Macrophyte associations on the soft bottoms of the south-west lagoon of New Caledonia: Description, structure and biomass

The structure and biomass of the benthic macroflora were studied at 120 randomly sampled stations in the south-west lagoon of New Caledonia. Three plant associations were identified. The deep nearshore lagoon association can be divided in two sub-associations: muddy bottom without macrophytes, close to the coast, and deep seagrass meadows, mainly composed of Halophila decipiens. The inner lagoon association, found in the middle of the lagoon, can also be divided into two sub-associations: seagrass meadows, located on shallow bottoms and mainly composed of Halodule uninervis and Cymodocea serrulata, and a lagoonal plain found on deep bottoms. This latter presents the highest species diversity in spite of the sparse distribution of the species. Further off the coast the back-reef association presented a dense growth of Sargassaceae which gave way to Cyanophyceae on the shallow bottoms closest to the reef. The weighted mean biomass of 12.9 g afdw m(-2) is unequally distributed between the plant communities with 7.9, 31.1 and 28.0 g afdw m(-2) for lagoonal plain and seagrass meadows sub-associations and back reef association respectively. The distribution of biomass between fleshy algae, calcified algae and phanerogams, which is not homogeneous, affected primary production as well as the amount of organic matter available for other trophic levels. The biomass of the primary producers group including benthic micro- and macro-flora reaches 7.6 g C m(-2). This result compared to the biomass of other trophic groups leads to the conclusion that from the trophic level point of view, primary producers dominated the macrobenthos biomass in the south-west lagoon of New Caledonia.