Diadinoxanthin cycle of the bottom ice algal community during spring in McMurdo Sound,Antarctica

Using the ice algal community growing at the bottom of the annual sea ice in McMurdo Sound Antarctica, the response of the photoprotective diadinoxanthin (DD)-cycle to exposure to light was investigated. Changes in pigment concentration were detected using high-performance liquid chromatography. A light mixing simulator (LMS) was developed and used to simulate the pigment response to mixing in the upper water column. No DD-cycle was detected under the sea ice under natural light conditions. The DD-cycle was activated after exposure to surface natural light conditions and artificial light conditions. The first-order kinetic rates of the DD-cycle under constant artificial irradiance, natural irradiance and simulations with the LMS were found to be similar to other studies suggesting that ice algae do not vary the rate of deepoxidation depending on light history. Simulations under natural light using the LMS demonstrated that the response of the DD-cycle to static incubations and when subject to vertical mixing was not similar, and that static incubations overestimate DD-cycle activity over the long term. Algae in a simulated vertically mixed environment were able to increase the pool of xanthophyll pigments compared to static conditions where the pool remained the same or decreased. The recovery of DD in the dark or under low light was found to be significantly faster than in temperate algal communities. These results suggest that ice algae at the sea ice bottom can activate the photoprotective DD-cycle to regulate excess thermal energy. Unlike temperate species of diatoms, ice algae can rapidly reconstruct the pigment pool under low light or in the dark and is likely a particular adaptation to the unique light environment in Antarctica.     

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 (     

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.     

Protist assemblages in winter sea ice: setting the stage for the spring ice algal bloom

This study documents, for the first time, the abundance and species composition of protist assemblages in Arctic sea ice during the dark winter period. Lack of knowledge of sea-ice assemblages during the dark period has left questions about the retention and survival of protist species that initiate the ice algal bloom. Sea-ice and surface water samples were collected between December 27, 2007 and January 31, 2008 within the Cape Bathurst flaw lead, Canadian Beaufort Sea. Samples were analyzed for protist identification and counts, chlorophyll (chl) a, and total particulate carbon and nitrogen concentrations. Sea-ice chl a concentrations (max. 0.27 μg l⁻¹) and total protist abundances (max. 4 × 10³ cells l⁻¹) were very low, indicating minimal retention of protists in the ice during winter. The diversity of winter ice protists (134 taxa) was comparable to spring ice assemblages. Pennate diatoms dominated the winter protist assemblage numerically (averaging 77% of total protist abundances), with Nitzschia frigida being the most abundant species. Only 56 taxa were identified in surface waters, where dinoflagellates were the dominant group. Our results indicate that differences in the timing of ice formation may have a greater impact on the abundance than structure of protist assemblages present in winter sea ice and at the onset of the spring ice algal bloom.     

Composition and abundance of zooplankton under the spring sea-ice of McMurdo Sound,Antarctica

Summary Zooplankton was sampled through holes in the sea-ice of McMurdo Sound from 8 November to 10 December, 1985. Replicated vertical hauls were made to 100 and 300 m off Pram Point in the inner Sound, near the edge of the permanent McMurdo Ice Shelf. The zooplankton was sparse, averaging 2.5 mg/m³ wet weight. The numbers of individual species varied between catches, depths, and occasions. Generally, small copepods, particularly Oithona similis, Ctenocalanus citer and Oncaea curvata, numerically dominated the catches, and higher densities of these were present in the shallower 100 m layer. Deeper hauls contained higher numbers of larger crustaceans, particularly copepods Metridia gerlachei, Calanoides acutus and Euchaeta spp., ostracod Conchoecia belgicae and euphausiid Euphausia crystallorophias. Pteropods Limacina helicina and Clione limacina were also consistently caught, but in equal densities in 100 m and 300 m hauls. Numerous other plankters were caught in low numbers, including amphipods, chaetognaths, medusae, radiolarians, and larval nemerteans, barnacles, shrimps, polychaetes and echinoderms. Comparative samples from 40 km further north, off Cape Royds and near the sea edge of the fast sea-ice in Wohlschlag Bay, and to 100 m deep, contained a similar species diversity to those near the McMurdo Ice Shelf, but always with higher densities of L. helicina. On the last sampling occasions, when microalgae were conspicuous under the ice off Cape Royds, there were increased densities of microcopepods and Paralabidocera antarcticus, indicating different ecosystem processes from the inner Sound location.     

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.     

Nutrient stress gradient in the bottom 5 cm of fast ice, McMurdo Sound, Antarctica

One-centimeter-scale vertical sampling of fast ice from McMurdo Sound, Antarctica reveals evidence of progressive nutrient limitation with distance above the ice/water interface. Over the bottom 6 cm photosynthetically active radiation increases by between 1.8 and 3 times, C:N increases from 6.8 to 19.8 and δ¹³C increases from −18 to −12. Fatty acid composition also changes with a consistent decline in polyunsaturated fatty acids and a rise in saturated fatty acids. These factors all suggest severe and progressive nutrient limitation with distance from the ice/water interface. Accepted: 5 September 1998     

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.     

舟山海域春季浮游植物生物量及东海原甲藻赤潮频发机制初探

通过2002和2003年春季2个航次对东海舟山群岛及其邻域大面站的浮游植物及期间爆发的大规模东海原甲藻(Prorocentrum donghaiense)赤潮的综合调查,研究了调查海区浮游植物叶绿素a和营养盐的分布特性,分析了赤潮高发区域的生态环境特征,探讨了诱发和控制海域赤潮发生的环境因子.结果表明,2002和2003年春季大面站表层平均叶绿素a浓度分别为1.09±1.63和4.21±5.33 mg·m^-3,调查海区平均为0.70±0.48和2.60±2.99 mg·m^-3,叶绿素a浓度的高值区基本上位于122.5°～123°E间冲淡水形成的锋面区域,此区域营养盐可以得到充分补充,光照条件适宜,也是浮游植物生产力的高值带.2002和2003年东海原甲藻赤潮跟踪期间,表层平均叶绿素a浓度分别高达18.45±11.04和12.47±8.15 mg·m^-3.赤潮发生海域盐度在26～30,赤潮藻生长易受磷的限制.光照条件适宜、营养盐(特别是磷酸盐)能得到较快的补充及锋面辐聚带的形成是赤潮形成的重要条件.     

Copepods in spring annual sea ice at Terra Nova Bay (Ross Sea,Antarctica)

The aim of this study was to investigate patterns of abundance, distribution, temporal changes and species composition of the dominant ice-associated copepods in the spring annual pack ice, platelet ice and water column at Terra Nova Bay, Ross Sea, during late spring 1997. Ice cores were drilled for temporal and spatial scales. Stephos longipes and Harpacticus furcifer dominated the sea ice meiofauna in terms of numbers in the lower few centimeters of the bottom ice associated with high chlorophyll a and phaeopigment levels. Nauplii dominated the S. longipes population (91.6%) and occurred in extremely high concentrations. In contrast, copepodids were the dominant stages in H. furcifer. How H. furcifer carries out its entire life cycle and how it differs from ecologically similar species such as Drescheriella glacialis should be examined in more detail.     

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     

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.     

Phytoplankton nutrient deficiency in lakes of the McMurdo dry valleys, Antarctica

1. The influence of inorganic nitrogen and phosphorus enrichment on phytoplankton photosynthesis was investigated in Lakes Bonney (east and west lobes), Hoare, Fryxell and Vanda, which lie in the ablation valleys adjacent to McMurdo Sound, Antarctica. Bioassay experiments were conducted during the austral summer on phytoplankton populations just beneath the permanent ice cover in all lakes and on populations forming deep-chlorophyll maxima in the east and west lobes of Lake Bonney. 2. Phytoplankton photosynthesis in surface and mid-depth (13 m) samples from both lobes of Lake Bonney were stimulated significantly (P < 0.01) by phosphorus enrichment (2 μM) with further stimulation by simultaneous phosphorus plus NH₄⁺ (20 μM) enrichment. Similar trends were observed in deeper waters (18 m) from the east lobe of Lake Bonney, although they were not statistically significant at P < 0.05. Photosynthesis in this lake was never enhanced by the addition of 20 μM NH₄⁺ alone. Simultaneous addition of phosphorus plus nitrogen stimulated photosynthesis significantly (P < 0.01) in both Lake Hoare and Lake Fryxell. No nutrient response occurred in Lake Vanda, where activity in nutrient-enriched samples was below unamended controls; results from Lake Vanda are suspect owing to excessively long sample storage in the field resulting from logistic constraints. 3. Ambient dissolved inorganic nitrogen (DIN) (NH4⁺+ NO₂^?+ NO₃^?): soluble reactive phosphorus (SRP) ratios partially support results from bioassay experiments indicating strong phosphorus deficiency in Lake Bonney and nitrogen deficiency in Lakes Hoare and Fryxell. DIN : SRP ratios also imply phosphorus deficiency in Lake Vanda, although not as strong as in Lake Bonney. Particulate carbon (PC): particulate nitrogen (PN) ratios all exceed published ratios for balanced phytoplankton growth, indicative of nitrogen deficiency. 4. Vertical nutrient profiles in concert with low advective flux, indicate that new (sensu Dugdale & Goering, 1967) phytoplankton production in these lakes is supported by upward diffusion of nutrients from deep nutrient pools. This contention was tested by computing upward DIN : SRP flux ratios across horizontal planes located immediately beneath each chlorophyll maximum and about 2 m beneath the ice (to examine flux to the phytoplankton immediately below the ice cover). These flux ratios further corroborated nutrient bioassay results and bulk DIN : SRP ratios indicating phosphorus deficiency in Lakes Bonney and Vanda and potential nitrogen deficiency in Lakes Hoare and Fryxell. 5. Neither biochemical reactions nor physical processes appear to be responsible for differences in nutrient deficiency among the study lakes. The differences may instead be related to conditions which existed before or during the evolution of the lakes.     

Two new species of Laophontodes (Copepoda, Harpacticoida, Ancorabolidae) from McMurdo Sound, Antarctica

Two new species of harpacticoid copepods of the family Ancorabolidae are described from a subtidal site in Cape Armitage, McMurdo Sound, Antarctica. Laophontodes macclintocki sp. n. and L. spongiosus sp. n. are easily distinguished from the remaining members of the genus Laophontodes by the setal formula of swimming legs P2–P4.     

Pleuragramma antarcticum (Pisces,Nototheniidae) as food for other fishes in McMurdo Sound,Antarctica

Summary Nine spcies of notothenioid fishes were captured near the southern limit of their range in ice covered McMurdo Sound, Antarctica. Stomach contents were examined using an occurrence method. Fishes were present in the diets of 8 of 9 species;Dissostichus mawsoni andGymnodraco acuticeps were predominantly piscivorous.Pleuragramma antarcticum was the most common prey fish consumed, being present in stomachs of 4 of 8 species.Pleuragramma was also partially piscivorous (22%) as well as cannibalistic (13%). As evidenced by their presence in the stomach contents of other fishes, all life history stages from 20 mm SL postlarvae to 160 mm SL adultPleuragramma were represented under the ice of the Sound.Pleuragramma was also a major food item for Weddell seals, birds and possibly invertebrates. As a widely distributed species in the pelagic zone,Pleuragramma may be an ecological substitute for euphausiids in the food web of the 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.     

Cultivable bacteria from ancient algal mats from the McMurdo Dry Valleys, Antarctica

The McMurdo Dry Valleys in Antarctica are a favorable location for preservation of dormant microbes due to their persistent cold and dry climate. In this study, we examined cultivable bacteria in a series of algal mat samples ranging from 8 to 26539 years old. Cultivable bacteria were found in all samples except one (12303 years old), but abundance and diversity of cultivable bacteria decreased with increasing sample age. Only members of the Actinobacteria, Bacteroidetes, and Firmicutes were found in the ancient samples, whereas bacteria in the 8-year-old sample also included Cyanobacteria, Proteobacteria, and Deinococcus-Thermus. Isolates of the Gram-positive spore-forming bacterium Sporosarcina were found in 5 of 8 samples. The growth of these isolates at different temperatures was related to the phylogenetic distance among genotypes measured by BOX-PCR. These findings suggest that adaptation to growth at different temperatures had occurred among Sporosarcina genotypes in the Dry Valleys, causing the existence of physiologically distinct but closely related genotypes. Additionally, fully psychrophilic isolates (that grew at 15°C, but not 25°C) were found in ancient samples, but not in the modern sample. The preservation of viable bacteria in the Dry Valleys could potentially represent a legacy of bacteria that impacts on current microbial communities of this environment.     

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.     

Biogeochemistry and microbial community composition in sea ice and underlying seawater off East Antarctica during early spring

Pack ice, brines and seawaters were sampled in October 2003 in the East Antarctic sector to investigate the structure of the microbial communities (algae, bacteria and protozoa) in relation to the associated physico-chemical conditions (ice structure, temperature, salinity, inorganic nutrients, chlorophyll a and organic matter). Ice cover ranged between 0.3 and 0.8 m, composed of granular and columnar ice. The brine volume fractions sharply increased above −4°C in the bottom ice, coinciding with an important increase of algal biomass (up to 3.9 mg C l⁻¹), suggesting a control of the algae growth by the space availability at that period of time. Large accumulation of NH₄ ⁺ and PO₄ ³⁻ was observed in the bottom ice. The high pool of organic matter, especially of transparent exopolymeric particles, likely led to nutrients retention and limitation of the protozoa grazing pressure, inducing therefore an algal accumulation. In contrast, the heterotrophs dominated in the underlying seawaters.