Cyanobacteria are the oldest oxygen-producing organisms on Earth and can be found in almost every land and water area. Their long evolutionary history has enabled them to develop adaptations in order to increase their survival in environments affected by natural and anthropogenic changes. The frequencies and intensity of cyanobacterial blooms in the Baltic Sea have increased during the last century. Summer blooms consisting of different cyanobacteria may cover up to 50 per cent of the Baltic Sea surface, which makes it the largest cyanobacterial blooms in the world.
Simultaneously, recruitment of spring spawning fishes such as Perch (Perca fluviatilis) and Pike (Esox lucius) have decreased along the Baltic Sea coast. Temporal changes in adult fish abundance have been linked to recruitment success, which is dependant on growth of juvenile fish. Generally, low growth rates affect survival of juvenile fish by causing an increase in time spent in stages with higher predation and by increasing winter mortality. Since growth is a crucial factor determining fish recruitment, all parameters that have the potential to influence growth could affect fish recruitment dynamics.
Cyanobacteria negatively influence fish growth by toxicity, turbidity, changed water quality, toxin transfer and changes in zooplankton community structure. Cyanobacterial toxins i.e. nodularin accumulates in fish species (Flounders, Perch and Roach) causing an energetic cost due to handling the toxins. Cyanobacteria, toxic or non-toxic, also affect the feeding behaviour of fish, which further increases energetic costs. Different fish populations react differently to cyanobacteria, i.e. a sea population had higher tolerance to cyanobacteria compared to a freshwater population
At a general coastal ecosystem level, cyanobacteria cannot solely explain the decline of juvenile fish. Nevertheless, at a local scale cyanobacteria certainly influence the recruitment of juvenile fish.
PhD, Case Officer,
County of Ministry Board Kronoberg
Persson, K-J 2013. Influence of cyanobacterial blooms on coastal fish recruitment, Linnaeus University Dissertation No 121/2013. ISBN: 978-91-87427-11-4.
The Swedish Research Council Formas
The Faculty of Health and Life Sciences, Linnaeus University