Declining salinity and rising temperatures detrimental to Baltic Sea bladder wrack

Bladder wrack, or bladder fucus, provides important habitat for several organisms living in the coastal ecosystems of the Baltic Sea. Bladder wrack fares particularly badly when exposed to high temperatures and low salinity, brought about by climate change.

The Baltic Sea is already a challenging environment for many species. Due to low salinity, its biodiversity is slender compared to oceans.  Foundation species, or species that provide a diverse environment to other species, are therefore important. Such species include the perennial bladder wrack (Fucus vesiculosus) that grows up to a metre in length.

The salinity of the Baltic Sea is predicted to fall even lower due to increased rainfall ushered in by climate change. Eutrophication is also on the rise and high temperatures are becoming increasingly common. Progressing eutrophication favours filamentous and quickly growing algae, of which green algae in particular cope well in relatively low salinity.

However, for bladder wrack, which isn’t exactly enjoying optimal conditions even today, such changes would be problematic.

“Bladder wrack would prefer a slightly higher salinity than the current level in the Baltic Sea. The temperature most hospitable to bladder wrack growth is roughly around 15 degrees Celsius,” says Antti Takolander, who defended his doctoral dissertation at the Faculty of Biological and Environmental Sciences of the University of Helsinki at the end of August.

Takolander’s findings indicate that bladder wrack may be in trouble if temperatures rise. Being exposed to higher temperatures for even a little over a week was found to be highly harmful.

“In temperatures exceeding 26 centigrade, the effects were particularly harmful. Short-term heat waves, such as were experienced this summer, may eradicate local populations of this foundation species, especially in shallow, sheltered locations. The negative impact of high temperature intensifies further if salinity declines according to climate model projections. ”

In the northern Baltic Sea, salinity is predicted to fall by the end of this century. The decline in salinity alone may eradicate bladder wrack from extensive regions if the species is unable to adapt to the changing conditions.


Takolander, Antti. Assessing the effects of climate change on Baltic Sea macroalgae – implications for the foundation species Fucus vesiculosus L. Doctoral dissertation, 2018.