Known as Golden Algae in popular media, Prymnesium parvum causes harmful algal blooms. When stressed, it secretes increased amounts of toxic chemicals called prymnesins, which have resulted in major fish kills in Texas. Although many options exist for mitigation of blooms, a feasible protocol for control of blooms on large-scale impoundments has yet to be identified.
Chemical control of P. parvum using six different enzyme inhibiting aquatic herbicides was explored in laboratory experiments. Of the six chemicals screened, one (Flumioxazin) was selected for further study due to a significant decrease in P. parvum cell numbers with increasing chemical concentration. It was applied to natural plankton communities during in-situ experiments (Lake Granbury, Texas). The first experiment was conducted during a period of P. parvum bloom initiation (March) and the second experiment conducted during a post bloom period (April). Experiments were carried out in 20 L polycarbonate carboys covered in 30% shade cloth to simulate natural light, temperature and turbulence conditions. Flumioxazin was additionally screened in the laboratory on the common game/forage fish bluegill sunfish (Lepomis macrochirus) for six weeks with weekly re-application of flumioxazin to treatment tanks.
Cell counts via light-microscopy, showed the chemical flumioxazin caused significant decreases in P. parvum, but no significant differences in zooplankton abundance during the period of bloom initiation. However, significant decreases in adult copepods were observed during the post bloom period, most likely due to decreased light penetration and inhibition of the photosensitive mode of action, but no significant decreases in P. parvum. No significant effects of flumioxazin were observed on growth, survival or feed conversion ratio for L. macrochirus.
- Roelke, Daniel Professor