Measuring the efficiency of the bioremediation of cyanobacterial harmful algal blooms using Viviparus georgianus

Abstract

With rising global temperatures, cyanobacterial harmful algal blooms (CHABs) have been increasing in size and frequency for several decades. These blooms produce toxins while severely reducing the oxygen levels of marine and freshwater ecosystems, resulting in large scale mortality events of aquatic life. A key element in a proactive approach to controlling CHABs may be bioremediation, the use of naturally occurring organisms to consume environmental pollutants. However, an optimal species for CHABs bioremediation has yet to be identified. Viviparus georgianus, the banded mystery snail, is ubiquitous to freshwaters, naturally occurs in high densities, and possesses gastropod relatives shown to be able to consume cyanobacteria with rapid detoxification effects, making them an ideal potential candidate. Despite this, little is known about their rate of consumption of CHABs, and how that may be affected by density of snails as well as affected by the species of cyanobacteria. I placed V. georgianus in microcosms with varying species of cyanobacteria or green algae, as well as varying densities of snails and then measured cyanobacteria ingested via the quantity of chlorophyll-a remaining in the water. My results demonstrated that snails in 200 mL of high cyanobacterial concentrations were able to decrease cyanobacteria by 60-70% within an hour of exposure, regardless of the presence of toxic cyanobacteria species. Over 24-hours, optimal snail density for cyanobacteria consumption occurred with 1-3 g of snails in 0.2 L microcosms, with increasing density of snails having diminishing efficacy returns. By understanding how to optimize V. georgianus’ consumption of cyanobacteria, we can make use of a widespread and highly populous species for efficient and effective inhibition of CHAB blooms.