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Deadly algae

Toxic algal bloom in a Norwegian fjord.
© Ø..Paulsen

The ocean is avenging itself as it can for man's carelessness. That is why coastal waters periodically witness the proliferation of toxin-producing microalgae, the effects of which are hazardous to human and animal health. From North to South, no European region escapes this phenomenon. Joining forces for the Nutox project and the EUROHAB European initiative, researchers have made considerable progress in understanding the physico-chemical and biological mechanisms behind this phenomenon.


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 DG.

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
Department for Marine Sciences
Natural Science Institute
University of Kalmar
Box 905, S-391 29 Kalmar
Fax : +46 480 447305
E-mail :

-Department of Aquatic Sciences, Natural Science Institute, Kalmar, Sweden
- Trondheim Biological Station, University of Trondheim, Trondheim, Norway
- Department of Applied Nuclear Physics, University of Lund, Lund, Sweden
- 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, L'Houmeau, France