The role of sexual reproduction in maintaining populations of Halophila decipiens: implications for the biodiversity and conservation of tropical seagrass ecosystems

Abstract

In subtropical and tropical communities, seagrass species commonly range over an order of magnitude in size and biomass. This biodiversity corresponds with differences in the relative importance of sexual (seed production) and asexual (clonal growth) life history strategies in the maintenance of seagrass populations. Clonal growth and vegetative reproduction are important in maintaining populations of larger-bodied species. As size of species and degree of clonality decrease, the importance of sexual reproduction increases. World-wide, the smallest species in tropical seagrass ecosystems are represented by the most taxonomically diverse, sexually fecund genus, Halophila. A four-year study of the submarine light regime and seasonal growth cycles of Halophila decipiens and other seagrasses in the Indian River Lagoon, Florida, USA provides a comparative context in which to illustrate the relative importance of different life history strategies in tropical seagrass ecosystems world-wide. While sexual reproduction is critical for maintaining some geographically extensive small-bodied seagrass systems in disturbed and extreme environments, there is also evidence to suggest that the quantitative importance of sexual reproduction may be underestimated for larger, highly clonal species like Thalassia testudinum. Future efforts to conserve tropical seagrass ecosystems necessitates a more comprehensive understanding of the evolutionary consequences of sexual reproduction and a more quantitative evaluation of the population dynamics resulting from the sexual life history strategies of different species.