Camilla Svensen

Ecosystem Function, Biodiversity and Vertical Flux Regulation in the Twilight Zone

The current lack of adequate investigations of the vertical export above the depth of 200-500 m where the majority of long-term sediment traps have been deployed, results in difficulties to understand and model the carbon flux. There exists a black box of several hundred metres between the surface layers where measurements and algorithms of primary production exists and where data on the carbon export to the ocean interior are available. In this black box, the twilight zone, we face a lack of basic understanding on how vertical export of biogenic matter into the oceans interior is regulated. Essential for this regulation are planktonic key organisms and the structure and dynamics of the pelagic food web. To better comprehend the pelagic carbon cycle and sequestration of CO2, it is instrumental to obtain a basic understanding how the biota determines and transforms the export production in the twilight zone. Here we discuss some of the key organisms involved in vertical flux regulation, present an idealised, conceptual model of vertical carbon export and focus upon the “pelagic mill” and vertical flux regulation in the upper 200 m. An adequate understanding of carbon cycling demands not only adequate investigations of primary production, but also concomitant research on the functional biodiversity of the pelagic zone, plankton dynamics, vertical flux and its regulation in the twilight zone.

Genetics redraws pelagic biogeography of Calanus

Planktonic copepods of the genus Calanus play a central role in North Atlantic/Arctic marine food webs. Here, using molecular markers, we redrew the distributional ranges of Calanus species inhabiting the North Atlantic and Arctic Oceans and revealed much wider and more broadly overlapping distributions than previously described. The Arctic shelf species, C. glacialis, dominated the zooplankton assemblage of many Norwegian fjords, where only C. finmarchicus has been reported previously. In these fjords, high occurrences of the Arctic species C. hyperboreus were also found. Molecular markers revealed that the most common method of species identification, prosome length, cannot reliably discriminate the species in Norwegian fjords. Differences in degree of genetic differentiation among fjord populations of the two species suggested that C. glacialis is a more permanent resident of the fjords than C. finmarchicus. We found no evidence of hybridization between the species. Our results indicate a critical need for the wider use of molecular markers to reliably identify and discriminate these morphologically similar copepod species, which serve as important indicators of climate responses.

Small copepods matter: population dynamics of Microsetella norvegica in a high-latitude coastal ecosystem

We investigated the population dynamics of a small and little-studied harpacticoid copepod, Microsetella norvegica, in a sub-Arctic Norwegian fjord (Balsfjord 69°N). We sampled with a 90 μm mesh WP-2 net and a 20 L Go-Flo bottle and found that the WP-2 under-sampled all juvenile stages. The abundance and biomass were high, peaking in June with 9349 × 10 ind. m and 1678 mg Cm. Microsetella were most abundant in the surface, but females and males demonstrated a distinct migration to below 50 m from October to March. Consistently, individual female body carbon content was highest in October (0.39 μg C ind) and lowest in March (0.18 μg C ind). Males were present throughout the year, and females with eggs were found from April to September. The average clutch size was 11 ± 2 eggs female, and our study supports the observation that females can release their egg sac before the eggs have hatched, possibly to produce a new one. With its high abundance and biomass, a flexible reproductive strategy and specialized feeding preferences, M. norvegica is likely a key species in high-latitude coastal ecosystems.