Grethe Rytter Hasle

A STUDY OF THE PSEUDO‐NITZSCHIA PSEUDODELICATISSIMA/CUSPIDATA COMPLEX (BACILLARIOPHYCEAE): WHAT IS P. PSEUDODELICATISSIMA? 1

Based on morphological variation found in specimens ascribed to Pseudo‐nitzschia pseudodelicatissima and uncertainty regarding the delineation of P. pseudodelicatissima and P. cuspidata, cultures and field material of diatoms in the P. pseudodelicatissima/cuspidata complex were studied in morphological detail. Four different species were identified. The descriptions of the species P. pseudodelicatissima and P. cuspidata were emended on the basis of studies of type material. In addition, P. calliantha sp. nov. and P. caciantha sp. nov. were described as new species based on morphological and molecular data. The morphological differences among the species were found in characters such as width and shape of the valve, density of fibulae and striae, structural pattern of the poroid hymen, and structure of the girdle bands. The morphological studies were supported by phylogenetic analyses of the nuclear‐encoded internal transcribed spacer 1, 5.8S, and internal transcribed spacer 2 rDNA of 24 strains representing 16 different Pseudo‐nitzschia species. The description of the four species helps to explain the variation observed in mating experiments on cultures originally designated as P. pseudodelicatissima. At least two previous reports of toxin production in species identified as P. pseudodelicatissima have been identified as being caused by P. calliantha, and one additional report of toxin production has been identified as either P. pseudodelicatissima or P. cuspidata.

Are most of the domoic acid-producing species of the diatom genus Pseudo-nitzschia cosmopolites?

Abstract Records from all oceans, most of them published during 1990–2000, and personal unpublished observations of nine Pseudo-nitzschia taxa known as potential domoic acid (DA) producers have been used to outline their geographical distribution. Pseudo-nitzschia seriata f. seriata as the only taxon was found in the North Atlantic Ocean exclusively. The records of P. multistriata were too few and the identification of P. turgidula from the North Atlantic too unreliable to provide an idea about their distribution. Pseudo-nitzschia pungens and the less frequently recorded P. fraudulenta, P. multiseries and P. australis appeared to be cosmopolites. The wide distribution of the apparently most efficient DA producers, P. australis and P. multiseries, is especially noteworthy. The records of P. delicatissima and P. pseudodelicatissima also indicate a cosmopolitan distribution although with the qualification of certain taxonomic and identification ambiguities. Hence, the question of whether most DA-producing Pseudo-nitzschia species are cosmopolites may be answered with a tentative “yes”.

Chapter 2 – Marine Diatoms

This chapter provides an introductory biology of marine diatoms, their classification, heteromorphy, evolution, and critical evaluation. It consists of sections on classification as well as generic atlas. A diatom system is based on results from light and electron microscopy and constructed key to the diatom families. Diatoms reproduce vegetatively by binary fission resulting in formation of two new individuals within the parent cell frustule. The probable size range of the diatom cells are species dependent, and the specific variation may be as large as 8–10 times the length of the apical axis or the diameter. Despite the availability of other publications, there is still a need to fill the gap with respect to the global aspect, especially when identifying Marine diatoms at the specific level. The entire discussion aims to meet the morphological need of new diatom information as well as the classical identification literature. This comprehensive volume explores the two Polar Regions and has an ecological interpretation as well as a taxonomic part with the key to the study of marine diatom species. General characteristics of marine diatoms together with their life cycles have also been discussed.

The biogeography of some marine planktonic diatoms

Abstract Phytoplankton net samples from all oceans were examined by advanced light microscopy or electron microscopy for the presence of 26 diatom species, and the records plotted on eight distribution maps. Some of the species are classified as cosmopolitan, some as warm-water species and some as cold-water species. The cold-water species belong either to the Northern Hemisphere or to the Southern Hemisphere, or are suggested as being bipolar, having a disjunct distribution. Some of the smallest marine planktonic diatoms collected have a cosmopolitan distribution. Thalassiosira species, forming gelatinous masses, seem to be most prominent in coastal waters where upwelling occurs. The distribution patterns of T. gravida and T. rotula indicate that they may be modifications of the same species. The finding of morphologically and taxonomically closely related species in distinctly different biogeographic regions emphasizes the importance of reliable identification at the specific level.

A review ofPseudo-nitzschia, with special reference to the Skagerrak, North Atlantic, and adjacent waters

ThePseudo-nitzschia flora of the Skagerrak, North Atlantic, and adjacent waters, comprisingP. pungens, P. multiseries, P. seriata, P. fraudulenta, P. heimii, P. delicatissima, andP. pseudodelicatissima, has been examined. Except forP. australis, allPseudo-nitzschia species shown to produce the toxin domoic acid are present in the area although an outbreak of amnesic shellfish poisoning has never been reported. For comparison of morphological and taxonomic characters,Pseudo-nitzschia seriata f.obtusa, P. australis, P. subfraudulenta, P. subpacifica, P. lineola, P. inflatula, andP. cuspidata have been included in this investigation. Fine details of band structure and poroid occlusions, previously ignored or unresolved, have proven to add to the morphological distinction betweenP. pungens andP. multiseries, P. seriata andP. fraudulenta, P. seriata andP. australis, andP. delicatissima andP. pseudodelicatissima. Additional information on the structure of the proximal mantle compared to that of the valve face has revealed similarities in most of the species but differences betweenP. pungens andP. multiseries. The species seasonal and long-term distributional patterns during the sampling period (October 1978 through September 1993) in the Skagerrak area are outlined. The greatest abundances ofP. seriata, a cold-water species most likely restricted to the northern hemisphere, occurred in the spring, and those of the presumably cosmopolitan diatomsP. pungens, P. multiseries andP. pseudodelicatissima, in the autumn. WhereasP. multiseries seems to have decreased in abundance in the 1990s,P. pseudodelicatissima has apparently increased.

Morphology, phylogeny and taxonomy of species within the Pseudo-nitzschia americana complex (Bacillariophyceae) with descriptions of two new species, Pseudo-nitzschia brasiliana and Pseudo-nitzschia linea

Abstract Pseudo-nitzschia americana and the two closely related species P. brasiliana Lundholm, Hasle & G.A. Fryxell sp. nov. and P. linea Lundholm, Hasle & G.A. Fryxell sp. nov. are described, based on morphology. The phylogenetic positions of P. americana and P. brasiliana are inferred from partial nuclear-encoded large-subunit ribosomal DNA and their toxin production is assessed. The new species P. brasiliana and P. linea form stepped colonies, whereas P. americana is single celled. Pseudo-nitzschia americana, P. brasiliana and P. linea possess morphological features typical of Pseudo-nitzschia and Fragilariopsis, differentiating them from Nitzschia. All three species possess valve shapes similar to many Fragilariopsis species and they seem to constitute a morphological continuum between Pseudo-nitzschia and Fragilariopsis. Molecular phylogenetic analyses showed P. americana and P. brasiliana to be sister taxa within a strongly supported monophyletic clade comprising Pseudo-nitzschia and Fragilariopsis. On the basis of both the morphological and phylogenetic results, we conclude that P. americana can be assigned to Pseudo-nitzschia, following previous uncertainty as to whether it might belong to Nitzschia. Both P. americana and P. linea have been observed as epiphytes on other diatoms, which might indicate physiological differences from P. brasiliana, which has only been found free-living. In addition, P. americana and P. brasiliana differ with respect to valve width (transapical axis), the density of the transapical ribs (interstriae) and fibulae and the structure of the girdle bands (copulae). The results of the phylogenetic analyses and differences in distribution support these morphological differences. Pseudo-nitzschia linea differs with respect to valve shape, density of interstriae and structure of the girdle bands.

PSEUDO‐NITZSCHIA PUNGENS AND P. MULTISERIES (BACILLARIOPHYCEAE): NOMENCLATURAL HISTORY, MORPHOLOGY, AND DISTRIBUTION1

Pseudo‐nitzschia pungens f: multiseries is raised in rank from form to species based on morphological, physiological, and genetic features. Distinctive details of the valve face striae, the valve mantle, and the girdle of P. pungens and P. multiseries are outlined. The nomenclatural history and the distribution of the two species and their relationship to other species of the genus are discussed.

THALASSIOSIRA ECCENTRICA (EHRENB.) CLEVE, T. SYMMETRICA SP. NOV., AND SOME RELATED CENTRIC DIATOMS1

Examination of original material from the Ehrenberg collection plus clonal cultures from the Gulf of Mexico and net hauls from widely separated stations in the worlds oceans confirms that Coscinodiscus eccentricus is correctly placed as Thalassiosira eccentrica (Ehrenb.) Cleve. A closely related species, T. symmetrica, is described, with, the main differences being found in the value processes and distribution patterns. The former species is more abundant in inshore waters; the latter has been found in oceanic waters. Comparisons are drawn between these 2 species, T. mendiolana and Planktoniella sol.

PSEUDO-NITZSCHIA AS A GENUS DISTINCT FROM NITZSCHIA (BACILLARIOPHYCEAE)1

Morphologic, diagnostic characters of the subgenus Nitzschia, genus Nitzschia Hassall 1845, and the marine planktonic genus Pseudo‐nitzschia H. Peragallo in H. & M. Peragallo 1900 were compared. Colony formation by overlap of cell ends; weakly silicified, shallow, and flattened valves; an extremely eccentric raphe, not elevated above the general level of the valve; lack of con‐opea; and striated girdle bands characterize Pseudo‐nitzschia as a natural group and a genus separate from Nitzschia.

A quantitative study of phytoplankton from the equatorial Pacific

Abstract The hydrography and abundance of phytoplankton were studied at three stations located in the equatorial Pacific, March 1957. Water bottle samples preserved with neutralized formalin were used for the phytoplankton study, which included the smaller forms of diatoms, dinoflagellates and coccolithophorids. Difficulties in obtaining reliable estimates in the case of poor populations were overcome by a simple concentration technique. The quantity of phytoplankton, computed as number of cells under 0·1 m 2 , was found to be much the same as the maximal figure for the Sargasso Sea and the amount obtained before and after the time of maximal population in the antarctic and subantarctic Pacific. In the equatorial Pacific phytoplankton abundance was restricted to the upper 50 to 100 m. Maxima in the numbers of diatoms were found nearer the surface than those of dinoflagellates, while the coccolithophorids showed different patterns in their vertical distribution. “Olivgrune Zellen” ( Hentschel ) were present at the greatest sampling depths. A pennate diatom species, athecate dinoflagellates and certain small coccolithophorids were the most numerous forms observed. Circumstantial evidence of seasonal variation is discussed.