Anna Panasiuk

Themisto gaudichaudii belongs to the pelagic amphipods which can be very abundant in the Antarctic waters and can be an important food source for many Antarctic predators. T. gaudichaudii is generally associated with relatively warmer, ice-free waters, although it may co-occur with Euphausia superba and can also occur at low densities in colder regions. Over the past few decades, Antarctic krill has been declining in some regions of the Southern Ocean, which may lead predators to seek alternative food sources. Due to the tendency of Themisto species to occur in aggregations and at high densities, these species may represent such an alternative. However, detailed studies on the ecology of this crustacean are still lacking. The present research was carried out during the expedition PS112 on R/V Polarstern in 2018 in the vicinity of Elephant Island, Weddell Sea, South Shetland Islands, and in the Bransfield Strait from March to May. The average recorded abundances of T. gaudichaudii were high in the areas under the direct influence of Antarctic Circumpolar Current, and the highest abundances were observed in the Elephant Island region, probably due to its location and unique hydrological conditions. The population was dominated by juveniles presumably because the samples were collected after the spawning period.

The Antarctic krill Euphausia superba is a key species in Antarctic waters, mainly because it is a major component of the diet of dominant predators, including penguins. It is also a marine living resource that is commercially harvested. Since 2000, krill fishing has become more concentrated. On the basis of several years of data, it has been reported that up to 57% of the krill fishery harvests occur in the Bransfield Strait area. The distribution of krill in the Southern Ocean is not well described. Studies that compare the size of krill caught by commercial vessels with that recorded in the diet of predators are even rarer. The main objectives of this study were to assess the spatial diversity in the size and putative age of krill in the CCAMLR subarea 48.1, to investigate the spatial availability of krill and its size and age structure, and to assess whether the diet of Pygoscelis penguins reflects the size structure of krill present in the environment. The results implied that the size and age structure of the krill population were similar throughout the Bransfield Strait during the study period, although those in the eastern and southern parts of the strait and the Brabant Island region were the most similar. The Livingston Island and Drake Passage areas were clearly distinguishable from the above regions, where larger and therefore older krill were recorded. All Pygoscelis penguin species showed size preferences for consumed krill; therefore, their diet is likely not a reliable indicator of the size of krill in the environment. Krill that had not yet reached sexual maturity, and thus not yet started reproducing were commercially caught in the Bransfield Strait during the investigated years.

Hg is considered as the most toxic metal in the environment. Sources of Hg in the environment include burning fossil fuels, burning waste, and forest fires. The long residence time of the gaseous form in the atmosphere allows mercury to be transported over long distances. The pelagic tunicate Salpa thompsoni is an important component of the Antarctic environment. Over the past few decades an expansion of this species to the higher latitudes has been noted, mainly due to the ongoing climate change. The study material consisted of samples of S. thompsoni individuals, collected in the waters surrounding Elephant Island (Western Antarctic). Total mercury and five of its fractions were determined. Whole organisms were analyzed as well as internal organs: stomachs, muscle strips, and tunics. Obtained results showed that the highest concentrations of mercury in salps were observed in stomachs. With the Hg fraction results, it can be concluded that the main route of exposure of S. thompsoni to Hg is presumably absorption from the food—filtered organic and non-organic particles. Moreover, the process of transformation of simple soluble forms into organic forms of Hg in stomachs and intestines and its distribution to other tissues was observed.

Numerous studies have revealed that large numbers of gelatinous invertebrates, Salpa thompsoni, are reported more often in high-latitude Antarctic waters (> 60°S) than were reported in data obtained from the early twentieth century. Previously published studies also suggested that this tunicate may form a small subpopulation in cold shelf Antarctic waters. However, many researchers claim that harsh environmental conditions inhibit the reproduction and development of this species. Therefore, the aim of this study was to examine S. thompsoni blastozooids and the development ability of their embryos within different zones of the eastern and western parts of the Southern Ocean. The samples used in this study were collected from two transects, (I) between the Weddell Sea and coastal waters of South Africa and (II) between South America and the South Shetland Islands (Drake Passage) during the summer season of 2009/2010. The presented results showed that the highest likelihood for the presence of mature salps is observed under both in the conditions considered favorable that are characterized for mid-latitude areas as well as those observed at higher latitudes in the Antarctic zone (60°S) of the Southern Ocean. This work indicated that the prevailing environmental conditions in the Antarctic zone were distinguished by the highest diversity of embryo development stages and the densest salp aggregations. Our work revealed evidence for dualistic environmental preferences, while blastozooid development and embryo fertilization were equally successful at lower temperatures and low chl-a concentrations as well as when these variables reached higher values. This study expands the knowledge about environmental preferences and provides evidence for flexibility of salp reproduction, which allows it to adapt to various environmental conditions of the Southern Ocean.

In recent years, functional changes in Southern Ocean are becoming more noticeable, due to climate change and increasing human impacts, including a growing fishery that is concentrating in the Antarctic Peninsula (AP) region. Antarctic krill Euphausia superba is often the primary prey species for animals such as Pygoscelis penguins, a sentinel species for ecosystem monitoring and management. During the last two decades in the AP gentoo penguin numbers (Pygoscelis papua) have increased and their range has shifted southward, in contrast to the decline in numbers of Adélie (P. adeliae) and chinstrap (P. antarcticus) penguins. Given divergent population trends, the goal of this study was to examine differences in their diet, and size structure of Antarctic krill recovered from penguin diet samples. The study is based on diet samples collected during the austral summers on King George Island (South Shetland Islands) where P. adeliae, P. antarcticus, and P. papua breed in mixed colonies. Results indicate that the penguins consumed krill of similar sizes during the breeding period. In contrast to prior diet studies, we found higher proportions of krill in the gentoo diet and changes in the percentage of krill in the diet relative obtained during 1970s. The similarity in diets among all three species suggests that the availability prey items (e. g., fishes) may be changing and driving higher dietary overlap. Moreover, we also check differences in krill length among penguin individuals and we did not find any statistically significant differences. We also found plastic debris in penguin stomachs during both summers.

Appendicularians are important but remain poorly studied groups of zooplankton in polar regions. The present research is based on samples collected in Admiralty Bay (King George Island) during a year-long period. Six larvacean species were noted, among which Fritillaria borealis and Oikopleura gaussica were found to be the most numerous, while the other species were relatively rare. Fritillaria borealis was a dominant part of the late summer (warm water) community, while O. gaussica had the highest presence in the winter (cold water) community. The abundance of appendicularians recorded in the bay was less numerous than that described by other authors. The most important factors influencing annual changes in the larvaceans in the bay was season, but only in the case of the two species. These facts were probably linked to the very dynamic changes in the abiotic conditions in the fjord, and the influx of specific masses of water.

Appendicularians are one of the most common animals found within zooplankton assemblages. They play a very important role as filter feeders but are, unfortunately, inconsistently reported in the Antarctic literature. The present paper attempts to describe the zonal diversity of appendicularians and the main environmental factors influencing their communities in the Drake Passage. Samples were collected during Antarctic summer in 2009–2010. A total of eight species of larvaceans were identified. Fritillaria borealis was the species found in the highest numbers in almost the entire studied area, and was observed at all sampling stations. The distributions of other taxa were limited to specific hydrological zones and hydrological conditions. F. fraudax and Oikopleura gaussica were typical of the areas between the Polar Front and the Subantarctic Front zones, and their distributions were significantly correlated with temperature and salinity, likely making them good indicator species. The F. fusiformis distribution was strictly related to South American waters. In summary, temperature was the strongest environmental factor influencing the larvacean community structure in the Drake Passage, and we also found that testing environmental factors on larvaceans as a whole group did not give entirely reliable results.

In the krill-based ecosystem of the Antarctic, fluctuations in the distribution and abundance of Euphausia superba may have strong impacts on predator populations; thus, it is crucial to observe the feeding ecology of Antarctic predators, especially in the light of climate change and increasing human pressure. We determined the composition of euphausiid species in diet samples collected from Adélie (Pygoscelis adeliae), chinstrap (Pygoscelis antarcticus) and gentoo (Pygoscelis papua) penguins on King George Island (South Shetlands Islands) during a breeding season. For all three penguin species, euphausiids (mainly E. superba) represented almost the entirety of researched stomach samples (i.e. 99.9% in the case of Adélie and chinstrap penguins), while gentoo penguins also proved to feed on fish (99.4% krill; 0.5% fish). Analysed material differed in the size of eaten E. superba specimens, with the smallest crustaceans consumed by Adélie penguins. Furthermore, we found differences in the ratio of consumed krill and krill size. Such disparities may be a result of sex-based differences and slight differences in feeding areas between the birds. Additionally, we noted some fragments of plastic debris in the investigated penguin diet samples.