Decomposition of leaves from Amphibolis antarctica (Labill.) Sonder et Aschers, and Posidonia australis Hook. f. the major seagrass species of Shark Bay, Western Australia

In situ decomposition studies were carried out using litter bags. Losses in dry weight, phosphorus, nitrogen and organic carbon were followed during two experiments, initiated at the times of highest and lowest water temperatures. Initial nutrient concentrations were low for both species, at both times of year, < 1 mg g- 1 total phosphorus, and < 11 mg g- 1 total nitrogen, but were higher in winter than in summer. Rates of loss of all material for both species were similar, and were best described mathematically by a linear equation. The loss rate was 0.5% day- 1, giving a time for complete decomposition of about 200 days. The significance of this fast rate is discussed in relation to the nutrient budget of seagrass meadows, in a nutrient poor environment