The effects of emergence and submergence on the photosynthesis and respiration of marine macrophytes

Abstract

Respiration and gross and net photosynthesis were measured for 3 spp. of intertidal algae growing at 10 and 18.degree. C when they were submerged and emerged. Evidence that the high intertidal alga, Fucus distichus is physiologically well adapted for its position in the intertidal zone comes from the following observations: maximum gross and net photosynthesis were greater for emerged than submerged thalli; net photosynthesis for emerged thalli was a maximum at 20% desiccation; only above 50% desiccation did net photosynthesis steadily decrease. The representative of the low intertidal region, Iridaea cordata, appears to be better adapted for submergence than emergence since values of maximum gross and net photosynthesis for submerged thalli were always greater than when emerged. When this alga was emerged, respiration was greater than when submerged. Ulva fenestrata, a low to mild-intertidal alga, exhibited an intermediate response to submergence and emergence, in terms of net photosynthesis, when compared to Fucus and Iridaea.