Quantifying zebra mussel impacts on harmful algal bloom species in Texas reservoirs using environmental DNA surveys

Zebra mussels are a major threat to freshwater habitats and have caused decreases in biodiversity and ecological health with their invasion and subsequent spread throughout the eastern United States. Zebra mussels are now in Texas reservoirs, and are continuing to be found in new reservoirs in the state. Because Texas reservoirs are more shallow and highly managed than natural lakes in the Great Lakes region where most studies about zebra mussels have taken place, it is largely unknown what impacts zebra mussels will have on the communities in Texas reservoirs. Previous studies in the Great Lakes region have shown that zebra mussel invasions cause an increase in toxic algae blooms. This community dynamic has not previously been studied in Texas. To this end, environmental DNA (eDNA) surveys were used to detect and quantify zebra mussels as well as Microcystis and golden alga in Texas reservoirs with and without zebra mussel populations. I found that there was no statistically significant increase in toxic algae abundance in reservoirs with zebra mussel populations relative to reservoirs without. However, because of unusual environmental conditions during sampling events (flooding), I recommend further studies to more fully explore this research question. A study of longer duration and in more typical environmental conditions is needed to more clearly describe the relationship of zebra mussels and toxic algae in Texas reservoirs. In addition, I recommend further study of the impacts of flooding events on the ecology of eDNA. This will allow for eDNA researchers to carry out more reliable quantitative field eDNA surveys.