THE EFFECT OF SALINITY ON THE REPRODUCTION OF COASTAL SUBMERGED MACROPHYTES IN EXPERIMENTAL COMMUNITIES

The effects of salinity on the reproduction of coastal submerged macro phyte species were studied on samples of communities from six seasonal marshes in two outdoor experiments performed in autumn and in spring. The submerged macrophyte communities were submitted to five different salinity levels (0, 1, 2, 4 and 6 g/l Cl-). In a companion paper (Gri llas, van Wijck & Bonis 1993) three groups of species were distinguish ed on the basis of their biomass production over the salinity range 0 to 6 g/l Cl-: (1) glycophytes (non-salt-tolerant species), (2) salt-to lerant species and (3) halophytes. This part of the study describes th e impact of salinity on the reproduction of the individual species dur ing the two experiments. The species differ in their capacity to repro duce in the autumn; only Zannichellia pedunculata and Tolypella hispan ica were able to produce fruits in that season. For all species reprod uction was greater in spring and strongly correlated with biomass, exc ept for Chara canescens. Differences in reproductive effort over the s alinity range amplified the halophytic nature of Ruppia maritima and C hara canescens and the intolerance of Callitriche truncata and Chara c ontraria. For the other species, reproductive effort did not differ si gnificantly over the salinity range. Regarding the effect of salinity on biomass and reproductive effort of individual species, there were l arge differences in the total weight of propagules produced at the com munity level and in the relative contribution of individual species. T he resulting quantitative changes in the species composition of the se ed bank could affect the structure of the communities by their effects on the establishment and survival of species populations.