In FY1984-85 (Laws 1985), the research was directed toward the study of more thermotolerant species. Algal strains collected by the ASP researchers in the southwestern United States were evaluated using the Type I and II waters (see Section II. A. 1.for a description of SERI Type I and Type II media). Several species, including Platymonas sp. (used previously), Amphora sp., C. gracilis, and Boekelovia sp. were grown in the two water types, each at two salinities and at four temperatures (25° to 32°C), with the data reported as the number of doublings per day. One interesting, but unexplained, observation was that at higher temperatures there was a consistent shift, among all four algae, of maximum doubling rates to the higher salinity and Type II waters.

The small outdoor flumes were used to test this cultivation strategy. The cultures were diluted each third day, to a concentration of 2 x 106 cells. The results were “consistent with those of earlier studies,” with solar conversion (PAR) efficiencies close to 10% (5% of total solar). The C. gracilis species was also tested, though at a 2-day dilution rate (requiring a one per day doubling time), with somewhat lower efficiencies (8%), though still rather high productivities. Also, Tetraselmis suecica was cultivated in the ponds with good results. Over a 78-day cycle, in spring 1984 and summer 1985, productivity was 37+5 g/m2/d, with a corresponding PAR efficiency of 9.1%.

Removing half the arrays had no significant effect on productivity; removing all foils reduced light conversion efficiencies from 8% to 5.5%. However, a major variable in such systems is the pO2 in the ponds, which may well account for the difference observed. The higher mixing (e. g., power inputs) caused by the foils may have increased outgassing of O2 from the pond enough to increase productivity, rather than to any flashing light effect. The reports of increased productivities caused by 3-day batch dilutions and foils remained controversial, and continued to be the major focus of this project.