Effects of salinity and light intensity on the resumption of photosynthesis in rehydrated cyanobacterial mats from Baja California Sur, Mexico

Lyngbya mats in the intertidal of the Laguna Ojo de Liebre are metabolically active for only a few days every 2 weeks during spring tides, with environmental conditions varying greatly during these periods of hydration. Pulse amplitude modulated fluorometry (PAM) and oxygen measurements were used to measure photosynthetic activity during the first few hours after rehydration under various light intensities and salinities. Upon rehydration, a transitory maximum in respiratory activity (10-30 min) occurred before the resumption of photosynthesis, which could recover in about 2 h. Salinities outside the mats' natural range (35-50 psu) were detrimental to photosynthetic recovery. Both high (100 psu) and low (0-10 psu) salinities slowed recovery as well as lowered the overall photosynthetic yield. Photosynthesis was initiated earlier and recovered more rapidly with increasing light intensity. In addition, the positive effect of light on rates of recovery was disproportionately greater at lower salinities (10-25 psu) where high light (500 W(.)m(-2)) counteracted the negative effects of low-salt stress early in recovery. However, higher light intensities became photoinhibitory later in recovery (> 2 h). Photosynthesis did not recover uniformly within the mat. Filaments deeper in the mat most likely recovered later than those near the surface due to high light attenuation. The ability of the mats to tolerate desiccation and take advantage of hydration periods even when conditions are suboptimal enables these mats to predominate in the intertidal environment.