Description: In this study, we investigate the role of macrozooplankton in the biogeochemistry of the Southern Ocean using a three-dimensional global ocean ecosystem model (FESOM- REcoM2). The macrozooplankton group was parameterized according to characteristics of Antarctic krill and a related fast-sinking detritus class (larger particles, e.g. fecal pellets) was introduced in the model. It was then analyzed how the ecosystem structure and major carbon export pathways in the Southern Ocean changed through this extension of the model. The spatial distribution of macrozooplankton biomass in the Southern Ocean was reproduced reasonably well. Preliminary results showed that the zooplankton proportion of living compartments (phytoplankton and zooplankton groups) in the model increased. Thus, zooplankton contribution to the particulate organic carbon (POC) flux increased. The contribution of macrozooplankton to POC export at 100 m depth was 0.12 Pg C per year or 15% of total export in the Southern Ocean. The transfer efficiency of organic carbon nearly doubled and reached up to 50% in regions with high macrozooplankton biomass. These results emphasize the important role of macrozooplankton in the Southern Ocean carbon cycle and have implications for studies of the biological carbon pump.

Description: The Arctic Ocean is rapidly changing. Air temperature is rising two to four times faster in the Arctic than the global average, with dramatic consequences for the ecosystems. Polar zooplankton species have to cope with those increasing temperatures, whilst simultaneously facing increasing competition by boreal-Atlantic sister species advected into the Arctic Ocean via a stronger Atlantic inflow. To assess the sensitivity of Arctic and Atlantic zooplankton to rising temperatures, respiration rates of dominant Arctic species (Calanus hyperboreus, Calanus glacialis, Paraeuchaeta glacialis, Themisto libellula) and their co-occurring Atlantic congeners (Calanus finmarchicus, Paraeuchaeta norvegica, Themisto abyssorum) were measured at ambient temperatures and simulated conditions of ocean warming from 0 to 10°C during three expeditions with RV Polarstern to the Arctic Fram Strait. Arctic zooplankton showed only slowly increasing respiration rates with increasing temperatures, also indicated by low Q10 ratios. In contrast, boreal-Atlantic representatives responded to higher temperatures by a rapid and steeper increase in their respiration rates (higher Q10), suggesting higher metabolic activity. These results imply that Arctic species are physiologically more tolerant to ocean warming than expected but might be outcompeted by their Atlantic congeners beyond a certain temperature threshold in areas of strong distribution overlap. Thus, the ‘Atlantification’ of the Arctic zooplankton community seems to be driven rather by ecological interactions than by physiological limitations. Changes in zooplankton community composition and biodiversity will have major consequences for trophodynamics and energy flux in Arctic ecosystems, since polar species tend to be larger than their southern counterparts and have a higher lipid content, providing more energy-rich food for higher trophic levels.

Description: Brown shrimp, Crangon crangon (L.), is the most valuable target of coastal fisheries in the southern North Sea. Annual landings exceeded 30,000 tons in the last decade, yielding up to 100 Mio Euro. The shrimp are boiled immediately after capture onboard the fishing vessel for preservation and easy peeling. After landing, the shrimp are collected by traders and exported for manual peeling. Only the muscle of the pleon is returned and sold as regional delicacy. The remains, comprising the cephalothorax, the shell of the pleon, and, in case, adhering eggs, account for up to 70% of the total body mass. This potential resource, for example as aquaculture feed, has not yet been considered for exploitation. In this respect, the fatty acid (FA) profile and the share of essential FAs are crucial quality factors. Since boiling alters the quality of shrimp, this study evaluates changes in the FA composition of shrimp muscle and remains by comparing frozen and boiled samples. Major FAs in C. crangon were the saturated palmitic acid (PA, 16:0), accounting for 16.6%–19.1% of total fatty acids (TFAs), and the long-chain polyunsaturated FAs (LC-PUFAs) eicosapentaenoic acid (EPA, 20:5(n-3), 16.1–21.6%TFA ) and docosahexaenoic acid (DHA, 22:6(n-3), 11.5–13.6%TFA ). Frozen muscle and frozen remains showed similar FA profiles. Boiling changed the FA profile. PA, EPA, and DHA decreased by up to 25%, whereas palmitoleic acid 16:1(n-7) and oleic acid 18:1(n-9) increased by 2% to 3% each. Boiled muscle and boiled remains showed similar FA profiles. Despite the loss of FAs, the boiled shrimp remains are suggested to be a suitable PUFA supplement for aquaculture feeds, deserving further investigation.

Description: The Southern Ocean, in particular the southwest Atlantic sector, is experiencing rapid environmental changes. A long-term trend of density changes of key pelagic species has been noted over the last decades: Antarctic krill populations are declining whilst salps are on the rise and shifting their distribution poleward. A similar poleward expansion is anticipated for a third key player, the hyperiid amphipod crustacean Themisto gaudichaudii, leading to an increasing overlap of the distributions of these three species. Due to major knowledge gaps in the ecology, and genetic connectivity of T. gaudichaudii, the likelihood of this shift and its consequences for the pelagic food web structure remain largely unexplored. In this context, Themisto’s genetic and trophic connectivity as well as thermal response were investigated with state-of-the-art molecular methods. Phylogeographic analyses showed genetic homogeneity between localities in the Southern Ocean and Atlantic waters combined with high degree of phenotypic plasticity enabling different lineages to thrive in regions further south. Diet analyses using DNA metabarcoding were applied to characterize regional variation in diet. These analyses showed a diet predominantly composed of krill, in particular in the Antarctic Peninsula region, showing that Themisto’s poleward range expansion can further impact the already declining krill stocks. It also unexpectedly revealed ctenophores to be an important prey, despite their reputation as “trophic dead-end”. Transcriptome analyses were used to study the thermal response of Themisto individuals from different geographic populations that were experimentally exposed to heat and cold treatments. The analysis of differentially expressed genes showed that genetic lineages differ in thermal tolerances. It also revealed a wide range of molecular mechanisms in Themisto amphipods to cope with thermal stress. These findings contribute to better predict the impact of climate-driven range shifts on the pelagic ecosystems in the Southern Ocean.

Description: Die Asiatische Felsenkrabbe Hemigrapsus sanguineus wurde erstmals vor Le Havre und in der Oosterschelde entdeckt. Seitdem breitete sie sich entlang der südlichen Nordseeküste bis in das Skagerrak aus. In diesem Lebensraum konkurriert sie mit der einheimischen Strandkrabbe Carcinus maenas. Zahleiche Arbeiten befassten sich mit dem Konkurrenzverhalten und dem Invasionserfolg von H. sanguinaeus. Wir haben im Helgoländer Eulitoral die Speicherlipide der Weibchen beider Arten im Hinblick auf ihre Reproduktionsstrategien untersucht. Eiertragende C. maenas wurden im April und Juni 2015 beprobt. Sie hatten einen Lipidgehalt von ca. 10 % der Trockenmasse (%TM) in der Mitteldarmdrüse und von 15-25 % in den Eiern. Eiertragende H. sanguineus hatten im Juni, August und Oktober jeweils einen Lipidgehalt von 35-45 %TM in den Mitteldarmdrüsen und 15-30%TM in den Eiern. Bei C. maenas war die Fettsäurezusammensetzung der Mitteldarmdrüsen und der Eier sehr ähnlich, was ein Hinweis auf das „capital breeding“-Prinzip ist: Konsumierte Energie wird zunächst in der Mitteldarmdrüse gespeichert und dann einmalig in die Ovarien transferiert. Im Gegensatz dazu unterschieden sich bei H. sanguineus die Fettsäuremuster der Mitteldarmdrüsen und der Eier deutlich voneinander, was auf das „income breeding“- Prinzip hinweist: Konsumierte Lipide werden direkt in die Ovarien transferiert. Dadurch kann diese Art lipidreichere Eier und mehrere Gelege pro Jahr produzieren, was ihren Ausbreitungserfolg steigert.