Bart Van de Vijver

Historical processes constrain patterns in global diatom diversity

There is a long-standing belief that microbial organisms have unlimited dispersal capabilities, are therefore ubiquitous, and show weak or absent latitudinal diversity gradients. In contrast, using a global freshwater diatom data set, we show that latitudinal gradients in local and regional genus richness are present and highly asymmetric between both hemispheres. Patterns in regional richness are explained by the degree of isolation of lake districts, while the number of locally coexisting diatom genera is highly constrained by the size of the regional diatom pool, habitat availability, and the connectivity between habitats within lake districts. At regional to global scales, historical factors explain significantly more of the observed geographic patterns in genus richness than do contemporary environmental conditions. Together, these results stress the importance of dispersal and migration in structuring diatom communities at regional to global scales. Our results are consistent with predictions from the theory of island biogeography and metacommunity concepts and likely underlie the strong provinciality and endemism observed in the relatively isolated diatom floras in the Southern Hemisphere.

Continent-wide risk assessment for the establishment of nonindigenous species in Antarctica

Invasive alien species are among the primary causes of biodiversity change globally, with the risks thereof broadly understood for most regions of the world. They are similarly thought to be among the most significant conservation threats to Antarctica, especially as climate change proceeds in the region. However, no comprehensive, continent-wide evaluation of the risks to Antarctica posed by such species has been undertaken. Here we do so by sampling, identifying, and mapping the vascular plant propagules carried by all categories of visitors to Antarctica during the International Polar Years first season (2007–2008) and assessing propagule establishment likelihood based on their identity and origins and on spatial variation in Antarcticas climate. For an evaluation of the situation in 2100, we use modeled climates based on the Intergovernmental Panel on Climate Changes Special Report on Emissions Scenarios Scenario A1B [Nakićenović N, Swart R, eds (2000) Special Report on Emissions Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate Change (Cambridge University Press, Cambridge, UK)]. Visitors carrying seeds average 9.5 seeds per person, although as vectors, scientists carry greater propagule loads than tourists. Annual tourist numbers (∼33,054) are higher than those of scientists (∼7,085), thus tempering these differences in propagule load. Alien species establishment is currently most likely for the Western Antarctic Peninsula. Recent founder populations of several alien species in this area corroborate these findings. With climate change, risks will grow in the Antarctic Peninsula, Ross Sea, and East Antarctic coastal regions. Our evidence-based assessment demonstrates which parts of Antarctica are at growing risk from alien species that may become invasive and provides the means to mitigate this threat now and into the future as the continents climate changes.

New and interesting species in the genus Luticola D.G. Mann (Bacillariophyta) from Deception Island (South Shetland Islands)

B. Van de Vijver and G. Mataloni. 2008. New and interesting species in the genus Luticola D.G. Mann (Bacillariophyta) from Deception Island (South Shetland Islands). Phycologia 47: 451–467. DOI: 10.2216/07-67.1 During a survey of the terrestrial diatom flora of Deception Island (South Shetland Islands, southern Atlantic Ocean), 10 taxa belonging to the genus Luticola were observed. Five of these, namely Luticola gigamuticopsis sp. nov., L. caubergsii sp. nov., L. quadriscrobiculata sp. nov., L. nelidae sp. nov. and L. australomutica sp. nov., are described as new species using light and scanning electron microscopy. Comments are made on their systematic position and on differences and similarities with other species. The morphology and taxonomy of the five other Luticola taxa, including Luticola muticopsis and two related forms, are also discussed. The high number of Luticola taxa on Deception Island is remarkable but not unusual for oceanic islands. From the biogeographical point of view, there is a clear separation between the sub-Antarctic localities in the southern Indian Ocean and the islands in the southern Atlantic Ocean with several species showing a restricted biogeography.

New and interesting species of the genus Muelleria (Bacillariophyta) from the Antarctic region and South Africa

Van de Vijver B., Mataloni G., Stanish L. and Spaulding S.A. 2010. New and interesting species of the genus Muelleria (Bacillariophyta) from the Antarctic region and South Africa. Phycologia 49: 22–41. DOI: 10.2216/09-27.1 During a survey of the terrestrial diatom flora of some sub-Antarctic islands in the southern Indian and Atlantic Oceans and of the Antarctic continent, more than 15 taxa belonging to the genus Muelleria were observed. Nine of these taxa are described as new species using light and scanning electron microscopy. Comments are made on their systematic position and how they are distinguished from other species in the genus. Additionally, two previously unrecognized taxa within the genus were discovered in samples from South Africa. One of these, Muelleria taylorii Van de Vijver & Cocquyt sp. nov., is new to science; the other, Muelleria vandermerwei (Cholnoky) Van de Vijver & Cocquyt nov. comb., had been included in the genus Diploneis. The large number of new Muelleria taxa on the (sub)-Antarctic locations is not surprising. Species in Muelleria occur rarely in collections; in many habitats, it is unusual to find more than 1–2 valves in any slide preparation. As a result, records are scarce. The practice of “force-fitting” (shoehorning) specimens into descriptions from common taxonomic keys (and species drift) results in European species, such as M. gibbula and M. linearis, being applied to Antarctic forms in ecological studies. Finally, the typical terrestrial habitats of soils, mosses and ephemeral water bodies of most of these taxa have been poorly studied in the past.

Molecular evidence for distinct Antarctic lineages in the cosmopolitan terrestrial diatoms Pinnularia borealis and Hantzschia amphioxys

Recent morphology-based studies indicate that freshwater diatom floras in the Antarctic comprise a significant share of endemics among a majority of apparently cosmopolitan species. Given the widespread (pseudo)cryptic species diversity in diatoms, we assessed the molecular divergence and temperature-dependent growth characteristics between Antarctic and non-Antarctic strains for two presumed species with a cosmopolitan distribution, namely Pinnularia borealis and Hantzschia amphioxys. Molecular phylogenies based on the plastid gene rbcL and the nuclear 28S rDNA (D1-D3 region) revealed that both taxa consist of multiple lineages, each including a distinct Antarctic lineage. A molecular clock estimates the origin of P. borealis at 35.8 (30-47) million years (Ma) ago, making this the oldest known diatom species complex. The Antarctic P. borealis lineage is estimated to have diverged 7.8 (2-15) Ma ago, after the geographical and thermal isolation of the Antarctic continent. Despite not being psychrophilic, the Antarctic lineages of P. borealis and H. amphioxys have a lower optimal growth temperature and upper lethal temperature than most lineages from more temperate regions, indicating niche differentiation. Together, this suggests that many presumed cosmopolitan Antarctic diatom species are in fact species complexes, possibly containing Antarctic endemics with low temperature preferences.

Diatom communities from the sub-Antarctic Prince Edward Islands: diversity and distribution patterns

During an extensive survey of the freshwater and moss-inhabiting diatoms of the Prince Edward Islands, a total of 214 taxa belonging to 60 genera were found. Three main communities can be found on the two islands. A large part of the samples was grouped into an aquatic group, bringing together all samples from lentic and lotic waterbodies. A second, contrasting, group was formed by all dry samples whereas in a third group all habitats with higher mineral contents were found. The habitats differed clearly in taxa composition reflecting that way possible environmental differences. Although the diatom composition between the two islands of this island group (Marion and Prince Edward Island) showed some minor qualitative differences, no marked quantitative differences have been observed. The diatom flora shows a distinct similarity with the other islands in the southern Indian Ocean, such as the Crozet archipelago and the Kerguelen Islands forming a biogeographical entity in this part of the ocean, distinctly separated from the non-marine diatom flora in other parts of the (sub-)Antarctic Region.

Moss-inhabiting diatom communities from Heard Island, sub-Antarctic

In this paper, we list 192 diatom taxa, collected from bryophyte samples from Heard Island (52°05′S, 73°30′E). The Heard Island diatom flora shows a marked similarity to those of the Crozet and Kerguelen archipelagos, and is quite dissimilar to the moss-dwelling diatom flora of Macquarie and Amsterdam Island. Based on species composition, three main groups of samples could be discerned. Each group represents a different habitat. Samples dominated by Diadesmis ingeae, Pinnularia borealis and several Psammothidium species seem to prefer the driest habitats. A special form of this community was found in shaded areas. Samples from wet habitats such as flush areas and pools were dominated by species such as Adlafia bryophila, Sellaphora tumida, Fragilaria capucina and Planothidium lanceolatum. An intermediate group was observed in more acid, but terrestrial, conditions, characterised by Eunotia paludosa and Chamaepinnularia soehrensis var. muscicola. These community patterns are similar to those found on other sub-Antarctic islands, and we suggest that a group of typical sub-Antarctic species and communities exists.

Habitat preferences in freshwater diatom communities from sub-Antarctic Îles Kerguelen

A limited sampling campaign on the main island of Îles Kerguelen revealed 170 freshwater diatom taxa, belonging to 29 genera. Four different communities were distinguished in two major groups, being determined principally by habitat type. The Fragilaria vaucheriae–Fragilaria germainii assemblage occurs exclusively in running waters. The three other communities, observed in standing waterbodies, are separated by their geographical position on the island with the Fragilaria exigua–Aulacoseira alpigena and the Fragilaria exigua–Fragilaria vaucheriae assemblages, mainly found in the Lac Studer area and the Fragilaria pinnata var. pinnata assemblage, recorded near the coastal line and the research station. Analysis of different waterbody types revealed the habitat preference of the various diatom taxa and identified a diatom flora for running waters and one preferring stagnant waterbodies.

Revision of the genus Navicula s.s. (Bacillariophyceae) in inland waters of the Sub-Antarctic and Antarctic with the description of five new species

Van de Vijver B., Zidarova R., Sterken M., Verleyen E., de Haan M., Vyverman W., Hinz F. and Sabbe K. 2011. Revision of the genus Navicula s.s. (Bacillariophyceae) in inland waters of the Sub-Antarctic and Antarctic with the description of five new species. Phycologia 50: 281–297. DOI: 10.2216/10-49.1 A revision of the diatom genus Navicula s.s. in inland water samples from the Sub-Antarctic and Antarctic resulted in the description of five new species, viz. Navicula australoshetlandica Van de Vijver sp. nov., N. dobrinatemniskovae Zidarova & Van de Vijver sp. nov., N. cremeri Van de Vijver & Zidarova sp. nov., N. conveyi Van de Vijver sp. nov. and Navicula bicephaloides Van de Vijver & Zidarova sp. nov. The new species are extensively compared with other similar species. The morphology and taxonomy of three other Navicula taxa present in the same materials are briefly discussed. A critical revision of literature reports of Navicula taxa in the Antarctic and Sub-Antarctic region indicates that despite the large number of records the genus is rather species-poor in the Sub-Antarctic and Antarctic. From a biogeographical point of view, there is a clear separation between the Sub-Antarctic localities in the southern Indian Ocean and the islands in the southern Atlantic Ocean, with several species showing a restricted biogeography.

The moss dwelling testacean fauna of Île de la Possession

An ecological study of the moss dwelling testacean fauna (Protozoa, Rhizopoda) on Île de la Possession (Crozet Archipelago, sub-Antarctica) revealed 83 taxa, belonging to 21 genera. The moss flora was dominated by cosmopolitan and ubiquitous taxa, such as Trinema lineare, T. enchelys, Euglypha laevis and E. rotunda. A cluster analysis and a correspondence analysis identified three communities: (1) a Corythion dubium assemblage found in a drier, slightly acidic terrestrial moss vegetation, (2) the Arcella arenaria, and (3) the Difflugiella crenulata assemblages, both characteristic of wetter, circumneutral habitats. The latter typified submerged mosses growing in running water, while the A. arenaria assemblage seemed to prefer mosses in standing waterbodies. Moisture conditions appeared to play a key role in determining the distribution pattern of testacean communities, while pH was only a secondary factor. A logistic regression emphasised the effect of the habitat type in controlling the variance in testacean assemblages. Moreover, the close relationship between bryophyte species and habitat type had a significant influence on the distribution pattern of the testate amoebae. Weighted averaging and calibration were used to estimate moisture optima and tolerances of the testate amoebae.