Spatial and temporal variations in the diet of nototheniid fish in McMurdo Sound,Antarctica

Specimens of 4 species of Antarctic fish were captured at different locations in McMurdo Sound during the early summer, and for one species also during late winter. Stomach contents were analysed to examine resource utilization across species, at different locations, and between late winter and early summer. The results are consistent with earlier findings that there is a gradation in resource utilization across these species.T. pennelli andT. bernacchii tend to take predominantly benthic crawling prey, though they also take prey from the water column.T. hansoni andT. nicolai tend to take more prey from the water column, a tendency which can be related to the visual feeding vector of these species. Substantial differences in diet for the same species captured in different locations indicated significant flexibility in prey selection which would allow utilization of spatial and temporal fluctuations in prey availability. Successful feeding byT. bernacchii in late winter is a further indication that this species can feed non-visually and supports the notion that non-visual feeding mechanisms are likely to be of importance in the biology of the Antarctic fishes.deceased     

Proximate composition and energy density of nototheniid and myctophid fish in McMurdo Sound and the Ross Sea,Antarctica

Nototheniid and myctophid fish are primary prey for marine piscivores, yet little is known about their nutritional value. In this study, we characterized the proximate composition [PC: water, fat (neutral lipids), crude protein (CP) and ash] and energy density (ED; kJ g⁻¹) of fifteen fish species from McMurdo Sound and the Ross Sea, Antarctica. We assayed the entire fish for all species except for the large Antarctic toothfish, Dissostichus mawsoni (muscle tissue only). On a wet mass basis (WM), fish were variable in composition: moisture content ranged from 64.9 to 87.3% WM, fat from 0.5 to 17.4% WM, CP from 7.7 to 16.7% WM, ash from 11.2 to 21.0% FFDM (fat-free dry mass), and ED from 2.9 to 10.3 kJ g⁻¹. Myctophids and pelagic nototheniids such as Pleuragramma antarcticum and D. mawsoni were high in fat content (7–17% WM), while a bathylagid and benthic nototheniids including most Trematomus spp. and Lepidonotothen squamifrons were low in fat (0.5–4% WM). The epibenthic Trematomus species (T. eulepidotus and T. lepidorhinus) were intermediate. Energy density tracked fat content, with highest values in myctophids and pelagic nototheniids. The variation in nutrient and energy density confirms that prey composition must be taken into account when modelling energy and nutrient fluxes within the Antarctic ecosystem. Further analyses of prey collected over a number of different locations and seasons are needed in order to determine how the nutritional value of certain species might affect annual or decadal variation in reproductive success or population size of top predators.     

Mesozooplankton beneath the summer sea ice in McMurdo Sound,Antarctica: abundance,species composition,and DMSP content

The summer Phaeocystis antarctica bloom increases under-ice phytoplankton biomass in McMurdo Sound, Antarctica. The magnitude of mesozooplankton grazing on this bloom is unknown, and determines whether this production is available to the pelagic food web. We measured mesozooplankton abundance and body content of dimethylsulfoniopropionate (DMSP) during the McMurdo Sound austral summer (2006 and 2006–2007). Abundance varied from 20 to 4,500 ind. m⁻³ (biomass 0.02–274.0 mg C m⁻³), with peaks in mid-December and late-January/February. Abundance was higher but total zooplankton biomass lower in our study compared to previous reports. Copepods and the pteropod Limacina helicina dominated the zooplankton in both abundance and biomass. DMSP was detected in all zooplankton groups, with highest concentrations in copepod nauplii and L. helicina (95 and 54 nmol mg⁻¹ body C, respectively). Experiments suggested that L. helicina obtains DMSP by directly grazing on P. antarctica, which often accumulates to high biomass under the summer sea ice in McMurdo Sound.     

Distribution patterns of benthic microalgal standing stock at McMurdo Sound,Antarctica

Summary During the austral summer of 1975–76 and winter of 1977 benthic and water column chlorophyll a and phaeopigments were measured at several sites along the east and west sides of McMurdo Sound, Antarctica. Estimates of in situ primary productivity were made at some McMurdo Sound locations. Additionally, water column samples were collected at 5 stations in the Ross Sea during January, 1976. Standing stock data are analyzed to identify seasonal and spatial patterns. Variability in algal standing stock was related to ambient light levels and appeared to be mediated by ice and snow cover whereby the highest algal standing stock was present under high light conditions (low ice and snow cover, shallow water, summer). Differences in published benthic invertebrate densities appear to be closely allied to differences in benthic primary production, and less so to in situ planktonic ice microalgal production.     

Sedimentation in McMurdo Sound, Antarctica: a disturbance mechanism for benthic invertebrates

A slumping event that occurred on permanent transect lines from 12- to 30- m depth located at Arrival Heights, McMurdo Sound, Antarctica in 1993, provided an opportunity to examine the effects of sediment-mediated disturbance on the benthic invertebrate fauna. The disturbance had a particularly significant impact on the soft coral Alcyonium paessleri, which resulted in 84% colony mortality downslope from the slump site compared to an average annual mortality rate of 14% on control transects. In contrast, anchor ice at the same site accounted for removal of 5% of the population in 1992. Laboratory experiments with A. paessleri colonies under conditions of periodic sediment resuspension indicate that the soft corals are susceptible to this form of disturbance. Our observations suggest they are capable of shedding fine silt in the laboratory, which might explain the presence of A. paessleri in soft-sediment sites around McMurdo Sound. However, scarring by larger gravel in laboratory assays was slow to heal and may account for much of the colony mortality we observed. Several invertebrate-barren rocky benthic regions in McMurdo Sound were suggestive of historical slumping events. Given the removal of the smaller grain size sediments from these areas – a typically slow process – it appears these communities are slow to recover. The long-term effects of sedimentation on the benthic communities are unknown, but the impact on A. paessleri, one of the most common and fastest growing species, suggests this disturbance mechanism could lead to significant restructuring of these communities. Received: 29 November 1996 / Accepted: 23 February 1997     

Hydrographic patterns in McMurdo Sound,Antarctica and their relationship to local benthic communities

Summary Measurements of hydrographic parameters (temperature, salinity, nitrate, nitrite, phosphate, chlorophyll a, phaeophytin, and oxygen) in McMurdo Sound, Antarctica during spring, 1984, before the regional phytoplankton bloom, and summer, 1984, after the peak of the bloom, indicate the several processes contribute to changes in the vertical and horizontal structure of the water column. Regional variation in the source of water masses within the Sound, ice cover patterns, and meltwater from the Ross Ice Shelf and nearby continental glaciers result in east-west and north-south gradients in the thermohaline, nutrient, and productivity characteristics of the Sound. These patterns are also related to the extremely variable structure and productivity of shallow water benthic macrofaunal communities in McMurdo Sound. Hydrographic patterns during Spring (November) were indicative of conditions at the end of winter prior to the spring phytoplankton bloom. The water column was nearly isothermal with temperatures near or below the surface freezing point of seawater with only a slight salinity increase with depth. Salinity was lower in the west Sound than in the east, probably in response to glacial meltwater input from the Ross Ice Shelf and/or terrestrial sources. Nutrient levels were high and nearly homogenous throughout the Sound. Chlorophyll a was low (<1.0 g/l) throughout most of the Sound, but was lowest in the western sound, as expected from the circulation pattern (Barry and Dayton 1988). Oxygen was uniformly low during spring. The summer hydrographic distributions, estimated from samples collected during the decline of the regional plankton bloom, were dramatically different than in during spring. Both the salinity and temperature were vertically stratified at all sites, particularly in the west Sound. Temperatures near the surface were well above the freezing point and occasionally near or above 0°C. Near surface salinity in the western Sound was nearly fresh (0.4 ppt) at some locations in the southwestern Sound. Chlorophyll a was high throughout the Sound relative to spring concentrations, and nutrient levels (NO₃, PO₄) were strongly depressed near the surface, due mainly to phytoplankton uptake rather than by dilution. Primary productivity estimates based on the summer nitrate and phosphate deficits over 90 days were 1.96–2.02 and 0.39–1.02 gCm^-2d^-1 for the east and west sound, respectively. Nutrient ratios indicated that glacial meltwater from the Ross Ice Shelf and/or nearby terrestrial sources may be an important component of the summer meltwater input to the western Sound. Enhanced water column stability due to this input may prolong the maintenance of high water column stability as this water mass flows northward and result in particularly high productivity in northern McMurdo Sound.     

Health and condition in the adult Weddell seal of McMurdo Sound, Antarctica

Weddell seals (Leptonychotes weddellii) are large-bodied, long-lived mammals that live only in the circumpolar Antarctic. As such, they represent an ideal sentinel species for the impacts of environmental change on polar species. However, longitudinal physiological studies of marine mammals are notoriously difficult due to their largely aquatic lifestyle, such that many baseline indicators of health and condition are not well defined. Fifty known-age, adult seals (9-27 years, 24 males, 26 females) in McMurdo Sound were sampled for mass, total body fat, blubber depth and a suite of blood parameters (21 variables) to assess hydration state, nutritional plane, reproductive hormones (females only), organ function and immune status. Total body mass increased with age, whereas variation in blubber depth was best described by mass and/or sex, with an overall greater blubber thickness in female seals (p < 0.001). Ten blood parameters showed a significant effect of one or more model variables, most prominently between the sexes. Serum chemistry suggested that females were better nourished and displayed lower indicators of acute stress compared to males. We noted limited age-related declines that might indicate impaired organ function. Overall, seals demonstrated clinically normal values for large mammals, even at the upper end of the age continuum. Future physiological studies in this species are strongly encouraged to incorporate potential sex effects in experimental design and analysis.     

Planktivory in Pagothenia borchgrevinki (Pisces: Nototheniidae) in McMurdo sound,Antarctica

Summary Specimens of the Antarctic fish P. borchgrevinki were collected from just beneath the sea-ice in McMurdo Sound over the period 8 November to 6 December, 1985. The stomach contents of 200 fish were analysed and compared with the co-occurrence of the prey species in the plankton. Numerically, the dominant prey was a thecosomatid pteropod Limacina helicina (83%), followed by a hyperiid amphipod Hyperiella dilatata (5%). Other prey species in decreasing order of occurrence were Euphausia crystallorophias, Euchaeta antarctica, other copepods, a decapod crustacean larva, chaetognaths, the amphipods Orchomene plebs and Epimiriella macronyx, and unidentified juvenile fish. The order of frequency of occurrence of these prey in the guts of all the fish was H. dilatata (in 73% of the fish), L. helicina (71%), calanoid copepods (55%), chaetognaths (51%), E. crystallorophias (42%), decapod crustacean larva (32%), O. plebs (27%), juvenile fish (20%), and E. macronyx (14%). In volumetric terms, the dominant diet contributors were O. plebs (38%), L. helicina (17%) and chaetognaths (15%). All prey except O. plebs and E. macronyx were taken in concurrent plankton samples. Although planktivory of Pagothenia borchgrevinki is confirmed, it is not certain whether feeding is confined to the immediate sub-ice environment.     

Fatty acid composition and microbial activity of benthic marine sediment from McMurdo Sound, Antarctica

Abstract Signature lipids from the phospholipid esterlinked fatty acids (PELFA) of cell membranes were used to describe benthic microbial communities of 4 Antarctic sediments. Metabolic activities of the communities were determined by incorporation of [³H]thymidine into bacterial DNA and sodium [¹⁴C]acetate into membrane lipids. Biomass measurements from extractable phospholipid fatty acids per g dry wt. ranged between 6 to 76 nmol, or when converted to number of bacteria, 3.7 × 10⁸ to 4.5 × 10⁹ cells per g dry wt. The West Sound site at New Harbor contained the lowest biomass, while Cape Evans on the East Sound contained the greatest. A marked difference was also noted between sites in their sediment microbial community structure. The East Sound sites at Cape Armitage and Cape Evans contained a greater abundance of diatom marker lipids, whilst both sides of the Sound contained approximately the same relative amounts of bacterial groups distinguished using PELFA. Activity of sediment microorganisms measured by radiolabel incorporation under ambient conditions followed the trends of the biomass measurements. The East Sound sites were more active by an average of 45–73% for [³H]thymidine and possibly also for sodium [¹⁴C]acetate.     

Ecological Studies of Seaweeds in McMurdo Sound, Antarctica

Three species of benthic marine macroalgae comprise the chiefcomponents of the seaweed flora of McMurdo Sound, Antarctica.Quantitative studies at Cape Evans demonstrate a depth-relateddistribution pattern, with Iridaea cordata (Turner) Bory inshallow water, Phyllophora antarctica A. and E. S. Gepp abundantand fertile at intermediate depths, and Leptophytum coulmanicum(Foslie) Adey dominant below 20 m. The vertical distributionof species is correlated with irradiance levels. At sites withthinner annual sea ice and less snow accumulation (e.g., CapeEvans, Cape Royds, and Granite Harbor), vertical distributionsare shifted downward relative to those at sites that remaincovered most of the year with thick or snow-covered fast ice(e.g., Cape Armitage and New Harbor). Disturbance caused byice scour and anchor ice probably determines the upper limitof algal distribution; herbivory is apparently absent. There is a disproportionate representation of cystocarpic femalegametophytes in populations of I. cordata and P. antarctica.Perennation via persistent basal crusts and apogamic recyclingof gametophytes are suggested as factors structuring phase distribution.Although the overall size of I. cordata blades is greater (andcystocarpic plants more abundant) at Cape Royds than at CapeEvans, cystocarpic blades are similar in minimum size at bothsites, indicating a threshhold size or age for the onset ofreproduction in this species.     

Soil Microorganisms of the McMurdo Sound Area, Antarctica

A study of soil microorganisms of Ross Island and the adjacent mainland was carried out during the brief austral summer of 1961-1962. In some cases, seasonal changes in microbial numbers were observed, although microorganisms could not be detected in some soils. Bacterial species common to temperate regions were isolated from a number of different samples. Thermophilic bacteria were present in some of the soils, and a significant portion of the bacterial population was capable of growth at 2 C. The soil microflora were capable of carrying out certain reactions of the nitrogen cycle at a very slow rate. In addition to temperature, other environmental factors which might influence growth and metabolic activity were discussed.     

Seasonal Patterns of Planktonic Production in McMurdo Sound, Antarctica

The prolonged periods of continuous darkness and light in polarregions have resulted in a unique seasonal partitioning of primaryand heterotrophic production. In McMurdo Sound for example,the biomass, size distribution and production by phytoplanktonand bacterioplankton undergo distinct seasonal cycles. The seasonalpattern of primary production appeared to be regulated by lightwhereas the three order of magnitude change in phytoplanktonbiomass during mid- to late December was largely controlledby the advection of planktonic algae from the Ross Sea intoMcMurdo Sound. The size distribution of phytoplankton was highlyseasonal; nano- and picoplankton were dominant from August throughNovember while netplankton were more abundant in December andJanuary. Seasonal variations of bacterial biomass and productionwere smaller than those of phytoplankton. During the late australwinter and spring, bacterial biomass and production exceededthose of phytoplankton. This implies that during this period,organic material from allochthonous sources sustained bacterialgrowth. During the late spring and summer, however, the patternwas reversed and autochthonous primary production was sufficientto support concurrent bacterioplankton production. The apparenttemporal disequilibrium in autochthonous bacterioplankton andphytoplankton production was maintained by the seasonal inputof allochthonous organic material into McMurdo Sound. The factsthat a) bacteria were both abundant and highly active, b) bacterivorywas common among many of the endemic protozoa and some planktonicmetazoa and c) these bacterivores consumed >95% of the bacterialproduction strongly suggest that bacteria are a crucial componentin the transfer of energy and material to metazoans in polarregions.     

Balanomorph barnacle larvae in the plankton at McMurdo Sound,Antarctica

Summary Ten larvae of a balanomorph barnacle were collected in plankton samples from under the sea-ice of McMurdo Sound in the austral spring 1985. This is the first record of planktonic barnacle larvae in the Antarctic Ocean. By deduction they are identified as Bathylasma corolliforme (Hoek) stage II nauplii and cyprids. They are described, the first of larvae of any species of the Bathylasmatidae. Their occurrence in McMurdo Sound is discussed in view of the apparent absence of adults in the Sound.     

X-cell gill disease in Pagothenia borchgrevinki from McMurdo Sound, Antarctica

The Antarctic nototheniid fish Pagothenia borchgrevinki is a schooling, cryopelagic fish growing to about 280 mm maximum length. It is affected by X-cell disease, which causes gross swelling of gill filaments. Overall, 22% of the fish sampled had X-cell disease with individual schools ranging from 9.2 to 43.9%, which is a very high incidence compared to figures of other fish with the disease. In P. borchgrevinki, the disease caused a doubling of gill mass but had no effect on liver mass. Condition factor of affected fish was low. Received: 24 March 1997 / Accepted: 12 July 1997     

Summer plankton beneath the McMurdo Ice Shelf at white Island,McMurdo Sound,Antarctica

 The zooplankton of the under-shelf-ice ecosystem at White Island (78^°10′ S, 167^°30′ E), McMurdo Sound, Antarctica was investigated during December 1976 and January 1977. The water column was sampled through a hole in the McMurdo Ice Shelf over a water depth of 67 m. Seawater temperatures under the ice shelf ranged from −1.91 to 1.96^°C. Dissolved oxygen levels ranged from 5.0–6.05 ml l^-1 in early December to 4.65–4.8 ml l^-1 in late January. Current speeds of up to 0.13 m s^-1 were recorded at a depth of 50 m and a predominantly northward flow was detected. Light levels under the shelf ice were low with less than 1% of the incident light being transmitted to a depth of 3 m. No chlorophyll a was detected within the water column throughout the investigation. Mean zooplankton biomass values in the water column ranged from 12 to 447 mg wet weight m^-3 and were similar to values recorded elsewhere from Antarctic inshore waters, but were very much higher than those recorded from under seasonal sea ice in McMurdo Sound. Thirty-two zooplankton species were recorded including 1 ostracod, 21 copepods (10 calanoids, 3 cyclopoids and 8 harpacticoids), 4 amphipods, 2 euphausiids, a chaetognath and 3 pteropods. Larvae of polychaetes and fish were found on some occasions. The species composition in general was similar to that recorded from McMurdo Sound and other Antarctic inshore localities. Among the Copepoda, however, there were a number of species, especially among the Harpacticoidea, that have not been found previously in McMurdo Sound and the Ross Sea, but that are known to be associated with ice in other localities in Antarctica. Two recently described species are known only from White Island. They were present in the water column but were most abundant in the surface water of the tide crack where they were the most abundant zooplankters. The tide crack, which probably is an extension of the under-ice habitat, is apparently a significant nursery area for amphipods and copepod species. Received: 23 November 1994/Accepted 7 May 1995     

Time and depth comparisons of sub-ice zooplankton in McMurdo Sound,Antarctica

Summary Zooplankton was sampled through a hole in the sea ice off Scott Base from 28 October to 17 November 1987. Vertical hauls through 100 m and 300 m were taken to compare with data from the same place two years earlier. Wide variations of abundance occurred for each taxon identified over each occasion, but there is general consistency between abundance and dominance for each species between years. For Clione limacina antarctica 1987 was demonstrably a poorer year, but better for Limacina helicina and Conchoecia belgicae. Samples taken by nets set to stream with water currents below the ice, showed increasing density of most species (and total zooplankton) with depth, with only Clione antarctica and pilidium larvae more abundant near the surface. Numbers were very low in the top 40 m. Rarer macrozooplankton were caught by using larger nets for longer times at 50 m and deeper.     

Winter sediment resuspension in McMurdo Sound,Antarctica, and its ecological implications

Summary Sediment resuspension is a common phenomenon whose importance may be magnified in nearshore environments surrounding Antarctica, especially during the austral winter. Analyses suggest that sediments in the vicinity of McMurdo Station contain viable algal material throughout this period of darkness. The resuspension of these sediments, shown by sediment trap collections and underwater observations, would introduce organics into the water column and may provide an alternative food source for planktonic herbivores inhabiting near-shore environments during the Antarctic winter.     

Photoadaptation in Phaeocystis pouchetii advected beneath annual sea ice in McMurdo Sound, Antarctica

A bloom of the colonial microalga Phaeocystis pouchetii wasadvected from ice-free waters to beneath 1.5 m of annual fastice in East McMurdo Sound, Antarctica in late December 1984.Strategies of photoadaptation to a reduction in growth irradianceinvolved a 3- to 4-fold increase in photosynthetic efficiencyper chlorophyll a (