Die Wirkung eines Licht-Temperatur-Salzgehalt Komplexes auf den Gaswechsel von Delesseria sanguinea (Rhodophyta) aus der westlichen Ostsee

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Abstract
Photosynthesis and respiration of young and adult thalli of D. sanguinea from the western Baltic were measured as O2 exchange in a factor complex of light, temperature and salinity in the laboratory. A relative value for gain in matter (relation of photosynthesis to respiration) and compensation points were calculated from these data. Response surfaces of photosynthesis and respiration show stable structures from young to old thalli. A relative increase in Ca content of the seawater causes minor modifications, which correspond with an increased osmotic tolerance. In different parts of the factor space the factors show variable degrees of influence and interaction. Photosynthesis shows an optimum for marine conditions at about 30.permill. S (salinity) and 10.degree. C. A tolerance for decreasing salinities expresses at optimal temperature and light. It develops with the alga aging and is interpreted as a facultative adaptation to ambient salinities. The response surfaces of respiration are similar to those of photosynthesis in the temperature salinity plane. No adaptation, e.g., change in plasticity, to the temperature salinity conditions of the Baltic, of the different seasons or to the culture conditions is detectable. This leads to the assumption that the observed response structures are characteristic of this species. The distribution of gain in matter and the compensation points show a distinct 2nd optimum at 15.permill. S (culture salinity) besides the marine one. Comparison of fictive response rates calculated from the response surface for a marine and for different depths of a Baltic location confirm the opinion of exclusively light-dependent growth in the marine habitat, while temperature mainly inhibits growth in the Baltic. The 1st growth period in winter must be only promoted by starch reserves, expressed by high respiration rates. The formation of starch reserves by adult Delesseria of the Baltic in summer is promoted in greater depths because of a vertical salinity gradient. This explains a vertical optimum of abundance and a simultaneous reduction in size.