These abstract swirls of colour are clusters of ancient plankton as viewed from a satellite.
Cyanobacteria are an ancient type of ocean bacteria that store solar energy by photosynthesis. Every summer these blooms have increased, with their clusters producing beautiful infrared rays captured by Nasa’s Operational Land Imager (OLI) telescope on 11 August 2015 as it passed over the Baltic Sea.
“Large colony-forming cyanobacteria are almost exclusively a freshwater or a brackish species,” says Erik Askov Mousing, a researcher at the Institute of Marine Research in Norway. “The Baltic Sea is special because it exhibits low surface salinity (salt content),” he adds.
Low salt content is required for these bloom-forming species to exist. Cyanobacteria are also found in the open ocean but there they are dominated by tiny picoplankton species. However these do not produce surface blooms like the ones captured above, says Mousing.
In the Baltic Sea, the yearly cycle of the phytoplankton starts in the spring when an increase in sunlight encourages photosynthesis. High temperatures in the summer when the rise in temperatures later promotes growth.
But cyanobacteria are not like most other phytoplankton. All phytoplankton require phosphorous and nitrogen but the cyanobacteria are able to make it themselves through synthesis. “In the spring, other phytoplankton species will increase in abundance until the nitrogen pool is exhausted,” explains Mousing. After the spring bloom lots of phosphorus remains, but no other species can access it because they also require nitrogen. This allows for a beautiful build up this unusual type of plankton.
However, the blooms can become toxic. Nodularia, a genus of the cyanobacteria, is a toxin producing species, producing nodularin. In high concentrations this can be harmful. “Nodularin is a very potent poison which can cause severe liver damage,” says Mousing. It is in principle dangerous for humans but Mousing comments that the low concentrations in the ocean make the toxin levels relatively harmless; “unless you drink large amounts of sea water which is unrealistic”.
“Cyanobacteria are naturally occurring species and as such they are not necessarily problematic, even when they bloom,” he adds.