CliSAP successfully finished in 2018. Climate research continues in the Cluster of Excellence "CLICCS".

Climate change: Will there be twice as much blue-green algae in the Baltic in the future?


As a result of climate change, the level of cyanobacteria, which are also called blue-green algae, in the Baltic Sea might double, as researchers at the University of Hamburg’s KlimaCampus have calculated. “Our findings show that rising water temperatures will produce not only a longer annual growth phase, but also more than twice the algae biomass by the end of the century,” states Prof. Inga Hense. The potential consequences: sudden algal blooms, which can be bad for tourism and in some cases even pose health risks. Further, other species could suddenly boom as well, which would disrupt the balance in the ecosystem, as blue-green algae enrich the surrounding seawater with the nitrogen needed for those species’ growth.

According to the climate researchers’ findings, the spread of the single-celled organisms is to be expected in light of the rising water temperatures. This factor is intensified by their unusual lifecycle: Cyanobacteria can only grow in very warm water, and otherwise linger in a type of dormancy at the bottom of still bodies of water. “It’s like sowing and harvesting – the more dormant cells survive the winter, the faster the population grows in the spring,” explains Hense. At the same time, the high concentration of cells close to the water’s surface further increases the temperature: a positive feedback that leads to even more growth, as Hense reports in the latest issue of the journal “Climatic Change.”

The effect of climate change on growth had previously been assumed to be far less prominent: “When it comes to forecasts for biological systems, non-linear effects must also be taken into account, which makes the calculations more complex,” claims Hense. In response, the biologist and her team worked together with colleagues from the Swedish Meteorological and Hydrological Institute to combine a physical climate model with a biological one, making it possible to depict the complete lifecycle of cyanobacteria for the first time.

Apparently, the sequence of cold and warm winters is also an important aspect: “If all other parameters in the model experiment remain constant, we nevertheless see different growth rates – depending on the distribution of cold periods, which can be conducive to or detrimental to the single-celled organisms’ productivity,” states Hense; a further indication that the biology of the cyanobacteria is essential in light of climate change.

The scientists compared the growth of a given blue-green algae population over thirty-year periods – under the conditions from 1969 to 1998, and in contrast under the general conditions we can expect for 2069 to 2098 in the wake of increasing global warming. “We can already see more cyanobacteria today, and our tests have produced the first indications that major changes are to be expected in the future,” reports Hense.

For example, the often unwelcome single-celled organisms can not only be found in the Baltic, but also in the Tropics and Subtropics, in still bodies of water and fresh-water lakes, where they spur the growth of other species: “Cyanobacteria fix the atmospheric nitrogen in water, which other water-borne organisms normally don’t have access to. As dominant primary producers, they can fundamentally change the nutrient budgets of entire habitats.” Accordingly, in the next stage of research the team plans to integrate horizontal sea currents, which influence algae drift, into its calculations.

The original article you can find here.

The press release und further information you can find here.

For questions:
Prof. Dr. Inga Hense
Universität Hamburg, KlimaCampus
Phone: 040-4 28 38-66 41

Ute Kreis
Universität Hamburg, KlimaCampus
Phone: 040-4 28 38-45 23