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Tintinnids (Ciliophora) are important microzooplankton grazers. In the Southern Ocean, they are found in the Antarctic Zone, Polar Front and Subantarctic Zone. The Antarctic Zone encompasses large gyres (Weddell Gyre and Ross Gyre) and the Antarctic Slope Current around the continent. The influence of these water masses on tintinnid communities has not been studied. This study investigated the tintinnid community structure in the Weddell and Cosmonaut seas in the summer of 2022. In the Weddell Gyre, tintinnid abundance was significantly lower in the interior than at the fronts. The dominant species differed between the east and west fronts: the proportion of Codonellopsis gaussi was high at the west front, whilst Laackmanniella naviculaefera, Salpingella sp. and Salpingella faurei showed high abundances at the east front. Tintinnid communities varied from inshore to offshore of the Cosmonaut Sea, possibly because of the influence from the Antarctic Slope Current and Antarctic Circumpolar Current. The Antarctic Slope Current was characterized by the occurrence of Cymatocylis drygalskii, whilst the Antarctic Circumpolar Current was characterized by Codonellopsis glacialis, Cymatocylis convallaria and Cy. calyciformis. We proposed that Cy. drygalskii can be used as an indicator of the Antarctic Slope Current. Moreover, we classify polymorphic C. gaussi into three types, in accordance with their loricae, and report their distribution characteristics in water masses. Our results contribute to a better understanding of tintinnid horizontal distribution in different parts of the Weddell Gyre and water masses and serve as a baseline for future studies of pelagic community responses to climate change in the Southern Ocean. [ABSTRACT FROM AUTHOR]

Tintinnid ciliates are an important link in marine food webs as they feed on phytoplankton and bacteria while providing nutrients to higher trophic levels. Tintinnids are known to agglutinate mineral particles or dead biogenic material such as diatom frustules to their shell-like housing (lorica), however, reasons for this agglutination remain questioned. We report on our observation of agglomeration of the living diatoms Fragilariopsis curta, F. cylindrus, F. pseudonana and F. rhombica to loricae of the Antarctic tintinnid ciliates Laackmanniella naviculaefera and Codonellopsis gaussi. These unusual associations between living diatoms and tintinnids were exclusively observed south of 63.59°S. We discuss the significance of our new finding and generate hypotheses to be tested by future research. It remains unclear where these living diatom-tintinnid associations are initially formed (in or near sea ice or also further north when abundances of L. naviculaefera, C. gaussi, F. curta, F. cylindrus, F. pseudonana and F. rhombica happen to be relatively high); who the beneficiary is in this association; what the exact benefits are; and how they might influence the Southern Ocean carbon cycle. Nevertheless, our observation provides a key step forward towards illuminating the largely unknown ecology of two Southern Ocean-endemic tintinnid species. [ABSTRACT FROM AUTHOR]

A bloom of loricate choanoflagellates was recorded for the first time in the Ross Sea polynya during the austral summer 2017. Both individual cells and uncommon large‐size colonies (200 μm length) represent the 42–55% of the total plankton community (i.e. specimens from 5 to 150 μm length). Choanoflagellates serve as a link between low and mid trophic levels since they prey on bacteria and in turn are ingested by zooplankton. This twofold role and the unusual abundance recorded in the Antarctic ecosystem may have relevant but still unknown effects on food web structure and dynamics in that area. [ABSTRACT FROM AUTHOR]

For the Ross Sea, the only Marine Protected Area in Antarctica, available data on the tintinnid ciliates of the marine microzooplankton are mostly limited to nearshore waters near Terra Nova Bay or the vicinity of the McMurdo Sound. Here, we report results from a geographically extensive sampling across the Ross Sea conducted in December 2020. Material from plankton net tows (20 µm mesh), made at 38 stations spanning over 30° of latitude, was examined. We found 11 tintinnid species of varying commonality or rarity, many showing considerable morphological variability that is here documented. We found four forms that had not been previously reported from the Ross Sea. Based on our findings and previous reports, we assembled a species accumulation curve showing the growth in the inventory of tintinnid species recorded from the Ross Sea as a function of sampling effort and time since 1983. Extrapolation of the species accumulation curve, derived from sampling over the last 37 years, indicates that continued sampling will likely provide new species records, suggesting that the Ross Sea is under-sampled at present. This complicates efforts to detect temporal changes in species compositions, at least with regard to tintinnid ciliates. Comparing species accumulation curves for the Ross Sea and the relatively well-studied Weddell Sea, it appears that the Ross Sea may be more species-rich. [ABSTRACT FROM AUTHOR]

The Ross Sea is characterized by a series of subsystems with different characteristics making it an extremely productive area. To understand whether species composition and functional traits of the plankton community can be used as biological tracers, we have analyzed the composition of phytoplankton and microzooplankton, and their potential relationships, in two different polynyas of the Ross Sea during the austral summer 2017. Sampling activities were carried out near Terra Nova Bay, between Cape Washington and the northern shore of the Drygalski Ice Tongue, and in the South-Central Ross Sea. We investigated the phytoplankton and microzooplankton structure using the phytoplankton body size classes and the tintinnids lorica oral diameter as functional traits, speculating on the relationship between the two plankton communities and their use as biological indicators in a changing Southern Ocean. Our data showed significant differences in terms of plankton composition and related functional traits between the two areas, suggesting the existence of distinct ecological dynamics despite the similar total carbon content. In Terra Nova Bay, heterotrophic dinoflagellates were the most abundant microzooplankton, in association with a large phytoplankton biomass mainly represented by diatoms and nano- and micro-phytoplankton. Tintinnids with large lorica oral diameters were abundant in Central Ross Sea, where phytoplankton was dominated by Phaeocystis antarctica and by the micro size class. Among microzooplankton , Protoperidinium defectum, P. applanatum and P. incertum were the most abundant dinoflagellates species, while Codonellopsis gaussi, C. gaussi forma cylindroconica, Laackmanniella prolongata and Cymatocylis drygalskii were the most abundant tintinnids. The phytoplankton was dominated by diatoms Pseudo-nitzschia subcurvata , Fragilariopsis cylindrus , F. curta and by the haptophyte P. antarctica. Our data indicate that beyond physical and chemical features defining distinct sectors of the Ross Sea, both species composition and functional traits of phytoplankton and microzooplankton represent a valid monitoring tool, especially with the ongoing global warming and its effects on Antarctic food webs. [ABSTRACT FROM AUTHOR]

During the next century, the Ross Sea is expected to reduce summer sea ice concentrations and consolidate the presence of shallower mixed layers. Those changes may have a potentially catastrophic effect on the zooplankton community. To investigate if Ross Sea's past physical and biological condition changes have affected the tintinnids population, and to understand future tintinnids' role in the plankton community, seawater samples collected in the Terra Nova Bay polynya area during eleven summer expeditions from 1988 to 2017 were analyzed. During this time period, tintinnids' abundance ranged from 0 to a maximum of 4980 indL−1. The most representative species were Cymatocylis drygalskii, Codonellopsis gaussi and Laackmanniella naviculifaera. These species can be considered keystone species and they can be used to monitor the long-term evolution of the whole microzooplankton community in Terra Nova Bay polynya. The tintinnids' abundance presented minimum values in 2001 after which there has been a significant increase in the most recent years. The increase in tintinnids' abundance showed a positive correlation with the temperature, while salinity did not indicate any relationship. In particular, the majority of genera detected showed a significant temperature correlation, with the only exception of Amphorides genus, recorded for the first time in the study area. Our results provide new insights into the spatial distribution and structure of the Antarctic tintinnids community. [ABSTRACT FROM AUTHOR]

Twenty-eight littoral ciliates including one new genus and seven new species were collected from King George Island, Antarctica. Among them, 21 species are morphologically and taxonomically described in this paper: Bickella antarctica nov. gen., nov. spec., Chlamydonella apoprostomata nov. spec., Condylostoma spatiosum Ozaki and Yagiu in Yagiu, 1944, Diophrys scutum Dujardin, 1842, Diophrys aff. oligothrix Borror, 1965, Diophrys appendiculata (Ehrenberg, 1838), Euplotes balteatus (Dujardin, 1841), Euplotes dragescoi nov. spec., Euplotes petzi nov. spec., Euplotes rariseta Curds et al., 1974, Euplotes vannus (Mueller, 1786), Hartmannula angustipilosa Deroux and Dragesco, 1968, Hemigastrostyla szaboi Wilbert and Song, 2005, Holosticha antarctica nov. spec., Holosticha apodiademata nov. spec., Holosticha diademata (Rees, 1884), Litonotus sp., Metaurostylopsis marina (Kahl, 1932), Pleuronema coronatum Kent, 1881, Pseudocohnilembus persalinus Evans and Thompson, 1964, Urotricha antarctica nov. spec. The new genus, Bickella nov. gen., is a free-swimming folliculinid having typical Folliculina morphology except for the absence of lorica. [ABSTRACT FROM AUTHOR]

Endolithic microorganisms, ranging from microeukaryotes to bacteria and archaea, live within the cracks and crevices of rocks. Deception Island in Antarctica constitutes an extreme environment in which endoliths face environmental threats such as intense cold, lack of light in winter, high solar radiation in summer, and heat emitted as the result of volcanic eruptions. In addition, the endolithic biome is considered the harshest one on Earth, since it suffers added threats such as dryness or lack of nutrients. Even so, samples from this hostile environment, collected at various points throughout the island, hosted diverse and numerous microorganisms such as bacteria, fungi, diatoms, ciliates, flagellates and unicellular algae. These endoliths were first identified by Scanning Electron Microscopy (SEM). To understand the molecular mechanisms of adaptation of these endoliths to their environment, genomics techniques were used, and prokaryotic and eukaryotic microorganisms were identified by metabarcoding, sequencing the V3–V4 and V4–V5 regions of the 16S and 18S rRNA genes, respectively. Subsequently, the sequences were analyzed by bioinformatic methods that allow their metabolism to be deduced from the taxonomy. The results obtained concluded that some of these microorganisms have activated the biosynthesis routes of pigments such as prodigiosin or flavonoids. These adaptation studies also revealed that microorganisms defend themselves against environmental toxins by activating metabolic pathways for the degradation of compounds such as ethylbenzene, xylene and dioxins and for the biosynthesis of antioxidant molecules such as glutathione. Finally, these Antarctic endolithic microorganisms are of great interest in astrobiology since endolithic settings are environmentally analogous to the primitive Earth or the surfaces of extraterrestrial bodies. [ABSTRACT FROM AUTHOR]

Understanding the spatial and temporal distribution of marine plankton is essential to detect trends and predict their response to climate change. Seasonality, fronts, and dispersion by currents and eddies condition the distribution from micro- to macroscales. Here, we address comparatively the structure of planktonic protist communities and the assemblages of tintinnid and diatom species in subsurface waters of the western Weddell Sea during February 2005. We analyze to which extent the biogeographic patterns based on different hierarchical levels and ecological variables reveal spatial similarities, and how these patterns reflect frontal processes. Abundance and carbon biomass were estimated for eight groups of protists and for diatom and tintinnid taxa in relation with chlorophyll-a and environmental variables. The Weddell Sea boosted the proliferation of flagellated cells. Diatoms showed an unclear distribution trend and, with the exception of a few species, those primarily contributing to abundance were clearly others than those primarily contributing to biomass. Biogeographic patterns differed according to hierarchical levels and the ecological variables considered. All levels explored showed an uneven distribution in most of the area except for the range of latitudes between ~67°S and 70°S, where the trends were notably homogeneous. Three rich carbon biomass patches were found, two of them in shelf waters (South Orkney Islands and Filchner Trough) and a major one in the Marginal Ice Zone. Based on a disruption of species distribution, the Antarctic Slope Front-Antarctic Slope Current system is suggested to be located at 73.35°S. A refinement of previous biogeographic schemes was provided. [ABSTRACT FROM AUTHOR]

The present study has revealed morphological differences of species assigned to the acanthoecid choanoflagellate genus Stephanoeca based on the relative position of transverse and longitudinal costae in the anterior lorica chamber. A detailed re-examination of published material of S. paucicostata Tong et al., 1998 combined with new data has shown that the species characteristic, a double transverse costa, is clearly located outside of the longitudinal costae excluding this taxon from an affiliation to Stephanoeca sensu stricto, confirmed also by molecular data of a clonal culture from Kos Islands, Greece. Two specimens of S. paucicostata with only a single, interiorly positioned transverse costa, namely from Marchant et al. (1987) and Nitsche et al. (2011) were erroneously assigned to this species. These facts have here led to the establishment of a new genus, Pseudostephanoeca with its type species P. paucicostata, and the description of S. ellisfiordensis for the two specimens mentioned above, corroborated by new material from Antarctica. In addition, two specimens previously assigned to S. cupula have been shown to share the core characteristic of Pseudostephanoeca with exteriorly positioned transverse elements. This has led to the description of the new species P. quasicupula including also new material from Iceland. [ABSTRACT FROM AUTHOR]

Temporal variations in the microbial community structure of plankton, which is composed of autotrophic and heterotrophic pico-, nano- and microplankton, were investigated during the austral summer of 2005/2006 under fast ice near Syowa Station, eastern Antarctica. Autotrophic algal populations were composed almost entirely of diatoms followed by phytoflagellates such as autotrophic dinoflagellates and cryptophytes. Among the microbial community, heterotrophic biomass was dominated by heterotrophic dinoflagellates and naked ciliates and finally exceeded autotrophic biomass. Qualitative microscopic analysis revealed that heterotrophic dinoflagellates were ingesting large number of diatoms. Synchronizing fluctuation of naked ciliates with phytoflagellates suggested a predator–prey relationship between them. Our results suggest that the pelagic food webs under the extensive ice-covered areas in coastal Antarctic regions are not short but complex. [ABSTRACT FROM AUTHOR]

Aim There is no previous direct evidence for the occurrence of lacustrine refuges for invertebrate fauna in Antarctica spanning the Last Glacial Maximum (LGM). In the absence of verified LGM lacustrine refuges many species are believed to result from Holocene dispersal from sub-Antarctic islands and continents further north. If freshwater lake environments were present throughout the LGM, extant freshwater species may have been associated with Antarctica prior to this glacial period. This study looked at faunal microfossils in a sediment core from an Antarctic freshwater lake. This lake is unusual in that, unlike most Antarctic lakes, the sediment record extends to c. 130,000 yrbp, i.e. prior to the LGM. Location Lake Reid, Larsemann Hills, East Antarctica (76°23′ E; 69°23′ S). Methods Palaeofaunal communities in Lake Reid were identified through examination of faunal microfossils in a sediment core that extended to c. 130,000 yrbp. Results Ephippia and mandibles from the cladoceran Daphniopsis studeri and loricae of the rotifer Notholca sp. were found at all depths in the sediment, indicating that these two species have been present in the lake for up to 130,000 years. Copepod mandibles were also present in the older section of the core, yet were absent from the most recent sediments, indicating extinction of this species from Lake Reid during the LGM. Main conclusion The presence of D. studeri and Notholca sp. microfossils throughout the entire Lake Reid core is the first direct evidence of a glacial lacustrine refugium for invertebrate animals in Antarctica, and indicates the presence of a relict fauna on the Antarctic continent. [ABSTRACT FROM AUTHOR]

Twenty-six marine benthic ciliates including seven new species were isolated from King George Island, Antarctic. The morphology and taxonomy of 19 of them are described in the present paper: Aegyriana paroliva , Amphileptus sp., Amphisiella antarctica nov. spec., Condylostoma cf. magnum , Dysteria parovalis nov. spec., Folliculina ? sp., Hartmannula cf. angustipilosa , Hemigastrostyla szaboi nov. spec., Heterostentor coeruleus , Holosticha sp., Intranstylum antarcticum nov. spec., Metaurostylopsis rubra , Orthodonella shenae , Philasterides cf. armatalis , Pithites pelagicus nov. spec., Pleuronema coronatum , Strombidium apolatum nov. spec., Telotrochidium sp., and Thigmokeronopsis magna nov. spec. Based on the new observations, an improved diagnosis for the genus Aegyriana is suggested: dorsoventrally flattened Dysteriidae with tail-shaped podite, which is positioned subcaudally in a glabrous region within somatic kineties; oral structure in two parts: ca three close-set fragments on right and one preoral kinety on left; left postoral kineties shortened posteriorly and continuous with right ones, leaving no median gap or suture; cytopharyngeal rods dominant. According to the new understanding and information obtained, a refined diagnosis of the genus Hemigastrostyla is also suggested: hypotrich with Oxytricha -like cirral pattern; eight to ten frontal (including one buccal) and five to seven ventral cirri; five transverse and three caudal cirri; no right-lateral anlagen of dorsal kineties occurring and the old adoral zone will be partly replaced by newly formed structure during morphogenesis; dorsal cilia located in small pits, fibre system highly developed; marine habitat. [ABSTRACT FROM AUTHOR]

Choanoflagellates are thought to be an important component of oceanic microbial food webs, but little quantitative data exists on their abundance,, distribution, or relationship to potential food sources. In an Antarctic ice edge zone (northern Weddell Sea, March 1986), choanoflagellate abundance varied over two orders of magnitude in the upper 100 m. The lowest abundances were recorded at the bottom of the water column under ice cover and the highest abundances occurred in the upper 30 m of open water. Species that were predominantly in colonies dominated the open-water samples. Abundances of total choanoflagellates and some individual species were correlated with primary and secondary biomass and production, indicating a response to gradients in potential food sources. This suggests that choanoflagellates are tightly coupled with their food sources and supports the contention that they may an important link between bacteria-sized particles and metazoan grazers. [ABSTRACT FROM AUTHOR]

The trophic structure of the midwater ecosystem of McMurdo Sound, Ross Sea, Antarctica in February, 1983 was examined through diet analysis of 35 species of zooplankton and micronekton. Ten feeding groups were suggested through cluster analysis. The two largest clusters consisted of small-particle grazers and omnivore generalists; the eight remaining clusters were of carnivores specializing on one or several types of metazoan prey. Diet composition often shifted with ontogeny and though exceptions occurred, diet diversity usually increased either during early growth or throughout development. Comparison with a krill-dominated area along the Antarctic Penisula (Croker Passage) indicated that species common to the two areas occupied approximately the same trophic position. Biomass in McMurdo Sound was much lower than in Croker Passage and large-sized particle grazers such as krill and salps were trophically less dominant in McMurdo Sound. Krill in Croker Passage in the fall entered the midwater food web primarily as detritus (molts); in McMurdo Sound it was mostly as live furcilia. Sampling in McMurdo Sound was during a plankton bloom and calculations of grazing rates suggest that much of the primary production settled through the water column uneaten. [ABSTRACT FROM AUTHOR]

A significant amount of the primary production in the Southern Ocean and other ice-covered oceans takes place in localized ice edge plankton blooms. The dynamics of these blooms appear to be closely related to seasonal melting of sea ice. Algal cells released from the ice are a possible source of ice edge planktonic assemblages, but evidence for this "seeding" has been equivocal. We compared algal assemblages in ice and water in the Weddell Sea during the austral spring of 1983 at a receding ice edge with a well-developed ice edge bloom. The high degree of similarity between ice and water column assemblages, the spatial and temporal patterns in the distribution and abundances of species, and preliminary evidence for the viability and growth of ice-associated species provide evidence for seeding from sea ice of some species in Antarctica. [ABSTRACT FROM AUTHOR]