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Abstract Euphausiid larvae were collected in the Weddell Scotia Confluence region in summer 2011, in the West Antarctic Peninsula and Scotia Sea in 2012, and in the South Orkneys Shelf in 2014. From 2011 to 2014 the larval stages geographic distribution and the distribution of water masses were consistent with published information. The densities observed were compared between the cruises and with the 1981 and 1995 values by means of a kernel estimate of absolute and relative densities at a fixed grid of points. The values of Thysanoessa macrura were higher in 2011 and 2012 and those of Euphausia superba were lower than those observed in 1981 and 1995. Euphausia frigida did not show significant variations in absolute density but their relative values were higher than those of E. superba. No significant variations were observed in absolute values between 1981 and 1995. The opposite pattern was found in 2014, with significantly higher densities of E. superba than those of T. macrura. No single factor could be identified to explain these variations in density, suggesting the existence of complex mechanisms coupling the reproductive biology with oceanographic phenomena. Their description will require ample spatial and temporal monitoring rather than locally detailed observations. [ABSTRACT FROM AUTHOR]

Abstract: The ocean ecosystems around the west Antarctic Peninsula and South Georgia are two of the best described regional ecosystems of the Southern Ocean. They therefore provide a useful basis for developing comparative analyses of ocean ecosystems around the Antarctic. There are clear and expected differences in seasonality and species composition between the two ecosystems, but these mask an underlying similarity in ecosystem structure and function. This similarity results from the two ecosystems being part of a continuum, from more ice covered regions in the south to open water regions in the north. Within this continuum the major factors affecting ecosystem structure and function are the sea ice, the biogeochemical conditions and the connectivity generated by the flow of the Antarctic Circumpolar Current. Antarctic krill are central to the food web in both ecosystems, but the other species of plankton and predators present are different. These different species provide alternative pathways of energy transfer from primary production to the highest trophic levels. The relative dominance of these species can provide indicators of change in ecosystem structure and function. Both ecosystems are changing as a result of physically and biologically driven processes, and the ecological responses being observed are complex and variable across different species and within the two regions. Species in parts of the northern Antarctic Peninsula are being replaced by species that currently dominate farther north in more oceanic areas such as at South Georgia. The similarity of structure and strong connectivity, mean that projections of future change will require generic models of these ecosystems that can encompass changes in structure and function within a connected continuum from ice covered to open water in winter. [Copyright &y& Elsevier]

Abstract: The zooplankton community of Marguerite Bay was studied during austral fall of 2001 and 2002 using net and concurrent environmental data. Interannual differences were observed in zooplankton species composition, developmental stages, and abundances, which were linked to unusually high chlorophyll concentrations in the Bellingshausen Sea and Marguerite Bay during spring–summer 2000/2001. Copepod abundance was significantly higher in 2001 than in 2002 (46.3 and 28.3indm−3 in 2001 and 2002, respectively). During 2001, the copepod community was dominated by two species. Calanoides acutus, a herbivore, and Metridia gerlachei, an omnivore, accounted for 46% and 45% of the community, respectively. During 2002, however, several species were relatively abundant, including M. gerlachei, Ctenocalanus spp., C. acutus, Oithona spp., and Paraeuchaeta spp. Euphausiids also showed a rapid population response to high chlorophyll levels in 2001. Even though average total euphausiid (juvenile/adult) abundances were similar during both years (0.20 and 0.15indm−3 for 2001 and 2002, respectively), species composition showed marked interannual differences due to varying life history strategies among species. Thysanoessa macrura, which has a relatively rapid development from larval to juvenile stages between spring and fall of the same year, was the most abundant euphausiid in 2001. In contrast, Euphausia crystallorophias and Euphausia superba juvenile/adult populations increased in 2002, owing to a slower development in which larval stages overwinter and recruit to juveniles during the following spring/summer. Other zooplankton groups those were abundant in Marguerite Bay, but showed little variability between years, included ostracods, pteropods, chaetognaths, medusae, amphipods, and mysids. Summer phytoplankton concentrations strongly influenced copepods and euphausiids; however, there were no clear associations between zooplankton distributions and fall environmental conditions (i.e., pigment concentrations and surface salinity) or bottom depth. It is notable that ostracods and pteropods had the highest abundances of non-copepod zooplankton. [Copyright &y& Elsevier]

Recent rapid changes of air temperature on the western side of the Antarctic Peninsula results in increased sediment discharge and ice scouring frequencies in coastal regions. These changes are bound to especially affect slow growing, sessile filter feeders such as the Antarctic bivalve, Laternula elliptica, a long-lived and abundant key species with circumpolar distribution. We investigated the effect of sedimentation and ice scouring on small/young and large/old individuals at two closely located stations, distinctly influenced by both types of disturbance. Small individuals dealt better with disturbance in terms of their respiratory response to sediment exposure, reburrowing ability, and survival after injury, compared to larger animals. At the more disturbed station L. elliptica population density was lower, but larger animals reburrowed faster after iceberg disturbance and reduced their metabolic rate under strong sediment coverage, compared to larger animals of the less disturbed station, indicating that an adaptation or learning response to both types of disturbance may be possible. Smaller individuals were not influenced. Laternula elliptica seems capable of coping with the rapidly changing environmental conditions. Due to a decrease in population density and mean population lifespan, L. elliptica could however lose its key role in the bentho-pelagic carbon flux in areas of high sediment deposition. [ABSTRACT FROM AUTHOR]

Abstract: Chromophoric dissolved and detrital organic matter (CDM), the optically active fraction of organic matter, affects significantly the underwater light environment and interferes with ocean color algorithms. Here, we studied the distribution and dynamics of CDM in waters around the Antarctic Peninsula, Southern Ocean, using remotely sensed data in austral summers from 1997 to 2005. First, we validated the global semi-analytic algorithm Garver–Siegel–Maritorena (GSM) by comparing simultaneous field and satellite measurements of CDM. These comparisons confirmed the validity of CDM satellite measurements obtained by the GSM algorithm (r2 =0.74, slope value=1.01±0.16, n=15).We found a higher (20%) contribution of detrital particles to the CDM signal compared to other studies in lower latitudes (average 12%). Patches of higher CDM were observed in coastal areas and zones with recent ice melting. The seasonal variability of CDM, with maximum values at the end of austral summer, appeared to be ultimately controlled by the dynamics of ice, both directly and indirectly through the growth of phytoplankton and other organisms which are potential sources of CDM. At an interannual timescale, CDM dynamics may be driven by climatic forcing such as the Antarctic Oscillation. [ABSTRACT FROM AUTHOR]