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

Leaf production, shoot demography and rhizome growth and branching were quantified for the common seagrass species in a mixed seagrass bed on the Bolinao reef flat (Luzon, The Philippines) to assess the contribution of these species to canopy maintenance, meadow biomass and productivity. We tested the hypothesis that seagrass growth rates correlated negatively with shoot size and age when compared across species, and found that shoot recruitment, leaf turnover and horizontal rhizome elongation and branching rates were lower for species with older and larger shoots. Median shoot ages for the short-lived species were generally less than a year; those for the longer-lived Enhalus acoroides (L. f.) Royle and Thalassia hemprichii (Ehrenb.) Aschers. were slightly more than 1.5 yr. The eldest E. acoroides had almost reached 10 yr. Generally, shoot mortality and recruitment balanced each other fairly well. The rhizomes of longer-lived E. acoroides and T. hemprichii elongated 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 elongation 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, constituting 91% of 2143 g DW m(-2) yr(-1) (roots excluded); this productivity was mainly due to T. hemprichii (74%), and not to the oldest and slowest-growing E. acoroides (10%).