Research during FY 1985-86 (Laws 1987a) elaborated on the two key findings mentioned earlier: effects of a 3-day dilution interval and of the foil arrays. The effects of foil arrays were tested over a 12-month period in the 48-m2 flume with Cyclotella sp., a diatom, which, like Chaetoceros, is a good lipid producer. The experiment involved alternatingly operating the pond with and without the foils for 2-week periods. The presence of foils increased productivity by almost a third, similar to the prior experiments.

The dilution effect was investigated with T. suecica, also in the 48-m2 flume, with similar results as before, in terms of both overall and maximal 3rd day productivity. However, solar conversion efficiencies were lower than observed in previous years, perhaps due to the approximately 3°C higher temperature during this year, compared to the previous one. The author speculated that this could have been close to the maximal permissible temperature for growth of T. suecica, and thus resulted in lower productivities.

However, the effect of dilution interval on production in the 48.4-m2 flume was somewhat puzzling (Laws 1986). These findings were a subject of considerable discussion and controversy. One possible explanation was the measurement of actual biomass density, which varied from about 27-28 g/m2 after dilution, to 80, 140, and 160 g/m2 for the 2-, 3-, and 4-day dilutions periods, respectively. However, this was considered an “unlikely” explanation. Indeed, the highest productivity was observed on day 3, with a steep decline on day 4. However, 4-day cycle cells still had lower productivity on day 3. Some “lingering effect of exposure to supraoptimal density conditions” was speculated to account for this phenomenon. The classical technique for studying such phenomena is the P versus I curve. Such studies were carried out with T. suecica cultures grown in the smaller 9.2-m2 flumes. However, as the author noted, the results were “somewhat discouraging” as there was no difference as a function of dilution intervals, and productivities were only about 24 g/m2/d, much lower than reported with the larger flumes. Thus, this issue remained as a major focus of this project.