VERTICAL GROWTH OF THALASSIA-TESTUDINUM - SEASONAL AND INTERANNUAL VARIABILITY

The vertical growth of shoots of the seagrass Thalassia testudinum Ban ks ex Konig in four meadows, along a range of exposure to waves, in th e Mexican Caribbean was examined to elucidate its magnitude and its re lationship to sediment dynamics. Average internodal length varied betw een 0.17 and 12.75 mm, and was greatest in the meadow which experience d the greatest burial by sand waves moved by Hurricane Gilbert (Septem ber 1988). Internodal length showed annual cycles, confirmed by the fl ower scars always preceding or coinciding with the annual minimum inte rnodal length. These annual cycles on the shoot allowed estimation of annual leaf production, which varied, on average, between 14.2 and 19. 3 leaves per shoot year-1. High vertical shoot growth was associated w ith long internodes and high leaf production rate, which increased wit h increasing vertical shoot growth to a maximum of approximately 25 le aves per shoot year-1, with vertical growth of about 30 mm year-1 or m ore. Average internodal length showed substantial interannual differen ces from perturbations derived from the passage of Hurricane Gilbert. The growth response of the plants surviving moderate burial and erosio n after the hurricane involved enhanced vertical growth and increased leaf production, and reduced vertical growth, respectively, after 1988 . The variability in shoot vertical growth of T testudinum can be sepa rated into seasonal changes in plant growth, and long-term variability associated with episodic perturbations involving sediment redistribut ion by hurricanes.