Plamen Ivanov

Achnanthes gainii, a marine diatom species, was described as Achnanthepyla gainii in 1921 by Maurice Peragallo from Petermann Island (Antarctic Peninsula area). For over a century, this taxon remained solely known from its original description and illustration of a single raphe valve. More detailed observations of the species are lacking, but a literature search showed that during the last century it was transferred to the genus Achnanthes three times. In this paper, we document and illustrate using both light and scanning electron microscope observations, the morphology of valves from a large population from South Bay, Livingston Island (Maritime Antarctica), matching well the description of this historic taxon. Since the search for the original material in the Peragallo Collection in Bordeaux a couple of years ago proved unsuccessful, in the absence of the original material and slides of A. gainii, the original drawing by M. Peragallo in 1921 is designated as lectotype, and the new population from Livingston Island is designated as epitype to the designated lectotype. The species is separated from other similar taxa, including a taxon recently identified as Achnanthes bongrainii, of which observations and scanning electron microscope illustrations are also provided in this work for comparison, based on populations from South Bay. Finally, several researchers previously commented the similarity of A. gainii to Achnanthes groenlandica. Therefore, the Antarctic records of the latter species were also verified, to the extent possible. This resulted in the discovery that a number of the published illustrations of A. groenlandica from Antarctica represent Achnanthes bongrainii, but not A. gainii.

In this work we present the observations on 19 Halamphora taxa found in a small set of samples originating from the summer biofilm on artificial substrates (plexiglass) in the western Black Sea or from macroalgae during winter in the Adriatic Sea. One taxon was also found on the carapace of a loggerhead sea turtle during summer in the Adriatic Sea. Most taxa had small valve dimensions, usually reaching not more than 20 µm in length and 2–3 µm in width, with only a few exceptions. Following extensive light (LM) and scanning electron microscope (SEM) observations, two taxa were identified based on the literature: H. bistriata was observed in the summer biofilm on artificial substrates in the Black Sea and on the carapace of a loggerhead sea turtle in the Adriatic Sea, whereas H. tenuicostata was detected as an epiphyte on macroalgae in the Adriatic Sea during winter. Eleven other taxa, of which 6 taxa from the Black Sea and 5 taxa from the Adriatic Sea, were described as new species, comparing their morphology to that of already known taxa. The remaining six unidentified taxa were observed sporadically. They are only illustrated and shortly discussed, without a formal description. The study demonstrates the remarkable and yet unexplored diversity of coastal marine benthic Halamphora species.

During a survey of the diatom flora present on an artificial substratum (plexiglass) submerged off the southern Bulgarian Black Sea coast, a small-celled diatom taxon, reported previously from the Black Sea as Amphora (Halamphora) sp. S21, was observed. Detailed light and scanning electron microscope observations showed that the original taxon actually included two different taxa: an unknown Halamphora species described here as H. valdeminutissima sp. nov., and a second taxon, which, based on SEM observations, could be identified as Amphora micrometra Giffen. The morphology of both taxa is described in detail and a comparison with similar taxa is provided. Additionally, environmental data of the habitat is also provided.

During a survey of diatoms present in tidal pools on the coasts of Livingston Island (South Shetland Islands), we found several populations, belonging presumably to the Antarctic endemic Craspedostauros laevissimus. Further analyses using light microscopy revealed that the populations show differences in stria density. Following scanning electron microscopy observations, only part of the investigated populations could be assigned to C. laevissimus, whereas the others are sufficiently morphologically different based on stria density and their cribrate areolae structure to be described as a new species: Craspedostauros confusus sp. nov. The new taxon is compared with known, morphologically similar, Craspedostauros taxa. The paper presents morphological and ecological data for both taxa discussed in the study. A detailed survey of the early Antarctic literature showed that the Craspedostauros taxa in Antarctica have convoluted taxonomic histories and that the new taxon has likely been hidden for long within the variability of C. laevissimus.

We used an artificial substratum (plexiglass tiles) to compare diatom communities at three different depths at two sites differing in their hydrological conditions and glacier melt-water influence. Samples at 1 m depth were taken during early summer in 2018, whereas samples at 3 m and 6.5 m were obtained in late summer 2020. The tiles were submerged for a period of up to 45 days in 2018, and up to 34 days in 2020. Water temperature, salinity, conductivity, oxygen saturation and concentrations, and Secchi depth were measured multiple times at both sites. During late summer of 2020 Photosynthetically Active Radiation (PAR) was also measured at depths of 3, 6.5 and 10 m at both sites. The communities constituted of a total of 50 taxa. Colonization and community development followed the same scheme at both sites and at all depths, with an early establishment of the dominant taxa, and a decline in species richness, diversity, and evenness indices over the time towards relatively stable low values. Based on the results of PERMANOVA, ANOSIM and SIMPER analyses, diatom communities were site-specific, with 49% dissimilarity between the sites. Mechanical disturbances, such as wave action and ice scouring, as well as depth (and light availability) seemed to be the main factors driving the differences. The motile Navicula aff. perminuta dominated under mechanical disturbances at various light conditions, Navicula glaciei preferred calm shallow waters, and erect diatom growth forms were present in higher numbers in deeper waters with deteriorated light conditions.

During a survey of the marine benthic diatom flora on the coasts off Livingston Island (South Shetland Islands, Maritime Antarctic Region), two Halamphora species that could not be identified based on the currently available literature, were observed. Detailed light and scanning electron microscopy observations and thorough comparison with similar taxa in the literature revealed that both taxa should be described as new species. The first taxon, Halamphora kenderoviana sp. nov., was most likely misidentified in past Antarctic studies, and included within the range of another taxon, Halamphora coffeaeformis. Analysis of literature data showed that the second new taxon, Halamphora moncheviana sp. nov., has been previously reported from the Antarctic Continent (but as an unidentified species). The new taxa are compared with similar Halamphora taxa worldwide. Data on their ecology and distribution are also provided.

During a survey of benthic diatoms from the Bulgarian Black Sea coast near the historic town of Sozopol, we found a high diversity of Amphora sensu lato taxa at a single site and on a single type of artificial substratum. A total of 40 taxa from the current genera Amphora, Halamphora, Seminavis and Tetramphora were recognized during light microscopy (LM) and scanning electron microscopy (SEM) observations. We were able to identify with a high degree of certainty only 6 taxa based on the literature, whereas for 19 taxa (or almost 50% of all taxa) we could not find even sufficiently similar species, and they remained unidentified to species level. Many of the species had small valve dimensions. The paper presents all taxa with short morphometric data and microphotographs under LM and SEM, where possible. All taxa are discussed and compared with similar known taxa. The illustrative materials in earlier works from the Black Sea and species descriptions, where such were available, were also consulted. Diversity of Amphora sensu lato in the Black Sea coastal waters seems to be underestimated, whereas some of the past records are uncertain. A discussion on the current state of knowledge of Amphora sensu lato species from the Black Sea is given.

Main aim of the study was to search for possible differences in diatom colonization and their communities under the influence of glacier meltwater inflow and when unaffected by glacier meltwater, and also to define the time needed for the development of diatom communities on newly submerged substrates at small depths in Antarctica. We used artificial substrates (Plexiglass© tiles), submerged at a depth of 1 m below the sea surface at two locations at the South Bay of Livingston Island: (1) Johnsons Dock – a cove, known to receive glacier meltwater with sediments, and (2) outside the cove, generally unaffected by glacial meltwater. Samples from the natural epilithon at similar depth were also taken as a reference for diatom community structure. Statistical testing the differences between the two sites was not possible this time, but the samples allowed us to compare the sites in terms of diatom growth, species richness, diversity and evenness changes in diatom communities along the time of the experiment at both sites and with the natural epilithon at similar depths. Diatom colonization followed the three-phases scheme (colonization, logarithmic growth and equilibrium) as in other latitudes. Based on the valve density and community indices e.g. species richness, diversity (1-D) and evenness (J’), we consider that at least three weeks might be necessary to obtain sufficiently representative for the environment diatom communities on new substrates at small depths in Antarctica, in conditions similar to those of South Bay. No particular differences between the sites were noted in the colonization scheme, but the diversity (1-D) and evenness (J’) were higher at glacier influenced site, as well as the number of the valves on the substrates. Sea ice diatoms prevailed at the glacier influenced site. We suggest that species exchange between the sea ice and other hard substrates do exist, at least for some taxa, and such species might be indicative for variations in both salinity and water transparency, related to glacial meltwater inflow.

The Red List presented in this paper is focused on Bulgarian non-marine microalgae which face a risk of extinction. The assignment to each IUCN Red List category is according to the seven specific criteria and their relative values in the new method for evaluation of the threatened status of microalgae (Stoyneva-Gärtner et al., this volume). The list contains 756 taxa (613 species, 82 varieties and 61 forms) from 7 divisions, classified in six IUCN categories and shows that threatened microalgae represent 14% the total algal biodiversity of Bulgaria.

Although the IUCN Red List Categories and Criteria is a widely internationally used system for classifying species at high risk of extinction, the micro-organisms are still practically excluded from the appropriately enlisted taxa. The present paper provides a method, which gives means to assess microalgae threat status much more objectively than it was possible before and in this way to achieve quite high degree of generalization in work with this peculiar group of organisms. The method described below uses the widely accepted standard IUCN Red List system of categories, but proposes their assignment on the basis of a complex application of seven criteria relevant to microalgae and classical data, available for them. These criteria can be interpreted in the same way for all taxonomic groups of algae and for all possible territorial levels (local, national, regional, global). The criteria are denominated with Latin capital letters A-G and each of them has a numerical expression with values (points) ranging between 4 and 1. The final assessment of the threat status is done on the basis of the total amount of points (T), which ranges between 7 and 28. In this way each alga is supplied with a formula (a combination of letters and numbers), which indicates its threat status and in the same time outlines its most critical, “weak spots” on which special attention has to be paid when conservation measures have to be proposed. As it is exemplifi ed in detail in the paper, the formula could be expressed in a table or in a text format, in full or in a short version, depending on the needs of the relevant studies or proposals (e.g. Anabaena lapponica Borge [VU – A3 B4 C4 D2 E2 F2 G3], or Anabaena lapponica Borge [VU – A3 B4 C4 D2 E2 F2 G3 T20], or Anabaena lapponica Borge [VU – T20]), or Anabaena lapponica Borge [VU]).