Igor V. Dovgal, Senior Research Scientist,
Office address: Department of Invertebrate Fauna and Systematics,
I.I. Schmalhausen Institute of Zoology of the Ukrainian Academy of Sciences
B.Khmelnitsky str.15, 01601- Kiev Ukraine
Fax: (38-044) 234-1569
protists are principally unicellular organisms that are attached to substrate
by special adhesive organelles (such as stalks, etc). These organisms are usually
have attached adult stage (trophont) and free-swimming larval stage (swarmer).
Two main morphotypes of sessile protists are distinguished (Dovgal, 2000): stalked
and flattened on substrate. These protists are inhabited on unanimate substrates
(stones, etc) and as commensals or ectoparasites on various water animals and
The attached mode of life is rather common among protists. There are sessile
species even among foraminifers and radiolarians. There are also many attached
species among autotrophic flagellates. The majority of heliozoans and representatives
of three orders of flagellates (Choanophlagellata, Bicosoecidae, and Chrysomonadida)
are sessile. Attached mode of life is quite characteristic for ciliates. Several
high taxa (class Suctorea, subclasses Peritrichia and Chonotrichia, order Pilisuctorida
and family Folliculinidae) are include hundreds sessile species. Evidences for
an important role of these protists in the fouling communities are not uncommon
in the literature (Burkovsky, 1984, Fenchel, 1987). The density of sessile predating
suctorian ciliates can comprise 140 million individuals per square meter in
rivers (Dovgal, 1990). Under this abundance their are a principal controllers
of planktonic ciliates numbers. It should be remarked that the abundance of
filter-feeding heterotrophic protists (such as bicosoecids, choanoflagellates
and peritrichous ciliates) may be greater (Fenchel, 1987). After I.V. Burkovsky
(1984) data the density of sessile ciliates only may comprise up 102
individuals per square meter.
Some additional evidence on sessile protists can be found in following review
- Burkovsky I.V. 1984. Ecology of free-living ciliates. Moskow: MGU. 208
p. In Russian.
- Dovgal I.V. 1990. Flowage effect on the fouling glasses colonization by
Suctoria (Ciliophora). - Hydrobiological journal. 26,N2:37-41 (In Russian).
- Dovgal I.V., Kochin V.A. 1997. Fluid boundary layer as an adaptive zone
for sessile protists. - Zurn. obsh. biol. 58, N2. P. 67-74.
- Dovgal I.V. 2000. The morphological and ontogenetic changes in Protista
under transition to the sessile mode of life. Zurn. obsh. biol. 61, N3.
P. 290-304. (In Russian).
- Dovgal I.V. 2001. Protozoans: inhabitants of the boundary layer. Priroda.
N9. P. 73-78. (In Russian).
- Fenchel T. 1987. Ecology of Protozoa. Berlin; Heidelberg etc.: Springer-Verlag.
- Railkin A.I. 1998. Colonization processes and defense against biofouling.
St. Peterburg: St. Peterburg University. 272 p.
Additional references on sessile protists (In English):
(Contributed by Don Anderson, Woods Hole Oceanographic Institution, MA, USA)
- Dovgal I.V. Some regularities in sessile protists evolution// Study and
protection of the animal world on the end of the century. Baku: Elm, 2001.
- P. 111-115.
- Febvre-Chevalier C. 1990. Phylum Actinopoda: Class Heliozoa// Handbook
of Protoctista. Eds. L. Marulis, J.O. Corliss., M. Melkonian, D.J. Chapman.
Boston. P. 347-362.
- Mikrjukov K.A. 2001. Heliozoa as a component of marine microbenthos: a
study of heliozoa of the White Sea// Ophelia. Vol. 54, No. 1. P. 51-73.
- Fig. 1. Sessile suctorian ciliates Discophrya elongata on leg of water
bug Ranatra linearis (according to Dovgal, 2001).
- The full texts of some I. Dovgals article can be obtained at his
Among the thousands of species of microscopic algae at the base of the marine
food chain are a few dozen that produce toxins. These species make their presence
known in many ways, ranging from massive "red tides" that discolor
the water, to dilute, inconspicuous concentrations of cells noticed only because
of the harm caused by their highly potent toxins. Impacts include mass mortalities
of wild and farmed fish and shellfish, human illness and death, alterations
of marine trophic structure, and death of marine mammals, seabirds, and other
"Blooms" of these algae are commonly called red tides, since, in some
cases, the tiny plants increase in abundance until they dominate the planktonic
community and change the color of the water with their pigments. The term is
misleading, however, since non-toxic species can bloom and harmlessly discolor
the water, or can cause ecosystem damages as severe as those linked to toxic
organisms. Adverse effects can also occur when toxic algal cell concentrations
are low and the water is not discolored. Given the confusion surrounding the
meaning of "red tide", the scientific community now prefers the term
"harmful algal bloom" or HAB. This new descriptor includes algae that
cause problems because of their toxicity, as well as non-toxic algae that cause
problems in other ways. It also applies to macroalgae (seaweeds) which can cause
major ecological impacts as well.
Impacts from Toxic Algae
HAB phenomena take a variety of forms, with multiple impacts. One major category
of impact occurs when toxic phytoplankton are filtered from the water as food
by shellfish which then accumulate the algal toxins to levels which can be lethal
to humans or other consumers. The poisoning syndromes have been given the names
paralytic, diarrhetic, neurotoxic, amnesic, and azaspiracid shellfish poisoning
(PSP, DSP, NSP, ASP, and AZP). Except for ASP and AZP, all are caused by biotoxins
synthesized by a class of marine algae called dinoflagellates. The ASP toxin,
domoic acid, is produced by diatoms that until recently were thought to be free
of toxins. The toxin responsible for the recently discovered poisoning syndrome
called AZP has not yet been linked to a particular algal species or group. A
fifth human illness, ciguatera fish poisoning (CFP) is caused by ciguatoxins
produced by dinoflagellates that attach to surfaces in many coral reef communities.
Ciguatoxins are transferred through the food chain from herbivorous reef fishes
to larger carnivorous, commercially valuable finfish. The final human illness
linked to toxic algae is called Possible Estuary-Associated Syndrome (PEAS).
This vague term reflects the poor state of knowledge of the human health effects
of the dinoflagellate Pfiesteria piscicida
and related organisms that
have been linked to symptoms such as deficiencies in learning and memory, skin
lesions, and acute respiratory and eye irritation all after exposure
to estuarine waters where Pfiesteria
-like organisms have been present.
Another type of HAB impact occurs when marine fauna are killed by algal species
that release toxins and other compounds into the water, or that kill without
toxins by physically damaging gills or by creating low oxygen conditions as
bloom biomass decays. Fish and shrimp mortalities from these types of HABs at
aquaculture sites have increased considerably in recent years. HABs also cause
mortalities of wild fish, seabirds, whales, dolphins, and other marine animals.
To understand the breadth of these ecosystem impacts, think of the transfer
of toxins through the food web as analogous to the flow of carbon. Just as phytoplankton
are the source of fixed carbon that moves through the food web, they can also
be the source of toxins which cause adverse effects either through toxin transmitted
directly from the algae to the affected organism or indirectly through food
A prominent example of direct toxin transfer was the death of 19 whales in Massachusetts
in 1987 due to saxitoxin that had accumulated in mackerel that the whales consumed.
Similar events occurred in Monterey Bay, California in 1998 and again in 2000
when hundreds of sea lions died from domoic acid (the ASP toxin) vectored to
them via anchovies. In both cases, the food fish accumulated algal toxins through
the food web and passed those toxins to the marine mammals.
Another significant concern relates to sublethal, chronic impacts from HABs
that can affect the structure and function of entire ecosystems. Adult fish
can be killed by the millions in a single outbreak, with obvious long- and short-term
ecosystem impacts. Likewise, larval or juvenile stages of fish or other commercially
important fisheries species can experience mortalities from algal toxins. Impacts
of this type are far more difficult to detect than the acute poisonings of humans
or higher predators, since exposures and mortalities are subtle and often unnoticed.
Impacts might not be apparent until years after a toxic outbreak, such as when
a year class of commercial fish reaches harvesting age but is in low abundance.
Chronic toxin exposure may therefore have long-term consequences that are critical
with respect to the sustainability or recovery of natural populations at higher
trophic levels. Many believe that ecosystem-level effects from toxic algae are
more pervasive than we realize, affecting multiple trophic levels, depending
on the ecosystem and the toxin involved.
Major journals appropriate to research on HABs:
Journal of Phycology
Journal of Plankton Research
Limnology and Oceanography
Marine Ecology Progress Series
Harmful Algal Blooms (HAB) images
Announcements of meetings, proposal requests, etc.
Links to major sites: