Bengoa-Ruigomez, M.V., Hatziathanasiou, A., Kentouri, M., Divanach, P.
Photosynthesis is the process by which CO2 is reduced to carbohydrates, with the water acting as the reducing agent. It takes place in the thilakoid membranes and is influenced by several factors including temperature, salinity and/or CO2 concentration. The normal CO2 concentration in the atmosphere or water is lower than the optimum for photosynthetic fixation of CO2 during Calvin cycle. Therefore, intensification of photosynthesis can be achieved by increasing the CO2 concentration in the medium. Bloom Technology is a technique which integrates two elements, one vegetal, Chlorella minutissima, and one animal, Brachionus plicatilis. The population dynamics of either of these elements are highly influenced by the other. The O2 produced by algae will be used by the rotifers, and CO2 produced by the rotifers will be used by the algae. However, high CO2 concentration can be harmful, even lethal, for the rotifers. The aim of this work is to study the role of CO2 in Bloom Technology as well as in the development of B. plicatilis and C. minutissima.
The experiments were carried out at the hatchery unit of the Institute of Marine Biology of Crete. The culture was carried out in 800 l tanks, equipped with 4 submerged fluorescent lamps, providing continuous illumination. The culture columns were filled with 25ppt salinity littoral well water. Sterilization was achieved by chlorination and subsequent neutralization. The medium was then enriched. The columns were inoculated with one million logarithmic phase Chlorella cells/ml, and five days later rotifers (5+/-1 rotifers/ml) were inoculated. The culture was ended when all the algae has been consumed. Each day the cultures were provided with CO2 and microalgae and rotifer densities were determined. The growth performance was also evaluated, and statistical analysis was performed.
The growth of Chlorella was rapid and stable, reaching 12.2 million cells/ml on day 5, and 12.6 million cells/ml on day 6. The algal population then began to decrease due to growth of the rotifer population, and was totally consumed by day 10. After the their inoculation (4.5 inv./ml), the rotifer population started increasing, reaching a concentration of 105 ind./ml on day 10.
The CO2 addition does not only avoid carbon-limiting conditions but also improves the culture conditions, allowing optimal algal growth. The rotifers do not graze the algae too rapidly and the culture can be kept longer before the algae are totally consumed, development of a larger rotifer population is possible. Moreover, as production costs are reduced by Bloom Technology and the use of submerged fluorescent lamps, we can conclude that this daily addition of CO2 may be considered the most cost effective solution for quick restoration of the rotifer productivity.
(Institute of Marine Biology of Crete, Dept. Aquaculture, Iraklion, Crete, Greece)
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