Macrobenthic communities in a tropical lagoon (Tahiti, French Polynesia, central Pacific)

Soft bottom communities were sampled quantitatively in Tahiti lagoon (Frenc h Polynesia) at 18 stations in five zones around the island over 1 year. In addition, various environmental parameters (silt/clay fractions, organic c ontent, chlorophyll and phaeopigment content) were sampled at the same stat ions over 2 years. The temporal and spatial variabilities of the macrobenth ic communities are described and related to these environmental parameters. Each zone ran from the fringing reef to the inner flat of the barrier reef . The macrofauna exhibited a high richness (392 taxa) with an average mean biomass of 1.8 g AFDW m(-2) (grams ash-free dry weight per square metro). T hese communities exhibited temporal but not seasonal fluctuations. The biom ass of the macrofauna increased from the fringing to the barrier reefs, and the density of individuals was significantly higher on the fringing reefs. Ordination techniques highlighted four groups of stations characterised by distinctive species composition, density and biomass. The first group incl uded stations located on the inner flat of the barrier reef and in the shal low lagoon area and was characterised by highly diverse communities dominat ed by polychaetes. The second group primarily included stations from the in dustrial and hotel zones. This group had the lowest diversity and was also dominated by polychaetes, especially the capitellid Dasybranchus sp. 1. The third group was dominated by gastropods and bivalves. The final group of s tations was represented only by station 51, in zone 5, which was characteri sed by mobile soft sediments and wave action and was dominated by the decap od Hippa cf. pacifica. Presumably, these mobile sediments facilitate the de velopment of this benthic community, which does not occur elsewhere in the lagoon. The diversity and biomass of these benthic communities are low comp ared with most other areas in the South Pacific.