Toxic Plankton Algae in the Baltic

Such blooms are not a new phenomenon, they are known to have occurred also a hundred years ago but they were favored last year as they develop to their maximum in warm, stable, nutrient-rich water.

The blue green algae Nodularia spumigena often causes algal blooms in the Baltic Sea. The alga produces nodularin, a liver toxin.

The blooms are often dominated by the filamentous species Nodularia spumigena, and all
samples tested were found to be toxic, producing the liver toxin nodularin. Mass occurrences of blue green algae are treated with some concern as the toxins produced by these algae are very diverse and not fully known.

In contrast to other plankton algae, many blue green algae (including Nodularia) are independent of nitrogen dissolved in the water as they are capable of incorporating nitrogen from the atmosphere into their cells. Blooms therefore occur as a response to release of phosphorus into the water, mainly from sewage, while nitrogen from agriculture has little effect.

The liver toxins affect animals and humans that drink or swallow the water. The toxins are
taken up by the liver whose cells are destroyed, resulting in severe bleeding from the liver and, if large amounts of toxins are taken up, destruction of the liver and death.

Since few animals drink brackish water this problem is more confined to nutrient rich (polluted) freshwater lakes and ponds which may develop huge blooms of blue green algae in summer.

In addition, swimming in the blue green algae blooms often causes itching of the skin but this usually disappears after a day or two, apparently without any permanent ill effect.
The toxins responsible for this phenomenon are poorly known, however, nor are the long term effects known and swimming in thick masses of blue green algae should therefore be avoided.

Most concern regarding blue green algae these years are related to drinking water, since the usual measures taken to clearing the water for drinking purposes do not remove the liver toxins. This is a serious problem in countries where drinking water is taken from lakes
(Sweden, Norway) while countries using ground water is spared of this problem

While blue green algae are confined to freshwater and brackish water, other toxic plankton algae show very different distribution patterns. The economically most serious group of toxic plankton algae in the Baltic, species of the dinoflagellate genus Dinophysis, dinoflagellates in laboratory culture have failed. Toxin produced by the dinoflagellate Dinophysis norvegica accumulates in mussels are distributed throughout the Baltic and further into the North Sea. Toxins produced by many species of the genus (D. acuminata, D. norvegica and others) accumulate in mussels which survive but become toxic to
predators, including humans.

Toxin produced by the dinoflagellate Dinophysis norvegica accumulates in mussels.

The short term effect of the toxins (dinophysis-toxin, okadaic acid) include diarrhea and vomiting (DSP, or diarrheic shellfish poisoning) but the long term effects are unknown.

The problem is world wide but in the Baltic has been mainly confined to the inner Danish waters and the Swedish West Coast and toxin concentrations in mussels are now being carefully monitored.

Many questions remain unanswered, however, as all attempts to maintain the dinoflagelates in laboratory culture have failed.

This is not the case with other toxic plankton algae from the Baltic area, practically all of which are being maintained and studied in laboratory culture. These algae fall into three main group whose members cause PSP (paralytic shellfish poisoning), ASP (amnesic shellfish poisoning) and fish kills.

PSP is not common in Baltic waters and the causative organisms, two species of the dinoflagellate genus Alexandrium (named after Alexandria Harbor in Egypt) occur mainly in the Kattegat, Skagerrak and the Limfjord.

PSP, one of the most serious plankton poisonings known, is occasionally found in mussels in the most highly saline waters of the Danish and Swedish waters (Skagerrak and the Limfjord).

It is caused by one or more nerve toxins collectively known as saxi toxins. ASP is likewise caused by a liver toxin, domoic acid. It has never been found in the Baltic but the causative organisms, members of the diatom genus Pseudonitzschia, occur from the Skagerrak throughout the Danish sounds.

Stress may cause production of fish killing toxin in the diatom Pseudo-nitschia (X 500)

They peter out south of the Øresund when salinity becomes too low. Toxin production has been proved in laboratory culture of Baltic isolates of Pseudo-nitzschia but the factors stimulating toxin production are not well understood, although stress is probably a factor. Toxins of the third group of toxic algae, the fish killers, are generally poorly known. Such algae are not common in the highly saline areas of the Baltic where only the unarmored
dinoflagellate Gymnodinium nagasakiense (previously known as Gyrodinium aureolum) is a regular cause of concern. Blooms of this species enter the Baltic from the North during summer, spreading through the Kattegat and killing fish in mariculture farms. Wild fish flee the toxic algae but bottom fauna succumb.

In more brackish water this species is replaced with species of Prymnesium, a
well known fish killer of the group Haptophyta. It occurs regularly in brackish
water and in 1997 was a major issue on Öland.

On the German coast this species has been known since the turn of the century
and fish kills are also regular in many low saline Danish lakes and fiords.

The haptophyte Chrysochromulina polyleris caused a massive bloom in northern Kattegat and Skagerak in 1988. Its toxin is real fish killer. (Scale bar = mm)

Other fish killers occur more irregularly, for example the haptophyte Chrysochromulina polylepis in the Northern Kattegat and the Skagerrak in 1988, and Heterosigma akashiwo (akashiwo is Japanese for algal bloom), a member of the Rphidophyceae. The latter is found at intervals, mainly in the Kattegat and the Limfjord, but so far without any known ill effects on the fish.

All these algae differ from blue green algae in lacking the ability to utilize nitrogen from the atmosphere. They all require both nitrogen and phosphorus dissolved in the water and in brackish water compete with blue green algae for phosphorus.

Have we always had the toxic plankton algae in our waters? Most of them probably yes, but their numbers keep fluctuating and they appear to compete and interact with other plankton algae in ways which are barely or not understood and therefore more or less unpredictable. We may expect them in the largest numbers in calm summers in any area polluted with nutrients. In cold and windy weather they become scattered and many of them are hardly seen.

On a world wide basis, toxic plankton algae are being watched with grave concern since increasing problems may be expected due to population growth and increased use of coastal waters for mariculture, and lake waters for drinking water. Ways of reducing nutrients in the waters are being hotly discussed and monitoring for toxic algae and toxins are introduced. The interest in the issue is perhaps illustrated best by the number of
applications received for participation in the international courses on toxic algae at the IOC / DANIDA Centre for Toxic Algae at the University of Copenhagen.

Each course has room for 15 participants but each year receives over 100 applications from all over the world.