PRIMARY PRODUCTION OF SEAGRASS BEDS IN SOUTH SULAWESI (INDONESIA) - ACOMPARISON OF HABITATS, METHODS AND SPECIES

Primary production of tropical seagrass meadows was studied between Ap ril and August 1990 in South Sulawesi, Indonesia. Oxygen evolution stu dies in enclosures over seagrass vegetation revealed gross community p roduction values between 900 and 4400 mg C m-2 day-1. Assumed communit y respiration ranged from 800 to 1800 mg C m-2 day-1 in non-vegetated areas and from 1400 to 5100 mg C m-2 day-1 for areas with varying amou nts of seagrass. Benthic community respiration varied considerably in response to diurnal fluctuations in the dissolved oxygen concentration in the water column. Net production was small (less than 500 mg C m-2 day-1) and slightly negative on seven of 12 occasions. Light compensa tion points ranged from 50 to 340 muE m-2 s-1. Bell jar measurements r evealed no significant differences in seagrass production between coas tal and reef island habitats. Leaf marking experiments with Enhalus ac oroides (L.f.) Royle revealed significantly higher leaf growth in a co astal muddy area (3.1+/-0.8 cm per shoot day-1) than at an offshore sa ndy reef site (1.6+/-0.5 cm per shoot day-1), but relative growth rate s were comparable between the two habitats (0.019+/-0.005 g g-1 leaf b iomass (AFDW) day-1 and 0.012+/-0.003 g g-1 AFDW day-1, respectively). Leaf marking and plastochrone interval methods revealed similar resul ts for net leaf production in a monospecific stand of Thalassia hempri chii (Ehrenb.) Aschers. at a reef site which averaged 1.6 g C m-2 day- 1. Rhizome tagging experiments revealed net rhizome production values of 0.1-0.3 g C m-2 day-1 for Thalassia hemprichii at this reef site. R elative growth rate of leaves of Thalassia hemprichii (0.039+/-0.010 g g-1 AFDW day-1) at the reef site was significantly higher than that o f E. acoroides (0.012+/-0.003 g g-1 AFDW day-1). The pioneering seagra ss species Halodule uninervis (Forssk.) Aschers. and Cymodocea rotunda ta Ehrenb. & Hempr. ex Aschers. had considerably higher horizontal api cal rhizome growth rates (0.7-0.8 cm per apex day-1) than the constant species Thalassia hemprichii (0.1 cm per apex day-1). The suitability of different methods to measure seagrass productivity is evaluated.