Germination and growth of Ruppia polycarpa and Lepilaena cylindrocarpa in ephemeral saltmarsh pools, Westernport bay, Victoria

Abstract

Changes in standing crop of the euryhaline macrophytes Ruppia polycarpa R. Mason and Lepilaena cylindrocarpa (Koernicke ex Walp.) Benth. were monitored from March to November 1983 in saltmarsh pools at Westernport Bay, Victoria. The salinities of these pools varied from 370‰ total dissolved salts (TDS) in February to 14‰ TDS in September. In March the bottom sediments contained approximately 10 3 seeds m −2 and 400–3500 turions m −2 of Ruppia and 10 5 seeds m −2 of Lepilaena. Germination commenced in April, at salinities of around 40‰ TDS. Counts of emerging seedlings suggest that less than 30% of Ruppia and 1% of Lepilaena propagules germinated. Maximum mean standing crops were 52 g AFDW m −2 for Ruppia and 60 g AFDW m −2 for Lepilaena. In laboratory experiments, Lepilaena and Ruppia seeds showed maximum germination (85 and 45%, respectively) in freshwater at 20°C. Ruppia turions germinated equally well (60%) in 50 and 100% seawater at 20°C, and after 25 days the germination percentage was higher in 225% seawater than in freshwater. Some propagules of both species germinated in 225% seawater, but none germinated in 450% seawater. The germination potential of seeds soaked in 225 and 450% seawater for 14 days and then transferred to freshwater was generally unaffected. Some propagules germinated in freshwater after soaking in 1000% seawater for six days. Shoot and root growth of seedlings of both species was better in 50 and 100% seawater than in freshwater. The life-histories of these species show them to be opportunists well adapted to survive in this ephemeral habitat of variable salinity.