Sensitive bacterioplankton communities in the Baltic

Bacteria are found everywhere in the sea, and play an important role in the ecosystem. They can, among other things, break down organic material, and make carbon dioxide and minerals available again to other organisms in the food web. In this way, they are the main players in the flow of energy and matter in the ecosystem.

Change or resist?

Climate change will lead to an increase in temperature and a decrease in salinity in the Baltic Sea. Will this affect the composition of bacterial communities, and will bacterial communities be able to adapt to these changes? And above all, will any changes in the composition affect bacterial function in the ecosystem? EcoChange researchers have compiled the state of research on how sensitive bacterial communities in the Baltic Sea are to environmental disturbances.
Bacterial communities can react in three ways when exposed to environmental changes. They can be sensitive, and change their community composition when exposed to disturbances; they can be resistant to the disturbances, and they can change but have the ability to return to their former state. How bacterial communities react is crucial to how the ecosystem will be affected by environmental disturbances.
Salinity has large-scale control
Many studies show the ability of bacteria to react differently to changes in the environment, such as temperature, salinity and nutrients. Given the important function of the bacteria, changes in the bacterial communities can also affect other parts of the food web.

On a large scale, salinity controls how the bacterial communities are composed. In the Baltic Sea, there is a salinity gradient from north to south, which greatly affects bacteria that are present in the various sea basins.

Within each sea basin however, other factors appear to control composition. For example, it may be a matter of the degree of oxygen deficiency. The bacteria are also linked to phytoplankton, and the composition of the bacterial communities is locally linked to the dynamics of the phytoplankton community.

A need for long-term studies

Bacterial communities in the Baltic Sea seem to be sensitive to disturbances, which means that communities change as a result of various environmental impacts. So far, however, very few studies have been conducted over periods of time lasting longer than a few weeks, which means that one does not actually know whether communities can return to their original composition. There is a seasonal variation in the composition of bacterial communities, with clear spring and autumn communities. Much of this variation is explained by differences in temperature.

Unknown consequences

Researchers also question whether the expected major changes in the composition of the bacterial communities will have any consequences as regards the function of the ecosystem itself. This issue has not yet been specifically investigated. Studies are needed on how changes in bacterial communities affect, for example, the carbon cycle, as an important part of decisions regarding measures for the marine environment in a changed climate.

The article has earlier been published in the EcoChange annual report 2018. The text is based on:

Lindh, Markus V.; Pinhassi, Jarone. 2018. Sensitivity of Bacterioplankton to Environmental Disturbance: A Review of Baltic Sea Field Studies and Experiments. Frontiers in Marine Science, Frontiers Media SA 2018, Vol. 5.