Power of Plankton: Effects of Algal Biodiversity on Biocrude Production and Stability

Anita Narwani, Aubrey R. Lashaway, David C. Hietala, Phillip E. Savage, Bradley J. Cardinale

Algae-derived biocrude oil is a possible renewable energy alternative to fossil fuel based crude oil. Outdoor cultivation in raceway ponds is estimated to provide a better return on energy invested than closed photobioreactor systems. However, in these open systems, algal crops are subjected to environmental variation in temperature and irradiance, as well as biotic invasions which can cause costly crop instabilities. In this paper, we used an experimental approach to investigate the ability of species richness to maximize and stabilize biocrude production in the face of weekly temperature fluctuations between 17 and 27 °C, relative to a constant-temperature control. We hypothesized that species richness would lead to higher mean biocrude production and greater stability of biocrude production over time in the variable temperature environment. Counter to our hypothesis, species richness tended to cause a decline in mean biocrude production, regardless of environmental temperature variation. However, biodiversity did have stabilizing effects on biocrude production over time in the variable temperature environment and not in the constant temperature environment. Altogether, our results suggest that when the most productive and stable monoculture is unknown, inoculating raceway ponds with a diverse mixture of algae will tend to ensure stable harvests over time.