Content of Organic Carbon, Nitrogen, and Phosphorus in Deep-Water Coralline Algae Biocenoses, South China Sea

Abstract

The influence of habitat depth on the content of organic carbon (C_org), as well as organic and mineral forms of nitrogen (N) and phosphorus (P), in the biocenosis of coralline algae at depths of 5 to 150 m was studied in spring in the South China Sea. It has been found that the C_org content in tissues decreased from 72 to 42 g/m² with increasing depth to 150 m. The N content also decreased with depth but to a lesser extent, from 15 to 10 g/m², while the P content increased linearly from 0.75 to 4.29 g/m². The atomic ratio C/N/P in the biocenosis at depths of 5–10 m did not vary significantly and averaged at 187 : 31 : 1, which is comparable to the mean values obtained for the common species of reef-building corals. Unlike C_org and N, the P content in the algal biocenosis increased with depth more than fivefold. Correspondingly, the C/N/P ratio amounted to 24 : 5 : 1 at a depth of 150 m. Such a depth-dependent increase in the proportion of phosphorus in the biocenosis, with simultaneous reduction in the C_org and, to a lesser extent, N contents, can be explained by the release of phosphorus during in the breakdown of organic matter in the biocenosis of coralline algae with the formation of insoluble calcium phosphates.