Analysis of the type material of Achnanthes minutissima var. macrocephala (Bacillariophyta) and description of two new small capitate Achnanthidium species from Europe and the Himalaya

Background and aims – Two unknown benthic diatom species belonging to the genus Achnanthidium Kütz., and found in French and Nepalese freshwater habitats, were investigated. Both species are here described as new and compared with the original material of Achnanthes minutissima var. macrocephala Hust. [≡ Achnanthidium macrocephalum (Hust.) Round & Bukht.] from Indonesia. Methods – The morphology of three small and capitate Achnanthidium species was investigated using light microscopy (LM) and scanning electron microscopy (SEM). Key results – Achnanthidium coxianum sp. nov. (from the Himalaya) belongs to the group of species with hooked terminal raphe endings, while Achnanthidium peetersianum sp. nov. (from France) has variable terminal raphe endings which are usually slightly bent. Achnanthidium macrocephalum is a much rarer species and illustrations concerning its identity in the literature do not conform to the type studied here. Conclusions – The three species are similar in LM but clearly distinct in SEM. The shape of the areolae and terminal raphe endings separate the species. Achnanthidium macrocephalum has often been misidentified in studies from many areas of the world. It is similar to the new species in valve outline and in its small dimensions.

Morphological variability within the Achnanthidium minutissimum species complex (Bacillariophyta): comparison between the type material of Achnanthes minutissima and related taxa, and new freshwater Achnanthidium species from Portugal

Two new taxa similar to Achnanthidium minutissimum were common and abundant in samples collected during a survey of benthic diatoms in watercourses from mainland Portugal. They are described here as A. duriense, sp. nov. and A. lusitanicum, sp. nov. In addition, the recently described A. pseudolineare is reported from various localities and its ecology is described in detail. The new Achnanthidium species from Portugal were compared with the type material of morphologically similar taxa: Achnanthidium microcephalum, Achnanthes minutissima, A. minutissima var. cryptocephala, A. minutissima var. inconspicua and A. nana. The analysis of this type material confirmed that Achnanthes minutissima var. cryptocephala should be regarded as a different taxon, and a new combination is proposed, Achnanthidium neocryptocephalum, stat., comb. et nom. nov. Achnanthes minutissima var. inconspicua is now considered as a younger synonym of Achnanthidium lineare. Based on a detailed morphological study of specimens of Achnanthes nana from Scotland, Nepal and Portugal, this taxon is transferred to the genus Achnanthidium as Achnanthidium nanum, comb. nov.

Epipelic Algae in Hemren Reservoir , Iraq

The study includes the epipelic algae in Hemren reservoir, for the period between Januarys to October 2000 .The samples were collected from three selected sites at north, middle and south of reservoir. A total of 96 taxa of epipelic algae were identified. The diatoms were the dominated by 82 taxa represented 85.4% of the total identified species, followed by blue-green algae (cyanophyta) of 6.3 taxa (6%), and then green algae (chlorophyta) of 5.2 taxa (5%). One species was recorded for each crysophyta, euglenophyta and pyrrophyta. The seasonal variation for the cell density showed two peaks during spring and autumn seasons. Few species were dominated during the most studied period such as Achnanthes minutissima, Navicula cryptocephala, N. cryptocephala var . veneta and Nitzschia palea .

Benthic Algae in Lower Zab Tributary and Tigris river

Benthic algae of Tigris river and one of its northern tributary the lower Zab were study at monthly intervals during Nov. 2001-Oct. 2002. Four sites were selected, a total of 115 species of algae were identified during this study, diatoms was the dominating group (86 species) followed by Chlorophyta (18 species), Cyanophyta (7species), Euglenophyta (2 species) and one species for each of Pyrrophyta and Chryzophyta. Pennate diatoms formed the major density within the identified algae and distributed among all stations especially the species Achnanthes minutissima, Navicula gracilis and Nitzschia palea, the diatoms bloomed in spring and autumn seasons. Bio-diversity and density of benthic algae in Tigris river was affected negatively by the entering waters from Lower Zab tributary, this was indicated by the decreasing values after the confluence.

Distribution and abundance of periphyton and phytoplankton species in two subarctic Canadian rivers

Periphytic and planktonic algal populations were sampled over a yearly cycle in the Ogilvie and Swift rivers located in the northern and southern Yukon, respectively. Diatoms and green algae dominated periphytic assemblages during spring, summer, and fall, whereas the bulk of the overwintering cells was diatoms. The 96 species of periphytic diatoms were dominated by Achnanthes minutissima Kütz., an unidentified species of Achnanthes, Cocconeis placentula Ehr., Diatoma hiemale var. mesodon (Ehr.) Grun., Diatoma tenue var. elongatum Lyngb., Anomoeoneis vitrea (Grun.) Ross, and Fragilaria crotonensis Kitton. Most diatoms encountered are also generally abundant in more temperate locations. Periphytic green algae were dominated by Mougeotia sp., Oedogonium sp., Ulothrix sp., and Stigeoclonium sp. In high flow regions of the Ogilvie River the red alga Lemanea fucina Bory was extremely abundant. Phytoplankton was sparse and generally represented by the same species as found in periphytic habitats. Results indicate that the phytoplankton cells were probably derived from sloughed periphytic cells. Achnanthes minutissima, Diatoma tenue var. elongatum, Fragilaria construens var. binodis (Ehr.) Grun., Fragilaria vaucheriae (Kütz.) Peters, and Synedra ulna (Nitz.) Ehr. were the most abundant species in the plankton.

Benthic algae in littoral and profundal areas of a deep subarctic lake

Collections of benthic algae were made in an isolated subarctic lake during July and August 1975. Samples were taken from 30 stations situated at depths of 0.1 to 35 m. The number of species associated with sediments declined with depth from 66 to 22 m. Achnanthes minutissima, Navicula pupula, Cymbella spp., and Nostoc pruniforme reached greatest relative abundance in shallow water whereas Nitzschia palea and Nitzschia dissipata were relatively common below 20 m. Amphora ovalis, Gyrosigma spenceri, and Tabellaria flocculosa did not exhibit a consistent distribution pattern. Standing crops of the epipelon ranged from3 × 106 cells cm−2 (8.5 × 10 μm3 cm−2) at a depth of 0.1–5 m to8 × 103 cells cm−2 (7 × 106 μm3 cm−2) below 20 m. Low light levels, and to a lesser degree, temperature were the most important factors influencing the diversity, species composition, and density of the epipelon in deep water.The epipsammic community consisted of 10 species at all depths. Although Achnanthes pinnata was rare in deep water, the relative abundance of other common species (Amphora ovalis var. pediculus, Fragilaria construens var. venter, and Achnanthes minutissima) was constant at all stations. Standing crops varied from 3.5 × 104 cells cm−2 (39 × 106 μm3 cm−2) at 0.1–5 m to0.3 × 104 cells cm−2 (0.3 × 106 μm3 cm−2) below 20 m. Although low light levels probably controlled densities in deep water, physical characteristics of the substrate determined the diversity and species composition of the community.

Epipelic and epiphytic algal communities in Great Slave Lake

Seasonal changes in the densities of epiphytic and epipelic algae were determined during 1975 and 1976 at two sites on the north shore of Great Slave Lake. The epiphyton waxed rapidly in May and reached maximum densities of 5–6 × 108 μm3/cm2 in June. Although densities remained high during the summer, they fell rapidly in October, followed by a secondary peak in November. The main species were Tabellaria flocculosa, Achnanthes minutissima, Achnanthes linearis, Gomphonema intricatum, and Lyngbya diguetii. The epipelon, consisting largely of Nitzschia palea, Nitzschia dissipata, Fragilaria construens, and Oscillatoria spp., also showed spring and fall peaks in densities, with maximum populations of 4.2 × 108 μm3/cm2 being recorded in June and July. The growing season for both communities was limited by the formation of ice in the fall, whereas the maximum standing crop of the flora was at least partially restricted by low nutrient levels (total phosphorus, 0.008 mg/L; total alkalinity, 30 mg/L).Seasonal changes in the density of epipelon were monitored during 1977 and 1978 at a third site on the north shore of the lake, where total phosphorus and total alkalinity ranged up to 0.010 and 94 mg/L, respectively. Prevalent taxa included Cymatopleura elliptica, Epithemia turgida, Rhopalodia gibba, Cymbella spp., and Nostoc spp. The growth cycles of the flora were again characterized by spring and fall peaks in numbers. Algal densities were, however, high (up to 2.3 × 109 μm3/cm2), possibly a reflection of nutrient availability.Samples of epiphyton and epipelon were taken at an additional seven sites in the east arm of the lake during June and July 1975. The main epiphytic species were Cocconeis placentula, Achnanthes minutissima, and Tabellaria flocculosa, while prevalent epipelic taxa included Navicula graciloides, Fragilaria vaucheriae, Tabellaria flocculosa, and Achnanthes minutissima. Densities were less than those recorded from the three sites on the north shore, again possibly a reflection of nutrient availability.

Distribution and abundance of attached, littoral algae in 21 lakes and streams in the Northwest Territories

Collections of epilithic, epipelic, epiphytic, and epipsammic algae were made from the littoral zone of 21 lakes and streams in the Northwest Territories during 1975 and 1976. Tabellaria flocculosa was the predominant species in the epilithon and epipelon, reaching maximum densities of 0.5–2.5 × 109 μm3/cm2 depending on watercourse. It was followed in importance by Achnanthes minutissima, Navicula spp., and Nitzschia frustulum, all of which occurred at densities of 0.1–0.3 × 109 μm3/cm2. While the only two common taxa in the epiphyton, A. minutissima and T. flocculosa, maintained populations of 1.0–1.3 × 109 μm3/cm2, the most frequently encountered epipsammic species, Amphora ovalis var. pediculus, Fragilaria construens var. venter, Achnanthes minutissima, and Achnanthes pinnata, reached maximum levels of 4 × 107 μm3/cm2. The growing season for the attached flora extended from June to October throughout the study area. All four communities displayed a unimodal growth curve during this period, reaching maximum abundance in either July or August. The end of the growing season came during the middle of October when the collection sites were frozen to the bottom.