1, were found in significantly lower relative amounts in the RR area than in the frontal area, thus indicating later ascent of the animals in the frontal area. Further support of this is provided by the fatty alcohols ratio 20:1/22:1 which differed significantly between the two areas. The d15N values were significantly higher in the frontal area compared to the RR area indicating higher trophic position and/or different pelagic-POM baseline in these areas