THE TOLERANCE TO DESICCATION OF THE SUBMERGED MACROPHYTES RUPPIA-CIRRHOSA (PETAGNA) GRANDE AND ZOSTERA-CAPENSIS SETCHELL

The effect of short-term desiccation (0-120 min) on Zostera capensis and Ruppia cirrhosa, two dominant submerged macrophytes in South African estuaries, was measured using chlorophyll fluorescence (Fv/Fm ratio). The Fv/Fm ratio for Zostera leaf tissue decreased to a constant minimum level after 30-min exposure. The Fv/Fm ratio for Ruppia leaf tissue decreased as the degree of desiccation (exposure time) increased. Zostera was 75% desiccated after 30 min, whereas Ruppia was 63% desiccated. Zostera recovered better than did Ruppia after 24 h of resubmergence. After 4 days of resubmergence both plants in all exposure treatments showed complete recovery, i.e. the Fv/Fm ratios had increased to the initial values. This recovery was related to the rapid growth of new leaves and not the recuperation of desiccated leaves. Neither species recovered from a desiccation treatment lasting 1 wk. A daily exposure of 5 h did not effect Zostera leaf production but was lethal for Ruppia. Ruppia is more sensitive to desiccation and Zostera possibly outcompetes Ruppia in tidal marine habitats.