Deposition of organic material in a coral reef lagoon,One Tree Island,Great Barrier Reef

Deposition of organic material was measured at four sites on One Tree Island coral reef using fixed sediment traps. Although no reliable data were obtained for the reef crest area because of problems of resuspension, mean deposition in the backreef area amounted to some 4 g organic C m⁻² day⁻¹ whereas in the lagoon it was about 1·5 g C m⁻² day⁻¹. This amounted to mean nitrogen deposition rates of 160 and 95 mg N m⁻² day⁻¹, respectively. As primary production by turf algae, the principal producers at One Tree Island, has been estimated at about 2·3 g C m⁻² day⁻¹ for the whole reef system and the weighted mean carbon deposition is estimated at 2·2 g C m⁻² day⁻¹, it is clear that the carbon produced by plants is largely retained in the system. Nitrogen deposition, on the other hand, amounted to only about 60% of that produced by turf algae and it must be assumed that much of this leached into the water during sedimentation. Losses of nitrogen may be minimized by incorporation of dissolved nitrogen by pelagic microheterotrophs which may in turn be consumed by filter feeders before they leave the reef.