Coccolithophorid algae culture in closed photobioreactors.

The feasibility of growth, calcium carbonate and lipid production of the coccolithophorid algae (Prymnesiophyceae), Pleurochrysis carterae, Emiliania huxleyi, and Gephyrocapsa oceanica, was investigated in plate, carboy, airlift, and tubular photobioreactors. The plate photobioreactor was the most promising closed cultivation system. All species could be grown in the carboy photobioreactor. However, P. carterae was the only species which grew in an airlift photobioreactor. Despite several attempts to grow these coccolithophorid species in the tubular photobioreactor (Biocoil), including modification of the airlift and sparger design, no net growth could be achieved. The shear produced by turbulence and bubble effects are the most likely reasons for this failure to grow in the Biocoil. The highest total dry weight, lipid and calcium carbonate productivities achieved by P. carterae in the plate photobioreactors were 0.54, 0.12, and 0.06 g L(-1) day(-1) respectively. Irrespective of the type of photobioreactor, the productivities were P. carterae > E. huxleyi > G. oceanica. Pleurochrysis carterae lipid (20-25% of dry weight) and calcium carbonate (11-12% of dry weight) contents were also the highest of all species tested.

Increased CO2 and the effect of pH on growth and calcification of Pleurochrysis carterae and Emiliania huxleyi (Haptophyta) in semicontinuous cultures.

The effects of changes in CO(2) and pH on biomass productivity and carbon uptake of Pleurochrysis carterae and Emiliania huxleyi in open raceway ponds and a plate photobioreactor were studied. The pH of P. carterae cultures increased during day and decreased at night, whereas the pH of E. huxleyi cultures showed no significant diurnal changes. P. carterae coccolith production occurs during the dark period, whereas in E. huxleyi, coccolith production is mainly during the day. Addition of CO(2) at constant pH (pH-stat) resulted in an increase in P. carterae biomass and coccolith productivity, while CO(2) addition lowered E. huxleyi biomass and coccolith production. Neither of these algae could grow at less than pH 7.5. Species-specific diurnal pH and pCO(2) variations could be indicative of significant differences in carbon uptake between these two species. While E. huxleyi has been suggested to be predominantly a bicarbonate user, our results indicate that P. carterae may be using CO(2) as the main C source for photosynthesis and calcification.

Future prospects of microalgal biofuel production systems.

Climate change mitigation, economic growth and stability, and the ongoing depletion of oil reserves are all major drivers for the development of economically rational, renewable energy technology platforms. Microalgae have re-emerged as a popular feedstock for the production of biofuels and other more valuable products. Even though integrated microalgal production systems have some clear advantages and present a promising alternative to highly controversial first generation biofuel systems, the associated hype has often exceeded the boundaries of reality. With a growing number of recent analyses demonstrating that despite the hype, these systems are conceptually sound and potentially sustainable given the available inputs, we review the research areas that are key to attaining economic reality and the future development of the industry.

Limits to productivity of the alga Pleurochrysis carterae (Haptophyta) grown in outdoor raceway ponds.

This study examined the effects of oxygen concentration, pond temperature and irradiance on productivity and CaCO(3) formation of the coccolith-forming alga, Pleurochrysis carterae CCMP647 grown in semi-continuous culture in outdoor raceway ponds. During the day the oxygen content of the pond increases markedly and P. carterae photosynthesis is inhibited by these high O(2) concentrations with the inhibition increasing with increasing temperature. The high irradiance outdoors presents less of a problem to photosynthesis and productivity as the algae can acclimate well to high irradiances over a period of several weeks. Pond depth also effects productivity and this effect varies with season. During autumn, productivities were highest at depths of 13 to 16 cm, and decreased when the depth was increased. During summer productivity was much lower at 13 cm pond depth and increased when the depth was increased to 16, 18 and 21 cm. Heating the ponds in the morning by approximately 3 to 5 degrees C improves productivity by 11%-21%, presumably because this allows the algae to photosynthesise faster in the conditions of low [O(2)] which occur in the early morning.

Heterotrophy on ultraplankton communities is an important source of nitrogen for a sponge-rhodophyte symbiosis.

Grazing on ultraplankton by the sponge partner of an invertebrate/algal symbiotic association can provide enough particulate organic nitrogen to support the nitrogen needs of both partners. The previously unknown natural diet of the sponge in the Haliclona-Ceratodictyon association consists of bacteria and protozoans, which are rich sources of nitrogen. Retention of ultraplankton varied with season and time of day. During the winter there was an order of magnitude more nitrogen taken up than in summer. Time of day during each season also affected the amount of ultraplankton retained. In summer retention was higher at night whereas the opposite was true during winter. Overall, the Haliclona-Ceratodictyon association is able to meet its metabolic nitrogen demands through grazing on the naturally occurring water column community.

Ammonium excretion by a symbiotic sponge supplies the nitrogen requirements of its rhodophyte partner.

Symbioses between sponges and algae are abundant in the nutrient-poor waters of tropical reefs, yet very little is known of the nutritional interactions that may promote this abundance. We measured nitrogen flux between the sponge Haliclona cymiformis and its symbiotic partner, the rhodophyte Ceratodictyon spongiosum, and assessed the potential importance of this flux to the symbiosis. While the association can take up dissolved inorganic nitrogen (DIN) as ammonium and nitrate from the surrounding sea water, enrichment of the water with nitrate did not affect its rates of photosynthesis and respiration. Much of the DIN normally assimilated by the alga is waste ammonium excreted by the sponge. A nitrogen budget for the symbiosis shows that the nitrogen required for algal growth can potentially be provided by sponge catabolism alone, but that only a small amount of nitrogen is available for translocation back to the sponge in organic compounds. The stable isotope composition (delta(15)N) was consistent with our interpretation of the sponge supplying excretory DIN to its algal partner, while the results also suggested that this DIN limits nitrogen deficiency in the alga. If our observations are typical of sponge-alga symbioses, then the supply of excretory nitrogen could be a major reason why so many algae form symbioses with sponges on coral reefs.