Antarctic and Southern Ocean science is vital to understanding natural variability, the processes that govern global change and the role of humans in the Earth and climate system. The potential for new knowledge to be gained from future Antarctic science is substantial. Therefore, the international Antarctic community came together to 'scan the horizon' to identify the highest priority scientific questions that researchers should aspire to answer in the next two decades and beyond. Wide consultation was a fundamental principle for the development of a collective, international view of the most important future directions in Antarctic science. From the many possibilities, the horizon scan identified 80 key scientific questions through structured debate, discussion, revision and voting. Questions were clustered into seven topics: i) Antarctic atmosphere and global connections, ii) Southern Ocean and sea ice in a warming world, iii) ice sheet and sea level, iv) the dynamic Earth, v) life on the precipice, vi) near-Earth space and beyond, and vii) human presence in Antarctica. Answering the questions identified by the horizon scan will require innovative experimental designs, novel applications of technology, invention of next-generation field and laboratory approaches, and expanded observing systems and networks. Unbiased, non-contaminating procedures will be required to retrieve the requisite air, biota, sediment, rock, ice and water samples. Sustained year-round access to Antarctica and the Southern Ocean will be essential to increase winter-time measurements. Improved models are needed that represent Antarctica and the Southern Ocean in the Earth System, and provide predictions at spatial and temporal resolutions useful for decision making. A co-ordinated portfolio of cross-disciplinary science, based on new models of international collaboration, will be essential as no scientist, programme or nation can realize these aspirations alone.

Eurythenes gryllus is one of the most widespread amphipod species, occurring in every ocean with a depth range covering the bathyal, abyssal and hadal zones. Previous studies, however, indicated the existence of several genetically and morphologically divergent lineages, questioning the assumption of its cosmopolitan and eurybathic distribution. For the first time, its genetic diversity was explored at the global scale (Arctic, Atlantic, Pacific and Southern oceans) by analyzing nuclear (28S rDNA) and mitochondrial (COI, 16S rDNA) sequence data using various species delimitation methods in a phylogeographic context. Nine putative species-level clades were identified within E. gryllus. A clear distinction was observed between samples collected at bathyal versus abyssal depths, with a genetic break occurring around 3,000 m. Two bathyal and two abyssal lineages showed a widespread distribution, while five other abyssal lineages each seemed to be restricted to a single ocean basin. The observed higher diversity in the abyss compared to the bathyal zone stands in contrast to the depth-differentiation hypothesis. Our results indicate that, despite the more uniform environment of the abyss and its presumed lack of obvious isolating barriers, abyssal populations might be more likely to show population differentiation and undergo speciation events than previously assumed. Potential factors influencing species’ origins and distributions, such as hydrostatic pressure, are discussed. In addition, morphological findings coincided with the molecular clades. Of all specimens available for examination, those of the bipolar bathyal clade seemed the most similar to the ‘true’ E. gryllus. We present the first molecular evidence for a bipolar distribution in a macro-benthic deep-sea organism.

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In the Southern Ocean, that is areas south of the Polar Front, long-term oceanographic cooling, geographic separation, development of isolating current and wind systems, tectonic drift and fluctuation of ice sheets amongst others have resulted in a highly endemic benthic fauna,\ud which is generally adapted to the long-lasting, relatively stable environmental conditions. The Southern Ocean benthic ecosystem has been subject to minimal direct anthropogenic impact (compared to elsewhere) and thus presents unique opportunities to study biodiversity and its\ud responses to environmental change. Since the beginning of the century, research under the Census of Marine Life and International Polar Year initiatives, as well as Scientific Committee of Antarctic Research biology programmes, have considerably advanced our understanding of the Southern Ocean benthos. In this paper, we evaluate recent progress in Southern Ocean benthic research and identify priorities for future research. Intense efforts to sample and describe the benthic fauna, coupled with coordination of information in global databases, have greatly enhanced\ud understanding of the biodiversity and biogeography of the region. Some habitats, such as chemosynthetic systems, have been sampled for the first time, while application of new technologies and methods are yielding new insights into ecosystem structure and function. These advances have\ud also highlighted important research gaps, notably the likely consequences of climate change. In a time of potentially pivotal environmental change, one of the greatest challenges is to balance conservation with increasing demands on the Southern Ocean’s natural resources and services. In\ud this context, the characterization of Southern Ocean biodiversity is an urgent priority requiring timely and accurate species identifications, application of standardized sampling and reporting procedures, as well as cooperation between disciplines and nations

There has been a significant body of literature on species flock definition but not so much about practical means to appraise them. We here apply the five criteria of Eastman and McCune for detecting species flocks in four taxonomic components of the benthic fauna of the Antarctic shelf: teleost fishes, crinoids (feather stars), echinoids (sea urchins) and crustacean arthropods. Practical limitations led us to prioritize the three historical criteria (endemicity, monophyly, species richness) over the two ecological ones (ecological diversity and habitat dominance). We propose a new protocol which includes an iterative fine-tuning of the monophyly and endemicity criteria in order to discover unsuspected flocks. As a result nine « full » species flocks (fulfilling the five criteria) are briefly described. Eight other flocks fit the three historical criteria but need to be further investigated from the ecological point of view (here called « core flocks »). The approach also shows that some candidate taxonomic components are no species flocks at all. The present study contradicts the paradigm that marine species flocks are rare. The hypothesis according to which the Antarctic shelf acts as a species flocks generator is supported, and the approach indicates paths for further ecological studies and may serve as a starting point to investigate the processes leading to flock-like patterning of biodiversity.

Additional material of the iconic giant amphipod Eurythenes was investigated. Recently, the species E. gryllus has been separated into 12 distinct species-level lineages of which several have been described as distinct species, based on both morphology and genetics. This study revealed three additional species-level lineages from unique sampling localities, showing that with minimal sampling effort, species diversity within Eurythenes can still increase. One species-level lineage was found in the Indian Ocean and another one in the Pacific, which was subsequently identified as E. thurstoni. In addition to the three species already reported from the Southern Ocean (E. maldoror, E. gryllus s.s. and E. andhakarae), a supplementary bathyal species was found in the Weddell Sea. E. gryllus was confirmed to be amphitropical including newly sampled localities around the Kerguelen Islands and additional samples from the Svalbard Archipelago. Building on new and earlier data, geographic and bathymetric distributions of the different species that have been discovered so far are presented here and several factors are evaluated for their likelihood of having triggered past speciation events in this scavenger. Topographic and hydrographical features are discussed but rejected as sufficient reasons for the distributional patterns observed. Bathymetric segregation is interpreted with regard to what is known about the ecology of the species. The previously reported genetic break around 3000 m persists in this new data-set for all species but one. This study underlines the need of processing all individuals sampled, since two or more sympatric species are found in different proportions, and that conclusions regarding diversity and distribution may drastically change when increasing sampling intensity and coverage. Finally, I suggest here that only a mere fraction of all Eurythenes species has yet been discovered and that a more complete knowledge of the ecology of the species is of paramount importance for interpreting their evolution.

Abstract:The global zoogeographic distribution of the most widespread peracarid species occurring in three or more ocean basins below 2000 m is analysed. Basing on the published data we investigated 45 peracarid species, which have a most widespread distribution and most likely are cosmopolitan. Thirty−three species have a wide distribution in the Northern Hemisphere. Most species occur in the North Atlantic, however, 16 of these species occur also in the North Pacific, a more limited number of species occurs in the South Atlantic or South Pacific The Southern Ocean displays some special zoogeographic features and 22 widespread species occur there below 2000 m, including highly eurybathic ones. In total, 11 of the analysed species occur in all oceans. Eucopia australis (Lophogastrida), Munneury− cope murrayi (Isopoda) and Eurythenes gryllus (Amphipoda) are the species with the wid− est distributions. Other peracarids occurring in all oceans are: the isopods Paramunnopsis oceanica and Eurycope sarsi, the mysid Caesaromysis hispida the lophogastrid Eucopia unguiculata, the amphipod Mesopleustes abyssorum and the tanaids Exspina typica, Para− narthura insignis and Pseudotanais nordenskioldi. No cumacean species has been reported with an ocean−wide distribution but Campylaspis glabra occurs in the Atlantic, Indian and Pacific oceans. Among plenty of rare species in each order there are only few species with wide distribution records. There is evidence from molecular genetic studies that some of the widespread peracarids represent several cryptic species, however, some, e.g. Eucopia aus− tralis, seem to be truly cosmopolitan species. Geography of sampling is biasing our view of biogeography. The history and quality of taxonomic work as well as the reliability of geo− graphic records (quality control of large databases) limits our investigations of widespread or cosmopolitan species as much as the limited knowledge of variation within most species causes difficulties in defining morpho−species with certainty.

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