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 a nd Ruppia cirrhosa, two dominant submerged macrophytes in South Africa n estuaries, was measured using chlorophyll fluorescence (Fv/Fm ratio) . The Fv/Fm ratio for Zostera leaf tissue decreased to a constant mini mum level after 30-min exposure. The Fv/Fm ratio for Ruppia leaf tissu e decreased as the degree of desiccation (exposure time) increased. Zo stera was 75% desiccated after 30 min, whereas Ruppia was 63% desiccat ed. Zostera recovered better than did Ruppia after 24 h of resubmergen ce. After 4 days of resubmergence both plants in all exposure treatmen ts showed complete recovery, i.e. the Fv/Fm ratios had increased to th e 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 Rupp ia. Ruppia is more sensitive to desiccation and Zostera possibly outco mpetes Ruppia in tidal marine habitats.