MEADOW MAINTENANCE, GROWTH AND PRODUCTIVITY OF A MIXED PHILIPPINE SEAGRASS BED

Leaf production, shoot demography and rhizome growth and branching wer e quantified for the common seagrass species in a mixed seagrass bed o n the Bolinao reef flat (Luzon, The Philippines) to assess the contrib ution of these species to canopy maintenance, meadow biomass and produ ctivity. We tested the hypothesis that seagrass growth rates correlate d negatively with shoot size and age when compared across species, and found that shoot recruitment, leaf turnover and horizontal rhizome el ongation and branching rates were lower for species with older and lar ger shoots. Median shoot ages for the short-lived species were general ly less than a year; those for the longer-lived Enhalus acoroides (L. f.) Royle and Thalassia hemprichii (Ehrenb.) Aschers. were slightly mo re than 1.5 yr. The eldest E. acoroides had almost reached 10 yr. Gene rally, shoot mortality and recruitment balanced each other fairly well . The rhizomes of longer-lived E. acoroides and T. hemprichii elongate d at rates of 5 and 21 cm yr(-1), respectively, and those of the short -lived Syringodium isoetifolium (Aschers.) Dandy and Halophila ovalis (R. Br.) Hook f. at rates of 135 and 141 cm yr(-1). Vertical shoot elo ngation ranged from 2 to 13 cm shoot(-1) yr(-1) and was not correlated with size or age. The meadow had a total biomass of 624 g dry wt (DW) m(-2) (roots excluded), to which the larger and longer-lived species T. hemprichii and E. acoroides contributed substantially (52 and 37%, respectively). Leaf production dominated total annual productivity, co nstituting 91% of 2143 g DW m(-2) yr(-1) (roots excluded); this produc tivity was mainly due to T. hemprichii (74%), and not to the oldest an d slowest-growing E. acoroides (10%).