Seasonal succession and strategies of phytoplankton development in two lakes of different trophic states

This study describes the metabolism and structure of phytoplanktoncommunities during seasonal periodicity and discusses strategiesof development adopted by species during succession. The studywas conducted in two trophically different lakes. Each lakedemonstrates a different degree of the ecological succession,which prescribes an increasingly complex taxocenose. In oligomesotrophicLake Pavin the autogenic succession lasts from spring overturnuntil mid-summer. In eutrophic Lake Aydat the autogenic successionis strictly limited to spring. The seasonal changes of the communityproductivity, turnover rate (P/B) and adenylate energy chargeconfirm the hypothesis of a change of the ‘metabolic orientation’of phytoplankton cells during seasonal succession. The autogenicsuccession represents the progression from a growth-orientedstrategy to an equilibrium-oriented one.     

Structure and diversity of soil algal communities from Cierva Point (Antarctic Peninsula)

Cyanobacteria and eukaryotic algae, together with bacteria and fungi, are known to be primary colonizers of mineral soils throughout Antarctica. Their species diversity and soil coverage were studied in 18 soil polygons located at Cierva Point, Antarctic Peninsula. Undisturbed assemblages were dominated by filamentous Cyanobacteria and diatoms, whilst almost 40% of the 49 species recorded were observed only after enrichment culture. Nearly all of the isolates from enrichment cultures were Chlorophyta and Tribophyceae. This revealed a higher degree of complexity than reported for similar communities on Signy Island. Water content and concentrations of nutrients were determined at four representative sites, and did not appear to account for the large inter-polygon variation found in species composition and relative frequencies of occurrence. Variables describing community development were not significantly correlated with either area of the polygons or the minimum distance between them. This suggested that these features are not an important short-range barrier to dispersal for those “weed” species dominating the community. Conversely, the relative frequencies of some of the most common species showed significant correlations with species diversity and soil coverage, and it is suggested that biotic interactions could account to a larger extent for community structure than previously reported from Signy Island fellfields. Accepted: 12 October 1999     

Community structure and photosynthetic activity of benthic biofilms from a waterfall in the maritime Antarctica

High-energy flowing water habitats such as waterfalls are uncommon in Antarctica, though they may become more regular as temperature increase. Both high spatial and temporal environmental variability is expected on them. The extent of their biological colonization will depend on the amount of ecological strategies displayed by the surrounding biota. We report here a study on phototrophic microbenthic communities inhabiting such environment in a stream on the Byers Peninsula of Livingston Island. Five different biofilms were distinguished by colour, and were located in specific microhabitat types in the waterfall, which flowed down a steep canyon. Photosynthetic pigment content and microscopic observations demonstrated a different assemblage of chlorophytes, cyanobacteria and diatoms among them. Biofilms were not randomly distributed in the stream channel, which may be related to water flow, nutrient availability and moisture. The exopolymeric substances content, stoichiometry and pigment composition varied among biofilms, likely reflecting differences in the water and nutrients availability. The photosynthetic rates were in the range of the observed in previous studies in the site and varied according to the habitat within the stream. Communities dominated by chlorophytes were restricted to the central channel, suggesting adaptation to faster flow regime. However, cyanobacterial biofilms appeared in a great range of environmental conditions. They were rare in the central channel where water flow was greatest, but achieved large biomass stocks on submerged and even exposed sites in the splash zone at the edge of the flowing water. This study shows how Antarctic biofilms can have a large variability in community structure and biomass over short length scales, reflecting the range of microhabitats in this Antarctic waterfall ecosystem, and the potential occurrence of different strategies to overcome fluctuating conditions.     

Determination of the trophic state by qualitative and quantitative phytoplankton analysis in two gravel pit lakes

The phytoplankton of two gravel pits with comparable nutrient concentrations but different chlorophyll-a concentrations and phytoplankton biovolume was investigated qualitatively and quantitatively over a period of two years. This study deals with the phytoplankton-rich ‘Rotter See’ and the phytoplankton-poor ‘Paulsmaar’, both South of Cologne. The trophic state of both lakes was determined comparatively according to Ryding &; Rast (1989) and the categories used by Brettum (1989). The results were compared with each other. The trophic lake index according to Hörnström (1981) was modified slightly and subsequently determined for both lakes. A combination of qualitative and quantitative phytoplankton analysis made a proposal of a rehabilitation for the Rotter See possible.     

Comparative analysis of bacterioplankton assemblages from maritime Antarctic freshwater lakes with contrasting trophic status

The bacterioplankton assemblages of eight maritime Antarctic lakes with a wide range of trophic status and geographic span (six lakes from Hope Bay, Antarctic Peninsula and two from Potter Peninsula, King George Island) were described using denaturing gradient gel electrophoresis and band sequencing during two consecutive austral summers (2003–2004). Analyses of the gels identified a total of 230 bands spread across 57 different positions. Among those bands, 14 were shared between lakes from Hope Bay and Potter Peninsula, 17 were observed only in particular lakes, and 17 were registered both years in the same lake. We successfully reamplified and sequenced 43 bands located in 36 different positions belonging to Bacteroidetes, Actinobacteria, Betaproteobacteria and Cyanobacteria. The closest matches for 63% of the sequenced bands were from Antarctic or from other cold environment clones and sequences already in the databases, suggesting the widespread dominance of microbial communities adapted to cold habitats. The results of the multivariate analyses (Cluster Analysis and CCA) indicated that the nutrient status of the lake influences the bacterioplankton assemblages. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Notes on the lichen genus Lepraria from maritime (South Shetlands) and continental (Schirmacher and Bunger Oases) Antarctica

Material of the genus Lepraria from maritime and continental Antarctica collected in 1986–2007 was studied. Four species were distinguished, L. alpina, L. caerulescens, L. straminea and one putative new taxon provisionally called Lepraria sp. AO. L. caerulescens is tentatively resurrected from the synonyms of L. alpina for the chemotype with atranorin and angardianic/roccellic acid. Lepraria sp. AO is characterized by its granular thallus similar to other members of the L. neglecta group and the presence of two fatty acids, so far unidentified and not known from other members of the genus. Morphological and chemical diagnostic characters of all taxa, their distribution and ecological features are discussed. An updated key for identification of all Antarctic species is provided.     

The same primary structure of the prion protein yields two distinct self-propagating states

The question of whether distinct self-propagating structures could be formed within the same amino acid sequence in the absence of external cofactors or templates has important implications for a number of issues, including the origin of prion strains and the engineering of smart, self-assembling peptide-based biomaterials. In the current study, we showed that chemically identical prion protein can give rise to conformationally distinct, self-propagating amyloid structures in the absence of cellular cofactors, post-translational modification, or PrP(Sc)-specified templates. Even more surprising, two self-replicating states were produced under identical solvent conditions, but under different shaking modes. Individual prion conformations were inherited by daughter fibrils in seeding experiments conducted under alternative shaking modes, illustrating the high fidelity of fibrillation reactions. Our study showed that the ability to acquire conformationally different self-propagating structures is an intrinsic ability of protein fibrillation and strongly supports the hypothesis that conformational variation in self-propagating protein states underlies prion strain diversity.     

Short-term stability of the microbial community structure in a maritime Antarctic lake

. Spatial and temporal changes in the microbial community structure in a maritime Antarctic freshwater lake were investigated over a single day/night cycle in December 1999. The community structure of key microbial planktonic groups varied with depth and this was related to both physical and chemical stratification. However, in most cases, the community structure observed at specific depths did not change over the time period studied. These results suggested short-term stability in community structure, with only some minor effects of the diel changes in irradiance on the vertical distribution of planktonic organisms. This is in marked contrast to medium- and long-term studies, which show significant changes in microbial community structure with both time and depth.     

Mites of the genus Eupodes (Acari, Prostigmata) from maritime Antarctica: a biometrical and taxonomic study

A series of 40 male and 40 female mites of the prostigmatid genus Eupodes from the maritime Antarctic were each scored for 58 morphological characters, and principal co-ordinate analyses were performed on each data set. The analyses produced three clusters of points, which were interpreted as representing three species. One of these species, identified as Eupodes minutus (Strandtmann), the only species of Eupodes currently known from the maritime Antarctic, is redescribed. The other two species, E. exiguus up. and E. parvus nsp., are described. Two subspecies are recognized for the latter species, E. p. parvus from the South Orkney Islands, and E. p. grahamensis nsp. from the Antarctic Peninsula and South Shetland Islands. The geographical distribution and habitat preferences of the four text are discussed, and a key to the species is presented.     

The population dynamics of Notothenia rossii from South Georgia (Antarctica)

Summary The population dynamics of nearshore juvenile Notothenia rossii were studied at South Georgia during 1978 and 1979. Mortality of the population was calculated from length-class abundance of fish sampled by trammel nets, and the population size estimated using a mark and recapture technique. Instantaneous natural mortality in the nearshore population was high (M=0.78) although other author's estimate for the mortality in the offshore population was only 0.35. Therefore it is likely that no single estimate of mortality will apply to fish of all ages. The population density of juvenile N. rossii was about 11 g m^-2 nearshore. The size of the offshore population was estimated by calculating survival from the nearshore age classes. The data suggest that the population around South Georgia has been reduced by overfishing to about one tenth of its previous unexploited level. Yield could have been increased by fishing less intensively, and the population maintained at or near its initial level if recruitment remained constant.     

Primary production,light absorption and quantum yields of phytoplankton from the Bellingshausen and Amundsen Seas (Antarctica)

Chlorophyll concentration, light intensity, primary production, light absorption and quantum yield were measured between 12 January 1994 and 27 March 1994 in the Bellingshausen and Amundsen Seas. Primary production and quantum yield within Bellingshausen and Amundsen Seas were typical of the high-nutrient, low-chlorophyll area of the Southern Ocean while small variations were found as a result of local conditions. Chlorophyll a (chl a) concentrations were generally low (<1 μg l⁻¹) in the water column, while in cases of blooms it reached 7–8 μg l⁻¹. The light intensity at which photosynthesis approaches saturation varied between 59 and 105 μmol q m⁻² s⁻¹.The initial slope of the photosynthesis curve varied between 0.02 and 0.07 μg C (μg chl a)⁻¹ h⁻¹ (μmol q m⁻² s⁻¹)⁻¹. The maximal photosynthetic rate at light saturation ranged between 1.6 and 5.4 μg C (μg chl a)⁻¹ h⁻¹. Light limitation was found within the mixing depth, while no photoinhibition was observed when surface light was 500 μmol q m⁻² s⁻¹. The mean spectral absorption coefficients of phytoplankton ranged between 0.018 and 0.042 m² (mg chl a)⁻¹ depending on the phytoplankton taxonomy. The quantum yield of photosynthesis varied between 0.027 and 0.076 mol C mol q⁻¹. These high quantum yields are explained by the prevailing high nutrient concentrations in this area. Light intensity plays a major role as limiting factor, even in very shallow water. The phytoplankton close to the surface did not show photoinhibition but had higher UV absorption capabilities.     

A mesoscale study of phytoplankton assemblages around the South Shetland Islands (Antarctica)

Phytoplankton assemblages around the South Shetland Islands (SSI) were closely related to mesoscale physical features, based on high spatial resolution sampling performed during the summer of 2010. Sampling was done in 8 transects with stations 9 km apart. Phytoplankton groups were described using flow cytometry, FlowCAM and HPLC/CHEMTAX pigment analysis. Nanophytoplankton (2–20 μm) was predominant throughout the study area, which was dominated by small diatoms. They were distributed along the stratified waters of the SSI shelf and in the centre of the Bransfield Strait where an anticyclonic eddy was detected, established between two frontal structures [Bransfield Front and Peninsula Front (PF)]. The highest concentrations correlated with mid-to-high temperatures (1.07 °C) and mid-salinities (34.03) corresponding with Transitional Bellinghausen Water stations. Haptophytes distribution co-varied with small diatoms but also appeared in those vertical mixed stations with Transitional Zonal Water with Weddell Sea influence. A shift from smaller to larger diatoms was detected at the ice edge in the Antarctic Sound. Cryptophytes were restricted to stratified stations of the SSI shelf and those associated with the PF, while small prasinophytes were the only group occupying deeper and colder waters of the Drake Passage, beneath the Antarctic Surface Water, north of a narrow frontal region described here for the first time (Shetland Front). Phytoplankton assemblages around the SSI were strongly connected with the Bransfield Current System, supporting a clockwise circulation around the archipelago. The Bransfield Current System components are permanent structures during the austral summer suggesting that the distribution of phytoplankton, which responds to these structures, must also be a quasi-permanent feature.     

Periphyton on artificial substrata from three lakes of different trophic status at Hope Bay (Antarctica)

The nutrient characteristics of aquatic environments at Hope Bay (Antarctica) depend on different factors, penguin enrichment being one of the most important. In this study we surveyed three water bodies of different morphometry and trophic status: Esperanza Lake (oligotrophic), Boeckella Lake (meso-eutrophic), and Pingüi Pond (hypereutrophic). This research provides a preliminary characterization of the periphyton colonization on artificial substrata (glass slides) of these water bodies from the end of January to mid-March 2000. Qualitative and quantitative analyses of the algae, chlorophyll a, dry weight, ash-free dry weight, and physical and chemical variables of the lakes were assessed. The Autotrophic Index and the Lakatos system of classification were also applied. All three lakes differed clearly in all the variables considered. The periphyton from Esperanza Lake was first dominated by Bacillariophyceae and subsequently by the chrysophyce Phaeogloea mucosa. P. mucosa was the dominant species at Boeckella Lake and Chlamydomonas subcaudata was dominant at Pingüi Pond. Highest mean maximum density values were reached at Pingüi Pond, followed by Boeckella and Esperanza Lakes. Highest biomass figures were registered with increasing trophic status. According to the Lakatos index, the periphyton of Esperanza Lake was the least developed and it was mainly organic and heterotrophic; Boeckella Lake showed intermediate development in periphyton mass, which was autotrophic and mainly inorganic whereas Pingüi Pond showed the highest development in periphytic mass, and it was mainly autotrophic.     

Unusual trophic strategies of Hydractinia angusta (Cnidaria, Hydrozoa) from Terra Nova Bay, Antarctica

Hydractinia angusta Hartlaub, 1904 has been recorded at Terra Nova Bay (Ross Sea, Antarctica) as epizoic on shells of the Antarctic scallop Adamussium colbecki. The species can exploit different trophic resources: first, polyps are able to detach and ingest tube feet and pedicellariae from the sea urchins Sterechinus neumayeri, grazing on the scallop shell, and second, they also eat masses of benthic diatoms settled among the hydrorhiza of the colony. The particular relationship observed between the hydroid and one of the most common Antarctic sea urchins may prevent or reduce the damage to A. colbecki shells, otherwise caused by the grazing of sea urchins on the algal film of the upper valve of the scallops. H. angusta is the first known species of hydroid that exploits prey several times its own size and the second that does not ingest entire prey but portions of them. The use of benthic diatoms as a food resource has previously been documented for the sub-Antarctic marine hydroid Silicularia rosea. Accepted: 20 December 1999     

Phytoplankton structure and dynamics in a volcanic lake in Deception Island (South Shetland Islands,Antarctica)

This work constitutes the first floristic and ecological analysis of the phytoplankton community of a volcanic freshwater lake in Deception Island (62°57′S, 60°38′W, South Shetland Islands, Antarctica). The main limnological features and phytoplankton size fractions were analyzed. Samples were taken during the austral summer of 2002 at two opposite sites. According to ANOVA results performed with abiotic variables, no significant differences between sites were found. The phytoplankton community showed low algal species richness, with an important contribution of the tychoplanktonic taxa. In terms of species number, Bacillariophyceae was the dominant class. Autotrophic picoplankton registered the highest densities from the second sampling date onwards. Nanophytoplankton was represented by unidentified chrysophycean organisms, which showed different distribution patterns between sites. The net phytoplankton abundance remained low during the sampling period and was strongly correlated with chlorophyll a concentration. Both nutrient concentrations and chlorophyll a values indicated oligotrophic conditions.     

Triosephosphate isomerase genes in two trophic modes of euglenoids (euglenophyceae) and their phylogenetic analysis

Two different length cDNAs encoding triosephosphate isomerase (TIM) were identified in the two trophic modes of euglenoids, the phototrophic Euglena gracilis and Euglena intermedia and the saprotrophic Astasia longa. Sequence analyses and presequence prediction indicated that the shorter cDNA encodes a cytosolic TIM and the longer cDNA encodes a plastid TIM (pTIM). The typical presequence of the putative A. longa pTIM and the high sequence similarity between A. longa pTIM and E. gracilis pTIM imply that A. longa pTIM is targeted to plastids. Therefore, although the plastids of A. longa have lost the ability of photosynthesis, they might retain other TIM-related function(s), such as glycolysis and the synthesis of isopentenyl diphosphate or fatty acids. Including the TIM sequences obtained by us from chlorophytes and rhodophytes, our phylogenetic analyses indicated that euglenoid TIMs group neither with TIMs of kinetoplastids, which share the nearest common ancestor with euglenoids, nor are closely related to TIMs of chlorophytes, which are considered to be the donors of euglenoid plastids through secondary endosymbiosis. Instead, they group with TIMs of rhodophytes. In addition, our amino acid sequence alignment and structure modeling showed that TIMs of euglenoids and rhodophytes share a unique 2-aa insertion within their loop-4 areas. Therefore, either tim convergent evolution or lateral gene transfer (more probably) might have occurred between euglenoids and rhodophytes after the divergence of euglenoids with kinetoplastids.     

熊河水库浮游植物群落结构的周年变化

自2007年5月至2008年4月对湖北省枣阳市熊河水库的浮游植物群落进行调查和分析.调查共发现浮游植物49属74种,绿藻在种类组成上占绝对优势,共40种,其次为蓝藻,有15种,硅藻11种,甲藻3种,金藻和裸藻各2种,隐藻仅1种.蓝藻存在夏季(7月)高峰,优势种为卷曲鱼腥藻(Anabaena circinalis);硅藻、隐藻和甲藻均存在一个春季(3或4月)高峰,优势种分别为双头针杆藻(Synedra amphicephala)、羽纹脆杆藻(Fragilaria pinnata)、卵形隐藻(Cryptomonas ovata)和二角多甲藻(Peridinium bipes).Simpson多样性指数、Shannon-Wiener多样性指数、Pielou均匀度指数和Margalef丰富度指数的年平均值分别是0.60、2.20、0.76和1.15.多样性指数和均匀度指数具有明显的季节变化规律,但无明显的空间分布规律.     

Application of trophic transfer efficiency and age structure in the trophic analysis of fossil assemblages

We evaluate onshore-offshore trends in age-frequency distributions and trophic transfer efficiencies using 11 modern death assemblages off the Texas coast. Trophic transfer efficiencies within trophic levels offer little insight over that achieved by a size-frequency distribution. Production/biomass ratios will always be 1 in the fossil record. Within trophic-level estimates of paleogrowth efficiency, the ratio of paleoproduction to paleoingestion (Pⁱ_glt/Iⁱ_lt where i indicates the i^th trophic level and lt indicates the time-averaged value) follow the expected ecological trend precisely in that paleogrowth efficiency is consistently higher in primary consumers than in predators in all 11 death assemblages. Paleoutilization efficiency, the ratio of predator paleoingestion to prey paleoproduction, I²_lt^°/P¹_glt^°, may provide information on the degree of bias in the preservation of primary (1 °) and secondary (2 °) consumer trophic groups. I²_lt^°/P¹_glt^° fell below 0.1 in most cold-seep and bay assemblages, indicating a large surplus of primary consumers. In sharp contrast, I²_lt^°/P¹_glt^°     

Short-term changes in zooplankton community in Paso Ancho basin (Strait of Magellan): functional trophic structure and diel vertical migration

Knowledge on community structure oriented to describe energy flow during late summer season in Paso Ancho basin (Strait of Magellan) is scarce and particularly affected by vertical diel migration (VDM). The main aim of this work is to identify the VDM patterns of selected species and functional feeding groups of mesozooplankton, collected by the electronic multinet BIONESS in 1995. Detailed studies were carried out on keystone components of the community: 7 species of copepods (Ctenocalanus citer, Drepanopus forcipatus, Metridia lucens, Clausocalanus brevipes, Scolecithricella minor, Paraeuchaeta antarctica, Calanus simillimus), one ostracod (Discoconchoecia elegans), one chaetognath (Sagitta tasmanica), one euphausiid (Euphausia vallentini), and two polychaetes (Pelagobia longicirrata, Tomopteris planktonis). Unexpected deviations from the classic pattern reported in literature were uncovered. The shallow layer mesozooplankton at night, although dominated by exclusively or preferentially herbivores, particularly by E. vallentini, was not represented by several species known as herbivores that remained in the deep layer throughout the day cycle. The deep-layer zooplankton throughout the day cycle was well represented by carnivores, detritivores, and omnivores. It is suggested that during low-chlorophyll summer conditions, the composition of functional groups and diet, and VDM patterns changed to take advantage of sinking phytoplankton and picoplankton in deep layers. Pelagic-benthic coupling would be strengthened due to animals that suppressed their vertical daily rise to the shallow layer at nights but remained in the deep layers to feed on a rain of particulate organic matter and other non-migrant zooplankton.