In the littoral algae Fucus virsoides, Ulva lactuca, Porphyra leucosticta and the sublittoral Wrangelia penicillata the combined effects of salinities and temperatures on the assimilation rate were studied. Experiments were made in two series in which the salinities below 37 % 0 S were performed by diluting sea water with distilled water or with fresh spring water. In all investigated algae net oxygen production increased in the salinity concentrations which were prepared by düuting sea water with fresh spring water. In dilutions performed with distilled water, the oxygen production was depressed by all concentrations. Parallel with lower temperatures and lower salinities, usually low or even negative net production resulted. In general, the fresh spring water of high alkalinity (6.70 milliequivalents/1) and large amount of nutrients (reactive phosphorus 1.12 Mgat/1 and nitrates 27 jjg-at/l) when mixing with sea water, especially during low tide, caused incieased photosynthesis in algae, in comparison with that of normal salinity.

FUCHS rirsoides, which is an endemic mediolittora) seaweed in the Adriatic Sea, was studied in rcspect of the seasonal variations in the rate of photosynthetic activity at three localities in situ and under constant light intensity and temperature in Jaboratory. This work also included investigations on the seasonal variations in the chcmical constitution of the Fttcm virsoides correlated with the physical and chemical properties of the sea. The results show that there is a correlation between the rates of photosynthesis, growth of the alga, temperature, light intensity and nutrients in the sea* Summer maximum values in the rate of gross productivity varied between 0.78-1,12 m/ (X'g/h and winter minima between 0.33-0,42 m/O^'g/h, depending on the investigated localities. In laboratory conditions under constant light intensity and temperature the values of gross production were usually less than those obtained in /·////, on account of the lower light intensity. Higher values were obtained in thc laboratory only on winter and they coincided with the highest pigment concentrations. The seasonal Variation in chemical composition of Fttetts virsoides varied in relation to the surrounding conditions which influence the development and growth of the atgae, Thc highest values of protein content were detected during the period of the most intensive growth of the alga in r nge of 11,14°0-12.35°0 > which was also related to the amount of nutrients in the sea. The fluctuations in alginic acid show a positive correlation with the calcium content and negative onc with the ash and protein content, The lowest values in the ether soluble substances (2.19-3.27%) were detected at the time when algac began to grow, and the maximum (5.72-6.81%) occurred after the reproduction cycle at the time of thallus degradation, The seasonal Variation in mannitol content followed the variations in the rate of photosynthesis. Variations in chlorinc content and phosphorus in the algae only partially corresponded with the variations in the concentration of these substances in the sea. Pigments showed their maximal concentration during the winter and were minimal during thc summer period, which seems to be related to the development of the seaweeds and to the light intensities.

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