The Arctic picoeukaryote <i>Micromonas pusilla</i> benefits synergistically from warming and ocean acidification

In the Arctic Ocean, climate change effects such as warming and ocean acidification (OA) are manifesting faster than in other regions. Yet, we are lacking a mechanistic understanding of the interactive effects of these drivers on Arctic primary producers. In the current study, one of the most abundant species of the Arctic Ocean, the prasinophyte Micromonas pusilla, was exposed to a range of different pCO2 levels at two temperatures representing realistic current and future scenarios for nutrient-replete conditions. We observed that warming and OA synergistically increased growth rates at intermediate to high pCO2 levels. Furthermore, elevated temperatures shifted the pCO2 optimum of biomass production to higher levels. Based on changes in cellular composition and photophysiology, we hypothesise that the observed synergies can be explained by beneficial effects of warming on carbon fixation in combination with facilitated carbon acquisition under OA. Our findings help to understand the higher abundances of picoeukaryotes such as M. pusilla under OA, as has been observed in many mesocosm studies.</p

A vast icefish breeding colony discovered in the Antarctic

A breeding colony of notothenioid icefish (Neopagetopsis ionah, Nybelin 1947) of globally unprecedented extent has been discovered in the southern Weddell Sea, Antarctica. The colony was estimated to cover at least similar to 240 km(2) of the eastern flank of the Filchner Trough, comprised of fish nests at a density of 0.26 nests per square meter, representing an estimated total of -60 million active nests and associated fish biomass of >60,000 tonnes. The majority of nests were each occupied by 1 adult fish guarding 1,735 eggs (+/- 433 SD). Bottom water temperatures measured across the nesting colony were up to 2 degrees C warmer than the surrounding bottom waters, indicating a spatial correlation between the modified Warm Deep Water (mWDW) upflow onto the Weddell Shelf and the active nesting area. Historical and concurrently collected seal movement data indicate that this concentrated fish biomass may be utilized by predators such as Weddell seals (Leptonychotes weddellii, Lesson 1826). Numerous degraded fish carcasses within and near the nesting colony suggest that, in death as well as life, these fish provide input for local food webs and influence local biogeochemical processing. To our knowledge, the area surveyed harbors the most spatially expansive continuous fish breeding colony discovered to date globally at any depth, as well as an exceptionally high Antarctic seafloor biomass. This discovery provides support for the establishment of a regional marine protected area in the Southern Ocean under the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) umbrella

Arbuscular mycorrhizas are present on Spitsbergen

A previous study of 76 plant species on Spitsbergen in the High Arctic concluded that structures resembling arbuscular mycorrhizas were absent from roots. Here, we report a survey examining the roots of 13 grass and forb species collected from 12 sites on the island for arbuscular mycorrhizal (AM) colonisation. Of the 102 individuals collected, we recorded AM endophytes in the roots of 41 plants of 11 species (Alopecurus ovatus, Deschampsia alpina, Festuca rubra ssp. richardsonii, putative viviparous hybrids of Poa arctica and Poa pratensis, Poa arctica ssp. arctica, Trisetum spicatum, Coptidium spitsbergense, Ranunculus nivalis, Ranunculuspygmaeus, Ranunculus sulphureus and Taraxacum arcticum) sampled from 10 sites. Both coarse AM endophyte, with hyphae of 5–10 μm width, vesicles and occasional arbuscules, and fine endophyte, consisting of hyphae of 1–3 μm width and sparse arbuscules, were recorded in roots. Coarse AM hyphae, vesicles, arbuscules and fine endophyte hyphae occupied 1.0–30.7, 0.8–18.3, 0.7–11.9 and 0.7–12.8% of the root lengths of colonised plants, respectively. Principal component analysis indicated no associations between the abundances of AM structures in roots and edaphic factors. We conclude that the AM symbiosis is present in grass and forb roots on Spitsbergen

Aggregate turnover at the base of the euphotic zone – Influences of diatom morphology on carbon export

The world’s oceans play an important role in sequestering carbon over timescales of 105 years and more. For the carbon to be transferred from the atmosphere to the deep ocean where it is stored, it first has to be fixed in the form of particulate organic matter. This is mostly done by microalgae like diatoms, which fix CO2 through photosynthesis. When particle abundances are high (for example during a phytoplankton bloom), diatoms and other organic and inorganic matter aggregate and sink through the water column to the deep sea. Only a small fraction of the carbon fixed by phytoplankton reaches the seafloor because it is getting degraded by microorganisms and higher animals while it is sinking through the water column. Therefore, understanding the factors that influence degradation and carbon release is important for predicting and analyzing local as well as global carbon fluxes. One factor that has been neglected so far is the effect of phytoplankton morphology on carbon export. For this thesis, I studied two species of diatoms exhibiting common but contrasting morphologies: chain-forming and non-chain-forming, and studied the aggregation process and other down-stream factors affected by aggregate morphology: size, sinking velocity, carbon and nitrogen content, and microbial degradation rate. The process of aggregate formation and the appearance and structure of the respective aggregates strongly suggested that in chain-forming diatoms physical aggregation via the entangling of chains is the predominating process, whereas in non-chain-forming diatoms, TEP was the main factor causing aggregation. This had large influences on the settling behavior and the carbon content, thus affecting the amount of bacterial colonization and aggregate degradation