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Proceedings of the Horiba International Conference "New Direction of Ocean Research in the Western Pacific" : Past, Present and Future of UNESCO/IOC/WESTPAC Activity for 50 years and the JSPS Project "Coastal Marine Science"Section I: Research Articles/Harmful microalgaeField studies in the Upper Gulf of Thailand and Manila Bay on red tides of green Noctiluca scintillans with the photosynthetic symbiont Pedinomonas noctilucae showed that vertical maximum of N. scintillans often occurred below halocline at 10 to 15 meter depths, suggesting that salinity influenced the vertical distribution of this organism. Then, we examined the influence of salinity on the vertical distribution of N. scintillans under laboratory conditions. A three layer system with varying salinity of 10, 20 and 31 was produced in the black polyethylene tubes of 20 cm in diameter and 1.5 m long. Tubes were exposed to a 12 : 12 LD cycle under the light intensity of 70μmolm(-2)s(-1) provided at the top. Two set of experiments were conducted to observe behaviors of N. scintillans for a week: in the first set N. scintillans cells were added at the surface of the tubes while in the second one cells were added at the bottom. In the stratified tubes, all cells released at the surface died immediately at the beginning of the experiment, while cells released at the bottom slowly migrated toward the upper layer, and uniformly distributed throughout the column within 24 h. In the control tubes with a uniform salinity of 28, it took shorter (3 h) for cells released from the bottom to attain the uniform distribution. During the latter half of the experiment most cells stayed at the surface. These results indicate that N. scintillans is able to tolerate a wide range of salinity, and that an acclimation period is needed to adapt to low salinity conditions; this adaptive feature may be an important factor to maintain its population and to form red tide in the river mouth areas.
- Coastal marine science
Coastal marine science 35(1), 70-72, 2012-00-00
International Coastal Research Center, Atmosphere and Ocean Research Institute, the University of Tokyo