Current patterns in McMurdo Sound,Antarctica and their relationship to local biotic communities

Summary Current speed and direction measurements collected during summer (January–February) and sping (November–December) of 1984 indicated that currents in McMurdo Sound, Antarctica were dominated by oscillatory flow associated with diurnal tidal components (O1, K1, P1). Net flow was southward in the eastern Sound, mixed in the central Sound, and northward in the western Sound. Short term observations (<5 days) from nearshore stations indicated a similar but more sluggish pattern of tidal and mean flow. Hydrographic data collected during the same period indicated a similar pattern of cold water with low chlorophyll a content flowing northward from under the Ross Ice Shelf in the western Sound and denser, slightly warmer water with higher chlorophyll a content flowing southward in the eastern Sound. Previous studies have shown that productivity is higher in the eastern Sound than in the west, apparently due to the circulation pattern. The western Sound consists of waters from beneath the Ross Ice Shelf which have a lower phytoplankton standing stock than eastern Sound waters which enter from the north. More sluggish current speeds in the western Sound result in even lower particle fluxes past benthic consumers. Finally, more persistent ice cover in the west further inhibits in situ primary productivity.     

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.     

Planktivory in benthic nototheniid fish in McMurdo Sound,Antarctica

Synopsis Four species of nototheniid fish were sampled from below the sea ice near Cape Armitage, McMurdo Sound:Pagothenia borchgrevinki from just below the ice 1.5 km offshore,Trematomus bernacchii, Trematomus hansoni andTrematomus centronotus from off the bottom in about 20 m of water near the shore. Scale worms and isopods were conspicuous non-planktonic prey, and present in the three benthic fish species. The planktonic pteropod molluscLimacina helicina was numerically common in all four species of fish. The planktonic hyperiid amphipodHyperiella dilatata was also found in all fish species. WhereasP. borchgrevinki is planktivorous in accord with its pelagic habit, theTrematomus spp. clearly also feed on plankton from the water column.T. hansoni is particularly planktivorous, taking smaller copepods thanP. borchgrevinki.     

Polar ecosystem dynamics: recovery of communities from organic enrichment in McMurdo Sound, Antarctica

Community structure and diversity are influenced by patterns of disturbance and input of food. In Antarctica, the marine ecosystem undergoes highly seasonal changes in availability of light and in primary production. Near research stations, organic input from human activities can disturb the regular productivity regime with a consistent input of sewage. McMurdo Sound has both high-productivity and low-productivity habitats, thereby providing an ideal test bed for community recovery dynamics under polar conditions. We used experimental manipulations of the subtidal communities to test the hypotheses that (1) benthic communities respond differently to disturbance from organic enrichment versus burial and (2) community response also varies in areas with different natural patterns of food supply. Both in low- and high-food habitats, the strongest community response was to organic enrichment and resulted in dominance of typical organic-enrichment specialists. In habitats with highly seasonal productivity, community response was predictable and recovery was rapid. In habitats with low productivity, community variability was high and caging treatments suggested that inconsistencies were due to patchy impacts by scavengers. In areas normally subject to regular organic enrichment, either from primary production or from further up the food web (defecation by marine mammals), recovery of benthic communities takes only years even in a polar system. However, a low-productivity regime is as common in near shore habitats around the continent; under these conditions, recovery of benthic communities from disturbance is likely to be much slower and follow a variable ecological trajectory.     

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.     

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.     

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     

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.     

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     

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.     

Isolated faecal bacterial communities found for Weddell seals,Leptonychotes weddellii,at White Island,McMurdo Sound,Antarctica

The microbial diversity of faecal communities co-existing with mega fauna is not well understood even though these faecal communities are critical for health and development. Additionally, the transfer of microbial taxa among host animals is little studied. Here, we used 16S sequences obtained from clone libraries to characterise the faecal microbiota of Weddell seals breeding in McMurdo Sound and at White Island, Antarctica. Faecal bacterial communities were dominated by four phyla; Actinobacteria (20 %), Bacteroidetes (13 %), Firmicutes (23 %), and Proteobacteria (13 %). We also used automated ribosomal intergenic spacer analysis to examine the dispersal of bacteria between populations of Weddell seals breeding at White Island and in McMurdo Sound. The Weddell seals at White Island are isolated by the Ross Ice Shelf from the larger population of Weddell seals breeding in McMurdo Sound. We found that the faecal bacteria communities of the seals at White Island had lower diversity and that the community composition was significantly different compared with the seals in the McMurdo Sound area.     

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.     

Planktonic communities of melt ponds on the McMurdo Ice Shelf,Antarctica

The planktonic community of 20 melt ponds on the McMurdo Ice Shelf was investigated to determine taxa abundance and diversity and the controlling environmental variables. Grazing rates were measured using fluorescent beads to examine trophic interactions between ciliates, bacteria and phytoplankton. The melt ponds contained a surprisingly varied planktonic community with relatively high abundance compared with Antarctic continental lakes. There was a clear distinction between small, productive ponds dominated by bactivorous small ciliates, hymenostomes and heterotrophic cryptophytes and the larger, less productive ponds where these taxa were less abundant. The benthic mats of cyanobacteria and diatoms were potentially a source of food for some ciliate species but the majority were bacterivores. The lack of large herbivorous ciliates, the heterotrophic capabilities of cryptophytes and the broad ecological tolerances contributed to a planktonic community dominated by cryptophytes.     

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 (     

Lipid composition and metabolic activities of benthic near-shore microbial communities of Arthur Harbor,antarctic peninsula: Comparisons with McMurdo Sound

Summary Benthic microbial communities of the Arthur Harbor area were described by analysis of their cell membrane phospholipid ester-linked fatty acids (PELFA) and metabolic rates. Analysis revealed a biomass averaging 6 nM (phospholipid) or 3.5×10⁸ cells per gram dry weight (gdw) of sediment for the four sites. Only slight biomass differences were detected between the four peninsula sites. All Arthur Harbor sites were determined to have a biomass similar to the lowest amount reported for a previously described McMurdo Sound site at New Harbor. Community structure based on signature phospholipids indicated only slight differences between the four peninsula sites with greater relative amounts of diatom marker lipids at a deeper site. Bacterial biomarker lipids were also determined in relatively equal proportions for the four Arthur Harbor sites with only one site indicating a somewhat decreased proportion. Metabolic rates of sodium [¹⁴C]-acetate and methyl [³H]-thymidine incorporation into lipid and bacterial DNA respectively also indicated only slight relative differences in microbial communities of Arthur Harbor study sites. Lipid metabolism (¹⁴C-acetate) ranged between 6 and 12 (x10⁴) DPM/g/h for the four sites with 8 being the average. Bacterial (excluding sulfate-reducing bacteria (SRB)) cell divisions per g per h indicated increased rates at a deeper site with 14×10⁵, compared to the average (5×10⁵) for the three remaining sites. Average estimated total bacterial (excluding SRB's) community turnover was on the order of 0.6%/h for the four sites. Metabolic rate comparisons of Arthur Harbor with those of previously determined McMurdo Sound indicated a somewhat increased lipid metabolism and an order of magnitude greater bacterial cell division rate at Arthur Harbor.This paper is part 4 in the series: Microbial Ecology in Antarctic Sea-Ice and Benthic Communities     

Microbial diversity of cryptoendolithic communities from the McMurdo Dry Valleys,Antarctica

In the McMurdo Dry Valleys of Antarctica, microorganisms colonize the pore spaces of exposed rocks and are thereby protected from the desiccating environmental conditions on the surface. These cryptoendolithic communities have received attention in microscopy and culture-based studies but have not been examined by molecular approaches. We surveyed the microbial biodiversity of selected cryptoendolithic communities by analyzing clone libraries of rRNA genes amplified from environmental DNA. Over 1,100 individual clones from two types of cryptoendolithic communities, cyanobacterium dominated and lichen dominated, were analyzed. Clones fell into 51 relatedness groups (phylotypes) with > or =98% rRNA sequence identity (46 bacterial and 5 eucaryal). No representatives of Archaea were detected. No phylotypes were shared between the two classes of endolithic communities studied. Clone libraries based on both types of communities were dominated by a relatively small number of phylotypes that, because of their relative abundance, presumably represent the main primary producers in these communities. In the lichen-dominated community, three rRNA sequences, from a fungus, a green alga, and a chloroplast, of the types known to be associated with lichens, accounted for over 70% of the clones. This high abundance confirms the dominance of lichens in this community. In contrast, analysis of the supposedly cyanobacterium-dominated community indicated, in addition to cyanobacteria, at least two unsuspected organisms that, because of their abundance, may play important roles in the community. These included a member of the alpha subdivision of the Proteobacteria that potentially is capable of aerobic anoxygenic photosynthesis and a distant relative of Deinococcus that defines, along with other Deinococcus-related sequences from Antarctica, a new clade within the Thermus-Deinococcus bacterial phylogenetic division.     

In situ oxygen microelectrode measurements of bottom-ice algal production in McMurdo Sound, Antarctica

In-situ estimates of fast-ice algal productivity at Cape Evans, McMurdo Sound, in 1999 were lower than at the same site in previous years. Under-ice irradiance was between 0 and 8 µmol photons m^-2 s^-1; the ice was between 1.9 and 2.0 m thick and the algal biomass averaged 150 mg chl a m^-2, although values as high as 378 mg chl a m^-2 were recorded. Production on 11 and 12 November was between 0.053 and 1.474 mg C m^-2 h^-1. When the data from 11 November were fitted to a hyperbolic tangent function, a multilinear regression gave estimates for P_max of 0.571 nmol O₂ cm^-2 s^-1, an ! of 0.167 nmol O₂ cm^-2 s^-1 µmol^-1 photons m^-2 s^-1 and an E_k of 3.419 µmol photons m^-2 s^-1. A P_max of 2.674 nmol O₂ cm^-2 s^-1, an ! of 0.275 nmol O₂ cm^-2 s^-1 µmol^-1 photons m^-2 s^-1, r of 0.305 nmol O₂ cm^-2 s^-1 and an E_k of 9.724 µmol^-1 photons m^-2 s^-1 were estimated from the 12 November data. The sea-ice algal community was principally comprised of Nitzschia stellata, Entomoneis kjellmanii and Berkeleya adeliensis. Other taxa present included N. lecointei, Fragilariopsis spp., Navicula glaciei, Pleurosigma spp. and Amphora spp. Variations in the method for estimating the thickness of the diffusive boundary layer were not found to significantly affect the measurements of oxygen flux. However, the inability to accurately measure fine-scale variations in biomass is thought to contribute to the scatter of the P versus E data.