FACTORS AFFECTING PHOTOSYNTHESIS IN THE MOZAMBICAN SEAGRASSES CYMODOCEA-SERRULATA AND THALASSODENDRON-CILIATUM

The effect of various environmental factors on net photosynthesis rate s (P(N)) of the differentially depth distributed Mozambican seagrasses , Cymodocea serrulata (R.Br.) Aschers and Magnus (Zannich), and Thalas sodendron ciliatum (Forsk.) den Hartog, was examined. At saturating ir radiances the deeper water species, T ciliatum, showed a maximum P(N) (as measured by short term O2 evolution) of 12.67 +/- 3.33 mmol(O2) kg -1(Chl) s-1 with added 40 mM NaHCO3 (0.89 mM dissolved CO2 at pH 8); t he shallower species, C. serrulata, showed maximum rates of 21.67 +/- 4.17 (10 mM NaHCO3; 0.26 mM dissolved CO2). Saturating irradiances wer e similar for both species. P(N) estimated by the lacunal gas discharg e technique was 16.00 +/- 5.00 mmol(O2) kg-1(Chl) s-1 for C. serrulata and 11.67 +/- 6.67 for T. ciliatum. P(N) of both species was reduced by increased water depth, and the pattern of the effect of depth was s imilar.