Meadow maintenance, growth and productivity of a mixed Philippine seagrass bed

Leaf product~on, shoot demography and rhlzome growth and branchlng were quantified for the common seagrass specles In a muted seagrass bed on the Bollnao leef flat (Luzon The Ph~llp- plnes) to assess the contribution of these spec~es to canopy maintenance meadow biornass and productlvlty. We tested the hypothesis that seagrass growth rates correlated negatively with shoot size and age when compared across specles, and found that shoot recruitment leaf turnover and honzontal rhizome elongation and branchlng rates were lower for speces wlth older and larger shoots ~Vedian shoot ages for the short-llved species were generally less than a year, those for the longer-llved Enhalus acoroides (L f ) Royle and Thalassla hempnchii (Ehrenb ) Aschers were sllghtly more than 1 5 yr. The oldest E acoroldes had almost reached 10 yr Generally, shoot mortality and ~ecrultment balanced each other falrly well The rhizomes of longer-lived E acoroldes and T hempnchli elongated at rates of 5 and 21 cm yr-l, respectively, and those of the short-llved Synngodi~lm isoetifobum (Aschers ) Dandy and Halophila ovalls (R Br ) Hook f at rates of 135 and 141 cm yr-' Vertical shoot elongat~on ranged from 2 to 13 cm shoot ' yr ' and was not correlated wlth size or age The meadow had a total bion~ass of 624 g dry wt (DW) m-' (roots excluded), to whlch the larger and longer-llved specles 7 hempnchil and E acoro~des contnbuted substantially (52 and 37%, respectively) Leaf product~on dominated total annual ploductlvity, constituting 91 % of 2143 g DW m ' yr ' (roots excluded) thls productlvlty was malnly due to T hempnchli (74 %), and not to the oldest and slowest-growing E acoroides (10%