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The trophic ecology of several cryonotothenioid species has been well studied, but scarcely on the juvenile fraction of their populations. Particularly, till date the inter-annual variation of the diet composition and feeding habits of these young notothenioid stages has not been explored. Herein, we analysed the trophic ecology of 755 specimens of the species Notothenia rossii, Notothenia coriiceps, Nototheniops nudifrons, Trematomus newnesi and Harpagifer antarcticus, collected in the inshore waters of Potter Cove, South Shetlands Islands, during four consecutive sampling periods from 2008 to 2012. The stomach-content analysis using the IRI % and the Amundsen et al. (1996) methods provided data on feeding habits and trophic niche breadth. Our results indicate that the species are demersal and benthophagous, have a generalized type of feeding strategy and prey chiefly on demersal–benthic amphipods (mainly genus Gondogeneia and Oradarea), and on other epibenthic invertebrates associated with macroalgal beds. Significant differences were observed in the diet of all species between sampling periods, and ontogenetically, only in N. rossii and T. newnesi. According to the estimated trophic levels, the juvenile cryonotothenioids were identified as secondary consumers. Ambush feeding was the predominant feeding behaviour in all species, and in N. rossii and N. coriiceps, also grazing. Likewise, these two fish species exhibited a wider diet diversity than the other notothenioids. Using literature information on the trophic ecology of the late juvenile–adult stages of the same species at Potter Cove, we identified differences and likenesses with our results on the early juvenile–juvenile fraction of the fish community. This study highlights the key role of nearshore areas in the cryonotothenioids life cycle. [ABSTRACT FROM AUTHOR]

The spatio-temporal delimitation of fish reproduction is essential for the appropriate management and conservation strategies in populations. Assessing this feature in Antarctic Ichthyology is particularly difficult because harsh environmental conditions limit sample collection. This study shows how physiology can contribute compelling evidence to understand reproduction in Antarctic fish using the notothenioid Lepidonotothen nudifrons as a model species. Sampling included 121 specimens caught at Potter Cove (PC), South Shetland Islands (SSI), from November to late March of 2016–2018. Gonadal macroscopic and histologic features are reported. Oocyte growth and change in testosterone and estradiol plasma levels throughout the ovarian growth of L. nudifrons adult females is provided. In March, females (n = 17) attained gonado-somatic index of 13–20% (16.73 ± 4.20), total fecundity of 2196–4652 oocytes/female, the leading clutch oocytes measured 1.7–2.1 mm, and males (n = 5) showed spermatozoids in their testicles. The leading clutch growth was significantly associated with photoperiod, with no diameter variation until the summer solstice, when it began to grow linearly with an estimated rate of 0.01 mm/day. Testosterone and estradiol increased together with the oocyte growing throughout the analysed months, with a higher rate of increase during March. The reproductive effort data, and especially the significant plasma level increase in both sex steroids observed in March, suggest that (1) females were at a late vitellogenesis stage, just prior to the oocyte final maturation, and thus L. nudifrons spawning period might begin in March at SSI; (2) PC is likely a spawning site for L. nudifrons, which indicates that nearshore areas are spawning grounds for some notothenioids. [ABSTRACT FROM AUTHOR]

Although many notothenioid fishes are primarily carnivorous, some species consistently feed on macroalgae and are therefore omnivorous. Among fish, the degree of herbivory is usually reflected in the morphology of the gastrointestinal system especially intestine length. We examined a large number of juvenile and adult specimens of nine sympatric notothenioid species collected sequentially over eight summer seasons at Potter Cove, South Shetland Islands. We provide relative intestine lengths (RIL), distinct proportions of algae and animal prey in the diets (W%), and numbers of pyloric caeca for all species. The sister species Notothenia coriiceps (NOC) and N. rossii (NOR) evidenced significantly different intestinal growth over ontogeny and ate distinctly different proportions of algae and animal prey. We establish a ranking of the degree of herbivory for the fish species in the local ecosystem, and this was found to be related to their distinct feeding types and strategies. There is a correspondence between intestine length/RILs and degree of herbivory in six of the nine species analysed but no clear association between the number of pyloric caeca and degree of omnivory or carnivory. Compared to other teleosts, our results, and those in the literature, indicate modest divergence in notothenioids that include a phylogenetic decrease in the number of pyloric caeca, from 6 to 7 in most nototheniids to 2–3 in channichthyids, and a 1.8-fold difference in average relative intestine lengths which are most frequently 50–70% of body length and never exceed body length. This is consistent with the unspecialized gastrointestinal morphology that reflects the dietary and ecological plasticity of many notothenioids, exemplified by the high degree of omnivory in species such as NOC and NOR. [ABSTRACT FROM AUTHOR]

Coastal areas of the West Antarctic Peninsula (WAP) constitute a rich and biodiverse marine zone. Despite these ecosystems being supported by the microorganism's activity, the structure of microbial communities is insufficiently studied. As WAP is the area most affected by global warming worldwide, the increased glacier melting caused by the global warming and the consequent increase of the water runoff could be deeply affecting these microbial communities. To advance knowledge about the structure of microbial communities and its response to the environmental factors, a full-year study of marine bacterioplankton was conducted at Potter Cove, Antarctica. Multivariate analysis based on denaturing gradient gel electrophoresis (DGGE) and environmental data revealed a seasonal pattern in the structure of the bacterioplankton community, with spring–summer clustering separately from autumn–winter samples. Salinity, temperature and particulated matter were the main environmental driving forces. Based on the seasonal patterns, five bacterial clone libraries were performed from three sampling sites (E1, inner cove; E2, outer cove; and E3, mouth of a creek). Phylogenetic analysis of libraries generated 301 operational taxonomic units (OTUs), revealing the enormous richness and high diversity of these communities. Proteobacteria (68%), Bacteroidetes (20%) and Actinobacteria (8%) were the most represented phyla. During summer, bacterial community from E1 resembled that observed in E3, whereas during winter it resembled the E2 community. Results evidenced the influence of glacial meltwater input and showed the high variability of the bacterioplankton from inner cove. This study contributes to the better understanding of the structure of the Potter Cove marine ecosystems and could be reflecting the behavior of other similar ecosystems from WAP. [ABSTRACT FROM AUTHOR]

The knowledge of the reproductive biology of blackfin icefish Chaenocephalus aceratus in the southern Scotia Arc has been based, primarily on macroscopic observations of its maturation cycle, and lately, on histological analysis of ovaries in developing phase exclusively. Our study on reproduction of C. aceratus collected at Potter Cove (PC), South Shetland Islands (SSI), highlights the importance of histologic techniques to validate gonadal macroscopic maturity stages to estimate reliable reproductive parameters, in this work obtained from gravid females. Gonado-somatic index (GSI) of 7–21% (13.50 ± 4.20, n = 21), mature oocytes of 2.5–4.0 mm and total fecundity (TF) of 7372–17,212 oocytes/female (12,466 ± 2911, n = 13) were estimated. Although it is known that variations in the reproductive parameters of C. aceratus between areas of the Scotia Arc are linked to local environmental factors (i.e. hydrographic or biotic), we found close agreement between our results from PC and recent literature data for the South Georgia population, which also arose from the analysis of gravid females. Differently, lower GSIs and oocyte sizes, and higher TF reported lately for the offshore SSI population might be at least partially explained by the fact that these parameters were estimated from the analysis of developing ovaries. Based on our sampling and reproductive effort data, we suggest: (1) the spawning period of C. aceratus at the SSI might be more extended than previous belief, starting from late December until June; (2) the sheltered waters of PC might be a spawning site for C. aceratus, which highlights the role of nearshore areas as spawning grounds of notothenioids. [ABSTRACT FROM AUTHOR]

Studies on feeding selectivity in Antarctic fish with comparison between diet organisms and those available in the wild are scarce. We explored this issue in Notothenia rossii (NOR) and N. coriiceps (NOC) at Potter Cove in summer 2016 to test: (1) their preference among different benthic groups, primarily species of algae and amphipods and (2) differences between these nototheniids given their distinct morphology but their known similar general ecology in the fjords. The methodology included a comparative analysis of benthic organisms identified in the stomachs and those collected on macroalgal beds (Ivlev Index). Benthic amphipods, mainly Gondogeneia antarctica and Cheirimedon femoratus, followed by macroalgae, mainly Palmaria decipiens and Desmarestia spp., were the most important and frequent dietary items (IRI%) for both nototheniids. However, NOC was more herbivorous and fed more intensively on a wider diversity of benthic organisms such as certain algal-associated groups like gastropods and bivalves, whereas NOR fed on a greater proportion of epibenthic amphipods and other epibenthic prey. Although in the last three decades the physiognomy of the inner cove has been changed due to the retreat of the Fourcade Glacier, at our sampling site in the outer cove the abundance and vertical distribution of macroalgae did not show substantial changes compared with those reported in the literature in 1994-1996. Temporal differences in the feeding selectivity of NOC on amphipod species, between contemporary and historical samples, may be explained by variations in the assemblage of the algal-associated epifauna. We suggest factors that may have produced these changes. [ABSTRACT FROM AUTHOR]

Several fish species of the suborder Notothenioidei (Perciformes) predominate in the Antarctic Convergence Zone; nevertheless, reproductive studies are scarce due to difficulties on regular sampling. This study takes the research area of reproductive biology of notothenioids to a new level by providing, for the first time, data on sex hormone and vitellogenin detection in the blood of females of Notothenia rossii and N. coriiceps and correlates this data with morphological maturity indices as well as ovarian histology. Fish were captured during the Antarctic summer at Potter Cove, 25 de Mayo (King George) Island, and blood and ovary were collected. Histological analysis revealed that females of both fish possess group synchronous ovarian development with two distinct clutches of oocytes: a more advanced batch of vitellogenic oocytes ready for spawning and a second batch of previtellogenic oocytes for the next spawning event. Since liver vitellogenin synthesis is stimulated by estradiol produced by the ovaries, gonadal development, estradiol levels, and vitellogenin showed that both species were at a more advanced stage of maturation in March than in January. On the other hand and irrespectively of the month, gonadosomatic index and plasma estradiol levels of N. coriiceps were higher than those of N. rossii. Furthermore, females of N. coriiceps showed an advanced stage of vitellogenesis or were ready for spawn, contrary to results of previous studies. Our results indicate the successful use of gonadal morphology, estradiol, and vitellogenin detection for the estimation of sexual maturity stage of female adults. [ABSTRACT FROM AUTHOR]

Trematomus newnesi is a common inshore species with a circum-Antarctic distribution. It provides the only known example of phenotypic plasticity in Antarctic notothenioid fish, existing as populations of typical, large mouth and intermediate morphs that can be difficult to identify. Using specimens from both Potter Cove, King George/25 de Mayo Island, and from McMurdo Sound, we found that the morphometric measurements gape width/head length (HL), upper jaw length/HL and, to a lesser extent, orbit diameter/HL reliably separated the morphs. For use in a key, we converted the ratios into the qualitative characters head shape, head width and upper jaw length relative to middle of the eye. To increase the reliability of the key, we also assessed intra-morph variability in these characters. The key is supplemented with colour photographs illustrating the distinctive features for separation of the morphs. We discovered that, in the case of the specimens from Potter Cove, each morph had a distinct pattern of colouration: typical-trunk blotched, with yellow or orange-brown predominating especially on pectoral and caudal fins; large mouth-trunk blotched, with green predominating especially in pectoral and opercular regions; and intermediate-trunk less blotched, with homogeneous dark brown-grey on trunk, pectoral and caudal fins. We also discuss the ecological implications of colour in the morphs. [ABSTRACT FROM AUTHOR]