Biogeography and ecology of freshwater diatoms in Subantarctica: a review

Subantarctica is situated between the Antarctic and the Subtropical Convergence and consists of the islands in the southern Atlantic, Indian and Pacific Oceans. Diatoms are an important component of all Subantarctic aquatic, moss and soil habitats. Taxonomic studies reveal a high diversity and species richness in both the present-day and the fossil diatom flora. Planktonic diatoms are almost completely absent. A similarity analysis of the diatom composition from different localities in the southern zone (below 40°S) resulted in a biogeographical zonation. Three regions could be formed, based on their diatom composition: Subantarctica, Maritime Antarctica and the Antarctic Continent. The diatom communities in the different regions are all characterized by a high proportion of cosmopolitan species. A second feature of the southern diatom floras is the decreasing diversity when moving southwards.     

Agglutinated loricae of some Baltic and Antarctic Tintinnina species (Ciliophora)

The abundance and species composition of diatoms adhering tothe loricae of four agglutinated Tintinnina species, Laackmanniellanaviculaefera, Codonellopsis gaussi, Cd.balechi and Tintinnopsislobiancoi, were determined. Diatoms from the Fragdariopsis group,F.cylindrus and F.pseudonana, dominated on tintinnid loricaefrom the Antarctic waters, whilst Thalassiosira spp. were predominanton loricae from the Baltic Sea. Although tintinnids utilizeddiatoms in the environment, it is not a rule that they use onlythese which are dominant. Our results suggest that certain diatomsare actively selected and agglutinated by particular tintinnidspecies.     

Introduction. Antarctic ecology: from genes to ecosystems. Part 2. Evolution, diversity and functional ecology

The Antarctic biota has evolved over the last 100 million years in increasingly isolated and cold conditions. As a result, Antarctic species, from micro-organisms to vertebrates, have adapted to life at extremely low temperatures, including changes in the genome, physiology and ecological traits such as life history. Coupled with cycles of glaciation that have promoted speciation in the Antarctic, this has led to a unique biota in terms of biogeography, patterns of species distribution and endemism. Specialization in the Antarctic biota has led to trade-offs in many ecologically important functions and Antarctic species may have a limited capacity to adapt to present climate change. These include the direct effects of changes in environmental parameters and indirect effects of increased competition and predation resulting from altered life histories of Antarctic species and the impacts of invasive species. Ultimately, climate change may alter the responses of Antarctic ecosystems to harvesting from humans. The unique adaptations of Antarctic species mean that they provide unique models of molecular evolution in natural populations. The simplicity of Antarctic communities, especially from terrestrial systems, makes them ideal to investigate the ecological implications of climate change, which are difficult to identify in more complex systems.     

Diversity and distribution patterns in high southern latitude sponges

Sponges play a key role in Antarctic marine benthic community structure and dynamics and are often a dominant component of many Southern Ocean benthic communities. Understanding the drivers of sponge distribution in Antarctica enables us to understand many of general benthic biodiversity patterns in the region. The sponges of the Antarctic and neighbouring oceanographic regions were assessed for species richness and biogeographic patterns using over 8,800 distribution records. Species-rich regions include the Antarctic Peninsula, South Shetland Islands, South Georgia, Eastern Weddell Sea, Kerguelen Plateau, Falkland Islands and north New Zealand. Sampling intensity varied greatly within the study area, with sampling hotspots found at the Antarctic Peninsula, South Georgia, north New Zealand and Tierra del Fuego, with limited sampling in the Bellingshausen and Amundsen seas in the Southern Ocean. In contrast to previous studies we found that eurybathy and circumpolar distributions are important but not dominant characteristics in Antarctic sponges. Overall Antarctic sponge species endemism is ～43%, with a higher level for the class Hexactinellida (68%). Endemism levels are lower than previous estimates, but still indicate the importance of the Polar Front in isolating the Southern Ocean fauna. Nineteen distinct sponge distribution patterns were found, ranging from regional endemics to cosmopolitan species. A single, distinct Antarctic demosponge fauna is found to encompass all areas within the Polar Front, and the sub-Antarctic regions of the Kerguelen Plateau and Macquarie Island. Biogeographical analyses indicate stronger faunal links between Antarctica and South America, with little evidence of links between Antarctica and South Africa, Southern Australia or New Zealand. We conclude that the biogeographic and species distribution patterns observed are largely driven by the Antarctic Circumpolar Current and the timing of past continent connectivity.     

南极鱼类后生动物寄生虫研究进展: 线虫、绦虫与桡足类

极端的环境造就了南极独特的生物群体, 其中鱼类是南大洋生态系统中最具多样性的脊椎动物, 也是许多寄生虫的中间或终末宿主。南极鱼类寄生虫种类丰富, 是南大洋海洋生物多样性的重要组成部分。探究南极鱼类及其寄生虫的营养关系可为阐释南极海洋生态系统功能及其变动提供重要的生态数据。虽然关于南极鱼类寄生虫的研究已有一百多年的历史, 但这些研究主要集中在寄生虫的种类鉴定、区系调查和组织病理等方面。由于南极鱼类寄生虫研究跨度时间长、地域范围广, 相关研究较为零散。文章综述了南极鱼类寄生线虫、绦虫以及桡足类的种类组成、宿主范围和地理分布等方面的研究, 并对今后开展南极鱼类寄生虫研究工作提出了展望。     

Phytoplankton species composition and abundance in the Indian sector of the Antarctic Ocean

Summary Water samples collected in the southwestern Indian Ocean between Africa and Antarctica in March 1980 were analyzed quantitatively for phytoplankton. Diatoms dominate the phytoplankton in this region and their numbers generally increase southward with peaks of abundance in both the northern Antarctic Zone and south of the Antarctic Divergence. Average cell numbers (i.e., 6.1×10⁵ diatoms l^-1 in the Antarctic Zone) are comparable to maximum numbers previously reported for the Southern Ocean. Dinoflagellates, flagellates and monads occur in highest concentrations north of the Polar Front. Their numbers are somewhat reduced south of the Antarctic Divergence, and are lowest in the Antarctic Zone. Various diatom assemblages are characteristic of different latitudinal zones. Waters north of and in the vicinity of the Polar Front are rich in the Nitzschia, Pseudonitzschia group of species. In the Antarctic Zone, Nitzschia nana and Dactyliosolen tenuijunctus dominate. Nitzschia species of the Fragilariopsis group are most numerous at stations south of the Antarctic Divergence. Striking differences are noted between the species compositions of quantitative and net-haul samples. A few nanoplanktonic diatoms (e.g. Nitzschia nana and single cells of Chaetoceros spp.) and the weakly silicified Dactyliosolen tenuijunctus, which are dominant in the quantitative samples, are either entirely absent or present only as solitary cells in the net collections.     

Evolution and biodiversity of Antarctic organisms: a molecular perspective

The Antarctic biota is highly endemic, and the diversity and abundance of taxonomic groups differ from elsewhere in the world. Such characteristics have resulted from evolution in isolation in an increasingly extreme environment over the last 100 Myr. Studies on Antarctic species represent some of the best examples of natural selection at the molecular, structural and physiological levels. Analyses of molecular genetics data are consistent with the diversity and distribution of marine and terrestrial taxa having been strongly influenced by geological and climatic cooling events over the last 70 Myr. Such events have resulted in vicariance driven by continental drift and thermal isolation of the Antarctic, and in pulses of species range contraction into refugia and subsequent expansion and secondary contact of genetically distinct populations or sister species during cycles of glaciation. Limited habitat availability has played a major role in structuring populations of species both in the past and in the present day. For these reasons, despite the apparent simplicity or homogeneity of Antarctic terrestrial and marine environments, populations of species are often geographically structured into genetically distinct lineages. In some cases, genetic studies have revealed that species defined by morphological characters are complexes of cryptic or sibling species. Climate change will cause changes in the distribution of many Antarctic and sub-Antarctic species through affecting population-level processes such as life history and dispersal.     

EVOLUTION OF THE ANTARCTIC MARINE BENTHIC ALGAL FLORA

There are many logistic difficulties associated with studying Antarctic marine algae and, as a consequence, the taxonomic information available is far from comprehensive and any generalizations should be regarded with caution. The Antarctic marine benthic flora is characterized by a low species richness. Biogeographical characteristics of the flora are outlined. There is a high degree of endemism, possibly around 35–40%. Other major floristic elements are a group of species with a distribution extending to Tierra del Fuego and subantarctic islands, a group spread through temperate regions of the Southern Hemisphere, and a cosmopolitan group. Ecological observations show that ice has a major effect on the occurrence and distribution of algae, and ecophysiological studies indicate that Antarctic macroalgae possess various adaptations to ice, low temperatures, and strongly seasonal light conditions. Possible trends in the evolution of the Antarctic benthic marine flora, including a reduction in species richness and the origins of biogeographical links with subantarctic and temperate regions of the Southern Hemisphere, are discussed in the context of tectonic and climatic changes over the past 100 million years. A comparison is made with studies on the evolution of shallow-water marine fauna.     

Diaspores and phyto-remains accidentally transported to the Antarctic Station during three expeditions

The aim of the project was to assess the size and species range of alien plant diaspores and phyto-remains transported into the Polish Antarctic Station during three Antarctic expeditions. Our study clearly demonstrates that many diaspores can be quite easily unintentionally transported in good conditions to the Antarctic. In the analyzed material there were present diaspores of invasive species. All identified species belong to 20 families. The most abundant were Asteraceae and Poaceae species. The most interesting finding was the presence of caryopses of Poa annua, the first alien angiosperm species which already established a stable breeding population in the Antarctic. Base on our results, we can predict that risk of establishment of anther alien plant species in the vicinity of “Arctowski” Station is very high.     

The roles of environment and space in shaping stream diatom communities

Diatoms are widely used in stream quality assessment due to their response to the local environment. Diatoms are also influenced by many large-scale processes and so the diatom communities of boreal streams incorporate a strong spatial component at a regional level. What is not properly known yet is whether the variation in diatom communities between regions is larger than the variation in measured environmental variables. We studied the roles of environment and space in accounting for variability in stream diatom communities across four regions in Finland. According to canonical correspondence analysis, geographical coordinates, nutrient concentrations (total N and P), and water conductivity were the most important factors affecting variation in diatom community composition. Of physical factors, depth and current velocity were also significant. According to Mantel tests, both environmental and geographical distances were related to dissimilarity in diatom community composition. Analysis of Similarities indicated that the regional differences in diatom community composition were larger than the regional differences in environmental variables. We also found many indicator species confined to certain regions. Our results suggest that the four study regions differ in their diatom species composition more than in their environmental features and that diatoms are structured not only by the local environment but also by large-scale processes, possibly related to history, climate and dispersal. These results imply that, while diatom species composition reflects well the environmental differences between regions, future bioassessments would benefit from regional stratification. Otherwise, relationships with environmental variables may be masked by trans-regional differences in species pools caused by the large-scale processes.     

Growth form analysis of epiphytic diatom communities of Terra Nova Bay (Ross Sea, Antarctica)

Diatoms have been long collected from the Southern Ocean but almost no data exist for epiphytic communities, despite their high ecological significance as an important food source in Antarctic coastal food chains. Here, we present a first growth form analysis of diatoms associated with rhodophyte hosts from Terra Nova Bay, Ross Sea, Antarctica. We performed this study to gather baseline information on the species composition of epiphytic diatom communities, determine the influence of some environmental variables on the diatom distribution patterns, and assess the caveats that must be taken into account in terms of sampling design. Macroalgal material was collected during the Italian Antarctic expeditions between 1990 and 2004. Epiphytic diatoms were studied by means of scanning electron microscopy. In terms of growth forms, there were no significant differences between the diatom communities on the different macroalgal host species. Motile (mainly small-celled Navicula perminuta and other Navicula spp.) and adnate (Cocconeis spp.) diatoms dominated the community throughout the study period. Many of the macroalgal blades examined were also covered by epiphytic animals (calcareous bryozoans, hydroids) over most of their surface, with a significant effect on the associated diatom community structure. Our findings suggest that the bio-physicochemical characteristics of each sampling site affected the epiphytic diatom communities more than the substrate type provided by the macroalgal host or the sampling depth.     

The biology, life cycle and ecophysiology of the Antarctic mite Alaskozetes antarcticus

This paper is dedicated to the late Nigel Bonner, who as Head of the Life Sciences Division at British Antarctic Survey, encouraged and supported this research with his characteristic enthusiasm.
The cryptostigmatid mite Alaskozetes antarcticus (Michael) is a dominant member of many terrestrial communities in the maritime Antarctic, where it survives extreme temperatures, short cold summers, numerous freeze-thaw cycles, desiccating conditions and a limited season for growth and reproduction. However, examination of features of its biology, from morphology, through life-history strategy to physiology, indicate very little specialization to the Antarctic environment. Alaskozetes antarcticus is a herbivore/detritivore, typical of the Cryptostigmata in general, with low feeding and growth rates, long life span and low reproductive output. Physiological specializations exist in the form of low enzyme activation energies and elevated metabolic rates at low temperatures when compared with temperate species, and associated low optimum temperatures for activity, feeding and growth. Growth rates comparable with temperate species are achieved in the field, with an extended life cycle of five years or more as a result of the short growing season, and the ability of all life stages to overwinter equally successfully. Overwintering survival, involving supercooling enhanced by the use of antifreezes such as glycerol, although initially described in Antarctic species, is now known to be characteristic of many temperate relatives, so it is not a specific adaptation to the polar environment. The obvious success of A. antarcticus in maritime Antarctic terrestrial environments must be attributed to a combination of several features characteristic of the Cryptostigmata in general, rather than to specific polar adaptations.     

Life history buffering in Antarctic mammals and birds against changing patterns of climate and environmental variation

The consequences of warming for Antarctic long‐lived organisms depend on their ability to survive changing patterns of climate and environmental variation. Among birds and mammals of different Antarctic regions, including emperor penguins, snow petrels, southern fulmars, Antarctic fur seals and Weddell seals, we found strong support for selection of life history traits that reduce interannual variation in fitness. These species maximize fitness by keeping a low interannual variance in the survival of adults and in their propensity to breed annually, which are the vital rates that influence most the variability in population growth rate (λ). All these species have been able to buffer these rates against the effects of recent climate‐driven habitat changes except for Antarctic fur seals, in the Southwest Atlantic. In this region of the Southern Ocean, the rapid increase in ecosystem fluctuation, associated with increasing climate variability observed since 1990, has limited and rendered less predictable the main fur seal food supply, Antarctic krill. This has increased the fitness costs of breeding for females, causing significant short‐term changes in population structure through mortality and low breeding output. Changes occur now with a frequency higher than the mean female fur seal generation time, and therefore are likely to limit their adaptive response. Fur seals are more likely to rely on phenotypic plasticity to cope with short‐term changes in order to maximize individual fitness. With more frequent extreme climatic events driving more frequent ecosystem fluctuation, the repercussions for life histories in many Antarctic birds and mammals are likely to increase, particularly at regional scales. In species with less flexible life histories that are more constrained by fluctuation in their critical habitats, like sea‐ice, this may cause demographic changes, population compensation and changes in distribution, as already observed in penguin species living in the Antarctic Peninsula and adjacent islands.     

Antarctic marine biodiversity and deep-sea hydrothermal vents

The diversity of many marine benthic groups is unlike that of most other taxa. Rather than declining from the tropics to the poles, much of the benthos shows high diversity in the Southern Ocean. Moreover, many species are unique to the Antarctic region. Recent work has shown that this is also true of the communities of Antarctic deep-sea hydrothermal vents. Vent ecosystems have been documented from many sites across the globe, associated with the thermally and chemically variable habitats found around these, typically high temperature, streams that are rich in reduced compounds and polymetallic sulphides. The animal communities of the East Scotia Ridge vent ecosystems are very different to those elsewhere, though the microbiota, which form the basis of vent food webs, show less differentiation. Much of the biological significance of deep-sea hydrothermal vents lies in their biodiversity, the diverse biochemistry of their bacteria, the remarkable symbioses among many of the marine animals and these bacteria, and the prospects that investigations of these systems hold for understanding the conditions that may have led to the first appearance of life. The discovery of diverse and unusual Antarctic hydrothermal vent ecosystems provides opportunities for new understanding in these fields. Moreover, the Antarctic vents south of 60°S benefit from automatic conservation under the Convention on the Conservation of Antarctic Marine Living Resources and the Antarctic Treaty. Other deep-sea hydrothermal vents located in international waters are not protected and may be threatened by growing interests in deep-sea mining.     

Size scaling of photophysiology and growth in four freshly isolated diatom species from Ryder Bay,western Antarctic peninsula

Diatoms are one of the dominant groups in phytoplankton communities of the western Antarctic Peninsula (WAP). Although generally well‐studied, little is known about size dependent photophysiological responses in diatom bloom formation and succession. To increase this understanding, four Antarctic diatom species covering two orders of magnitude in cell size were isolated in northern Marguerite Bay (WAP). Fragilariopsis sp., Pseudo‐nitzschia cf. subcurvata, Thalassiosira cf. antarctica, and Proboscia cf. alata were acclimated to three different irradiances after which photophysiology, electron transport, carbon fixation, and growth were assessed. The small species Fragilariopsis sp., Pseudo‐nitzschia cf. subcurvata, and large species Proboscia cf. alata showed similar photoacclimation to higher irradiances with a decrease in cellular chlorophyll a and an increase in chlorophyll a specific absorption and xanthophyll cycle pigments and activity. In contrast, pigment concentrations and absorption remained unaffected by higher irradiances in the large species Thalassiosira cf. antarctica. Overall, the small species showed significantly higher growth rates compared to the large species, which was related to relatively high light harvesting capacity and electron transport rates in the smaller species. However, photophysiological responses related to photoinhibition and photoprotection and carbon fixation showed no relationship with cell size. This study supports the dominance of small diatoms at low irradiances during winter and early spring, but does not provide photophysiological evidence for the dominance of large diatoms during the phytoplankton bloom in the WAP. This suggests that other factors such as grazing and nutrient availability are likely to play a major role in diatom bloom formation.     

HSP70 heat shock proteins and environmental stress in Antarctic marine organisms: A mini-review

The ability to understand and predict the effects of environmental stress on biodiversity is becoming increasingly important in our changing environment. Antarctic marine species are some of the most stenothermal on the planet and many inhabit the waters off the Antarctic Peninsula which is one of the areas where there is rapid regional climate change. Therefore these animals are highly vulnerable to changing environmental temperatures and clearly we need to understand the complexities of their response, not just at the individual species level, but also the implications for the ecosystem as a whole. Heat shock proteins have a long history of use in studies of organism stress responses and have frequently been proposed as potential universal molecular biomarkers, especially for non-model species. In this mini-review, the heat shock response and heat shock proteins (specifically the HSP70 family) are examined in Antarctic marine species alongside their physiological capabilities and limits to answer a series of questions: do these animals have a heat shock response which includes the expression of HSP70 genes? What is the relationship between their heat shock response and physiological capabilities? Can HSP70 genes be used as molecular biomarkers for these species?     

Prospects for surviving climate change in Antarctic aquatic species

Maritime Antarctic freshwater habitats are amongst the fastest changing environments on Earth. Temperatures have risen around 1°C and ice cover has dramatically decreased in 15 years. Few animal species inhabit these sites, but the fairy shrimp Branchinecta gaini typifies those that do. This species survives up to 25°C daily temperature fluctuations in summer and passes winter as eggs at temperatures down to -25°C. Its annual temperature envelope is, therefore around 50°C. This is typical of Antarctic terrestrial species, which exhibit great physiological flexibility in coping with temperature fluctuations. The rapidly changing conditions in the Maritime Antarctic are enhancing fitness in these species by increasing the time available for feeding, growth and reproduction, as well as increasing productivity in lakes. The future problem these animals face is via displacement by alien species from lower latitudes. Such invasions are now well documented from sub-Antarctic sites. In contrast the marine Antarctic environment has very stable temperatures. However, seasonality is intense with very short summers and long winter periods of low to no algal productivity. Marine animals grow slowly, have long generation times, low metabolic rates and low levels of activity. They also die at temperatures between +5°C and +10°C. Failure of oxygen supply mechanisms and loss of aerobic scope defines upper temperature limits. As temperature rises, their ability to perform work declines rapidly before lethal limits are reached, such that 50% of populations of clams and limpets cannot perform essential activities at 2–3°C, and all scallops are incapable of swimming at 2°C. Currently there is little evidence of temperature change in Antarctic marine sites. Models predict average global sea temperatures will rise by around 2°C by 2100. Such a rise would take many Antarctic marine animals beyond their survival limits. Animals have 3 mechanisms for coping with change: they can 1) use physiological flexibility, 2) evolve new adaptations, 3) migrate to better sites. Antarctic marine species have poor physiological scopes, long generation times and live on a continent whose coastline covers fewer degrees of latitude than all others. On all 3 counts Antarctic marine species have poorer prospects than most large faunal groups elsewhere.     

Spatial and temporal variability across life's hierarchies in the terrestrial Antarctic

Antarctica and its surrounding islands lie at one extreme of global variation in diversity. Typically, these regions are characterized as being species poor and having simple food webs. Here, we show that terrestrial systems in the region are nonetheless characterized by substantial spatial and temporal variations at virtually all of the levels of the genealogical and ecological hierarchies which have been thoroughly investigated. Spatial variation at the individual and population levels has been documented in a variety of genetic studies, and in mosses it appears that UV-B radiation might be responsible for within-clump mutagenesis. At the species level, modern molecular methods have revealed considerable endemism of the Antarctic biota, questioning ideas that small organisms are likely to be ubiquitous and the taxa to which they belong species poor. At the biogeographic level, much of the relatively small ice-free area of Antarctica remains unsurveyed making analyses difficult. Nonetheless, it is clear that a major biogeographic discontinuity separates the Antarctic Peninsula and continental Antarctica, here named the 'Gressitt Line'. Across the Southern Ocean islands, patterns are clearer, and energy availability is an important correlate of indigenous and exotic species richness, while human visitor numbers explain much of the variation in the latter too. Temporal variation at the individual level has much to do with phenotypic plasticity, and considerable life-history and physiological plasticity seems to be a characteristic of Antarctic terrestrial species. Environmental unpredictability is an important driver of this trait and has significantly influenced life histories across the region and probably throughout much of the temperate Southern Hemisphere. Rapid climate change-related alterations in the range and abundance of several Antarctic and sub-Antarctic populations have taken place over the past several decades. In many sub-Antarctic locations, these have been exacerbated by direct and indirect effects of invasive alien species. Interactions between climate change and invasion seem set to become one of the most significant conservation problems in the Antarctic. We conclude that despite the substantial body of work on the terrestrial biodiversity of the Antarctic, investigations of interactions between hierarchical levels remain scarce. Moreover, little of the available information is being integrated into terrestrial conservation planning, which lags far behind in this region by comparison with most others.