Abstract
The shoot demography and rhizome growth of Syringodium filiforme Kϋtz. and Halodule wrightii Aschers. were studied, based on plant dating techniques, to account for their role as pioneer in the succession sequence of Caribbean seagrasses. Results demonstrated that these species are able to develop dense meadows, supporting biomasses in excess of 500 g DW m−2. They produced more than 2000 g DW m−2 yr−1 due to their high leaf (5.0 to 8.5 yr−1) and rhizome (2.0 to 3.3 yr−1) turnover. Rhizome growth and branching rates were very high, allowing these seagrasses to rapidly occupy the space they colonise. The rapid rhizome turnover involved, however, a high shoot mortality rate and low life expectancy (average shoot life expectancy 100 to 180 d). This implies that, while these pioneer species are able to rapidly occupy the space they colonise, their established shoots cannot occupy that space for as long as the more longlived species Thalassia testudinum. We suggest, therefore, that the role of seagrass species as pioneer or climax species is independent of their capacity to support dense, productive populations, and is closely related to shoot longevity and rhizome turnover.