Photo: Joakim Hansen

The researchers in the project have combined studies at different spatial scales and methods to address the hypothesis that vegetation and predatory fish facilitate each other via a positive feedback loop, which enhances ecosystem health.

Data collection, modelling and experiments combined

Modelling of vegetation and juvenile fish data across the entire Swedish Baltic Sea Coast have been combined with detailed examinations of the food web in 32 bays, and small-scale manipulative field experiments of about half a square meter.

Results from the studies show that:

  1. High cover of benthic vegetation results in less turbid water partly through stabilizing the soft sediment bottoms (link to research article).
  2. The benthic vegetation is important for coastal fish; the abundance of juveniles of pike, perch and cyprinids increase with increasing cover of vegetation. (link to research article).
  3. Boat marinas have a negative effect on the cover and height of benthic vegetation, and alter the species composition. This can in turn influence the recruitment of fish (link to research article).
  4. Predatory fish, such as pike and perch, have a positive effect on benthic vegetation though a trophic cascade, where they control meso-predatory fish, such as sticklebacks, which in turn regulate small invertebrates such as insect larvae, snails and amphipods (link to research article). These invertebrates can in turn through grazing control nuisance algae which smother the benthic vegetation (link to research article).
  5. The density of benthic vegetation is important for maintaining healthy plants when large predatory fish disappear and the water is enriched with excessive nutrients (link to research article).

Strong links between vegetation and fish

The results from the project strengthen previous suggestions that the seabed vegetation perform important ecosystem functions such as improving water quality and recruitment success of coastal fish, whereas predatory fish indirectly control nuisance algae that otherwise smother the vegetation.