Biomanipulation as a nature-based solution to reduce cyanobacterial blooms

We considered the limnological literature for an overview of biomanipulation methods that were implemented to avoid or reduce cyanobacterial bloom development in ponds and lakes. For this purpose, we reviewed 48 publications representing 34 whole-lake and large-scale case studies of different biomanipulation approaches clearly mentioning the extent of a cyanobacteria bloom problem and the cyanobacteria taxa involved. This delivered complementary information to the suite of review papers already providing elaborated syntheses on biomanipulation and associated ecotechnological measures as a restoration tool for overall eutrophication reduction and control. We considered nature-based solutions such as fish removal and associated water drawdown, addition of piscivorous fish, filter-feeding planktivorous fish, Daphnia or bivalves, re-introduction of macrophytes and a combination of accompanying restoration methods. Reasons for success or failure to control cyanobacterial blooms of especially Anabaena, Pseudanabaena, Aphanizomenon, Aphanocapsa, Limnothrix, Microcystis, Oscillatoria or Spirulina spp. could be explained through bottlenecks encountered with fish removal, stocking densities, cascading effects, associated zooplankton grazing, diet shifts away from cyanobacteria, macrophyte recovery, nutrient or pH status. Threshold values to avoid failures are synthesized from experiments or monitoring studies and presented in a conceptual scheme about cyanobacteria reduction through (1) direct abatement of existing blooms and forcing/maximization of biotic key interactions (2) reducing risk of blooms and improving lake or pond multi-functionality and (3) avoiding blooms, balancing biotic communities and enhancing existing ecosystem services. More information will be required on temporal dynamics and abundances of cyanobacteria taxa in whole-lake pre- and post-biomanipulation conditions to better evaluate the applicability and effectiveness of such nature-based solutions.