VERTICAL GROWTH AND SHORT-SHOOT DEMOGRAPHY OF SYRINGODIUM-FILIFORME IN OUTER FLORIDA BAY, USA

The vertical growth, short-shoot age structure, and demography of a Sy ringodium filiforme population were examined at 3 sites in a large mea dow in outer Florida Bay, USA. Based on in situ marking experiments, w e determined that the first 3 or 4 leaves on a short-shoot are produce d in less than or equal to 45 d; thereafter new leaves are formed abou t every 40 d. We were able to confirm this estimate of leaf plastochro ne interval (leaf PI) by examining the alternating internodal sequence s resulting from differential growth of the vertical stems. Analysis o f short-shoot age in leaf PI versus frequency histograms also indicate d that each short-shoot produces approximately 12 leaves during the fi rst year of growth and 9 leaves each year thereafter. Short-shoot age is skewed toward younger ages, with a median short-shoot age of approx imately 0.6 yr, maximum age of 3.5 yr, and very few short-shoots livin g beyond 2.5 yr. Short-shoot recruitment appeared nearly continuous du ring the 3 yr study period. The vertical stem internodes were very lar ge, ranging in length from 0.1 to 7.5 cm and averaging 2.1 cm. Vertica l stem growth was independent of the sediment surface, raising photosy nthetic tissue 25 to 60 cm above the sediments and forming a multidime nsional shoot canopy at an average rate of 17 cm yr(-1). We determined that during the first year of life short-shoots could produce upwards of 25 cm of vertical stem. The vertical stem growth rate of S. filifo rme is, therefore, among the highest reported for any species of seagr ass. The developing techniques of seagrass demography proved to be val uable tools for analyzing the growth dynamics and population structure of S. filiforme in outer Florida Bay.