Leaf production rates of Thalassodendron ciliatum from rocky and sandy habitats

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Growth and structure of Thalassodendron ciliatum were compared in plants from rocky and sandy habitats in southern Mozambique. Growth rate dynamics differed significantly between rocky and sandy plants: rocky plants had a leaf growth rate of 25.5 g DW m −2 per day compared to 9.5 g DW m −2 per day for sand. These differences depended on the number of shoots per area (4561 shoots m −2 in rocky areas versus 888 shoots m −2 on sand). Length increase was 56.9 m m −2 per day in rocky areas and 22.3 m m −2 per day for sand. In rocky areas 195 new leaves m −2 per day were born compared to 75 new leaves m −2 per day on sand. Total annual leaf production was high: 9322 g DW m −2 for rocky areas and 3468 g DW m −2 for sand. Leaf growth rate per shoot was generally 100% higher in sandy habitats than in rocky areas. The youngest leaf grew 2.9 mm per day (or 1 mg DW per day) in rocky areas and 5.4 mm per day (or 2 mg DW per day) on sand, giving a leaf turnover time (leaf renewal) around 23 days in rocky areas and around 12 days on sand. All five leaves on a shoot of rocky plants changed 3.2 times a year, while the average seven leaves changed 4.4 times a year on sand. Leaf biomass was 257.5 g DW m −2 in rocky habitats, statistically different from 123.7 g DW m −2 on sand, while leaf area indices were not statistically different. T. ciliatum from rocky habitats had a slightly higher root/rhizome biomass, probably as an adaptation for better anchorage of T. ciliatum in rock pools and crevices. Total rhizome length was 9 m m −2 for rocks and 6.9 m m −2 for sand. Seaweed epiphytes in rocky areas corresponded to 47.9% of the seagrass biomass while only 4.7% on sand.