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
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
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
biostatigraphy, environmental and climate
relationships of fossil dinoflagellates has advanced considerably during the
last four decades.
This is due in part to the comprehensive studies of such authors as
William R. Evitt
William R. Sarjeant
Graham L. Williams, and many others.
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
after MacRae et al.
Dinoflagellate cyst record
, 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
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
The motile stage
Examples of living dinoflagellates:
spp. (including a chain of spp.), and
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.
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.
encysting creating the cyst
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
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.
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
Edwards, L.E., 1993: Chapter 7: Dinoflagellates. In: Lipps, J.H. (ed.), Fossil Prokaryotes and Protists. Boston: Blackwell Scientific
Evitt, W.R., 1985: Sporopollenin Dinoflagellate Cysts: Their Morphology
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
, 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
MacRae, R.A., Fensome, R.A., & Williams, G.L. 1996: Fossil dinoflagellate
diversity, originations, and extinctions and their significance. Canadian Journal
Poulsen, N. E. 1996: Dinoflagellate cysts from marine Jurassic
deposits in the Danish Subbasin and from Poland. American Association of
Stratigraphic Palynologists, Contribution Series,
, 227 pp.
Poulsen, N. E., 1998: Upper Bajocian to Callovian (Jurassic)
dinoflagellate cysts from central Poland. Acta Geologica
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
, 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,
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., &
(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
. 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.
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,
, 137 pp., 2 pl.
Niels E. Poulsen,
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