In most of the Baltic Sea, there are two annual blooms – the spring bloom and the cyanobacterial (also called blue-green algae) bloom in late summer. The Baltic Sea faces many serious challenges, including toxic pollutants, deep-water oxygen deficiencies, and toxic blooms of cyanobacteria affecting the ecosystem, aquaculture, and tourism.
Cyanobacteria have qualities similar to algae and thrive on phosphorus in the water. High water temperatures and sunny, calm weather often lead to particularly large blooms that pose problems to the ecosystem. In this image captured on July 20, 2019, the streaks, eddies, and whirls of the late summer blooms, mixed by winds and currents, are clearly visible. Without in situ measurements, it is difficult to distinguish the type of algae that covers the sea as many different types of algae grow in these waters. The highest concentrations of algal blooms are said to occur in the Central Baltic and around the island of Gotland, visible to the left in the image. Although algal blooms are a natural and essential part of life in the sea, human activity is also said to increase the number of annual blooms. Agricultural and industrial run-off pours fertilizers into the sea, providing additional nutrients algae need to form large blooms. The bacteria that consume the decaying plants suck the oxygen out of the water, creating dead zones where fish cannot survive. Large summer blooms can contain toxic algae that are dangerous for both humans and other animals. Satellite data can track the growth and spread of harmful algae blooms in order to alert and mitigate damaging impacts on the tourism and fishing industries.
