Not all culture is created equal: A comparative study in search of the most productive cultivation methodology

Considerable investment through public/private consortia has been towards increasing the productivity from mass algal cultivation for making the industries involved more economically viable. Although high-tech solutions have been popular in recent years, I questioned whether low-tech answers through the method that algae are cultivated could shed light on increasing productivity in mass cultivation systems. Shade-limited growth was studied for Thalassiosira pseudonana (marine diatom) cultures exposed to 85 Ein m− 2 d− 1 under continuous light, and mixed through a 20 cm water column (a standard depth for open pond cultivation), to compare ash-free dry weight (AFDW) and chlorophyll-a (Chl-a) concentrations, net primary productivity (P) and specific growth rates (μ) obtained by batch culture, continuous culture, and semi-continuous culture. Under shade-limiting conditions, both AFDW and Chl-a concentrations varied inversely with μ for the three cultivation methods. During the linear growth phase of batch culture, P did not vary in relation to μ or biomass (B), therefore μ = P / B, and growth rate varied as a power for biomass. For continuous culture methods, B is a function of μ (as dilution rate), therefore B = P μm, and m = − 1 if linear growth is modeled. Net primary production did vary in relation to μ for both continuous and semi-continuous cultures, and m > − 1. Therefore continuous and semi-continuous culture methods did not reproduce a linear growth phase as found for shade-limited growth. For growth rate > 0.5 doubling d− 1, semi-continuous culture had highest, and continuous culture had lowest P for the three methods compared. These results provide evidence that the method of cultivation introduces large variability to net primary productivity under shade-limiting conditions, and needs consideration in the design of cultivation systems and microbiological experiments.