Spatial Distribution Patterns of Appendicularians in the Drake Passage: Potential Indicators of Water Masses?

Abstract

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.

Appendicularia (Tunicata) in an Antarctic Glacial Fjord–Chaotic Fjordic Structure Community or Good Indicators of Oceanic Water Masses?

“…Other species, i.e., F. antarctica, F. aberrans, O. fusiformis and O. parva had not been previously noted in the investigated region or in the entire area of the Antarctic Peninsula. However, we observed the presence of these species in the Drake Passage [16]. The larvacean abundance recorded in this study was higher than that found by Freire et al [27], i.e., 1200 ind.…”

“…Similar observations were made by Tsujimoto et al [20]. Daponte and Esnal [21] validated the Antarctic species of the "Oikopleura gaussica group" in the regions near South Georgia and in the Bellingshausen Sea, and Kalarus and Panasiuk [16] researched the zonal distribution of these animals in the Drake Passage. Most other studies conducted in recent decades have examined entire zooplankton communities and have examined appendicularians only as a single group or by focusing on the dominant species [22][23][24][25].…”

“…In addition, larvaceans can play a crucial role in the diet of copepods, fish or jellyfish [60]. Nonetheless, these animals are still very poorly studied, especially in polar regions, which is often due to the use of inadequate plankton nets, as well as difficulties in taxonomic identification [16,61]. Considering the above facts, the results of the research presented in this paper may offer a significant contribution to a better understanding of this group of animals in polar fjord environments, where the effects of ongoing climate change are most clearly and readily visible [28,35,62].…”

“…Larvaceans are not well studied by using in situ collection methods, e.g., plankton nets or bottles [14]. This is mainly due to their patchy distribution [15] and fragility, which makes them very difficult to identify [14,16] and leads to underestimations of their abundance and biomass [17,18]. In the Southern Ocean area, including the Antarctic, studies on larvacean taxonomy, distribution and abundance are very rare.…”

“…Gelatinous zooplankton, which includes appendicularians, may play an important role in the functioning of pelagic food webs and biogeochemical cycles due to their important role in the circulation of organic matter [8,16,[29][30][31][32]. Increased melting of glaciers has been observed in Antarctic shelf regions in recent decades [28,[33][34][35].…”