A quantitative assessment of observed and projected environmental changes in the Southern Ocean (SO) with a potential impact on the marine ecosystem shows: (i) large proportions of the SO are and ...will be affected by one or more climate change processes; areas projected to be affected in the future are larger than areas that are already under environmental stress, (ii) areas affected by changes in sea‐ice in the past and likely in the future are much larger than areas affected by ocean warming. The smallest areas (<1% area of the SO) are affected by glacier retreat and warming in the deeper euphotic layer. In the future, decrease in the sea‐ice is expected to be widespread. Changes in iceberg impact resulting from further collapse of ice‐shelves can potentially affect large parts of shelf and ephemerally in the off‐shore regions. However, aragonite undersaturation (acidification) might become one of the biggest problems for the Antarctic marine ecosystem by affecting almost the entire SO. Direct and indirect impacts of various environmental changes to the three major habitats, sea‐ice, pelagic and benthos and their biota are complex. The areas affected by environmental stressors range from 33% of the SO for a single stressor, 11% for two and 2% for three, to <1% for four and five overlapping factors. In the future, areas expected to be affected by 2 and 3 overlapping factors are equally large, including potential iceberg changes, and together cover almost 86% of the SO ecosystem.
Megafauna play an important role in benthic ecosystem function and are sensitive indicators of environmental change. Non-invasive monitoring of benthic communities can be accomplished by seafloor ...imaging. However, manual quantification of megafauna in images is labor-intensive and therefore, this organism size class is often neglected in ecosystem studies. Automated image analysis has been proposed as a possible approach to such analysis, but the heterogeneity of megafaunal communities poses a non-trivial challenge for such automated techniques. Here, the potential of a generalized object detection architecture, referred to as iSIS (intelligent Screening of underwater Image Sequences), for the quantification of a heterogenous group of megafauna taxa is investigated. The iSIS system is tuned for a particular image sequence (i.e. a transect) using a small subset of the images, in which megafauna taxa positions were previously marked by an expert. To investigate the potential of iSIS and compare its results with those obtained from human experts, a group of eight different taxa from one camera transect of seafloor images taken at the Arctic deep-sea observatory HAUSGARTEN is used. The results show that inter- and intra-observer agreements of human experts exhibit considerable variation between the species, with a similar degree of variation apparent in the automatically derived results obtained by iSIS. Whilst some taxa (e. g. Bathycrinus stalks, Kolga hyalina, small white sea anemone) were well detected by iSIS (i. e. overall Sensitivity: 87%, overall Positive Predictive Value: 67%), some taxa such as the small sea cucumber Elpidia heckeri remain challenging, for both human observers and iSIS.
The manuscript assesses the current and expected future global drivers of Southern Ocean (SO) ecosystems. Atmospheric ozone depletion over the Antarctic since the 1970s, has been a key driver, ...resulting in springtime cooling of the stratosphere and intensification of the polar vortex, increasing the frequency of positive phases of the Southern Annular Mode (SAM). This increases warm air-flow over the East Pacific sector (Western Antarctic Peninsula) and cold air flow over the West Pacific sector. SAM as well as El Niño Southern Oscillation events also affect the Amundsen Sea Low leading to either positive or negative sea ice anomalies in the west and east Pacific sectors, respectively. The strengthening of westerly winds is also linked to shoaling of deep warmer water onto the continental shelves, particularly in the East Pacific and Atlantic sectors. Air and ocean warming has led to changes in the cryosphere, with glacial and ice sheet melting in both sectors, opening up new ice free areas to biological productivity, but increasing seafloor disturbance by icebergs. The increased melting is correlated with a salinity decrease particularly in the surface 100 m. Such processes could increase the availability of iron, which is currently limiting primary production over much of the SO. Increasing CO
2
is one of the most important SO anthropogenic drivers and is likely to affect marine ecosystems in the coming decades. While levels of many pollutants are lower than elsewhere, persistent organic pollutants (POPs) and plastics have been detected in the SO, with concentrations likely enhanced by migratory species. With increased marine traffic and weakening of ocean barriers the risk of the establishment of non-indigenous species is increased. The continued recovery of the ozone hole creates uncertainty over the reversal in sea ice trends, especially in the light of the abrupt transition from record high to record low Antarctic sea ice extent since spring 2016. The current rate of change in physical and anthropogenic drivers is certain to impact the Marine Ecosystem Assessment of the Southern Ocean (MEASO) region in the near future and will have a wide range of impacts across the marine ecosystem.
A dedicated aerial cetacean survey was conducted concurrently to a standardised net trawl survey for krill in order to investigate distribution patterns of large whales and different krill species ...and to investigate relationships of these. Distance sampling data were used to produce density surface models for humpback (
Megaptera novaeangliae
) and fin whales (
Balaenoptera physalus
) around the West Antarctic Peninsula (WAP). Abundance for both species was estimated over two strata in the Bransfield Strait and Drake Passage. Distinct distribution patterns suggest horizontal niche partitioning of the two whale species around the WAP, with fin whales aggregating at the shelf edge of the South Shetland Islands in the Drake Passage and humpback whales in the Bransfield Strait. Krill biomass estimated from the concurrent krill survey was used along with CTD data from the same expedition, bathymetric parameters and satellite data on chlorophyll-
a
and ice concentration to model krill distribution. Comparisons of the predicted distributions of both whale species with the predicted distributions of
Euphausia superba, Euphausia crystallorophias
and
Thysanoessa macrura
suggest a complex relationship rather than a straightforward correlation between krill and whales. However, results indicate that fin whales were feeding in an area dominated by
T. macrura
, while humpback whales were found in areas of higher
E. superba
biomass. Our results provide abundance estimates for humpback whales and, for the first time, fin whales in the WAP and contribute important information on feeding ecology and habitat use of these two species in the Southern Ocean.
Recent climate-induced ice-shelf disintegration in the Larsen A (1995) and B (2002) areas along the Eastern Antarctic Peninsula formed a unique opportunity to assess sub-ice-shelf benthic community ...structure and led to the discovery of unexplored habitats, including a low-activity methane seep beneath the former Larsen B ice shelf. Since both limited particle sedimentation under previously permanent ice coverage and reduced cold-seep activity are likely to influence benthic meiofauna communities, we characterised the nematode assemblage of this low-activity cold seep and compared it with other, now seasonally ice-free, Larsen A and B stations and other Antarctic shelf areas (Weddell Sea and Drake Passage), as well as cold-seep ecosystems world-wide.
The nematode community at the Larsen B seep site differed significantly from other Antarctic sites in terms of dominant genera, diversity and abundance. Densities in the seep samples were high (>2000 individuals per 10 cm(2)) and showed below-surface maxima at a sediment depth of 2-3 cm in three out of four replicates. All samples were dominated by one species of the family Monhysteridae, which was identified as a Halomonhystera species that comprised between 80 and 86% of the total community. The combination of high densities, deeper density maxima and dominance of one species is shared by many cold-seep ecosystems world-wide and suggested a possible dependence upon a chemosynthetic food source. Yet stable (13)C isotopic signals (ranging between -21.97±0.86‰ and -24.85±1.89‰) were indicative of a phytoplankton-derived food source.
The recent ice-shelf collapse and enhanced food input from surface phytoplankton blooms were responsible for the shift from oligotrophic pre-collapse conditions to a phytodetritus-based community with high densities and low diversity. The parthenogenetic reproduction of the highly dominant Halomonhystera species is rather unusual for marine nematodes and may be responsible for the successful colonisation by this single species.
Marine free-living nematode communities were studied at similar depths (~500 m) at two sides of the Antarctic Peninsula, characterised by different environmental and oceanographic conditions. At the ...Weddell Sea side, benthic communities are influenced by cold deep-water formation and seasonal sea-ice conditions, whereas the Drake Passage side experiences milder oceanic conditions and strong dynamics of the Antarctic Circumpolar Current. This resulted in different surface primary productivity, which contrasted with observed benthic pigment patterns and varied according to the area studied: chlorophyll a concentrations (as a proxy for primary production) were high in the Weddell Sea sediments, but low in the surface waters above; this pattern was reversed in the Drake Passage. Differences between areas were largely mirrored by the nematode communities: nematode densities peaked in Weddell stations and showed deeper vertical occurrence in the sediment, associated with deeper penetration of chlorophyll a and indicative of a strong bentho-pelagic coupling. Generic composition showed some similarities across both areas, though differences in the relative contribution of certain genera were noted, together with distinct community shifts with depth in the sediment at all locations.
Many countries are very active in marine research and operate their own research fleets. In this decade, a number of research vessels have been renewed and equipped with the most modern navigation ...systems and tools. However, much of the research gear used for biological sampling, especially in the deep-sea, is outdated and dependent on wired operations. The deployment of gear can be very time consuming and, thus, expensive. The present paper reviews wire-dependent, as well as autonomous research gear for biological sampling at the deep seafloor. We describe the requirements that new gear could fulfil, including the improvement of spatial and temporal sampling resolution, increased autonomy, more efficient sample conservation methodologies for morphological and molecular studies and the potential for extensive in situ real-time studies. We present applicable technologies from robotics research, which could be used to develop novel autonomous marine research gear, which may be deployed independently and/or simultaneously with traditional wired equipment. A variety of technological advancements make such ventures feasible and timely. In proportion to the running costs of modern research vessels, the development of such autonomous devices might be already paid off after a discrete number of pioneer expeditions.
The marine ecosystem on the eastern shelf of the Antarctic Peninsula was surveyed 5 and 12 years after the climate-induced collapse of the Larsen A and B ice shelves. An impoverished benthic fauna ...was discovered, that included deep-sea species presumed to be remnants from ice-covered conditions. The current structure of various ecosystem components appears to result from extremely different response rates to the change from an oligotrophic sub-ice-shelf ecosystem to a productive shelf ecosystem. Meiobenthic communities remained impoverished only inside the embayments. On local scales, macro- and mega-epibenthic diversity was generally low, with pioneer species and typical Antarctic megabenthic shelf species interspersed. Antarctic Minke whales and seals utilised the Larsen A/B area to feed on presumably newly established krill and pelagic fish biomass. Ecosystem impacts also extended well beyond the zone of ice-shelf collapse, with areas of high benthic disturbance resulting from scour by icebergs discharged from the Larsen embayments.
The aim of this study was to contribute to a general understanding of the response of the Antarctic macrobenthos to environmental variability and climate-induced changes. The change in population ...size of selected macrobenthic organisms was investigated in the Larsen A area east of the Antarctic Peninsula in 2007 and 2011 using ROV-based imaging methods. The results were complemented by data from the Larsen B collected in 2007 to allow a conceptual reconstruction of the environment-driven changes before the period of investigation. Both Larsen areas are characterised by ice-shelf disintegration in 1995 and 2002, respectively, as well as high inter-annual variability in sea-ice cover and oceanographic conditions. In 2007 one ascidian species,
Molgula pedunculata
, was abundant north and south of the stripe of remaining ice shelf between Larsen A and B. Population densities decreased drastically in the Larsen A between 2007 and 2011, coincident with the decrease in
Corella eumyota,
another ascidian. Among the ophiuroids, the population of deposit feeders increased, while suspension feeders halved their abundance. Current measurements indicated a northward flow between the Larsen B and Larsen A, suggesting that a major physical forcing on benthic population development comes from the South. The results demonstrate that Antarctic macrobenthic populations can exhibit dramatic population dynamics. Analyses of sea-ice dynamics, salinity, temperature and surprisingly ice-shelf disintegration history, however, did not provide any clear evidence for environmental drivers underlying the apparent changes.
PDF
