Harmful diatoms introduction, page 1of 9
Module II
Harmful diatoms (Bacillariophyceae) (10 hours)
Contents
1.1
1.2
Suggested reading
Some basic features of diatoms
Diatom frustule, see separate document
Diatom reproduction, see separate document
1.3. Identification of diatoms
Procedure for cleaning diatom valves, see separate document
1.4 Harmful diatom species
1.5.1
Pseudo-nitzschia
1.5.2
Nitzschia
1.5.3
Chaetoceros
Terminology of Pseudo-nitzschia and Chaetoceros, see separate document
Morphology of Nitzschia navis-varingica, see separate document
1.5. References and identification literature
References in bold are available as pdf files on the course CD.
1.1. Suggested reading
Bates, S.S. Garrison, D.L. & Horner, R.A. 1998. Bloom dynamics and physiology of
domoic-acid-producing Pseudo-nitzschia species - In: Anderson, D.M., Cembella, A.D.
& Hallegraeff, G.M. (eds), Physiological ecology of harmful algal blooms, NATO ASI
series, Series G, Ecological sciences, vol. 41, Springer-Verlag, Berlin, pp. 267-292,
(see Books, pdf file NATO ASI)
Bates, S.S. 1998. Ecophysiology and metabolism of ASP toxin production - In: Anderson,
D.M., Cembella, A.D. & Hallegraeff, G.M. (eds), Physiological ecology of harmful algal
blooms, NATO ASI series, Series G, Ecological sciences, vol. 41, Springer-Verlag,
Berlin, pp. 405-426, (see Books, pdf file NATO ASI).
Graham & Wilcox 2000: Chapter 12, pp. 232-235 (Tripartite flagellar hairs of ochrophytes );
pp. 238 (Plastids) – 239; pp. 241 (Diatoms) – 248 (Diatom Motility and Mucilage
Secretion).
Fryxell, G.A. & Hasle, G.R. 2004. Taxonomy of harmful diatoms. – In: Hallegraeff, G.M.,
Anderson & D.M., Cembella, A.D. (eds), Manual on Harmful Marine Microalgae. –
Monographs on oceanographic methodology 11, Unesco, Paris, pp. 465-510.
Hasle, G.R & Syvertsen, E. 1997. Marine Diatoms. – In Tomas, C. (ed.) Identifying Marine
Phytoplankton, Academic Press, pp. 5-27.
Harmful diatoms introduction, page 2 of 9
1.2. Basic features of diatoms
Diatoms are ecologically one of the most important algal groups. It has been estimated that
diatoms account for 40-45% of the oceans primary production (Mann 1999) and 20-25% of
the global primary production (Werner 1977). Diatoms are also one of the largest algal
groups known with respect to species number, comprising ca. 12.000 accepted species.
Much of the species diversity of diatoms is, however, still undescribed and estimates of more
than 200.000 species have been suggested by experienced taxonomists (Mann & Droop
1996). Diatoms are distributed in all aquatic environments and they appear at all latitudes
(Round et al. 1990).
Diatoms are eukaryotic, unicellular, organisms. The vast majority are photosynthetic; only
less than ten species have been found to be heterotrophic (Round et al. 1990). The
characteristics of diatoms are: type of colony, chloroplast number and shape, cell shape and
characters of the siliceous cell wall.
The cell wall
This consists mainly of amorphous polymerized silicic acid, but it contains also protein,
polysaccharide, and lipids. Each siliceous element (valve or girdle band) is formed inside a
vesicle. The wall always consists of two large parts called the valves, and a number of
smaller structures linking the valves and called the bands. Together, the valves and the
bands are called the frustule (see separate document, II-1-DiatomFrustule).
Reproduction
Vegetative reproduction causes a reduction in cell size in most species of diatoms, and after
a number of successive divisions the cells reach a critical minimal size where mitosis can no
longer take place. This may induce sexual reproduction and restores the size of the diatom
cell to its maximum (see separate document, II-2-DiatomReproduction).
Phylogenetic affinity
The diatoms are included in the Heterokontophyta because they share a number of features
characteristic of this division, most importantly the tripartite flagellar hairs (stiff tubular hairs)
on the flagellum of the spermatozoids produced by the centric species.
Taxonomy
The diatoms are traditionally divided into two orders ‘Pennales’ and ‘Centrales’ based on
valve symmetry, following e.g. Simonsen (1979). More recently, many more classes, orders,
families and genera have been proposed by Round et al. (1990) and due to their work it is
presently widely accepted that the diatoms are divided into 3 groups: the centric diatoms, the
araphid, pennate diatoms and the raphid, pennate diatoms. Based on phylogenetic studies of
the 18S rDNA supported by morphological data, Medlin & Kaczmarska (2004) divide the
diatoms into three groups (classes), which, however, do not correspond to the groups by
Round et al. (1990). The suggested groups are 1. radial centric diatoms, 2. bi- or multipolar
and some radial centric diatoms and 3: the pennate diatoms (see Medlin & Kaczmarska 2004
for further details).
Harmful diatoms introduction, page 3 of 9
1.3. Identification of diatoms
Examination of samples
Many planktonic diatoms, e.g. species of Bacteriastrum and most species of Chaetoceros,
can be identified directly by LM, as the features used to discriminate between the species
can be observed without any particular preparation of the samples. In other genera, e.g.
Thalassiosira, Pseudo-nitzschia and Nitzschia, it is necessary to clean the valves (remove
organic material from the silica frustule) and examine these under the light and/or electron
microscope in order to observe the micro-morphology of the frustules, which provide the
features for species identification.
Preparation of samples
Cleaning of the frustules may be done in different ways, but application of gentle oxidizing
chemical agents, e.g. KMnO4, usually works well with both natural samples and culture
material (see separate document, II-3-DiatomCleaning).
For general identification literature on planktonic diatoms, see Hasle & Syvertsen (1997).
1.4. Harmful diatom species
All diatoms that occur in bloom proportions may be considered potentially harmful (Fryxell &
Hasle 2004). The ecological effects of diatom blooms have been related to dissolved oxygen
deficit, production of large amounts of mucus, bitter taste of shellf as well as various effects
on fish. A number of different diatom species have been implicated in such harmful events,
e.g. Thalassiosira mala, Rhizosolenia chunii, Cerataulina pelagica, but often it is difficult to
verify the exact cause of the effects. Harmful effects are also caused by secondary effects,
e.g. clogging of gills of fish or shellfish because of mucilage production (e.g. Thalassiosira
mala and Coscinodiscus wailesii), or clogging and physical damage of fish gills, for example
by large species of Chaetoceros (Fryxell & Hasle 2004).
A number of diatoms may cause harmful effects by production of toxin, such as in species of
Pseudo-nitzschia (e.g. Bates 2000) Nitzschia navis-varingica (Kotaki et al. 2000), and
perhaps Amphora coffeaeformis (Maranda et al. 1990, Sala et al. 1998). The poisoning
caused by accumulation of the toxin is called amnesic shellfish poisoning.
Amnesic shellfish poisoning
Potentially toxic diatoms produce the neurotoxin domoic acid (DA), which may cause
amnesic shellfish poisoning (ASP). The name ASP refers to one of the symptoms of domoic
acid, apart from several gastro-intestinal and neurological symptoms, namely amnesia
(memory loss). Domoic acid may accumulate in the food webs in a number of organisms like
crabs, lobsters, fish and shellfish. Very little is known about the effect of domoic acid on most
of these organisms. But mass death of seabirds and marine mammals having eaten toxic
mackerel or anchovies has been seen at the coast of California and Mexico (see Bates
1998, Bates et al. 1998).
The rather few detailed studies of DA production in Pseudo-nitzschia indicate that production
of DA is affected by a number of chemical and physical parameters and that most factors
enhancing DA production seem to be related to restriction of growth. Examples of such
Harmful diatoms introduction, page 4 of 9
factors are depletion of phosphate, silicate, high pH and presence of bacteria (see Bates
1998, Lundholm et al. 2005). The effects of iron and copper are still controversial (Bates et
al. 2001, Maldonado et al. 2002). Further studies on physiology of DA-production of toxic
diatoms are still needed, as studies have only been performed on a few species, mainly P.
multiseries.
1.4.1 Pseudo-nitzschia
Pseudo-nitzschia species are marine planktonic organisms. They are easily recognised to
genus level due to their ability to form colonies. In these colonies the cells are linked tip by tip
to each other (Fig. 1). The colonies may be very long, comprising up to 30 cells. Species of
Pseudo-nitzschia may, however, also be found as single cells, as the colonies are formed
during exponential growth and are broken down during stationary growth.
Fig. 1. Colony of Pseudo-nitzschia delicatissima (in girdle view)
The genus Pseudo-nitzschia comprises more than 30 taxa of which 11 are potential toxin
producers. The following list of species is based on Fryxell et al. (1997), Priisholm et al.
(2002), Fryxell & Hasle (2004), Lundholm & Moestrup 2002 and Lundholm et al. (2003).
Potentially toxic species are indicated in bold. P. pseudodelicatissima is here indicated as
potentially toxic, but due to the taxonomic problems in the P. pseudodelicatissima complex in
the past, it is at present uncertain whether it is potentially toxic, see Lundholm et al. (2003).
P. americana (Hasle) Fryxell
P. antarctica Manguin
P. australis Frenguelli
P. brasiliana Lundholm, Hasle et Fryxell
P. caciantha Lundholm, Moestrup et Hasle
P. calliantha Lundholm, Moestrup et Hasle
P. cuspidata (Hasle) Hasle
P. decipiens Lundholm et Moestrup
P. delicatissima (Cleve) Heiden
P. dolorosa Lundholm et Moestrup
P. fraudulenta (Cleve) Hasle
P. galaxiae Lundholm et Moestrup
P. granii (Hasle) Hasle
P. heimii Manguin
P. inflatula (Hasle) Hasle
P. linea Lundholm, Hasle et Fryxell
P. lineola (Cleve) Hasle
P. micropora Priisholm et Moestrup
P. multiseries (Hasle) Hasle
P. multistriata (Takano) Takano
P. obtusa (Hasle) Hasle et Lundholm
P. prolongatoides (Hasle) Hasle
P. pseudodelicatissima (Hasle) Hasle
P. pungens (Cleve) Hasle
P. pungiformis (Hasle) Hasle
P. seriata (Cleve) Peragallo f. seriata
P. sinica Qi et Wang
P. subcurvata (Hasle) Fryxell
P. subfraudulenta (Hasle) Hasle
P. subpacifica (Hasle) Hasle
P. turgidula (Hustedt) Hasle
P. turgiduloides (Hasle) Hasle
The geographical distribution of the potentially toxic species has been reviewed by Hasle
(2002). Seasonal variation in valve morphology has been shown in P. galaxiae (Cerino et al.
Harmful diatoms introduction, page 5 of 9
2005). The phylogenetic relationships of Pseudo-nitzschia have been studied by Lundholm
et al. (2002, 2003, 2006) and Orsini et al. (2002).
Identification of Pseudo-nitzschia
Identification of species of Pseudo-nitzschia requires observation of the detailed morphology
of the valve (and sometimes of the bands) and can generally be done only by EM. The valve
structure, the descriptive terminology, and the application of this are explained in a separate
document, see II-4-Terninology.
For identification of Pseudo-nitzschia, the following literature is relevant: Fryxell & Hasle
(2004), Hasle & Syvertsen (1997), Lundholm et al. (2003), Priisholm et al. (2002), Qi et al.
(1994), Skov et al. (1999), and Skov et al. (2004).
In some cases, molecular probes have been applied for identification of Pseudonitzschia (Fig. 2), but more research is needed before they can be generally applied
(Scholin et al. 1999). When molecular probes have been developed for monitoring,
identification of Pseudo-nitzschia will become much faster and easier and identification will
then not depend on expensive equipment like electron microscopes.
Fig. 2. Application of molecular probes. A. Normal bright field microscopy of a sample of
Pseudo-nitzschia containing two different species. B. & C. Application of molecular probes
detecting the two different species in B and C, respectively (from Miller et al. 1998).
1.4.2. Nitzschia
Several toxic strains of the benthic species Nitzschia navis-varingica have been isolated from
both temperate (Japan) and tropical (the Philippines) areas (Kotaki et al. 2004). No harmful
effects of the species have with certainty been detected in the field, but the species was
originally isolated and detected as toxic during a search for the causes of dead shrimp in
shrimp ponds in Vietnam (Kotaki et al. 2000). Presently, it has not been documented that
domoic acid was responsible for the death of the shrimps.
Identification of Nitzschia navis-varingica
Nitzschia is one of the largest and most difficult diatom genera. It comprises around 900 valid
species and as no comprehensive monograph exists, one is left to search in the original
Harmful diatoms introduction, page 6 of 9
literature, much of it being very old. Most of the species are only described using light
microscopy. Furthermore, the grouping of the species in the genus seriously needs revision.
Hence, we will during this course not focus on Nitzschia, but only present the morphological
characteristics of the toxic Nitzschia navis-varingica (see Lundholm & Moestrup 2000).
1.4.3. Chaetoceros
According to Hasle & Syvertsen (1997), Chaetoceros is one the largest, if not the largest
genus of marine planktonic diatoms, with ca. 400 species described. High concentrations of
Chaetoceros spp. may clog the gills of farmed fish and the spiny Chaetoceros setae can
penetrate the gill tissue. Fish mortality is therefore caused by induced hypoxia (mucus
produced by the gill tissue) and hypercapnia (excessive amount of carbon dioxide in the
blood).
Identification of Chaetoceros
Two main groups can be recognized within the genus Chaetoceros: subgenus Phaeoceros
and subgenus Hyalochaetae, whose characteristics easily observed under LM are presented
below. The valve structure, the descriptive terminology, and its application are explained in
the separate document, II-4-Terninology. The species C. convolutus and C. concavicornis
(both subgenus Phaeoceros) have been directly implicated in mortality of farmed fish on the
Pacific coast of North America (e.g., Horner et al. 1990, Rensell 1993), while the presence
of C. convolutus and gelatinous masses of C. socialis (subgenus Hyalochaetae) were
associated to impacts of farmed fish in Chile (Clement & Lembeye 1993).
subgenus Phaeoceros
Large, robust cell
Setae strong, thick, often very long, striated,
and with conspicuous spines
Numerous, small chloroplasts throughout the
whole cell, the setae included
Mostly oceanic
subgenus Hyalochaetae
More delicate cell
Setae thin, often hair-like, without chloroplasts,
spines seen in some species
Chloroplasts, one or a few plates or, more
rarely, small granules
Mainly distributed in coastal and inshore waters
1.5. References and identification literature (comments in italics)
A comprehensive and regularly up-dated list of references can be found on:
http://www.glf.dfo-mpo.gc.ca/pls/inter/dapr_view_intro?langE=en
Bates, S.S.1998. Ecophysiology and metabolism of ASP toxin production - In: Anderson,
D.M., Cembella, A.D. & Hallegraeff, G.M. (eds), Physiological Ecology of Harmful Algal
Blooms, NATO ASI series, Series G, Ecological sciences, vol. 41, Springer-Verlag,
Berlin, pp. 405-426.
Bates, S.S. 2000. Domoic-acid-producing diatoms: another genus added! - J. Phycol. 36:
978-983.
Bates, S. S., Garrison, D. L. & Horner, R. A. 1998. Bloom dynamics and physiology of
domoic-acid-producing Pseudo-nitzschia species. - In: Anderson, D.M., Cembella, A. D.
Harmful diatoms introduction, page 7 of 9
& Hallegraeff, G. M. (eds), Physiological Ecology of Harmful Algal Blooms, NATO ASI
series, Series G, Ecological sciences, vol. 41, Springer-Verlag, Berlin, pp. 267-292.
Bates, S.S., C. Léger, M.F. Satchwell, and G.L. Boyer. 2001. The effects of iron on domoic
acid production by Pseudo-nitzschia multiseries, - In: G.M. Hallegraeff, S.I. Blackburn,
C.J. Bolch, and R.J. Lewis (eds.) Harmful Algal Blooms 2000. Intergovernmental
Oceanographic Commission of UNESCO, Paris, pp. 320-323.
Cerino F., L. Orsini, D. Sarno, C. Dell’Aversano, L. Tartaglione, and A. Zingone. 2005.
The alternation of different morphotypes in the seasonal cycle of the toxic diatom
Pseudo-nitzschia galaxiae. - Harmful Algae 4: 33-48.
Christensen, T. 1988. Alger i naturen og i laboratoriet. - Københavns Universitet. Institut for
Sporeplanter, 137 pp.
Clément, A. & Lembeye, G. 1993. Phytoplankton monitoring program in the fish farming
region of South Chile. - In: Smayda, T.J. & Shimizu, Y. (eds.). Toxic Phytoplankton
Blooms in the Sea. Elsevier, New Cork, pp. 223-228.
Fryxell, G.A. & Hasle, G.R. 2004. Taxonomy of harmful diatoms. – In: Hallegraeff, G.M.,
Anderson & D.M., Cembella, A.D. (eds), Manual on Harmful Marine Microalgae. –
Monographs on oceanographic methodology 11, Unesco, Paris, pp. 465-510.
Fryxell, G.A., Villac, M.C. & Shapiro, L.P. 1997. The occurrence of the toxic diatom genus
Pseudo-nitzschia (Bacillariophyceae) on the West Coast of the USA, 1920 -1996: a
review. - Phycologia 36: 419-437.
Hasle, G.R. 2002. Are most of the domoic acid-producing species of the diatom genus
Pseudo-nitzshica cosmopolites ? – Harmful Algae 1: 137-146.
Hasle, G.R. & Fryxell, G.A. 1970. Diatoms: cleaning and mounting for light and electron
microscopy. - Transactions of the American microscopical society 89: 469-474.
Hasle, G.R. & Syvertsen, E.E. 1997. Marine Diatoms. – In: Tomas, C. (ed.), Identifying
Marine Phytoplankton, Academic Press, pp.5-385. A modern account of diatoms
including many recent name changes and lists of synonyms, useful for identification of
planktonic diatoms.
Horner, R. A., Postel, J.R. & Rensel, L.E. 1990. Noxious phytoplankton blooms in western
Washington waters: a review. - In: Granéli, E. Sundström, B., Edler, L. & Anderson,
D.M. (eds.). Toxic Marine Phytoplankton. Elsevier, New York, pp.171-176.
Kotaki, Y., Koike, K., Yoshida, M., Thuoc, C. V., Huyen, N.T.M., Hoi, N.C., Fukuyo, Y. &
Kodama, M. 2000. Domoic acid production in Nitzschia sp. (Bacillariophyceae) isolated
from a shrimp-culture pond in Do Son, Vietnam. - J. Phycol. 36: 1057-1060.
Kotaki, Y., Lundholm, N., Onodera, H., Kobayashi, K., Bajarias, F.F.A., Furio, E.F., Iwataki,
M., Fukuyo, Y. & Kodama, M. 2004. Wide distribution of Nitzschia navis-varingica, a
new domoic-acid-producing benthic diatom found in Vietnam. - Fish. Sci. 70: 28-32.
Lundholm, N. & Moestrup, Ø. 2000. Morphology of the marine diatom Nitzschia navisvaringica sp. nov. (Bacillariophyceae), another producer of the neurotoxin domoic acid.
- J. Phycol. 36: 1162-1174.
Lundholm, N. & Moestrup, Ø. 2002. The marine diatom Pseudo-nitzschia galaxiae sp. nov.
(Bacillariophyceae): morphology and phylogenetic relationships. - Phycologia 41: 594605.
Lundholm, N., Daugbjerg, N. & Moestrup, Ø. 2002. Phylogeny of the Bacillariaceae with
emphasis on the genus Pseudo-nitzschia (Bacillariophyceae) based on partial
LSUrDNA. – Eur. J. Phycol. 37: 115-134.
Lundholm, N., Moestrup, Ø., Hasle, G.R. & Hoef-Emden, K. 2003. A study of the Pseudonitzshcia pseudodelicatissima/cuspidata complex (Bacillariophyceae): what is P.
pseudodelicatissima? – J. Phycol. 39: 797-813.
Lundholm N., Hansen PJ, Kotaki Y. 2005. Lack of allelopathic effects of the domoic acidproducing marine diatom Pseudo-nitzschia multiseries. - Mar. Ecol. Prog. Ser. 288: 21-
Harmful diatoms introduction, page 8 of 9
33.
Lundholm, N., Moestrup, Ø., Kotaki, Y., Hoef-Emden, K., Scholin, C. & Miller, P. 2006.
Inter- and intraspecific variation of the Pseudo-nitzschia delicatissima complex
(Bacillariophyceae) illustrated by rRNA probes, morphological data and phylogenetic
analyses. - J. Phycol. 42: 464-481.
Maldonado, M.T., M.P. Hughes, E.L. Rue, & M.L. Wells. 2002. The effect of Fe and Cu on
growth and domoic acid production by Pseudo-nitzschia multiseries and Pseudonitzschia australis. - Limnol. Oceanogr. 47: 515-526.
Mann, D.G. (1999). The species concept in diatoms. - Phycologia 38: 437-495.
Mann, D.G. & Droop, S.J.M. 1996. Biodiversity, biogeography and conservation of diatoms. Hydrobiologia 336: 19-32.
Maranda, L., Wang, R., Musauda, K. & Shimizu, Y. 1990. Investigation of the source of
domoic acid in mussels. - In: Granéli, E. Sundström, B., Edler, L. & Anderson, D. M.
(eds.) Toxic Marine Phytoplankton. Elsevier Sci. Publ. Co., Inc., New York, pp. 300304.
Medlin, L.K. & Kaczmarska, I. 2004. Evolution of the diatoms: V. Morphological and
cytological support for the major clades and a taxonomic revision. - Phycologia 43: 245270.
Miller, P.E. & C.A. Scholin. 1998. Identification and enumeration of cultured and wild Pseudonitzschia (Bacillariophyceae) using species-specific LSU rRNA-targeted fluorescent
probes and filter-based whole cell hybridization. - J. Phycol. 34: 371-382.
Orsini, L, Sarno, D., Procaccini, G., Poletti, R., Dahlmann, J. & Montresor, M. 2002.
Toxic Pseudo-nitzschia multistriata (Bacillariophyceae) from the Gulf of Naples:
morphology, toxin analysis and phylogenetic relationships with other Pseudo-nitzschia
species. - European J. Phycol. 37: 247-257.
Priisholm, K., Moestrup, Ø. & Lundholm, N. 2002. Taxonomic notes on the marine diatom
genus Pseudo-nitzschia in the Andaman sea near the Island of Phuket, Thailand, with a
description of Pseudo-nitzschia micropora sp. nov. – Diatom Research 17: 153-175.
Qi, Y., Ju, W. & Lei, Z. 1994. The taxonomy and bloom ecology of Pseudo-nitzschia on the
coasts of China. - In: Nontji, A., Soemodihardjo, S., Ilahude, A. G., Setiapermana, D.,
Preseno, D.P., Moosa, M.K. & Ongkosongo, O.T.R. (eds), Proceedings IOCWESTPAC Third Internat. Scientific Symp., Bali, Indonesia, 22-26 Nov., 1994.
Research and Development Centre for Oceanology, Indonesian Institute of Science,
pp. 88-95.
Rensel, L.E. 1993. Severe blood hypoxia of Atlantic salmon (Salmo salar) exposed to the
marine diatom Chaetoceros concavicornis. - In: Smayda, T.J. & Shimizu, Y. (eds),
Toxic Phytoplankton Blooms in the Sea. Elsevier, New York: 625-630.
Round, F.E., Crawford, R.M. & Mann, D.G. 1990. The Diatoms. Biology and Morphology of
the Genera. – Cambridge University Press, 747 pp. (ISBN 0-521-36318-7). This book
includes a comprehensive account of the diatom genera thoroughly illustrated with light
and scanning micrographs. It introduces a new classification with one division:
Bacillariophyta; 3 classes: Coscinodiscophyceae (centric diatoms), Fragilariophyceae
(araphid, pennate diatoms), and Bacillariophyceae (mono- and biraphid, pennate
diatoms); and a number of new subclasses, orders, and families.
Sala, S.E., Sar, E.A., Ferrario, M.E. 1998. Review of the materials reported as containing
Amphora coffeaeformis (Agardh) Kützing in Argentina. – Diatom Research 13: 323-336.
Scholin, C. A., Marin III, R., Miller, P. E., Doucette, G. J., Powell, C. L., Haydock, P.,
Howard, J. & Ray, J. 1999. DNA probes and a receptor-binding assay for detection of
Pseudo-nitzschia (Bacillariophyceae) species and domoic acid activity in cultured and
natural samples. - J. Phycol. 25: 1356-1367.
Simonsen, R. 1979. The diatom system: Ideas on phylogeny. - Bacillaria 2: 9-71.
Harmful diatoms introduction, page 9 of 9
Skov, J., Ton, T.P. & Do, T.B.L. 2004. Bacillariophyceae. – In: Larsen, J. & Nguyen, N.L.
(eds), Potentially Toxic Microalgae of Vietnamese Waters. - Opera Botanica 140: 203216.
Skov, J., Lundholm, N., Moestrup, Ø. & Larsen, J. 1999. Potentially toxic phytoplankton.
4. The diatom genus Pseudo-nitzschia (Diatomophyceae/Bacillariophyceae). - In:
Lindley, J. A. (ed.), ICES Identification Leaflets for Phytoplankton, Leaflet No. 185.
International Council for the Exploration of the Sea, Copenhagen, pp.1-23.
Werner, D. 1977. The Biology of Diatoms. - Botanical Monographs. Vol. 13. Univ. of
California Press. 498 pp.