University of Gothenburg

Predicting future distributions

The warming and salinity decrease predicted for the Baltic Sea will affect species ranges and might result in loss of marine populations. As a task in BONUS BAMBI, we have predicted future distributions of bladder wrack under the most plausible climate and nutrient loading scenarios.

As shown in the maps below, there will be a dramatic change in the distribution of bladder wrack, mainly due to the expected salinity decrease. Since bladder wrack provides an important habitat for many other species, the impact of this decline could be significant.

Maps of the present and future distribution of bladderwrack in the Baltic Sea.
Distribution of bladder wrack, today (right) and future (left). "Future" pictures the mean distribution modelled for the years 2070–2099.

Dramatic decline
Our modelling work (see below) predicts that the future distribution of Fucus in the Baltic Sea could shrink up to 30 percent, as compared to the present. The mechanism behind is an impressive southward and westward expansion of low-salinity water. The effect is most notable in the Gulf of Bothnia and the Gulf of Finland, see left map above.

Marginal populations at risk
The loss of suitable habitat for bladder wrack, mainly due to lower salinity, may result in fragmentation and reduced connectivity. As a consequence, the risk for populations to go extinct will be higher. This is especially true for marginal populations, e.g the populations in the Bothnian Sea and in the Gulf of Finland. 

Crucial populations may be lost
Bladder wrack in the Bothnian Sea and the Gulf of Finland has evolved to tolerate low salinity. These populations harbour locally adapted genes that can help the species survive in a future Baltic Sea environment with lower salinity. Losing them may lead to an even more severe decline than our model predicts, see below.

Adapted genotypes need to disperse
Our model assumes that, as the salinity decreases in the Baltic, adapted genotypes can disperse into new areas and establish new populations. If not, the future decline could be even more severe. Present (not adapted) populations will probably not cope in the new environmental condition, since they are unlikely to adapt fast enough.

Critical relocation rate of 50 km/decade
We have calculated the rate a locally adapted population needs to relocate in order to "track" a salinity change in the Baltic Sea. For many areas, the rate exceeds 50 kilometers per decade. This may be a critical rate for bladder-wrack, indicating that the loss of this species may be even higher than predicted by our model. There may be management options to facilitate the dispersal of local genotypes, see below.

Management recommendations

  • Minimize environmental impact in areas that harbour bladder wrack today, to mitigate the risk of losing populations.
  • Protect areas with a predicted future presence, through MPA:s and adequate management plans.
  • Enhance the dispersal of adapted genotypes through additional MPA:s in critical areas to overcome connectivity barriers. 
  • Although not normally advised, consider to translocate individuals from low salinity-adapted populations into areas that face rapid salinity decrease and risk for local extinctions. 

Integrating experimental and distribution data to predict future species patterns, by Jonne Kotta, Jarno Vanhatalo, Holger Jänes, Helen Orav-Kotta, Luca Rugiu, Veijo Jormalainen, Ivo Bobsien, Markku Viitasalo, Elina Virtanen, Antonia Nyström Sandman, Martin Isaeus, Sonja Leidenberger, Per R. Jonsson & Kerstin Johannesson. Scientific Reports, February 2019.

The future distribution of bladder wrack in the Baltic Sea was estimated with a model, using data from a climate-change scenario and two different nutrient emission scenarios (current and increased levels).

Climate scenario
The climate change scenario we used in our model to predict the future bladder wrack distribution is emission scenario A1b, proposed in the "Special Report on Emissions Scenarios by the Intergovernmental Panel on Climate Change" (see references below).

Nutrient scenarios
To predict the distribution of bladder wrack in the future Baltic Sea we used two nutrient emission scenarios :

  • Business as usual (BAU) with increased river nutrient concentrations from the report "Climate change in the Baltic Sea area", and with current levels of atmospheric deposition.
  • Reference scenario (REF) where nutrient concentrations in rivers and atmospheric deposition remain at current levels, from the scientific publication "On the dynamics of oxygen, phosphorous and cyanobacteria in the Baltic Sea: a model study".


On the dynamics of oxygen, phosphorous and cyanobacteria in the Baltic Sea: a model studyEilola, K., Meier, H.E.M. & Almroth, E. In: Journal of Marine Systems, 75, 163-184 (2009).

Climate change in the Baltic Sea area. HELCOM Thematic Assessment in 2007. In: Baltic Sea Environment Proceedings No 111 (2007).

Special report on emissions scenarios: a special report of Working Group III of the Intergovernmental Panel on Climate Change. Nakićenović, N., Alcamo, J., Davis, G., DeVries, B., Fenhann, J., Gaffin, S., Gregory, K., Gruebler, A., Jung, T.Y., Kram, T., Lebre LaRovere, E., Michaelis, L., Mori, S., Morita, T., Pepper, W., Pitcher, H., Price, L., Riahi, K., Roehrl, A., Rogner, H.-H., Sankovski, A., Schlesinger, M., Shukla, P., Smith, S., Swart, R., VanRooijen, S., Victor, N. & Dadi, Z. Cambridge University Press, Cambridge (2000).