MEPS 184:105-118 (1999)  -  doi:10.3354/meps184105

Growth, flowering, and population dynamics of temperate Western Australian seagrasses

Núria Marbà1,*, Diana I. Walker2

1Institut Mediterrani d'Estudis Avançats (CSIC-UIB), Carretera de Valldemossa km 7.5, E-07071 Palma de Mallorca (Illes Balears), Spain
2Department of Botany, The University of Western Australia, Nedlands, Western Australia 6907, Australia

ABSTRACT: Quantification of module size, leaf, rhizome and clonal growth, flowering intensity and shoot population dynamics of 7 temperate Western Australian seagrasses (Amphibolis antarctica, A. griffithii, Posidonia australis, P. sinuosa, P. angustifolia, Heterozostera tasmanica, Thalassodendron pachyrhizum) developing 8 monospecific stands reveals that these plants have different plant morphologies, display a wide repertoire of growth patterns, and exhibit substantial variability in their capacity to flower. Leaf production rate ranged between 2.6 (P. sinuosa) and 26 leaves yr-1 (A. antarctica), and leaf life-span varied between 85 (A. antarctica) and 245 d (P. sinuosa). Most of the species extended their horizontal rhizomes at rates slower than 10 cm yr-1. The highest rate of new short shoot formation by vertical rhizomes was observed in A. antarctica (on average each vertical rhizome annually produced 1.5 new short shoots), and the lowest in T. pachyrhizum (only 1 new short shoot would be recruited from 65 vertical rhizomes). Horizontal rhizomes produced 1 new short shoot every 17 (H. tasmanica) or 582 d (P. sinuosa). Flowering intensity varied from 0 (P. sinuosa) to 7% flowering short shoots yr-1 (P. australis). The median age of the short shoots in these populations ranged from 367 (H. tasmanica) to 1000 d (P. sinuosa). Clonal growth was the main mechanism providing short shoots in these temperate Western Australian meadows. Short shoot recruitment balanced short shoot mortality rate in most populations, indicating that they were in steady-state with the colonisation process. These species maintain their meadows through different plant strategies as a result of their different growth programmes and the variability in sexual reproduction success. The large differences in flowering intensity found across temperate Western Australian seagrasses suggest that sexual reproduction may play an important role for meadow maintenance and recovery.

KEY WORDS: Amphibolis sp. · Heterozostera tasmanica · Posidonia sp. · Thalassodendron pachyrhizum · Leaf growth · Rhizome elongation · Flowering intensity · Demography

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