Description: The Asian shore crab Hemigrapsus sanguineus was initially introduced to the French Atlantic coast in the late 1990´s. Since then it has successfully established persistent populations along the European Atlantic coasts propagating further north. The invasive crab was found in the German part of the Wadden Sea for the first time in 2007 and at Helgoland in 2008. There, it now shares its intertidal habitat with the native European green crab Carcinus maenas. In order to test for potential interspecific effects between these two ecological equivalents, we analysed populations of both species in the rocky intertidal of the island of Helgoland (German Bight, North Sea) in 2009 and 2014. Numbers of animals and their biomasses of both species from four sites around the island were recorded. Although mean abundances of H. sanguineus around Helgoland more than doubled from 2009 to 2014, they were still lower than the abundances of C. maenas, which were similar between the years. In contrast, mean biomass of C. maenas slightly decreased from 2009 to 2014, while values for H. sanguineus increased almost sevenfold. Differences between sites may be due to differences in local habitat characteristics such as topography, algae coverage, wave exposure, and/or predation risk. Nonetheless, the results showed that both species co-occur and reproduce in the rocky intertidal of Helgoland, providing no clear evidence for a displacement of either species.

Description: The Asian shore crab Hemigrapsus sanguineus is a recent invader of intertidal ecosystems along the western European coasts and the North Sea. In order to estimate whether this species is capable of colonizing the estuarine areas of the larger rivers, we studied the tolerance of the crabs towards extreme temperatures and salinities as they can appear in shallow tidal pools and during the outflow of riverine water, respectively. Individuals of H. sanguineus were incubated at salinities of 0, 10, 20, 30 and 40 and tem-peratures of 5, 10, 15 and 20°C. The animals were removed from the basins after 1, 5 and 10 days and tested for their ability to right into the normal position when turned on their backsides. Independent of the incubation time, all crabs showed average maximum righting times of up to 5 s at temperatures of 10, 15 and 20°C and salinities of 10 to 40. In freshwater, righting times were considerably extended at any temperature and mortality was high. Longer righting times were also observed at the lowest temperature of 5°C. Our preliminary results show that H. sanguineus is highly tolerant towards a wide range of temperatures and salinities which characterizes this species as highly adapted to changing environmental conditions. However, H. sanguineus cannot persist in fresh¬water conditions which prevents this species to colonize inner estuarine regions. Future studies on the osmoregula¬tion capacities and respiration rates will better define the thermal and osmotic limits of adult and juvenile Asian shore crabs.

Description: Adult Euphausia superba survive winter without or with little feeding. It is not exactly known whether the scarcity of food or an internal clock, set by the natural Antarctic light regime, are responsible for non-feeding. Our research questions were therefore the following: (1) How will physiological and biochemical conditions of krill change during long-term starvation at constant light regime? (2) If and how do enzyme activities change during such starvation? (3) What is the influence of food availability versus that of light regime? To answer these questions, adult krill were starved under laboratory conditions for 12 weeks with constant light regime (12:12; dark/light) and the impact on physiological functions was studied. Initial experimental condition of krill resembled the condition of late spring krill in the field with fully active metabolism and low lipid reserves. Metabolic activity and activities of enzymes catabolising lipids decreased after the onset of starvation and remained low throughout, whereas lipid reserves declined and lipid composition changed. Mass and size of krill decreased while the inter-moult period increased. Depletion of storage- and structural metabolites occurred in the order of depot lipids and glycogen reserves after onset of starvation until proteins were almost exclusively used after 6–7 weeks of starvation. Results confirmed various proposed overwintering mechanisms such as metabolic slowdown, slow growth or shrinkage and use of lipid reserves. However, these changes were set in motion by food shortage only, i.e.without the trigger of a changing light regime.

Description: Migrant biomass and carbon fux of vertically migrating meso- and macrozooplankton was calculated for shelf (〈 200 m bottom depth) and oceanic (〉 200 m bottom depth) regions in the northern Benguela upwelling system. Active carbon fux is based on migrant biomass and respiration rates. Especially in upwelling regions, oxygen minimum zones (OMZ) are a common feature and thus the impact of low oxygen concentrations (i.e. hypoxia) on metabolic rates also should be considered. Copepods were sampled with a 0.25 m2 multiple opening and closing net (Multinet midi), while a larger net (1 m MOCNESS) was used for the collection of euphausiids and decapods. Copepods were dominant in the upper 50 m of shelf areas with a migrant biomass between 23 and 47 mg C m-2, whereas euphausiids were more abundant at oceanic regions with up to 1437 mg C m-2. Decapods were absent at the shelf but important in greater depth at oceanic stations (〉 150 mg C m-2). Mass-specifc respiration rates of individuals from the OMZ were reduced by 46-64% as compared to metabolic rates of specimens from surface waters. The resulting active carbon fux out of the upper 100 m by vertically migrating species was estimated with 4.3 mg C m-2 d-1 for shelf regions and 11.2 mg C m-2 d-1 for oceanic areas, which is equivalent to 4% and 35% of sinking POC, respectively. These data emphasize the crucial role of the OMZ for future developments of realistic carbon budgets under climate change scenarios.

Description: Calanoid copepods in boreal and polar habitats are confronted with a strong variability in food supply. The abundant species in the Southern North Sea, Temora longicornis, cannot accumulate extensive energy stores to buffer longer periods of food paucity. These copepods react immediately to dietary changes and therefore, recent trophic conditions must strongly influence their metabolic and functional responses. To elucidate the implications of feeding history, we collected two cohorts of T. longicornis females, which were characterized by different feeding histories and consequently different physiological backgrounds. In the North Sea in April 2005, females fed at a higher trophic level than in May, were poor in lipids, showed low proteinase activity and produced 41 eggs female-1 d-1. In May, females were significantly smaller than in April, contained more lipids, had a higher proteinase activity and produced 26 eggs female-1 d-1. In the laboratory, females from each group were fed with either autotrophic diatoms or heterotrophic dinoflagellates for three days. Irrespective of different initial conditions, all T. longicornis females incorporated diet-specific fatty acids within 24 h. Also in both experiments and each dietary treatment, egg production increased after 24 h indicating that females were food-limited in situ in April and in May. Responses differed, however, with regard to lipid accumulation and enzyme activities . Total lipid contents increased significantly in females during experiment I (April) but not during experiment II (May), despite higher algal lipid levels during experiment II. Proteolytic activity increased during experiment I, but decreased during experiment II. These deviating responses of T. longicornis females to food conditions suggest that detailed knowledge about the initial physiological state of specimens is required, when investigating adaptive mechanisms and metabolic performances of copepods by means of experiments.