The Photosynthesis of Diatom Cultures in the Sea

Abstract

With 24 Figures in the Text.PHOTOSYNTHESIS in the opensea is duemainly to two groupsoforganisms, the diatoms and the dinoflagellates. In British seas the diatoms are so much more numerous that the chemical changes which are due to photosynthetic activity can be almost entirely ascribed to their influence. Recent work on these chemical chang.es has shown that they do not ,extend deeper than about 30 metres. Of the external limiting factors light is among the most important and the depth to which photosynthesis can go on must, of course, depend on the light intensity. In the study ()f the phytoplankton under natural conditions the results are compli-(Jated by the interaction of many other factors such as temperature, viscosity, or lack of food salts, so that it is difficult to come to definite (Jonclusions on the effect of light alone.Early experimental work on the effect of light at different depths was carried out at Monaco by Regnard (1891), who germinated seeds of ,cress and radish at different depths, and found that little chlorophyll was formed at 30 metres. He also estimated the oxygen production of DIva over a day, and found that this was too low to measure at 8 and 10 metres. His method, however, was not a delicate one. Jonsson (1903), in the Oslo fjord, using the moss Olimacium dendroides, found that photo-,synthesis fell off rapidly from the surface, and was not appreciable below 17-27 metres. More recently Gaarder and Gran (1927), using samples of sea-water rich in diatoms, found that photosynthesis was ,considerably less below than at the surface, and that at about 10 metres photosynthesis and respiration just balanced each other. Considering the methods used, and the differences in latitude and season there is probably no real discrepancy in the results of these different observers.While the results of Gaarder and Gran probably give a true picture of

Oxygen Production by the Diatom Coscinodiscus Excentricus Ehr. in Relation to Submarine Illumination in the English Channel

“…7, with the oxygen as ordinates, and the time of day as abscissae, for the various depths. The relation of the oxygen production to the waxing and waning of daylight is clearly shown, as well as the midday inhibition near the surface; this result is closely similar to that obtained by Marshall & Orr (1928, fig. 7, p. 328) for a sunny summer day in the Clyde.…”

Convection and primary production in winter

“…The only conclusion we could draw from this finding was that production had caused the observed distribution in biomass. A winter production was already postulated long ago by Marshall & Orr (1928). Viability tests showing high F DCMU :F ratios confirmed that algae were indeed actively photosynthesising (Roy & Legendre 1979).…”

Photosynthesis in the Ocean as a Function of Light Intensity1

“…28), showing the same general trend in every case of a linear increase of photosynthesis with light intensity up to a saturation point, beyond which higher intensities do not increase photosynthesis but eventually result in an inhibition, the physiology of which is discussed by Steemann Nielsen (1952). The majority of laboratory studies with terrestrial or freshwater plants have not been concerned with the high intensities at which this inhibition occurs, but the phenomenon has been clearly demonstrated in all measurements of photosynthesis in natural waters by a marked depression at or near the surface where the organisms are exposed to nearly full incident solar radiation (Marshall and Orr 1928, Jenkin 1937, Steemann Nielsen 1951, 1952.…”