Summer visitors to beaches are periodically
asked not to harvest shellfish, to bathe or to eat aquacultural
products. Those who ignore this warning risk - depending on the
individual concerned - suffering from a paralytic, diarrhoetic or
neurological syndrome, or even death. The culprit is phytoplankton,
consisting of microorganisms which scientists habitually refer to
as "harmful algal blooms" (HAB). We have been aware of
the existence of these algae for some time, but the frequency with
which they appear and their volume have increased considerably in
recent years. One of the explanations put forward is the ecological
imbalance caused by human activities, in particular the excess of
waste products rich in nitrates and phosphates. One of the main
goals of the Nutox project was to verify this hypothesis and to
qualitatively and quantitatively analyse this process.
Reasons for an imbalance
There are two major categories of phytoplankton. The first includes
diatoms, which need silicon to develop. The toxic phytoplankton
belongs to the second category and can perfectly well do without
silicon. Among the latter can be found dinoflagellates, prymnesiophytes
and blue-green algae (cyanobacteria), which the Nutox scientists
focused on. These three species are found everywhere in the world,
particularly in the coastal areas of northern and southern Europe.
But what causes them to proliferate in this way? "These areas
receive water from rivers, the coastal runoff and possibly acid
rain", explains Serge Maestrini of CREMA-L'Houmeau (a CNRS
and IFREMER joint institute), one of the Nutox partners. "In
the last few decades, huge quantities of nitrates and phosphates
from many different origins - agricultural, domestic (from washing
powder), etc. - have flooded into these soft waters. Their eutrophisation
has been reflected in an excessive development of diatoms which
consume silicon. As a result, there is less silicon in coastal water
and a relative increase in nitrogen and phosphorous content. This
creates an environment which is favourable to the development of
algae which do not feed much on silicon".
Nuclear physics and genetics
Six European teams have launched an assault against these unpleasant
algae. Three are working in northern Europe, where experiments have
been carried out on large volumes (in the Norwegian and Baltic Seas).
The Swedish team, led by Edna Granéli of the Department for
Marine Sciences of the University of Kalmar, was responsible for
coordinating Nutox. This team focused primarily on the possibilities
of controlling toxin production according to the nutrients available.
A second Swedish team, made up of specialists from the Department
of Applied Nuclear Physics of the University of Lund, analysed the
chemical composition of the algae using PIXE (Particule-Induced
X-ray Emissions) nuclear microprobes. It was the task of a Norwegian
team from the Trondheim biological station to pilot interspecific
comparisons between the toxic species of various European regions.
The three other teams worked on the material sampled. German researchers
from the Insitute of Nutrition and the Environment (University of
Jena) concentrated on the toxicological aspects. A Spanish laboratory
from the Department of Aquatic and Environmental Sciences and Techniques
(Santander) had the task of comparing the populations of a single
species according to their origin (from the North to the South of
Europe) using molecular genetic methods. The species chosen was
Alexandrium Tamarense, a dinoflagellate which produces
a toxin causing paralysis (Paralytic Shellfish Poisoning,
or PSP). A French team from the Marine Ecology and Aquaculture Research
Centre (CREMA-L'Houmeau) concentrated more specifically on the impact
of nitrogen and phosphorous levels on toxin production.
"One of the merits of this European cooperation exercise has
been therefore to associate people from many different disciplines
and with different skills, such as eco-physiology, marine biology,
chemistry and physics, and have them work on a common topic"
points out Catherine Legrand, one of Edna Granéli's colleagues.
"This is the first time, for example, that we have had access
to the carbon, nitrogen and phosphorous composition of a dinoflagellate
(Dinophysis spp.), whose toxin provokes diarrhorea (Diarrhoeic
Shellfish Poisoning, or DSP). This result was obtained by using
nuclear microprobes". Various other techniques have been employed.
High resolution liquid chromatography and nuclear magnetic resonance
were used, in particular, to study the toxins while PCR (Polymerase
Chain Reaction) - a technique for DNA sequence amplification - was
used for molecular and genetic analyses.
When "better" is worse than "bad"
The research has shown that toxin production is at a minimal level
when nitrogen and phosphorous levels maintain a certain balance.
There is only one exception, the algae which contain saxitoxin,
a toxin rich in nitrogen and with paralysing effects. Saxitoxin
production increases if the phosphorous load is reduced, whereas
it falls considerably if the nitrogen load is limited. Another significant
finding from this research is that the composition of algae of the
same species differs according to their origin and the environment
in which they develop.
"We can inhibit toxin production very rapidly, in one or two
days", states Edna Granéli. "All we need to do
is to add the elements which have not been provided to the environment.
But this is only a poor solution and which is, moreover, not without
its dangers. In a manner of speaking, it is like putting oil on
the fire because, by doing this, we accelerate biomass production.
The only long-term solution, therefore, is to reduce the phosphorous
and nitrogen loads in the water", she concludes.
Europe intends to take heed of this warning. The Nutox project
in fact comes under the EUROHAB framework (European Initiative
on Harmful Algal Blooms), a vast initiative to combat these
algae. "This project has played a pioneering role. It has made
it possible to set up a network of concerned scientists equivalent
to the one which already existed on the other side of the Atlantic",
explains Elisabeth Lipiatou, scientific officer in the Research
But what is to be done when reduction of the phosphorous load,
while reducing biomass production, nevertheless increases the production
of toxins per biomass unit? What is the precise impact of these
toxins on marine fauna? Scientists will be investigating algae for
some time to come yet.
Effect of nutrient ratios on harmful phytoplancton and their
toxin production. Nutox 1997-2000
Edna Granéli (coordinator)
Department for Marine Sciences
Natural Science Institute
University of Kalmar
Box 905, S-391 29 Kalmar
Fax : +46 480 447305
E-mail : email@example.com
-Department of Aquatic Sciences, Natural Science Institute,
- Trondheim Biological Station, University of Trondheim, Trondheim,
- Department of Applied Nuclear Physics, University of Lund,
- Institute of Nutrition and the Environment, University of
Jena, Jena, Germany
- Department of Marine and Environmental Sciences, University
of Santander, Santander, Spain
- Centre for Marine Research and Aquaculture, IFREMER-CNRS,