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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 clown anemonefish ‘Nemo’ Amphiprion ocellaris is the most popular fish species in the global marine ornamental trade and also its host sea anemones Heteractis magnifica, Stichodactyla gigantea, and Stichodactyla mertensii are traded. However, total catch and the potential impact of exploitation of these target organisms in Spermonde Archipelago, Indonesia, are not known. Therefore, the main objective of this study was to investigate the impact of the fishery on populations of A. ocellaris and its host anemones and how management could be improved. In order to obtain a comprehensive view on the marine ornamental fishery and trade of these species in Spermonde, this study also investigated the socioeconomics of the marine ornamental fishery and the catch records for A. ocellaris and it's host anemones. The study revealed that both, A. ocellaris and sea anemone densities were significantly lower at coral reefs with high exploitation (HE) than at reefs with low exploitation (LE). The total body length and group size of A. ocellaris was also significantly smaller at HE than at HL sites. The yearly amount traded by middlemen is estimated to 140 000 specimens of A. ocellaris and 31 000 anemones. The socioeconomic analysis showed that educational level of marine fishermen family members was low; most of them only finished elementary school. The household income analysis showed that marine ornamental fishery was not the major source of income, covering 13−43% of the expenses, with the exception of one studied island (84%). These findings revealed a considerable negative impact of marine ornamental fishery on the target populations and therefore, the implications for management strategies and conservation are discussed, including fish size restrictions for collectors, marine protected areas and regular monitoring of the amount of trade at middlemen.

It is unclear whether habitat degradation correlates with tolerance of marine invertebrates to abiotic stress. We therefore tested whether resistance to climate change-related stressors differs between populations of the green mussel Perna viridis from a heavily impacted and a mostly pristine site in West Java, Indonesia. In laboratory experiments, we compared their oxygen consumption and mortality under lowered salinity (-13 and -18 units, both responses), hypoxia (0.5 mg/l, mortality only) and thermal stress (+7 degrees C, mortality only). Mussels from the eutrophied and polluted Jakarta Bay showed a significantly smaller deviation from their normal oxygen consumption and higher survival rates when stressed than their conspecifics from the unaffected Lada Bay. This shows that human induced habitat degradation correlates with mussel tolerance to environmental stress. We discuss possible mechanisms - e.g. the selection of tolerant genotypes or habitat-specific differences in the nutritional status of the mussels - that could explain our observation.

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.

The distribution and structure of zoobenthic communities have been investigated in the northern North Atlantic. The principal goal of these studies is to assess the degree to which benthic community patterns depend on and/ or mediate carbon flux between the pelagic and benthic realms, as well as between seabed, sediment-water interface and benthic boundary layer. A common rationale is that these patterns integrate the impact of environmental factors over longer periods of time and reflect relatively long-lasting or predictably recurrent environmental states, thus providing clues to the relative significance of potential community determinants on a time scale of months to years. Since 1992, several meso-scale field studies have been carried out in three regions at the East Greenland continental margin between 68° N and 81° N at water depths ranging from 40 to 3,700 m. A suite of sampling methods was employed (corers, trawls, seabed imaging) to adequately probe various benthic community fractions, such as foraminifers, poriferans, macrobenthic endofauna, peracarid crustaceans and megabenthic epifauna.A depth zonation in the faunal composition, accompanied by a shift in the predominance of different feeding types and a significant decline in biomass and abundance by as much as two and three orders of magnitude was the most conspicuous general pattern detected. However, in terms of species richness, no common trend for water depth or latitude was perceivable. The general depth zonation of the macrobenthos as well as the spatial concordance of high macrobenthic abundance and biomass with relatively productive hydrographic zones, such as marginal ice zones, polynyas and anti-cyclonic gyres, provide evidence for the importance of water column processes and, hence, for subsequent food availability as major determinants for benthic assemblages and the significance of pelago -benthic coupling in the study area in general. However, for megafaunal species such as echinoderms, community patterns on a 10-1an scale and the dispersion of organisms on a 100-m scale, are best explained by seafloor properties. There is no evidence of direct pelago-benthic coupling, irrespective of water depth. These contrasting findings emphasize that the relative importance of potential community determinants can change with both spatial scale and life traits, e.g. body size, mobility and feeding ecology, of the organisms considered.