Beschreibung: Kelps, perennial brown seaweeds of the order Laminariales, are foundational species in Arctic coastal ecosystems. Presently, their ability to persist under polar night conditions might be significantly affected by increasing winter temperatures. We assessed physiological parameters (photosynthesis, pigment content, respiration, carbohydrate storage) in two species of Arctic kelp, the boreal-temperate Saccharina latissima and the Arctic-endemic Laminaria solidungula, during the polar night 2016/17. Algae were sampled from Kongsfjorden, Svalbard, 78° 55' N, shortly before the onset of the dark period in October, and at the end of the polar night in early February. Analyses were conducted for different tissue sections along the phylloid (Meristem, Centre Region, Distal Region). Data suggest that kelp maintain their photosynthetic competence throughout the entire winter period, as indicated by PE-curve-parameters, and photosynthetic pigment contents. Overall laminarin content was reduced by 96 % in S. latissima, and by 90 % in L. solidungula during winter indicating that this storage glucan fuelled metabolic function during the polar night. Marked differences in laminarin content between the phylloid regions and across species indicated specific adaptive mechanisms between boreal-temperate and Arctic-endemic kelp. We suggest that laminarin turnover represents a sensitive parameter to assess kelp physiology under a changing temperature regime.

Beschreibung: In coastal waters, Antarctic rhodophytes are exposed to harsh environmental conditions throughout the year, like low water temperatures ranging from -1.8°C to 2°C and high light during the summer season. Photosynthetic performance under these conditions may be affected by slowed down enzymatic reactions and the increased generation of reactive oxygen species. The consequence might be a chronic photoinhibition of photosynthetic primary reactions related to increased fragmentation of the D1 reaction centre protein in photosystem II. It is hypothesized that changes in lipid composition of biomembranes may represent an adaptive trait to maintain D1 turnover in response to temperature variation. The interactive effects of high light and low temperature were studied on an endemic Antarctic red alga, Palmaria decipiens, sampled from two shore levels, intertidal and subtidal, and exposed to mesocosm experiments using two levels of natural solar radiation and two different temperature regimes (2-5°C and 5-10°C). During the experimental period of 23 days, maximum quantum yield of photosynthesis decreased in all treatments, with the intertidal specimens exposed at 5-10°C being most affected. On the pigment level, a decreasing ratio of phycobiliproteins to chlorophyll a was found in all treatments. A pronounced decrease in D1 protein concentration occurred in subtidal specimens exposed at 2-5°C. Marked changes in lipid composition, i.e. the ratio of saturated to unsaturated fatty acids, indicated an effective response of specimens to temperature change. Results provide new insights into mechanisms of stress adaptation in this key species of shallow Antarctic benthic communities.

Beschreibung: In some parts of the Southern Ocean (SO), even though low surface concentrations of iron (Fe) and manganese (Mn) indicate FeMn co-limitation, we still lack an understanding on how Mn and Fe availability influences SO phytoplankton ecophysiology. Therefore, this study investigated the effects of Fe and Mn limitation alone as well as their combination on growth, photophysiology and particulate organic carbon production of the bloom-forming Antarctic diatom Chaetoceros debilis. Our results clearly show that growth, photochemical efficiency and carbon production of C. debilis were co-limited by Fe and Mn as highest values were only reached when both nutrients were provided. Even though Mn-deficient cells had higher photochemical efficiencies than Fe-limited ones, they, however, displayed similar low growth and POC production rates, indicating that Mn limitation alone drastically impeded the cell's performance. These results demonstrate that similar to low Fe concentrations, low Mn availability inhibits growth and carbon production of C. debilis. As a result from different species-specific trace metal requirements, SO phytoplankton species distribution and productivity may therefore not solely depend on the input of Fe alone, but also critically on Mn acting together as important drivers of SO phytoplankton ecology and biogeochemistry.