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It is unclear whether transport by human vectors can increase the robustness of translocated populations and thereby enhance their invasiveness. To test this concept, we investigated the effect of heat stress on the tolerance of mussel populations towards a second stress event of the same kind. The heat challenges we mimicked can be faced by marine invertebrates that are transported through regions with high sea surface temperatures on ship hulls or in ballast water tanks. The study included 5 mussel species that were collected at sites in Brazil, Chile, Finland, Germany (Baltic Sea) and Portugal. In parallel laboratory experiments, monospecific groups of individuals were exposed to heat challenges that caused 60–83% mortality in the experimental groups within 15–28 days. The surviving individuals were exposed to a second stress event of the same kind, while their survival was then compared to the robustness of conspecifics that had not been exposed to elevated temperatures before. We observed that thermal tolerance was significantly enhanced by previous heat stress experience in case of Semimytilus algosus from Chile and in case of Mytilus edulis from Germany. Our results suggest that heat challenges, which marine invertebrates experience during transport, can enhance stress tolerance in founder populations of these species in their non-native range by potentially increasing the frequency of genetically adapted genotypes. This points at the necessity to learn more about selection acting on organisms during human-mediated transport—in the aquatic but also in the terrestrial environment.

The colonisation of hard substrata (HS) by epibenthic megafauna was studied by photographic surveys along the Ardencaple Canyon in the deep western Greenland Sea in 2000. Seven transects at 2,700–3,200 m water depth showed generally low densities of dropstones, sunken wood, and other substrata including anthropogenic material (range: 2–11 HS km−1). Overall, 30 different taxa and morphotypes were found on or associated with HS. While the sea anemone Bathyphellia margaritacea and the pantopod Ascorhynchus abyssi dominated the fauna on the substrate surfaces, a ball-shaped morphotype of uncertain taxonomic origin characterised assemblages marginally associated with HS. Community analysis revealed differences in faunal patterns near the continental rise and towards the deep sea, but diversity and evenness did not differ significantly between the various regions. However, we conclude that dropstones and other hard substrata at the seafloor serve as colonisation islands and thereby generally increase small-scale habitat diversity in polar deep-sea environments.

The Asian green mussel Perna viridis is tolerant to environmental stress, but its robustness varies between populations from habitats that differ in quality. So far, it is unclear whether local adaptations through stress-induced selection or phenotypic plasticity are responsible for these inter-population differences. We tested for the relevance of both mechanisms by comparing survival under hypoxia in mussels that were transplanted from an anthropogenically impacted (Jakarta Bay, Indonesia) to a natural habitat (Lada Bay, Indonesia) and vice versa. Mussels were retrieved 8 weeks after transplantation and exposed to hypoxia in the laboratory. Additional hypoxia tests were conducted with juvenile mussels collected directly from both sites. To elucidate possible relationships between habitat quality and mussel tolerance, we monitored concentrations of inorganic nutrients, temperature, dissolved oxygen, salinity, phytoplankton density and the mussels’ body condition index (BCI) for 20 months before, during and after the experiments. Survival under hypoxia depended mainly on the quality of the habitat where the mussels lived before the hypoxia tests and only to a small degree on their site of origin. Furthermore, stress tolerance was only higher in Jakarta than in Lada Bay mussels when the BCIs were substantially higher, which in turn correlated with the phytoplankton densities. We explain why phenotypic plasticity and high BCIs are more likely the causes of population-specific differences in hypoxia tolerance in P. viridis than stress-induced selection for robust genotypes. This is relevant to understanding the role of P. viridis as mariculture organism in eutrophic ecosystems and invasive species in the (sub)tropical world.

It is an open question whether adverse habitat conditions, characteristic for many anthropogenically impacted coastal habitats, can determine resistance to abiotic stress in populations of residing invertebrates. We tested experimentally for differences in stress tolerance between individuals of the Asian green mussel Perna viridis stemming from the heavily impacted Jakarta Bay and from two natural sites, Lada Bay and Pelabuhan Ratu, West Java. Mussel performance under hyposalinity and hypoxia was assessed in laboratory assays by measuring fitness-related response variables, e.g. body condition index, relative shell weight, byssus production, respiration rates and survival. We found stress-specific and population-specific differences in mussel resistance to adverse conditions: Individuals from the impacted Jakarta Bay performed better under hypoxia than their conspecifics from the natural sites, whereas the latter were more resistant to hyposalinity. We explain these differences by differential acclimation to environmental conditions in the respective habitats and by diverging degrees of food supply.

Sediments sampled during summers 1999–2002 with the German ice-breaker RV “ Polarstern ” were analyzed to estimate benthic microbial activity and biomass of the smallest sediment-inhabiting organisms (size range: bacteria to meiofauna) along a channel system in the deep western Greenland Sea at about 75°N. Biochemical investigations were expanded by direct counts of bacteria and meiofaunal organisms, including foraminiferans. A total of 36 stations was sampled along the Ardencaple Canyon, extending over 200 km in north-easterly direction from the Greenland continental rise towards the central Greenland Basin. Stations were grouped in defined regions, generally with sampling sites inside the canyon plus accompanying sites on the northern and southern levees. An additional eight stations were sampled along a depth transect crossing the Greenland continental margin and traversing the channel in its midsection. All parameters investigated confirmed no differences between stations within the channel compared to stations on the levees, opposing the hypothesis that the Ardencaple Canyon displays a major pathway for suspension-driven shelf drainage flows. However, investigations showed some general trends in the data: parameters indicating food availability at the seafloor and total microbial biomass generally decreased with increasing water depth and distance from the Eastern Greenland continental margin. Along the depth transect crossing the Greenland margin both parameters exhibited increased values at deep stations on the continental rise. The position of these stations coincides with the position of the ice edge during sampling in summer 2000. Increased food availability and microbial biomass in the sediments most probably reflect raised levels of primary productivity and enhanced sedimentation in the marginal ice zone, thereby pointing to a close pelago-benthic coupling. Bacterial activities in the sediments showed a different picture with generally increasing values with increasing distance from the continental margin, which could probably be explained by a change in bacterial assemblages.

Although the use of deep-sea imagery considerably increased during the last decades, reports on nekton falls to the deep seafloor are very scarce. Whereas there are a few reports describing the finding of whale carcasses in the deep north-eastern and south-eastern Pacific, descriptions of invertebrate or vertebrate food-falls at centimetre to metre scale are extremely rare. After 4 years of extensive work at a deep-sea long-term station in northern polar regions (AWI-“Hausgarten”), including large-scale visual observations with various camera systems covering some 10 000 m 2 of seafloor at water depths between 1250 and 5600 m, this paper describes the first observation of a fish carcass at about 1280 m water depth, west off Svalbard. The fish skeleton had a total length of 36 cm and an approximated biomass of 0.5 kg wet weight. On the basis of in situ experiments, we estimated a very short residence time of this particular carcass of about 7 h at the bottom. The fast response of the motile deep-sea scavenger community to such events and the rapid utilisation of this kind of organic carbon supply might partly explain the extreme rarity of such an observation.