Variability in Calanus spp. abundance on fine- to mesoscales in an Arctic fjord : implications for little auk feeding

Paid Open Acces

Lipid sac area as a proxy for individual lipid content of arctic calanoid copepods

We present an accurate, fast, simple and non-destructive photographic method to estimate wax ester and lipid content in single individuals of the calanoid copepod genus Calanus and test this method against gas-chromatographic lipid measurements

Diel vertical migration of Arctic zooplankton during the polar night

High-latitude environments show extreme seasonal variation in physical and biological variables. The classic paradigm of Arctic marine ecosystems holds that most biological processes slow down or cease during the polar night. One key process that is generally assumed to cease during winter is diel vertical migration (DVM) of zooplankton. DVM constitutes the largest synchronized movement of biomass on the planet, and is of paramount importance for marine ecosystem function and carbon cycling. Here we present acoustic data that demonstrate a synchronized DVM behaviour of zooplankton that continues throughout the Arctic winter, in both open and ice-covered waters. We argue that even during the polar night, DVM is regulated by diel variations in solar and lunar illumination, which are at intensities far below the threshold of human perception. We also demonstrate that winter DVM is stronger in open waters compared with ice-covered waters. This suggests that the biologically mediated vertical flux of carbon will increase if there is a continued retreat of the Arctic winter sea ice cover

All-sky camera system providing high temporal resolution annual time series of irradiance in the arctic

The ArcLight observatory provides hourly continuous time series of light regime data (intensity, spectral composition, and photoperiod) fromthe Arctic, Svalbard at 79_ N.Until now, no complete annual time series of biologically relevant light has been provided from the high Arctic due to insufficient sensitivity of commercial light sensors during the Polar Night. We describe a camera system providing all-sky images and the corresponding integrated spectral irradiance (EPAR) in energy or quanta units, throughout a complete annual cycle. We present hourly- diel-annual dynamics from 2017 to 2020 of irradiance and its relation to weather conditions, sun and moon trajectories

Calanus spp. in the Arctic ecosystem - a story on predation, distribution and methodology

The calanoid copepods of the genus Calanus (C. finmarchicus, C. glacialis and C. hyperboreus) are key elements in the Arctic ecosystem. They link primary producers (ice algae, phytoplankton) and higher trophic levels through their ability to convert low energy carbohydrates and proteins to high energy wax esters. This energy is stored in a separate and conspicuous lipid sac. This ability to store large amounts of compact energy is considered an essential adaptation towards the strong seasonality in the Arctic environments. Also the calanoid copepods are known to conduct pronounced seasonal vertical migration and diapause at depth. Due to the large amount of stored energy, Calanus spp. is a preferred prey for a number of planktivorous predators such as herring, polar cod and little auks. The three Calanus spp. share a very similar morphology but have a very different life history and they are bound to different types of water masses: C. finmarchicus has a one year life cycle, indicator of Atlantic water; C. glacialis 1-3 year cycle, indicator of Arctic shelf water; C. hyperboreus 1-5 years, indicator of Arctic water. For this reason the Calanus spp. have long been considered a reliable climate indicator species. Also, they vary in size and thus in total amount of stored lipids, an important factor for those species foraging on Calanus spp. The aim of this thesis was to evaluate the ecological role of the important climate indicator Calanus spp. Two technical papers provide tools for Calanus spp. research. In paper 1 the potential misidentification of C. glacialis as C. finmarchicus is discussed. Genetic analysis revealed that at several localities a variable percentage of C. finmarchicus is wrongly identified as C. finmarchicus when traditional morphological identification methods are applied. Paper 4 provides an equation to convert copepod lipid sac area obtained by optical measurements to energy content and thus allows comparison of individual state of copepods within and across all three species. Prey selection of chick-rearing little auks depending on zooplankton availability in the adjacent waters was the focus of paper 2 and 3. Little auks displayed a bimodal foraging strategy, presumably as a response to poor feeding conditions close to the colony. Prey count and travel time recordings indicate long travels to the shelf edge for self-maintenance feeding on high energetic C. hyperboreus and C. glacialis and short trips for collection of food for the chicks. An unexplained mismatch of prey ratio in returning birds versus samples at sea remains. Close to the bird colony a high-resolution zooplankton sampling grid was applied which revealed the occurrence of a zooplankton patch of 0.2 to 2 km. Total energy content of little auk prey m-3 was 16 times higher in the patch than in the place of lowest abundance. The presence of zooplankton patches is highly relevant not only for little auks searching for their food (concentration of food – less feeding effort), but in fact also for zooplankton research itself (hitting or missing a patch during a sampling campaign will give largely different results). In paper 5 the focus is on variations in vertical distribution of Calanus spp. and Metridia longa in autumn. Older and larger copepodite stages were located deeper in the water column and the distribution reflected the variation in seasonality on a south-north gradient. Diel vertical migration (DVM) was only observed for M. longa. It was a paradigm that biological activity in the polar night more or less comes to a halt, but in paper 6 a pattern of synchronized DVM could for the first time be demonstrated for two Arctic fjords, Kongsfjorden and Rijpfjorden, during the darkest time of the year. In this paper calanoid copepods were suggested as actively migrating during winter

Little auks ( Alle alle ) breeding in a High Arctic fjord system: bimodal foraging strategies as a response to poor food quality?

The foraging behaviour of little auks ( Alle alle ) in the Bjørndalen colony on the western coast of Spitsbergen was studied during the breeding season 2005. The duration of foraging trips and contents of gular pouches were analysed. Quantitative zooplankton samples procured in the vicinity of the colony facilitated a comparison between gular pouch contents and the availability of prey species. Zooplankton and gular pouch samples were all sampled within a time window of approximately one week. Using the Bray–Curtis similarity index, we determined that little auks in this colony have a bimodal foraging strategy consisting of long and short foraging trips with two corresponding distinct diets. Short trips are most likely to be centred on areas within the Isfjorden complex, whereas the birds are most likely to use the long trips (of typically more than 10 hours) to reach areas off the continental slope where they are able to feed selectively on large, energy-rich food items such as Calanus hyperboreus . This bimodal foraging strategy may be a response to the low availability of nutrientrich food close to the colony, which is insufficient to sustain both parents and chicks. Bimodal foraging trip strategies are well documented in many species in the Southern Ocean. This is the first study to show a similar feeding pattern in an Alcidae species in the Northern Hemisphere

(Supplement Table 1) Individual measurements of prosome length, dry weight and lipid sacs (length, width, area) in arctic calanoid copepods

We present an accurate, fast, simple and non-destructive photographic method to estimate wax ester and lipid content in single individuals of the calanoid copepod genus Calanus and test this method against gas-chromatographic lipid measurements

All-sky camera system providing high temporal resolution annual time series of irradiance in the arctic

The ArcLight observatory provides hourly continuous time series of light regime data (intensity, spectral composition, and photoperiod) from the Arctic, Svalbard at 79° N. Until now, no complete annual time series of biologically relevant light has been provided from the high Arctic due to insufficient sensitivity of commercial light sensors during the Polar Night. We describe a camera system providing all-sky images and the corresponding integrated spectral irradiance (�PAR) in energy or quanta units, throughout a complete annual cycle. We present hourly–diel–annual dynamics from 2017 to 2020 of irradiance and its relation to weather conditions, sun and moon trajectories