Can solar powered circulation control Prymnesium parvum blooms and toxicity in fish hatchery ponds?

Abstract

The harmful alga Prymnesium parvum can be controlled with chemicals that also can kill non-target organisms including fish. Currently, there is no ecologically safe and sustainable method for controlling this alga. Therefore, we evaluated SolarBee ® solar powered water circulation (SPC) for efficacy in controlling P. parvum blooms and ichthyotoxicity. We hypothesized that SPC can alter the ecological niche that promotes P. parvum blooms and toxicity, and thereby control this alga. Ecological niche variables considered were inorganic phosphorus (P) and nitrogen (N), conductivity, pH, temperature, and cations. The effects of SPC on total algal biomass and community structure and zooplankton were also investigated. The study was conducted in six 0.4 ha plastic-lined fish hatchery ponds from September 2007 to March 2008. Three ponds received SPC and another three without SPC served as control. Variables tested were P. parvum cell density and ichthyotoxicity, total algal density, algal population diversity, chlorophyll a, P, N, pH, water temperature, dissolved oxygen, conductivity, calcium, magnesium, potassium, and sodium. The algal community consisted of 69 taxa (genera and species) from eight divisions, including Haptophyta and Chlorophyta, and two unidentified algae. The SPC suppressed the chlorophytes population and otherwise had no effect on any of the tested variables. The SPC was unable to alter water quality and nutrient levels in hatchery ponds and thus failed to control P. parvum.