Genus Skeletonema Research Articles

Allelopathic interactions between Prorocentrum micans and Skeletonema costatum or Karenia mikimotoi in laboratory cultures

Algal allelopathy is an ecological/physiological phenomenon that has focused attention on the interactions among algae and the production of algal toxins. We investigated the allelopathic interactions between the dinoflagellate genus Prorocentrum micans and diatom genus Skeletonema costatum and between P. micans and dinoflagellate genus Karenia mikimotoi using bi-algal cultures. Because the effects were species-specific and size-dependent, we evaluated the effect of different initial densities. At low densities of P. micans and high densities of S. costatum inoculated into the same medium, the growth of P. micans was weakly restrained, whereas the growth of S. costatum was significantly suppressed. S. costatum and K. mikimotoi were strongly inhibited by P. micans, in both the bi-algal cultures and enriched filtrates. Direct cell-to-cell contact was not necessary to gain a competitive advantage, thus, our results suggest that P. micans inhibited the growth of S. costatum and K. mikimotoi by the release of allelochemical(s). Last, a mathematical model was used to simulate growth and interactions between P. micans and S. costatum and between P. micans and K. mikimotoi in bi-algal cultures.

Livingstonia (Thalassiosirales, Bacillariophyta), a new genus of fultoportulate centric diatoms from an Atlantic coastal plain river in Florida, southeastern United States

Prasad A.K.S.K and Nienow J.A. 2011. Livingstonia (Thalassiosirales, Bacillariophyta), a new genus of fultoportulate centric diatoms from an Atlantic coastal plain river in Florida, southeastern United States. Phycologia 50: 264–280. DOI: 10.2216/09-89.1A morphological and taxonomic account of Livingstonia palatkaensis, a new genus and species of centric diatoms belonging to the order Thalassiosirales Glezer & Makarova, is provided. Descriptions are based on material collected from the St. Johns River, a major, highly colored blackwater river in the Atlantic coastal plain in the southeastern United States. Scanning electron microscopic observations clearly show that although the valve structure in Livingstonia shares broad similarities with the genera Thalassiosira and Skeletonema, the types of the two fultoportulate families Thalassiosiraceae and Skeletonemataceae, respectively, it is sufficiently dissimilar to warrant the description of a new genus. Livingstonia is characterized by the presence of compound marginal processes, each formed from the external extension of a fultoportula and a semielliptical hyaline hood or cover. The areolae have semicontinuous internal cribra. A single rimoportula is present near the valve center. No fultoportulae are found at or near the center of the valve face. Furthermore, Livingstonia lacks connecting threads of marginal fultoportulae and an external extension of the rimoportula on the valve face, a combination of features that is unusual in the genus Skeletonema. Livingstonia is also distinguished from two recently described freshwater genera in the Thalassiosiraceae from the southeastern United States, Cyclotubicoalitus and Spicaticribra, in having a rimoportula away from the margin but close to the center of the valve and in other key characteristics. A note on another freshwater, co-occurring, more frequent and widespread, chain-forming, closely related diatom, Skeletonema potamas, is also included. Livingstonia is tentatively placed in the family Thalassiosiraceae.

Species diversity of the genus Skeletonema (Bacillariophyceae) in the industrial harbor Dokai Bay, Japan

Seven Skeletonema species were identified at one station in the industrial harbor Dokai Bay, Japan, in October 2007 and then monthly from January 2008 to December 2009 by morphological scanning electron microscopy observations and molecular analyses of mainly the large subunit (LSU) rDNA. We refer to one species identified as S. dohrnii using LSU rDNA, but as S. marinoi using the small subunit (SSU) rDNA and consequently we use the term S. marinoi-dohrnii complex. This is the first time that S. ardens, S. costatum s.s., and S. pseudocostatum have been recorded in Japan and that S. menzelii and S. tropicum have been identified by molecular methods in Japan. The S. marinoi-dohrnii complex was isolated with high frequency all year-round, and S. japonicum was also isolated with high frequency but not so in summer. S. Tropicum was isolated from September to December, but S. ardens and S. costatum s.s. were isolated only when the water temperature exceeded 20°C. S. pseudocostatum bloomed just once, in summer, but S. menzelii was isolated in May and again in October. The continuous year-round occurrence of S. costatum s.l. in the bay is supported by the succession of these seven species. Six of the species, except S. menzelii, were important components of algal blooms in the bay. One to four species of Skeletonema were isolated every month. Monthly species diversity was higher when S. ardens, S. costatum s.s., and S. tropicum that are usually associated with tropical or subtropical waters, were isolated. In general, species diversity of the genus Skeletonema was very high in Dokai Bay.

Morphological Characteristics of Four Species in the Genus Skeletonema in Coastal Waters of South Korea

Most Skeletonema species have been identified under the name of S. costatum. To assess the morphological species diversity in the genus Skeletonema, we surveyed the nine localities in the coastal waters of South Korea. The light microscopy (LM) and scanning electron microscopy (SEM) observations in this study showed that ultrastructural features of genus Skeletonema discriminated among four species: S. dohrnii Sarno & Kooistra, S. marinoi Sarno & Zingone, S. subsalsum (Cleve) Bethge, and S. tropicum Cleve. In S. dohrnii, cell diameters were 3-6 μm and the pervalvar axes were 13-19 μm. One or two partial chloroplasts were visible in a cell. Cells of S. marinoi were 4-10 μm and the pervalvar axes were 8-18 μm. Each cell contained one chloroplast. Cells of S. subsalsum which contained 1-2 chloroplasts were 8-13 μm and the pervalvar axes were 11-20 μm. Cells of S. tropicum were 10-18 μm and the pervalvar axes were 4-9 μm. 2-4 chloroplasts were seen in each cell. Tip width of fultoportula in S. dohrnii and S. marioni was flared and flat, but that in S. subsalsum and S. tropicum was narrow. Morphological groups among them, S. dohrnii and S. marinoi were the most widely distributed in all seasons, while S. tropicum was only occurred in a summer season.

DIVERSITY AND MORPHOLOGY OF SKELETONEMA SPECIES IN SOUTHERN BRAZIL, SOUTHWESTERN ATLANTIC OCEAN(1).

We examined the morphology of Skeletonema species occurring in coastal waters of southern Brazil, on the basis of LM, SEM, and TEM analyses of six isolated strains and of 13 field samples from the Patos Lagoon estuary and the adjacent Cassino Beach. We concluded that the genus Skeletonema is highly diverse in coastal waters of southern Brazil, with the occurrence of four confirmed species: S. costatum, S. pseudocostatum, S. potamos, and S. tropicum. In addition, EM details must still be provided for S. menzelii, and genetic studies should be conducted to confirm the identity of S. cf. grethae and S. subsalsum. The high diversity in this geographic area can be attributed to the proximity of the Subtropical Convergence and to the freshwater ecosystems of Patos Lagoon and La Plata River that favor the presence of warm-, cold-, and brackish-water species.

The species concept in a marine diatom: LSU rDNA–based phylogenetic differentiation in Skeletonema marinoi/dohrnii (Bacillariophyceae) is not reflected in morphology

M. Ellegaard, A. Godhe, K. Härnström and M. McQuoid. 2008. The species concept in a marine diatom: LSU rDNA–based phylogenetic differentiation in Skeletonema marinoi/dohrnii (Bacillariophyceae) is not reflected in morphology. Phycologia 47: 156–167. DOI: 10.2216/07-09.1The ubiquitous marine diatom genus Skeletonema includes several newly described species. This paper presents a study of morphology and LSU sequence diversity of one of these new species, Skeletonema marinoi. The 15 monoclonal strains (from the Swedish west coast, the Swedish east coast, Portugal and Canada) included in the study showed differences in LSU rDNA sequence within the morphospecies, with differences seen even among clones established from a single plankton net sample. Morphologically, all clones were indistinguishable from each other and from the closely related species Skeletonema dohrnii. In the original description of these two species, they were differentiated by the structure of the girdle bands. However, the girdle band types of both species were found within single samples of almost all clones of S. marinoi in this study. The LSU-based phylogeny is consistent with the split into two species, and there may be a difference in their biogeographical distribution. We therefore do not at present suggest that the two species be merged. Questions regarding species delimitation and cryptic species within protists often arise from such studies that include data from both morphological and DNA sequence analysis, and such questions are addressed here.

Morphology and distribution of species of the diatom genusSkeletonemain a tropical coastal lagoon

Phytoplankton collected bimonthly by net during 1991–2 from the Sontecomapan lagoon (12 km long and 1·5 km wide), in the Gulf of Mexico, included four species and several forms of the diatom genus Skeletonema. The spatial and temporal distribution of Skeletonema subsalsum, S. pseudocostatum and S. costatum in the lagoon varied with the salinity. S. subsalsum was dominant in the rainy season (July–February), when salinity was 0–6 ppt. S. costatum was abundant in the adjacent marine zone, occasionally with S. tropicum, and occurred in the lagoon during the dry season (March) at salinities of 3·2–37·0 ppt. S. pseudocostatum was present the whole year showing a preference for brackish conditions (4–25 ppt). Morphological variation in three species was observed by light microscopy and studied in detail by electron microscopy. The shape of the external tubes of the fultoportulae, considered as an important taxonomic character, varied in S. subsalsum and S. pseudocostatum. We observed long threads in S. subsalsu...

THE FOSSIL GENUSTROCHOSIRA, ITS MORPHOLOGY, TAXONOMY AND SYSTEMATICS

An expanded description of the small fossil genus Trochosira is presented, and Trochosira mirabilis Kitton, T. spinosa Kitton and T. coronata Schrader & Fenner are described and illustrated. One species hitherto placed in the genus Skeletonema, S. polychaeta Strel'nikova, is transferred to Trochosira and the characters distinguishing Trochosira and Skeletonema are discussed. The complex linking mechanism of each Trochosira species is described and illustrated. This information, together with associated characters, confirms that the genus belongs in the family Melosiraceae. Relationships with other genera and families are discussed.