Dinoflagellates

Dr. Maria Faust would like to dedicate this work to her mentor, Dr. Grethe Hasle, Professor of Marine Botany, University of Oslo, Norway. Dr. Hasle has devoted much of her life to teaching and sharing her understanding of the patterns and order in the diversity of marine phytoplankton species, their morphological relationships, and their global distribution. Nearly 19 years ago Dr. Faust was introduced to identifying marine plankton in a course taught by Dr. Hasle. To this day she is still fascinated by the beauty and diversity of dinoflagellate structures and morphological patterns which manage to restore one's perspective and faith in nature.

See individual species

Dinoflagellates are unicellular eukaryotic microorganisms. They are free swimming protests with a forward spiraling motion propelled by two dimorphic flagella. They possess a large nucleus with condensed chromosomes, chloroplasts, mitochondria and golgi bodies. Biochemically, photosynthetic species have chlorophylls a and c, and light harvesting pigments peridinin, fucoxanthin and xanthophylls. Dinoflagellates mainly reproduce asexually via binary fission, but some species reproduce sexually and form resting cysts. Their nutrition varies from autotrophy (photosynthesis) to heterotrophy (absorption of organic matter) to mixotrophy (autotrophic cells engulf prey organisms). These features are species-specific (Spector 1984).

Dinoflagellate species are adapted to a variety of habitats: from pelagic to benthic, from temperate to tropical seas, and from estuaries to freshwater. Many species are cosmopolitan and can survive in variety of habitats: in the plankton, or attached to sediments, sand, corals, or macroalgal surfaces. Some species produce resting cysts that can survive in sediments for an extended period of time, and then germinate to initiate blooms (Spector 1984).

Dinoflagellate 'blooms' (cell population explosions) can cause discoloration of the water (known as red tides) which can have harmful effects on the surrounding sea life and their consumers: mass mortalities in fish, invertebrates, birds, and mammals. When toxic species are in bloom conditions the toxins can be quickly carried up the food chain and indirectly passed onto humans via fish and shellfish consumption, sometimes resulting in gastrointestinal disorders, permanent neurological damage, or even death. While harmful dinoflagellate blooms are at times a natural phenomenon and have been recorded throughout history, in the past two decades the public health and economic impacts of such events appear to have increased in frequency, intensity and geographic distribution (Taylor 1987). 

Dinoflagellates exhibit a wide divergence in morphology and size that are essential features used to identify species, as well as surface ornamentation (pores, areolae, spines, ridges, etc.). Armored or thecate species, those that possess a multi-layered cell wall, can be distinguished from unarmored or athecate species, those that lack a cell wall. Surface morphology of thecate cells, often critical to proper identification, can be discerned after cell fixation. However, identification of athecate species is mainly based on live cells since many morphological features that may destroyed by fixation (Steidinger & Tangen 1996).

Another distinction used in dinoflagellate identification is morphological cell type : 1. desmokont type where two dissimilar flagella are inserted apically (e.g. Prorocentrum); and 2. dinokont type where two dissimilar flagella are inserted ventrally (e.g. Alexandrium). Terminology to describe orientation is also used: the forward end when the cell moves is called the apical pole; the opposite end is the antapical pole.

Desmokonts are laterally flattened species with two large lateral plates: right valve and left valve. In lateral view the right valve reveals flagellar placement in the anterior V-shaped depression. Dinokonts are, in general, divided into 2 main sections (epitheca and hypotheca) and divided by a girdle (cingulum) . The side the flagella arise from is the ventral side, the opposite side is the dorsal. Ventral view reveals the position of the flagella in relation to the cingulum and sulcus (Taylor 1987).

Other important features include position of the cingulum and whether it is displaced or not . If displaced and the left side is more anterior, the displacement is left-handed. If the opposite is true, it is right-handed. The former is much more common. The degree of displacement is given in cingulum widths (Taylor et al. 1995).

In thecated species the plate pattern, or tabulation, is crucial (see Balech & Tangen 1985) . The description of new species or any critical taxonomy requires complete elucidation of the plate pattern, which can be difficult, requiring special techniques (see Steidinger et al. 1996).

Dr. Maria A. Faust thanks Dr. Klaus Ruetzler, Curator of Sponges, National Museum of Natural History, Smithsonian Institution, for introducing her to the magnificient world of coral reef-mangrove ecosystem at Belize and encouraging her studies.

We are greatly indebted to Drs. Patricia A. Tester (National Ocean Service, NOAA) and Steve L. Morton (Marine Biotoxin Program, NOAA) for contributing photomicrographs and critically reviewing the manuscript. We thank S.H. Brawley, editor of Journal of Phycology, for permission to use published pictures (University of Maine), and D.G. Mann, editor of Phycologia, for permission to use published pictures (Royal Botanic Garden Edinburgh). We also thank the following scientists and colleagues for providing photomicrographs of harmful dinoflagellate species: Drs. C. Andreis (University of Milan), G.T. Boalch (The Laboratory-Citadel Hill), S. Blackburn (CSIRO Marine Research), J.M. Bruckholder (North Carolina State University), B. Dale (Universiry of Oslo), J.D. Dodge (Royal Holloway College), Y. Fukuyo (University Tokyo), D. Grzebyk (CREMA-L Houmeau, CNRS-IFREMER), G. Hallegraeff (University of Tasmania), G. Honsell (University of Udine), T. Horiguchi (Hokkaido University), J. Larsen (University of Copenhagen), J. Lewis (University of Westminster), A.J. Lewitus (University of South Carolina), L. Mackenzie (Cawthron Institute), K. Matsuoka (Nagasaki University), M. Montresor ('A. Dohrn' Zoological Station), T. Nishijima (Kochi University), D.R. Norris (Florida Institute of Technology), A. Prakash (Bedford Institute of Oceanography), K.A. Steidinger (Florida Marine Research Institute), H. Takayama (Hiroshima Fisheries Experiment Station), F.J.R. Taylor (University of British Columbia), S. Toriumi (Higashi Senior High School), K. Yuki (Matoya Oyster Research Laboratory) and A. Zingone ('A. Dohrn' Zoological Station). We also thank Dan Hulbert for technical help (Smithsonian Office of Imaging, Printing & Photographic Services). Finally, we wish to express our appreciation to Dr. P.M. Peterson, editor, for his useful suggestions to improve the clarity of presentation of this work.