Halimeda biomass, growth rates and sediment generation on reefs in the central Great Barrier Reef Province

The average biomass of Halimeda per m super(2) of solid substratum increased progressively on a series of reefs situated at increasing distances from the shore in the central Great Barrier Reef. There was none on a reef close inshore, increasing to nearly 500 g m super(-2) total biomass ( approximately equals 90% calcium carbonate) on an oceanic atoll system in the Coral Sea. The biomass measured contained 13 species of halimeda but was dominated by only two species, H. copiosa and H. opuntia , except on the atoll where H. minima was dominant. Growth rates of the dominant species were measured by tagging individual branch tips. The number of branch tips per unit biomass was very constant and has been used in conjunction with growth rates and biomass to calculate productivity rates, and thence sedimentation, in the lagoon of one of the reefs. Those values indicate annual accretion of 184.9 g m super(-2) year super(-1) of Halimeda segment debris over the entire lagoon floor (5.9 km super(2)) of Davies Reef, equivalent to 0.13 mm year super(-1) due to Halimeda alone, or 1 m every 1,892 years when other contributions to that sediment are taken into account.