The photo-inhibition of phytoplankton photosynthesis at higher intensities was examined with a cultured marine diatom, Phaeodactylum tricornutum, and natural samples. The question was to determine whether photo-inhibition results from excretion of photosynthetic products from cell or from an actual decrease in photosynthetic rate.
P. tricornutum culturedat 15 klux showed very little photo-inhibition up to 70 klux, and, in the sample cultured at 1 klux, most marked photo-inhibition was observed in 3 hours experiment. Extracellular release was less than 30% of particulate fixation, and did not show any extremeincrease to supplement photosynthesis depression at higher light intensities. When the photosynthesis was measured during 10 minutes, both samples showed no photo-inhibition. The photosynthesis by low light sample lost the linearity of time-course with prolonged exposure at high light intensity. Observed photo-inhibition, therefore, we explained with the actual decrease in photosynthetic rate. Similar photo-inhibition could be seen in marine phytoplankton samples concentrated by filtration

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The bacterial populations of mangrove swamps of Killai backwaters (11°21'-11°29'N, 79°46'-79°50'E, South India) were studied during August 1968 (Pre monsoon period) and December (post monsoon period). The presence of these groups such as agar digesters, algin digesters, cellulose digesters, sulphate reducers etc., bring about transformation oforganic matter in the mangrove swamps. The presence of denitrifiers in mangrove swamps andin association with the molluscs may bring about the precipitation of calcium carbonate byremoving the acid radicals such as sulphate and nitrite, increasing alkalinity. The luminiscent bacteria such asVibrioandAeromonaswere also isolated in mangrove swamps of Killai backwaters. The iron bacteria likeLeptothrix sp.andGallionella sp.were also isolated from mangrove swamps of Killai backwaters.

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A specific community of heterotrophic microorganisms-bacterioneuston-was detected in the near surface microlayers of the sea (microhorizons 150μ, 1-2cm) by means of original methods and sampling devices. Investigation of bacterioneuston in the different seas (the Black Sea, the Sea of Azov, the north-eastern part of the Pacific Ocean) revealed its peculiar features which are high content of microorganisms, its flourishing during the period of wind and wave action increase, a rich specific composition with a bright pigmentation of strains and somewhat specific biochemical properties.
The ways and sources of bacterioneuston formation as well as its part in the life of water ecosystems are discussed in this paper.

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Iodine in sea water of the Pacific was determined with special interest in the relation between iodide and iodate in the surface water of the ocean. The result was discussed with reference to the mechanism of iodide formation proposed by TSUNOGAI and SASE. The concentration of iodide varies widely from the lower value than the detection limit to 0.21μg at./l, while the concentration of total iodine is nearly constant and the mean value is 0.41 μg at./l.The vertical profile of iodide often shows the maximum in the surface layer. In the surface layer, the concentration of iodide is higher in warm water (0, 10 g at./lon the average) than that in cold water of lower temperature than 20°C (0.03μg at E/l).The highest concentration of iodide among the warm waters isfound in the surface water of the equatorial area (0.13μg at./l) where the biological productivity is also high. Iodide is generally more enriched in the water having higherbiological activity even in the cold water. These results are considered to be compatible with the mechanism of iodide formation proposed.

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Vertical distribution of underwater scattering radiances of the first, the second and the third order is estimated by the Jerlov's method. In the estimation the volume attenuation coefficient and the volume scattering function are assumed to be constant in near surface layer, and the sky radiation separated from solar radiation to be a parallel beam and to fall into the sea in the vertical direction only.
In the zenith direction the second scattering radiance is more intense than the first scattering radiance in near surface layer.As for the total radiance which is a sum of radiances up to the third order, the zenith radiation is largest, the nadir radiation is moderate and the horizontal radiation is least.

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