ABSTRACT: The vertical growth, short-shoot age structure, and demography of a Syringodium filiforme population were examined at 3 sites in a large meadow in outer Florida Bay, USA. Based on in situ marking experiments, we determined that the first 3 or 4 leaves on a short-shoot are produced in <=45 d; thereafter new leaves are formed about every 40 d. We were able to confirm this estimate of leaf plastochrone interval (leaf PI) by examining the alternating internodal sequences resulting from differential growth of the vertical stems. Analysis of short-shoot age in leaf PI versus frequency histograms also indicated that each short-shoot produces approximately 12 leaves during the first year of growth and 9 leaves each year thereafter. Short-shoot age is skewed toward younger ages, with a median short-shoot age of approximately 0.6 yr, maximum age of 3.5 yr, and very few short-shoots living beyond 2.5 yr. Short-shoot recruitment appeared nearly continuous during the 3 yr study period. The vertical stem internodes were very large, ranging in length from 0.1 to 7.5 cm and averaging 2.1 cm. Vertical stem growth was independent of the sediment surface, raising photosynthetic tissue 25 to 60 cm above the sediments and forming a multidimensional 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. filiforme is, therefore, among the highest reported for any species of seagrass. The developing techniques of seagrass demography proved to be valuable tools for analyzing the growth dynamics and population structure of S. filiforme in outer Florida Bay.

KEY WORDS: Seagrass · Syringodium filiforme · Vertical growth · Age · Demography · Competition · Florida Bay

Published in MEPS Vol. 173 (1998) on November 12
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1998