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Introduction Hyperiid amphipods of the genus Themisto are a key polar zooplankton group in terms of biomass and play an important role as prey for higher trophic levels. They are prone to undergo changes in abundance and distribution in the course of the ongoing environmental changes. In the Southern Ocean, Themisto gaudichaudii is predicted to expand its distribution poleward. In the Arctic, the boreal-Atlantic T. abyssorum increases in abundance, resulting in an increased competition with a genuine polar congener. It is not known, however, whether T. gaudichaudii and T. abyssorum have the potential to efficiently adapt to changing water temperatures at their current distribution range or whether they will be shifting their ranges poleward. Methods We exposed the two Themisto species from different geographic populations to temperature-change experiments, a cold treatment and a heat-shock treatment. After that, we carried out transcriptome sequencing to compare gene expression patterns in the different treatments and species. Results We show that under similar heat conditions, T. gaudichaudii differentially expressed more genes (26-fold change) than T. abyssorum. Furthermore, we observed qualitative differences between genetic clusters in T. gaudichaudii. Discussion The differences observed between genetic clusters in T. gaudichaudii suggest that evolutionary divergence can be linked to changes in the regulatory pathways involved in temperature stress. These could influence the capacity of each genetic cluster to cope differently with temperature changes. In contrast to its congeneric species, T. abyssorum showed a pronounced adaptive flexibility to thermal stress; it appears to have the ability to continue its poleward expansion but may also cope with increasing temperatures in its current environments. Our findings contribute to understand the response of two range-shifting Themisto species to thermal stress in view of the environmental gradients they encounter t

Species identification is pivotal in biodiversity assessments and proteomic fingerprinting by MALDI-TOF mass spectrometry has already been shown to reliably identify calanoid copepods to species level. However, MALDI-TOF data may contain more information beyond mere species identification. In this study, we investigated different ontogenetic stages (copepodids C1–C6 females) of three co-occurring Calanus species from the Arctic Fram Strait, which cannot be identified to species level based on morphological characters alone. Differentiation of the three species based on mass spectrometry data was without any error. In addition, a clear stage-specific signal was detected in all species, supported by clustering approaches as well as machine learning using Random Forest. More complex mass spectra in later ontogenetic stages as well as relative intensities of certain mass peaks were found as the main drivers of stage distinction in these species. Through a dilution series, we were able to show that this did not result from the higher amount of biomass that was used in tissue processing of the larger stages. Finally, the data were tested in a simulation for application in a real biodiversity assessment by using Random Forest for stage classification of specimens absent from the training data. This resulted in a successful stage-identification rate of almost 90%, making proteomic fingerprinting a promising tool to investigate polewards shifts of Atlantic Calanus species and, in general, to assess stage compositions in biodiversity assessments of Calanoida, which can be notoriously difficult using conventional identification methods.

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.

Zooplankton plays a notable role in ocean biogeochemical cycles. However, it is often simulated as one generic group and top closure term in ocean biogeochemical models. This study presents the description of three zooplankton functional types (zPFTs, micro-, meso- and macrozooplankton) in the ocean biogeochemical model FESOM-REcoM. In the presented model, microzooplankton is a fast-growing herbivore group, mesozooplankton is another major consumer of phytoplankton, and macrozooplankton is a slow-growing group with a low temperature optimum. Meso- and macrozooplankton produce fast-sinking fecal pellets. With three zPFTs, the annual mean zooplankton biomass increases threefold to 210 Tg C. The new food web structure leads to a 25% increase in net primary production and a 10% decrease in export production globally. Consequently, the export ratio decreases from 17% to 12% in the model. The description of three zPFTs reduces model mismatches with observed dissolved inorganic nitrogen and chlorophyll concentrations in the South Pacific and the Arctic Ocean, respectively. Representation of three zPFTs also strongly affects phytoplankton phenology: Fast nutrient recycling by zooplankton sustains higher chlorophyll concentrations in summer and autumn. Additional zooplankton grazing delays the start of the phytoplankton bloom by 3 weeks and controls the magnitude of the bloom peak in the Southern Ocean. As a result, the system switches from a light-controlled Sverdrup system to a dilution-controlled Behrenfeld system. Overall, the results suggest that representation of multiple zPFTs is important to capture underlying processes that may shape the response of ecosystems and ecosystem services to on-going and future environmental change in model projections.

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.

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.

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 rang