What are dinoflagellates?
Dinoflagellates are a group of microscopic, usually between 20 and 150 µm long, generally single-celled organisms, commonly regarded as "ALGAE". They are characterized by two flagella: a transverse flagellum, that encircles the bo dy in the cingulum and a longitudinal flagellum, from the mid ventral area, sulcus, towards the apex. This imparts a distinctive spiral to their swimming motion.
The cell wall of many dinoflagellates is divided into plates of cellulose ("ARMOR"), known as a theca. These plates form a distinctive geometry/topology known as tabulation, which is the main means for classification.
Both heterotrophic (eat other organisms) and autotrophic (photosynthetic) dinoflagellates are known. Some are both. They form a significant part of primary planktonic production in both oceans and lakes. Most dinoflagellates go through moderately complex life cycles involving several steps, both sexual and asexual, motile and non-motile. Some species form cysts composed of sporopollenin (an organic materials resistant to bacterial decay), and preserve as fossils. Often the tabulation of the cell wall is somehow expressed in the shape and/or ornamentation of the cyst.
Although these motile cells are abundant and wide ranging, it is the resistant resting cyst which leaves a fossil record. Dinoflagellate cysts have proved to be of value as biostratigraphic index fossils and also to ecological, environmental and climate studies.
Toxic dinoflagellate cysts
Besides being important primary producers, and therefore an important part of the food chain, dinoflagellates are also known for producing nasty toxins, particularly when they occur in large numbers. Besides being bad for a large range of marine life, red tides can also introduce deadly amounts of toxins into animals (particularly shellfish) that may be eaten by humans, who are also affected by the toxins. Take on this to the that abundant toxic dinoflagellate cysts may be more common thanks to human inputs of phosphates and to global warming. (See links
Fossil dinoflagellates have been known since the pioneering investigations of Ehrenberg, over a century and a quarter ago. In many samples dinoflagellates have been found associated with enigmatic fossils of similar size and composition which came to be known as hystrichospheres (Wetzel, 1933). In the 1930's and 1940's the studies of dinoflagellate cysts was influenced the workers Alfred Eisenack (1891-1982) and Georges Deflandre (1897-1973). Our understanding of the diverse morphology biostatigraphy, environmental and climate relationships of fossil dinoflagellates has advanced considerably during the last four decades.
Advances in the comprehension of dinoflagellate cyst morphology are accompanied by a concomitant growth in the utilization of fossil dinoflagellates in biostratigraphic and allied studies. Triassic to Pleistocene dinoflagellate zonations proposed through the mid-1980s and onwards. Recently, a trend is developing to correlate dinoflagellate zonations to the Cretaceous and Tertiary planktonic foraminiferal and calcareous nannofossil zones, to Jurassic and Cretaceous ammonite zones, and also being made to relate such zonations to an absolute time scale and to sequences stratigraphy (see references
Rhaetogonyaulax rhaetica , a latest Triassic dinoflagellate cyst
The fossil record beginning with the Late Triassic, but especially with the latest Early Jurassic, abundant and diverse dinoflagellate cyst floras emerged. Dinoflagellate cyst diversity increases further in the Middle Jurassic and the trend of rapidly evolving dinoflagellate cyst floras are widespread in Late Jurassic to the present day marine sedimentary rocks and also occur in some strata of non-marine origin. Living dinoflagellates are found in most aqueous environments. (See references
SEM photographs of
Amiculosphaera umbracula a mid-Miocene to early Pleistocene (Quaternary) dinoflagellate cyst, Brigantedinium simplex (al. Protoperidinium conicoides and Quinquecuspis concreta (al. P. leonis) two mid-late Quaternary to Holocene dinoflagellate cysts.
The living dinoflagellate
Dinoflagellates exhibit two states with distinct morphology: a planktonic motile stage and a planktonic - benthic cyst stage. Only the cysts are preserved as fossils.
Examples of living dinoflagellates: Dinophysis spp., Gonyaulax spp. (including a chain of spp.), and Peridinium spp.
The motile stage
The cell wall may be either plastic and unarmoured or firm and armoured. Within the cell may photosynthetic pigments, be present. A light sensory eye spots may also be present. The two flagella arise either from the anterior end or from the ventral surface. Tabulation refers to the arrangement of plates in the armoured motile cells.
Ceratium hirundinella , a freshwater dinoflagellate
The cyst stage
Although most, if not all, fossil dinoflagellates are cysts, only a few living genera are known to encyst, either in response to adverse environmental conditions or following sexual reproduction. The cyst is formed within the formerly motile cell.
Quinquecuspis leonis encysting creating the cyst Peridinium leone inside the theca
The tabulation, cingulum and sulcus of the motile cell may be reflected in the sculpture of the cyst. Three basic kinds of cyst are recognised, termed proximate, chorate and cavate. Proximate cysts develop with the wall in contact with the wall of the motile cell. Chorate cysts develop further within the original cell and are linked to it by spines or processes. Cavate cysts are a type in which the two layers of the cyst wall are partially separated. The surface of cysts may be smooth or bear fine granules, irregular ridges, short spines, crests or processes and horns. The cyst may display an escape hole, called an archaeopyle. This is formed by the removal of one or several plates (thereby comprising an operculum).
Dinoflagellate life history
Asexual reproduction predominates and involves a division of the cell into two halves. Sexual reproduction is known in very few dinoflagellates. Cysts form in the autumn with lowered temperatures, remaining dormant on the sea floor through the winter. With the amelioration of conditions in spring, the motile stage excysts through the archaeopyle. Before developing any armour, however, the new dinoflagellate must pass through a naked gymnodinioid stage.
Schematic life cycle history of dinoflagellates
Dinoflagellates currently form a major part of the ocean plankton, especially the armoured and autotrophic forms, and they play a prominent role in the food chains of the marine realm. The autotrophic forms blossom in areas of upwelling currents rich in nutrients.
Heterotrophic dinoflagellate cysts are grazing (feeding) on phytoplankton cells e.g. variety of diatom (and dinoflagellate) species species. In mixed food supply, they feeds selectively on diatoms over dinoflagellates, and selects between diatom species. Selectivity between different diatom species does not appear to be related to size.
As a whole, the dinoflagellate has a wide temperature tolerance 1-35° C. Many dinoflagellates have geographic distributions reflecting oceanic temperature zones and hence may be used as indicators of climate oscillations. Some genera are found in both fresh and salt water although the majority of species are marine and sensitive to changes in water mass, including salinity changes.
Planktonic forms with a predatory or parasitic mode of life are usually unarmoured. Other forms are immobile, benthic, colonial forms and may live symbiotically in the tissues of reef-building corals and larger foraminifera.
There are several problems in interpreting the palaeoecology of fossil dinoflagellates, e.g. those cysts which are formed may sink and drift. Recent studies, however, suggest that modern cyst assemblages from the sea floor in fact bear a strong resemblance to the main overlying water-mass distributions, so that the transport of cysts is probably not very great (see Wall et al. 1977
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Illustrations and other dinoflagellate information
Red Tides and dinoflagellate toxins
Bold, H.C. & Wynne, M.J., 1985: Introduction to the Algae: Structure and Reproduction. Second Edition. 720 pp. Englewood Cliffs, New Jersey: Prentice-Hall, Inc.
Downie, C. & Sarjeant, W.A.S., 1965: Bibliography and index of fossil dinoflagellates and acritarchs; Geological Society of America, Memior 94 , 1-180.
Edwards, L.E., 1993: Chapter 7: Dinoflagellates. In: Lipps, J.H. (ed.), Fossil Prokaryotes and Protists. Boston: Blackwell Scientific Publications, 105-129.
Evitt, W.R., 1985: Sporopollenin Dinoflagellate Cysts: Their Morphology and Interpretation.<EM> American Association of Stratigraphic Palynologists Foundation, 333 pp.
Fensome, R.A.; Taylor, F.J.R.; Norris, G.; Sarjeant, W.A.S.; Wharton, D.I; & Williams, G.L., 1993: A Classification of Living and Fossil Dinoflagellates. American Museum of Natural History, Micropaleontology, Special Publication Number 7 , 351 pp.
Laursen, G. V., Poulsen, N. E., & Rasmussen, L. B., 1998: Correlation of north-western European Miocene Stages with the global stratotypes - preliminary results. Newsletter on Stratigraphy 36 (1): 55-61.
MacRae, R.A., Fensome, R.A., & Williams, G.L. 1996: Fossil dinoflagellate diversity, originations, and extinctions and their significance. Canadian Journal of Botany, 74 (11), 1687-1694.
Poulsen, N. E. 1996: Dinoflagellate cysts from marine Jurassic deposits in the Danish Subbasin and from Poland. American Association of Stratigraphic Palynologists, Contribution Series, 31 , 227 pp.
Poulsen, N. E., 1998: Upper Bajocian to Callovian (Jurassic) dinoflagellate cysts from central Poland. Acta Geologica Polonica 48 (3): 237-245.
Poulsen, N. E., Gudmundsson, L., Hansen, J. M., & Husfeldt, Y., 1990: Palynological preparation techniques, a new macerationtank-method and other modifications. Geological Survey of Denmark. Series C 10 , 22 pp.
Poulsen, N. E., Manum S. B., Williams, G. L., & Ellegaard, M., 1996: Tertiary dinoflagellate biostratigraphy, ODP Sites 907, 908 and 908 in the Norwegian-Greenland Sea. In: Thiede, J., Myhre, A.M., Firth, J. V., Johnson, G. L., & Ruddiman, W.F. (Eds.), Proc. ODP, Sci. Results, 151 : College Station, TX: Ocean Drilling Program, 255-287.
Poulsen, N.E. & Riding, J.B., (In press): The Jurassic dinoflagellate cyst zonation of Subboreal north-west Europe, with a supplement: Oxygen isotope palaeotemperatures from the Jurassic in north-west Europe by Bjørn Buchardt. In: Surlyk, F., & Ineson, J., et al., (eds): The Jurassic of Denmark and Greenland (provicial title). Special Issue of the Geological Survey of Denmark and Greenland.
Powell, A. J. (ed.), 1992: A Stratigraphic Index of Dinoflagellate Cysts. London: Chapman & Hall, 300 pp.
Sarjeant, W.A.S., 1974: Fossil and living dinoflagellates. London: Academic Press, 182 pp.
Taylor, F.J.R. (ed.), 1987: The Biology of Dinoflagellates. Botanical Monographs, Volume 21 . Oxford: Blackwell Scientific Publications, 785 pp.
Wall, D., Dale, B., Lohman, G.P., & Smith, W.K., 1977: The environmental and climatic distribution of dinoflagellate cysts in modern sediments from regions in the North and South Atlantic oceans and adjacent seas. Marine Micropaleontology 2 : 121-200.
Williams, G.L., Stover, L.E., & Kidson, E.J., 1993: Morphology and stratigraphic ranges of selected Mesozoic-Cenozoic dinoflagellate taxa in the northern hemisphere. Geological Survey of Canada, Paper. 92-10 , 137 pp., 2 pl.
Niels E. Poulsen,