Description: Many species of the genus Octopus are important resources for fisheries worldwide. Its approximately 200 species show a strong similarity in structural morphology and a wide diversity in skin coloration and patterning, behaviour and life strategies that have hampered the study of phylogenetic relationships. We used a Bayesian approach to estimate as yet unknown phylogenetic relationships among O. tehuelchus from the southwestern Atlantic, new specimens of O. mimus (Chile and Peru) and other Octopus species, and used Bayes factors to test phylogenetic hypotheses. O. tehuelchus was more closely related to the genera Callistoctopus , Grimpella and Macroctopus than to Octopus , and therefore its generic placement may need a revision. O. vulgaris specimens from Costa Rica (Pacific Ocean) and O. oculifer grouped with O. mimus. Bayes factors showed positive evidence in favor of this grouping and therefore these individuals could have been misidentified, being in fact O. mimus. O. vulgaris specimens from the Costa Rican Caribbean were more related to O. mimus than to other O. vulgaris and could represent a cryptic species. The remaining O. vulgaris clustered with O. tetricus . Bayes factors found strong evidence against the monophyly of O. vulgaris as currently defined, giving statistical support to the monophyly of an O. vulgaris s. str. + O. tetricus group proposed previously by other authors.

Description: For marine invertebrates living at low temperatures of high latitudes Thorson’s rule suggests a comparatively reduced speed of development. Several studies conducted in different climatic zones have revealed the processes involved in the maturation of benthic assemblages. However, the duration and chronology of succession, as well as the influence of environmental impacts on arctic benthic assemblages is only scarcely analysed. Long-term studies are still rare. By analysing species abundances and substrate coverage over an exposure time of one decade the following hypotheses are tested: (i) Exposition time significantly modifies the structure of arctic benthic hard-bottom assemblages, (ii) the macroscopic structure of the substrate surface has a significant influence on the structure of benthic hard-bottom assemblages, and (iii) the succession of benthic hard-bottom assemblages in the Arctic is in general slower compared to the benthic succession in all non-polar climatic zones. In 2002 forty Polyethylene growth panels were installed on an underwater cliff in Kongsfjorden (Svalbard, Norway) in about 20 m water depth. Six of these were grooved to create structural diversity on the panel surface. Once a year the ripening epibenthic assemblages were photographed by scientific divers. Until 2007 annually about eight panels were sampled and replaced, thus creating starting points for succession in different years. Additionally a ground truthing was carried out for reference. The findings of this study indicate a resilience time exceeding a decade. A strong heterogeneity can be observed between the assemblages on different panels, signifying an influence of different starting points. The results are discussed in comparison with results of related studies from this and other cold-water regions.

Description: In the Arctic, the currently observed rising air temperature results in more frequent calving of icebergs. The latter derive from tidewater glaciers. Arctic macrozoobenthic soft-sediment communities are considerably disturbed by direct hits and sediment reallocation caused by iceberg scouring. With the aim to describe the primary succession of macrozoobenthic communities following these events, scientific divers installed 28 terracotta containers in the soft-sediment off Brandal (Kongsfjorden, Svalbard, Norway) at 20 m water depth in 2002. The containers were filled with a bentonite–sand mixture resembling the natural sediment. Samples were taken annually between 2003 and 2007. A shift from pioneering species (e.g. Cumacea: Lamprops fuscatus) towards more specialised taxa, as well as from surface detritivores towards subsurface detritivores was observed. This is typical for an ecological succession following the facilitation and inhibition succession model. Similarity between experimental and non-manipulated communities from 2003 was significantly highest after 3 years of succession. In the following years, similarity decreased, probably due to elevated temperatures, which prevented the fjord system from freezing. Some organisms, numerically important in the non-manipulated community (e.g. the polychaete Dipolydora quadrilobata) did not colonise the substrate during the experiment. This suggests that the community had not fully matured within the first 3 years. Later, the settlement was probably impeded by consequences of rising temperatures. This demonstrates the long-lasting effects of severe disturbances on Arctic macrozoobenthic communities. Furthermore, environmental changes, such as rising temperatures coupled with enhanced food availability due to an increasing frequency of sea-ice-free days per year, may have a stronger effect on succession than exposure time.

Description: Ascidians are abundant and well-represented members of worldwide benthic communities, including Antarctica and the Arctic. These organisms exhibit different reproductive patterns usually related to a latitudinal gradient, as do many marine invertebrate species. Reproductive seasonality varies from one or two annual peaks in cold and temperate water species to continuous reproduction throughout the year in warm water species. Styela rustica (Linnaeus 1767) and Halocynthia pyriformis (Rathke 1806) are solitary species with external fertilization and a wide distribution range, from the North Atlantic to the Arctic. The reproductive patterns of these two species were assessed for Arctic populations by year-round sampling and structural analysis of the gonads. Both species are hermaphrodites and showed marked seasonality in oocyte maturity and spawning; S. rustica peaked during the boreal summer and H. pyriformis in late spring. The two species also showed marked differences in mature oocyte sizes: H. pyriformis almost doubled those of S. rustica and, while spermatocytes of H. pyriformis were mature year-round, the maturity of male and female gametes was synchronized in S. rustica. The species thus showed an annual reproductive cycle coupled with a higher production period in the ecosystem, but also exhibited different strategies developed under the same environmental pressures.

Description: The Southern Ocean is one of the most isolated marine ecosystems, characterized by high levels of endemism, diversity, and biomass. Ascidians are among the dominant groups in Antarctic benthic assemblages; thus, recording the evolutionary patterns of this group is crucial to improve our current understanding of the assembly of this polar ocean. We studied the genetic variation within Cnemidocarpa verrucosa sensu lato, one of the most widely distributed abundant and studied ascidian species in Antarctica. Using a mitochondrial and a nuclear gene (COI and 18S), the phylogeography of fifteen populations distributed along the West Antarctic Peninsula and Burdwood Bank/MPA Namuncurá (South American shelf) was characterized, where the distribution of the genetic distance suggested the existence of, at least, two species within nominal C. verrucosa. When reevaluating morphological traits to distinguish between genetically defined species, the presence of a basal disk in one of the genotypes could be a diagnostic morphological trait to differentiate the species. These results are surprising due to the large research that has been carried out with the conspicuous C. verrucosa with no differentiation between species. Furthermore, it provides important tools to distinguish species in the field and laboratory. But also, these results give new insights into patterns of differentiation between closely related species that are distributed in sympatry, where the permeability of species boundaries still needs to be well understood.

Description: The scallop Argopecten purpuratus is a heavily exploited resource along the coasts of Peru and north-central Chile, especially after El Niño events, when the species undergoes high increases in abundance. Little is known about its genetic structure or demographic history, two important factors to ensure sustainable exploitation. We sequenced the cytochrome oxidase I and cytochrome b genes of 116 individuals from six localities (between 05°44′S 80°53′W and 23°31′S 70°33′W). We found high levels of genetic diversity in the analyzed populations. No geographical structuring was observed in the haplotype network, which consisted of a few central, widely distributed haplotypes, and many derived population-specific haplotypes separated by few mutations. This pattern suggests a recent population expansion and moderate to low current gene flow among populations. Mismatch analysis, neutrality tests, and a Bayesian skyline analysis confirmed the occurrence of a past event of population expansion approximately 5,000 years ago, which coincides with increasingly stronger and more frequent El Niño events.

Description: The glacier retreat observed during the last decades at Potter Cove (PC) causes an increasing amount of suspended particulate matter (SPM) in the water column, which has a high impact on sessile filter feeder’ species at PC located at the West Antarctic Peninsula. SPM presents a highly-fluctuating dynamic pattern on a daily, monthly, seasonal, and interannual basis. Geostatistical interpolation techniques are widely used by default to generate reliable spatial information and thereby to improve the ecological understanding of environmental variables, which is often fundamental for guiding decision-makers and scientists. In this study, we compared the results of default and configured settings of three geostatistical algorithms (Simple Kriging, Ordinary Kriging, and Empirical Bayesian) and developed a performance index. In order to interpolate SPM data from the summer season 2010/2011 at PC, the best performance was obtained with Empirical Bayesian Kriging (Standard mean = -0.001 and Root mean square standardized = 0.995). It showed an excellent performance (Performance Index = 0.004) improving both evaluation parameters when radio and neighbourhood were configured. About 69% of the models showed improved standard means when configured compared to the default settings following a here proposed guideline.

Description: The Antarctic Peninsula (AP) is one of three places on Earth that registered the most intense warming in the last 50 years, almost five times the global mean. The cryosphere was rapidly affected registering the largest ice-shelves collapses ever observed and 87 % of glaciers in retreat. Ecosystem responses, although increasingly predicted, have been mainly reported for pelagic systems. However, and despite that most Antarctic species being benthic, registered responses in the Antarctic benthos were restricted to few species and major effects at community level are unknown. This is probably due to the scarcity of baselines against which to assess change. We performed repeat surveys of coastal benthos in 1994, 1998 and 2010 analyzing community structure and environmental variables at King George Island, Antarctica. Here we report a marked shift in an Antarctic benthic community that can be linked to ongoing climate change. However, rather than temperature as the primary factor, we highlight the resulting increased sediment run-off, triggered by glacier retreat as the potential causal factor. The sudden shift from a “filter feeders-ascidian domination” to a “mixed assemblage” suggests that thresholds (e.g. of tolerable sedimentation) and alternative equilibrium states, depending on the reversibility of the changes, could be possible traits in this ecosystem. Sedimentation processes will be increasing under the current scenario of glacier retreat and attention needs to be paid to its effects along the AP.