The effect of salinity on growth,photosynthesis and respiration in the estuarine red algaBostrychia radicans mont

The estuarine red alga,Bostrychia radicans, was subjected to osmotic stresses ranging from hypo-osmotic (9.9‰) to hyperosmotic conditions (37.4‰). The growth rate decreased with increasing salinities and showed a maximum in a mesohaline medium, while the photosynthetic rate and the chlorophyll a content increased under hyper-osmotic conditions. The rate of respiration remained constant over the salinity range tested.B. radicans revealed typical characteristics of “shade plants” having a low light compensation point at 3–4 μE m⁻² s⁻¹ correlated with a low photon flux density of 70–100 μE m⁻² s⁻¹ for saturation of photosynthesis. These physiological properties may explain the success ofB. radicans in estuarine habitats.