Nontraditional biomanipulation: A powerful ecotechnology to combat cyanobacterial blooms in eutrophic freshwaters

Abstract

<p>Cyanobacterial blooms, occurring frequently in eutrophic freshwaters worldwide, are considered as potential hazards to ecosystems and human health, and it is often difficult and expensive to control their outbreaks in large lakes through reduction of nutrient loadings. Biomanipulation, launched as an ecology-based solution in the 1970s, was once believed to be an effective way to counteract cyanobacterial blooms. It is divided into traditional biomanipulation (TB) and nontraditional biomanipulation (NTB) that use filter-feeding <i>Daphnia</i> and filter-feeding fish, respectively. There have been numerous reviews on the former, yet few on the latter. Here, we first revisit the debate on the digestibility of cyanobacteria in silver and bighead carp. Then, we review 42 experiments that clearly mention cyanobacterial changes and reveal substantial reductions in cyanobacterial abundance by filter-feeding carp in 88% of the cases. In particular, in a whole-lake experiment in Lake Donghu, increased stock of silver and bighead carp effectively decreased <i>Microcystis</i> blooms from a coverage of 87% in 2021 to 0% in 2022. Finally, we discuss possible factors related to NTB��s effectiveness that depends not only on standing stock, niche divergence and shape preference of the fish but also on trophic status of the waterbodies. Particularly, silver and bighead carp feed more effectively on colony-forming <i>Microcystis</i> than on filamentous cyanobacteria, but are capable of increasing small-sized algae. NTB can be used to prevent or diminish cyanobacterial blooms that are poorly grazed by <i>Daphnia</i>, providing an effective and sustainable in-lake ecotechnology to combat heavy cyanobacterial blooms in eutrophic waterbodies.</p>