Algae infestation jeopardises the ailing Baltic Sea

The lovely weather during the summer of 2006 brought it to light: the Baltic Sea is sick. It is suffering particularly from over-fertilisation, allowing an astronomical development of algae. The result: yellow carpets lap against the shoreline of many beaches. Bathing in the Baltic Sea has become unpleasant, sometimes even hazardous. Several local authorities are imposing temporary bathing bans. The causes are cyanobacteria. Although they are yellow in colour, they are called blue-green algae because they contain toxic hydrocyanic acids.

The algae profit from ample sunlight and literally blossom because of the nutrients mainly provided by agriculture. “Whilst nitrates and phosphates are natural, so-called minimum materials which previously restricted the growth of the algae,” says Petra Deimer, marine biologist and President of the GSM, “the fertilisers used in modern mass-production farming guarantee over-fertilisation – in almost all waters”.

The blue-green algae in the Baltic Sea are composed of threads, looking rather like noodle soup, before winds and currents push them together to form slimy carpets. “The Baltic Sea is balancing on an ecological knife-edge,” prophesied the marine biologist, Prof. Dr. Olaf Giere from Hamburg, as early as 2003, “which can end up as an ecological catastrophe”. After the blue-green algae blooms die and break up, the remains decompose on the seabed causing a massive decrease in oxygen. The toxic substances remain in the ecosystem.

Almost all the deeper zones of the Baltic are already ecologically dead and have little chance of regeneration due to the lack of supply of fresh, oxygen-rich water from the North Sea.

The carpets of blue-green algae and dead seaweed present a further problem. What many administration offices of the spa resorts consider to be a nightmare, is for the Baltic Sea almost a blessing in disguise: seaweed, which is gathered up and removed from the beach and not left to rot in the water – which would otherwise cause yet more oxygen depletion. The green-brown thread algae, which also multiply at an amazing rate, cover mussel banks and other marine organisms living on the seabed like “shrouds”, causing death by suffocation. The prospects of recovery for the ailing Baltic Sea are not looking good.

The deficiency in oxygen will lead to mass mortalities of fish and other creatures, such as crabs, barnacles and mussels which, under normal circumstances, act as filters, so ensuring the cleanliness of the water. The death of the blue-green algae, of which there are more than 2,000 species worldwide, causes a release of toxic substances with alarming consequences for waterfowl, for example, which drink from the water. They can die as a result.

A further burden for the Baltic’s ecosystem is the resulting, almost unavoidable mass development of jellyfish, as in 2004. Too many jellyfish eat too many young fish and other small organisms.

“When an infestation of algae broke out in the Atlantic in 1988, it wasn’t only fish that died in their masses, but also many dolphins,” says Deimer. “They had eaten poisoned fish. For the Baltic harbour porpoise poisoned fish could mean their demise”.

“Infestations of algae and plagues of jellyfish in the Baltic Sea are a sure sign that even our seas, especially those with no open access to the ocean, are in desperate need of agricultural reform with less mass production,” says Jörg Dürr-Pucher from the DUH.