The Feeding Mechanism of the Freshwater Gastropod (Bellamya Aeruginosa) – Realizing its Potential in Controlling Cyanobacterial Harmful Algal Blooms
Cyanobacterial harmful algal blooms (CHABs) caused by eutrophication seriously impact aquatic ecosystems and human health. Biomanipulation using foraging organisms to regulate and eradicate harmful algal growth has been receiving considerable attention. However, successful cases are limited to small scale operations, and organisms have included only herbivorous fish and zooplankton. Freshwater gastropods are diverse and abundant, and can be used in biomanipulation because they are easily collected and transported. The aim of this dissertation is to investigate the freshwater gastropod, Bellamya aeruginosa, in controlling CHABs. Results showed: 1) B. aeruginosa use suspension filtration to capture floating colony-forming cyanobacterial species Microcystis aeruginosa and produce pseudofaeces containing M. aeruginosa removing them from the water column; 2) Rate of suspension filtration depends on distribution overlap of B. aeruginosa and M. aeruginosa; 3) The suspension filtration is not detrimental to M. aeruginosa as the pseudofaeces containing M. aeruginosa float, decompose rapidly, and release viable Microcystis back to the water body; 4) B. aeruginosa showed low grazing ability to floating pseudofaeces, but it can graze on pseudofaeces that remain on the bottom; 5) Faeces produced by Bellamya have as low density as pseudofaeces, ruptured rapidly and subsequently released undigested Microcystis back to the water body causing secondary blooms. The combined effect of points 2 - 5 resulted in a low control efficiency; 6) Silt or turbidity significantly improved control efficiency on Microcystis due to alterations in pseudofaeces and faeces. Suspended particles and silt increased the density of pseudofaeces and faeces, respectively, so they settled to the bottom allowing increased grazing and ingestion rates, and led to significantly increased digestion. In addition, silt and suspended particles wrapped with M. aeruginosa in the pseudofaeces and faeces enhanced structural robustness, significantly increasing decomposition time, and therefore reduced M. aeruginosa viability. These findings were validated in a whole-lake experiment that successfully controlled CHABs through B. aeruginosa. B. aeruginosa’s digestive ability is not the major factor determining control efficiency over Microcystis, but rather the properties of the pseudofaeces and faeces. These findings suggest that instead of manipulating food-chains at different trophic levels by introducing remediating species to where cyanobacterial infestations are located, relocation of Microcystis to lake bottoms may keep it in check by co-habituating organisms.
URI for this recordhttp://hdl.handle.net/1974/15582
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