The role of fish in cyanobacterial blooms in Australia

Abstract

Potential pathways for interaction between fish and cyanobacteria include fish grazing directly on cyanobacteria, fish preying on grazers of cyanobacteria, fish supplying nutrients through excretion, fish providing nutrients by resuspending sediments, and fish altering the availability of nutrients and light by damaging macrophytes. The dominant interactions in Australia are likely to be through pathways that increase the availability of nutrients at the bottom of the food web. Carp probably contribute to these pathways more than do other species by excreting nutrients, resuspending sediments and damaging macrophytes. Further research, on both alien and native fish species, is needed to quantify these processes. Grazing of cyanobacteria by fish is probably trivial because freshwater fish in Australia lack mechanisms to process cyanobacterial cells effectively. Trophic interactions between planktivorous fish, zooplankton and cyanobacteria require closer study to assess the potential for preventing cyanobacterial blooms by manipulating natural predator communities in Australia. However, the need to protect and strengthen native fish stocks precludes removal of native fish to reduce predation pressure on zooplankton communities. Alternative solutions that combine control of nutrients entering waterways and removal of carp have a higher likelihood of success.