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Comprehensive studies of the ecosystem of the Atlantic sector of the Antarctic were carried out in the period between 2020 and 2022, during the 79th and 87th sea expeditions on the R/V "Akademik Mstislav Keldysh". Concentrations of soluble forms of 15 trace elements, except Mo, in surface waters of the Southern Ocean were matched the lower limit of their background concentrations in oceanic waters. A high spatial variability of chlorophyll a—an indicator of phytoplankton biomass, which is the main food object of the Antarctic krill—was revealed. In the Bransfield Strait, the abundance of bacterioplankton exhibited a weak relationship with water temperature and a pronounced dependence on chlorophyll fluorescence. It was determined, by using the bioluminescence method, that the largest concentrations of larvae and juveniles of krill were noted in the Bransfield Strait, on the shelf of the Antarctic Peninsula. Against the background of a decline in krill abundance in recent years, there has been an intensive development of Salpa thompsoni, the main food competitor of krill. New data on the distribution of mesoparasitic copepods on endemic fish of the Southern Ocean were also obtained, and their pathogenic effect on the body of fish hosts has been revealed. [ABSTRACT FROM AUTHOR]

Antarctic krill ( Euphausia superba) and salps (mainly Salpa thompsoni) are main components of Southern Ocean ecosystem, but little is known about their coastal distribution at a fine scale (<1 km). We deployed miniaturised cameras on breeding chinstrap ( n = 9 birds) and gentoo penguins ( n = 9 birds) in the Antarctic Peninsula region and obtained 2,333 krill images, 93 salp images and 609 sea floor images from 1,843 dives. 51.2 % of penguin dives that had salps present in the images occurred near the dives with krill images (within 5 min). The vertical distribution of salp images showed overlap with the upper depth zone of krill images. While 16.3 % of dives with krill images were associated in time with the sea floor, only 1.2 % of dives with salp images did. These results revealed close proximity between krill and salps within the penguin’s foraging range in an Antarctic coastal ecosystem. These results also imply that krill patches were common in both pelagic and benthic habitat, whereas salps were common mainly in pelagic habitat. If the effects of deployments are similar between the years or regions, inter-annual or regional comparison using the penguin-mounted camera will be valid for characterising prey environment in the penguin foraging area. [ABSTRACT FROM AUTHOR]

Abstract: Four grid surveys were carried out in the top 200m layer of the Lazarev Sea during fall 2004, summer 2005–06, winter 2006 and summer 2007–08 onboard the R.V. Polarstern as a part of the German SO-GLOBEC. The distribution, abundance and biology of two species of salps, Salpa thompsoni and Ihlea racovitzai, were investigated. With the exception of fall 2004, I. racovitzai dominated the salp community although being represented by low densities (<20ind.1000m−3). S. thompsoni was scarce during the summers of 2005–06 and 2007–08 and almost absent from the region during winter 2006. Nevertheless, it was modestly numerous during fall 2004 reaching densities of up to 33ind.1000m−3 in the south-western stations of the grid. The data on the seasonal population structure and life cycle of I. racovitzai showed that this species followed the generalized pattern typical of S. thompsoni, i.e. sexual/asexual reproduction and spawning during fall. I. racovitzai densities were the lowest during summer, increased during fall and peaked in during winter. Numerous offspring were produced by I. racovitzai during fall, just before the area became ice-covered. Conversely, S. thompsoni was not able to complete its life cycle in the Lazarev Sea, with a high occurrence of stage X (unfertilized) aggregates present. Highest S. thompsoni densities in summer and fall, and its disappearance in winter are indicative of a population of the expatriate origin that is sustained by advection. [Copyright &y& Elsevier]

Depth-stratified vertical sampling was carried out during the New Zealand International Polar Year cruise to the Ross Sea on board the RV Tangaroa in February-March 2008. The distribution (horizontal and vertical), density and population biology of Salpa thompsoni were investigated. Salps were found at two of the four major sampling locations, e.g. near the continental slope of the Ross Sea and in the vicinity of seamounts to the north of the Ross Sea. Both abundance and biomass of S. thompsoni were highest near the seamounts in the Antarctic Circumpolar Current reaching ~2,500 ind 1,000 m and 8.2 g dry wt 1,000 m in the water column sampled. The data showed that S. thompsoni populations were able to utilize horizontal and vertical discontinuities in water column structure, in particular the warm Circumpolar Deep Water (CDW), to persist in the high Antarctic. Although salps appeared to continue migrating to the surface colder layers to feed, both aggregate chain and young embryo release seem to be restricted to the CDW. This study for the first time has provided evidence that low Antarctic salp species may successfully reproduce in the hostile high Antarctic realm. [ABSTRACT FROM AUTHOR]

The Southern Ocean ecosystem is thought to be experiencing a long-term increase in Salpa thompsoni. Uncertainty surrounds the environmental drivers behind variable S. thompsoni abundances, particularly within the East Antarctic region. In this study, S. thompsoni populations were sampled in the Indian Sector of the Southern Ocean, as part of the January–February 2016 Kerguelen Axis voyage. These recent data were compared against historical density records in the broader Kerguelen Plateau region from voyages during 1985–2006. Results show that 2016 maximum S. thompsoni densities across the Kerguelen Plateau were higher, and more southerly located, than those previously sampled in the area. The highest 2016 S. thompsoni abundances exceeded 2500 individuals 1000 m-3 and were located between the Southern Boundary of the Antarctic Circumpolar Current and the Southern Antarctic Circumpolar Current Front. The life-stage composition of S. thompsoni comprised approximately 90% aggregates (blastozooids) and 10% solitaries (oozoids). Generalised Additive Models associated low chlorophyll- a concentration and low solar elevation (outside of peak daylight) with higher S. thompsoni abundances. In addition, elevated abundances occurred in locations from where the sea ice retreated at least eight weeks previously. These abundance-environment relationships are consistent with results from several previous surveys in the region and the West Antarctic. Due to the complex life cycle of S. thompsoni , and the unpredictability of their distribution patterns, multi-seasonal and multi-year surveys are needed to confirm whether the 2016 distribution patterns are indicative of a long-term increase or southerly shift in abundances. The new information from this study provides much needed baseline abundance and distribution data (which can be used to assess future change in a currently understudied oceanographic region) on a species capable of shaping the future ecosystem structure and function in the Indian Sector of the Southern Ocean. [ABSTRACT FROM AUTHOR]