Golden Alga Workshop Summary Report - Texas Parks & Wildlife ...

Kill Your Enemies and Eat Them: The Role of Prymnesium Toxins
Edna Graneli
Marine Sciences Department, University of Kalmar, SE-39182 Kalmar, Sweden
Abstract.--The haptophyte Prymnesium parvum is known to produce a set of highly
potent exotoxins commonly called prymnesins. These toxins have been shown to have
several biological effects, including ichthyotoxic, neurotoxic, cytotoxic, hepatotoxic and
hemolytic activity towards a range of marine organisms. Toxic incidents of the haptophyte
Prymnesium parvum have been known since the end of the 19th century. Since then, toxic
blooms have been reported from brackish water localities in Europe, the Middle East,
Ukraine, China and U.S.A. These blooms have affected coastal marine ecosystems heavily,
and caused economic problems for commercial aquaculture. Therefore, it is important to
understand the selective forces leading to bloom formation of this species. The ability of a
specific phytoplankton species to become dominant and form blooms in natural
environments is, apart from its competitive ability, also dependent on mortality losses.
Grazing by herbivorous zooplankton is considered a major loss factor, preventing the
development of phytoplankton blooms. Adaptations of algae to escape grazing would
therefore directly favor the ecological success of that particular species. Several studies
have shown that Prymnesium-species are able to diminish or completely avoid grazing by
excretion of toxins into the water. Another important aspect in bloom formation is the
ability to out-compete co-occurring algal species for nutrients. Over the last few years
strong evidence has accumulated that Prymnesium spp. are able to kill not only their
grazers but also other algal species, a process called allelopathy. Killing the nutrientcompeting
phytoplankton species enables Prymnesium to freely utilize limiting resources.
Mixotrophy, i. e., the capability to ingest bacteria, other algae and even potential grazers,
also contributes to the bloom-forming ability of Prymnesium spp. Allelopathy, mixotrophy
and grazer deterrence increase dramatically when Prymnesium spp. cells are grown under
N or P deficiency, and so does toxicity. On the other hand, if cells are grown in a medium
with high amounts of N and P in balanced proportions, allelopathy, mixotrophy, grazer
deterrence and toxicity decrease in intensity or cease completely. Usually additions of
Prymnesium filtrates from nutrient deficient cultures have almost the same strong effect on
grazers and other plankton cells as Prymnesium cells grown together with their target. This
suggests that the toxins and the allelopathic/grazer deterring compounds are the same
substances. In conclusion, it seems that toxin production in Prymnesium spp. works not
only as a defense mechanism, but also, by killing competitors, improve the competitive
ability of Prymnesium under conditions of severe nutrient depletion. Also, it seems that
stress in general, rather than solely P- or N-limitation, is the cause for an increase in toxin
production. Prymnesium toxins are poor in N and P, but have a high C content. Toxin
production might be a way to store excess organic carbon, made available in
photosynthesis under nutrient stress. This is thus similar to the way e.g. lipids or
carbohydrates are produced in excess by most "normal" phytoplankton cells when there is
not enough N or P available to build up material for cell division (DNA, proteins, etc).
View the presentation
PWD RP T3200-1203