Linking clonal growth patterns and ecophysiology allows the prediction of meadow-scale dynamics of seagrass beds

Seagrasses are a group of 12 genera of monocotyledonous plants in four families that have successfully colonised shallow coastal seas, probably since the Cretaceous. Variations in light availability and water movement are prime environmental factors for the growth of these marine angiosperms. An overall similarity in growth form and modular clonal architecture allows the generalisation that small species have short-lived shoots with rapidly elongating rhizome axes, whilst the larger species have longer-lived shoots that do not expand rapidly with rhizomes. Annual rhizome elongation rates range between 2 cm and 4 m among species. This range in expansion capacity is correlated with rhizome diameter in an allometric fashion (y=191x−1.5, r2=0.58, p<0.05). Rhizomes with a wider diameter also allow the storage of larger quantities of reserve carbohydrates to be mobilized during the adverse winter season at higher latitudes or for flowering. Repeated branching and the basal positioning of the meristems allow the formation and maintenance of seagrass meadows, and these are a prominent feature creating spatial heterogeneity on the sea floor down to a mean colonisation depth of 15.1±1.3 m (median 8 m, range 0.7–90 m, n=150). Spatial complexity is highest in multi-species seagrass beds, such as those of the Indo-Pacific region and Australia. Seagrass beds function as important coastal filters for nutrients and pollutants and display high carbon sequestration rates. Due to the recalcitrant nature of seagrass detritus, it forms a disproportionally high contribution (12%, but only 1% of productivity) to the carbon stored in ocean sediments. The services provided by these ecosystems to human society range from water quality improvement via nursery and feeding grounds for economically important fish to storm buffering and recreative amenity.