. Le bulletin biologique. Biologie ; zoologie ; biologie marine. 416 par photo-oxydation HALLDAL à toutes les intensités appliquées. Les échantillons prélevés dans les couches ou des parcelles d'Ostreobium au-dessous de la couche la plus proche de la surface n'a généralement pas répondre à la lumière. Dans certains cas, on a observé peu de photo-oxydation. Les spectres d'action. Les spectres d'action de la photosynthèse et photo-oxydation peut être effectuée. Dans le cas de la réduction de la photo-oxydation /'Og a été ré- versible doux avec des doses de l'irradiation. En raison de cela, les spectres d'action de l'oxydation photo- pourraient être enregistrées avec l'appareil de terrain, si une correction

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. The Biological bulletin. Biology; Zoology; Marine biology. 416 PER HALLDAL photooxidation at all intensities applied. Samples taken from layers or patches of Ostreobium below the layer nearest the surface did usually not respond to light. In some few cases photooxidation was observed. Action spectra. Action spectra of both photosynthesis and photooxidation could be performed. In the case of photooxidation the reduction in /'Og was re- versible with gentle doses of irradiation. Because of this, action spectra of photo- oxidation could be recorded with the field apparatus, though corrections and adjustments were needed (see Fig. 8). The action spectrum of photosynthesis is presented in Figure 7. It was shown that Ostreobium in the ultraviolet responded with photosynthesis down to 300 nm, that is, the same spectral region in the ultraviolet which was photosynthetically effective for zooxanthellae. Below 300 nm photooxidation occurred during expo- sures of more than 15 seconds duration of moderate intensity (about 500 erg. cm."^ sec"^, but highly dependent upon the sample; see above). However, the far ultra-. FiGURE 5. Schematic drawing of a cut from the massive coral Favia. A. Living part of coral with zooxanthellae. B. Green layer of the Siphonales Ostreobium within the dead part of the coral. The numbers illustrate positions of sampling, which correspond to the numbered curves in Figure 6. violet response of this alga gave a rather complicated picture, evidently highly dependent upon sample and radiation intensity. Both very rapid increases and decreases in pO^ were observed. These fast changes were always succeeded by a slower degree of photooxidation. Data are available from several such far-ultra- violet experiments, but it is uncertain whether they suffice for analysis of the rather complicated response. Above 300 nm photosynthesis occurs. Small, but significant, inflexions are noticeable around 310 and 340 nm. At 440 nm the chlorophyll a peak in the

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