Page 303 - Algae

286 Algae: Anatomy, Biochemistry, and Biotechnology

iron-deficient. In general, temperature, sunlight, and nutrient loads have a substantial impact on the
proliferation of the bloom.
Haptophyta contain a few toxic species. Prymnesium parvum produces a potent toxin that
causes extensive fish mortality in brackish water. Another flagellate Chrysochromulina polylepis
produces and excretes glycolipids with hemolytic and ichtytoxic properties causing osmoregola-
tory failure similar to that brought about by P. parvum. Another widely distributed marine hapto-
phyte Phaeocystis sp. is familiar to fishermen in the form of extensive blooms of mucilaginous
colonies, which are avoided by herring. It produces large quantities of acrylic acid, which has
strong bacteriocidal properties.
Already 70 years ago, P. pouchetii was suspected to cause avoidance of herring. Later it was
demonstrated that copepods avoided gracing on healthy P. pouchetii colonies, food intake and
growth were reduced in sea cage cultivated salmon during the spring bloom of P. pouchetii and
water from P. pouchetii cultures acted toxic towards cod larvae.
Species belonging to the genus Phaeocystis are important in all oceans, and P. pouchetii is an
important component of the spring bloom of phytoplankton in northern waters. Its life cycle is
only partly resolved but is known to be polymorphic consisting of at least two solitary and one colo-
nial stage.
P. pouchetii has been reported to produce a polyunsaturated aldehyde (PUA) as diatoms,
namely the 2-trans-4-trans-decadienal. This compound is known to interfere with the proliferation
of different cell types, both prokaryotic and eukaryotic. As mechanical stress is known to induce the
release of PUAs in other phytoplankton species, the release of 2-trans-4-trans-decadienal has been
suggested to be a mean of deterring grazers, for example, zooplankton or fish larvae. P. pouchetii is
a common component of northern and temperate spring blooms; it is grazed by zooplankton at
normal rates and can also be a diet preferable to diatoms. Copepods may avoid gracing on
healthy colonies of P. pouchetii, thus, the production and excretion of PUAs seems to be depending
on the state of the cells or on environmental factors, or both. It has been reported that this PUA can
be released into the sea in the absence of grazers, indicating that it may serve as an allelochemical,
that is, a compound which gives P. pouchetii a competitive advantage over phytoplankton species
blooming at the same time by inhibiting their growth.
The Dinophyta includes about a dozen genera, with at least 30 species, producing water and lipid
soluble, low molecular weight, neuroactive secondary metabolites that are among the most potent
nonproteinaceous poisons known. In general, these toxins have been shown to block the influx of
sodium through excitable nerve membranes, thus preventing the formation of action potentials.
The toxins are accumulated and sometimes metabolized by the shellfish which feed upon these dino-
flagellates, causing different types of shellfish poisoning, such as PSP, DSP, and NSP.
Ingestion of contaminated shellfish results in a wide variety of symptoms, depending on the
toxins(s) present, their concentrations in the shellfish and the amount of contaminated shellfish con-
sumed. In the case of PSP, caused by toxin of Alexandrium spp., the effects are predominantly
neurological and include tingling, burning, numbness, drowsiness, incoherent speech, and respirat-
ory paralysis. Less well characterized are the symptoms associated with DSP and NSP.
DSP is caused by okadaic acid, a diarrhoric shellfish toxin and tumor promoter found in many
dinoflagellates of the genera Dinophysis and in Prorocentrum lima. DSP is primarily observed as a
generally mild gastrointestinal disorder, that is, nausea, vomiting, diarrhoea, and abdominal pain
accompanied by chills, headache, and fever.
Both gastrointestinal and neurological symptoms characterize NSP, including tingling and
numbness of lips, tongue, and throat, muscular aches, dizziness, reversal of the sensations of hot
and cold, diarrhea, and vomiting. The NSP toxins are produced by Gymnodinium breve, also
denominated as Ptychodiscus brevis.
Another syndrome caused by dinoflagellate toxins is the ciguatera poisoning, connected with
eating contaminated tropical reef fish. Ciguatoxins that cause ciguatera poisoning are actually
produced by Gambierdiscus toxicus, a photosynthetic dinoflagellate that normally grows as an