Maria Fredrika Norrbin

Zooplankton consumption of sinking aggregates affects the quality and quantity of organic carbon exported to the deep ocean. Increasing laboratory evidence shows that small particle‐associated copepods impact the flux attenuation by feeding on sinking particles, but this has not been quantified in situ. We investigated the impact of an abundant particle‐colonizing copepod, Microsetella norvegica, on the attenuation of the vertical carbon flux in a sub‐Arctic fjord. This study combines field measurements of vertical carbon flux, abundance, and size‐distribution of marine snow and degradation rates of fecal pellets and algal aggregates. Female M. norvegica altered their feeding behavior when exposed to aggregates, and ingestion rates were 0.20 μg C ind.⁻¹ d⁻¹ on marine snow and 0.11 μg C ind.⁻¹ d⁻¹ on intact krill fecal pellets, corresponding to 48% and 26% of the females' body carbon mass. Due to high sea surface abundance of up to ~ 50 ind. L⁻¹, the population of M. norvegica had the potential to account for almost all the carbon removal in the upper 50 m of the water column, depending on the type of the aggregate. Our observations highlight the potential importance of abundant small‐sized copepods for biogeochemical cycles through their impact on export flux and its attenuation in the twilight zone.

We present a large-scale survey of mesozooplankton (size range 0.2–20 mm) across coastal, shelf, and slope locations in Northeast Greenland (latitudes 74–79° N, August 2015 and September 2017). Our study is centred on the Video Plankton Recorder (VPR) for non-invasive in situ observations of taxa distribution and abundance while simultaneously recording oceanographic profiles. A modified WP-2 plankton net (85-μm mesh size) was used primarily not only to verify taxa detected by the VPR but also to make a preliminary comparison of abundance estimates by the two gears. A total of 35 zooplankton taxa were identified with 10 genera alone among copepods (Hexanauplia). Selected taxa from the VPR (N=16) were associated with the temperature-salinity spaces and the chlorophylla-depth profiles in the study area. From surface to > 900 m depth, the overall temperature and salinity ranged between −1.9 and 6.8 °C and 26.6 and 35.3, respectively. Two copepod genera dominated, i.e.Pseudocalanusprevailed in the upper sub-zero layers in coastal waters whereasCalanuswas omnipresent, but mainly abundant in the warmer Atlantic waters at the shelf break. Chlorophyllalevels were in general very low (< 2 mg m^-3) and peaked at 30–50 m depth, suggesting post-bloom conditions. Overall, zooplankton abundances tended to increase from the coast towards the slope (9–344×10³individuals m^-2). Biodiversity in terms of taxon richness, on the other hand, showed the opposite trend and decreased from 16 taxa at the coast to 5 taxa further offshore.

“One strain many compounds” (OSMAC) based approaches have been widely used in the search for bioactive compounds. Introducing stress factors like nutrient limitation, UV-light or cocultivation with competing organisms has successfully been used in prokaryote cultivation. It is known that diatom physiology is affected by changed cultivation conditions such as temperature, nutrient concentration and light conditions. Cocultivation, though, is less explored. Hence, we wanted to investigate whether grazing pressure can affect the metabolome of the marine diatom Porosira glacialis, and if the stress reaction could be detected as changes in bioactivity. P. glacialis cultures were mass cultivated in large volume bioreactor (6000 L), first as a monoculture and then as a coculture with live zooplankton. Extracts of the diatom biomass were screened in a selection of bioactivity assays: inhibition of biofilm formation, antibacterial and cell viability assay on human cells. Bioactivity was found in all bioassays performed. The viability assay towards normal lung fibroblasts revealed that P. glacialis had higher bioactivity when cocultivated with zooplankton than in monoculture. Cocultivation with diatoms had no noticeable effect on the activity against biofilm formation or bacterial growth. The metabolic profiles were analyzed showing the differences in diatom metabolomes between the two culture conditions. The experiment demonstrates that grazing stress affects the biochemistry of P. glacialis and thus represents a potential tool in the OSMAC toolkit.