抄録
The experimental data presented above show clearly that the unicellular algae such as Chlorella, Scenedesmus and Chlamydomonas, are excellent feed for daphnids. Although less effective than these algae, filamentous blue-green algae Tolypothrix and Nostoc, also serve as nutrient for daphnids. For the past several years we have been conducting experiments of seeding Tolypothrix and other nitrogen-fixing blue green algae on the paddy-field in order to test the possibility of increasing rice crop by virtue of their nitrogen-fixing capacity(9). One of the serious problems arising in these field-experiments was that, occasionally, the seeded algae dissappeared 1955 Micro-algae as a Source of Nutrients for Daphnids 141 completely from the field within 1 or 2 weeks In such cases we found, almost without exception, that the field water became abundant first with unicellular algae such as Chlorella and Scenedesnzus, and then with water- fleas which eventually ate up the seeded blue-green algae. We learn from the above experiments that in order to assure the growth of nitrogen-fixing blue-green algae in the paddy-field, some measure must be taken to prevent the growth of water-fleas or to suppress the growth of unicellular green algae which remarkably favors the increase of the population of daphnids.