Diversity of algae in rice paddies in the Philippines and their uses

Of the 228 species algae noted in rice paddies of the Philippines, one species dominates because of its relative widespread occurrence and its potential economic importance as source of human food, i.e. Nostoc commune Vauch. The ecological distribution of these algae was observed to be related to the growth cycle of rice with the planktonic green algae and the diatoms dominating at the start of the growth of rice while the bloom-forming cyanobacteria tend to increase their biomass with the growth of the rice plant till before maximum tillering. Planktonic algae favored inorganic fertilization more than the bloom-forming nitrogen-fixing cyanobacteria. Rice plants tend to decrease the algae in the flood water, probably due to shading. Heavy pesticide user farm lands showed significant depressive effects on the algae as compared to the low-pesticide user farms. The diatoms showed greater resistance to the pesticides more than any other groups of algae because their population density did not change as much as the other groups of algae. Low pesticide user farms had a quick recovery in population density of the algae and sometimes their number even increased overwhelmingly probably because the low dose of the pesticides became a carbon source to the algae that consequently stimulated their growth. Thirteen years after the Mt. Pinatubo's eruption, the effect of lahar showed damaging effect on the types and density of the algae and the yield of the rice when the heavily damaged-lahar fields were compared to the minimally-damaged rice paddies. Physiological studies on the cyanobacterium, Nostoc commune Vauch. showed that it has a high protein content (up to 25% CP), high amount of dietary fiber called oxalate-oxalic acid soluble substances (OOSS), and its low protein digestability can be improved by extracting its chlorophyll and extracting some of the phenolic compounds. Algalization technology for rice production has been developed together with the mass production of some of the economically useful algae, such as N. commune, that could give a maximum yield of 29 m (dw), m-2 day-1. Dual cultivation with rice could yield as much as 200 kg biomass of the algae per ha per crop. Their uses range from biofertilizers, human food, pigment source, fine chemicals, and source of nutraceutical of high values.