Carbonate sediments from Maui bay (coral coast, Fiji) reflect importance of coral reef conservation

Abstract

This study describes the origin and characteristics of unconsolidated coral reef sediments from Maui Bay (Coral Coast, Viti Levu Island, Fiji), a site declared under customary law as Marine Protected Area (MPA) by traditional owners in Tagaqe village since the year 2000. Sediment samples were collected from five transect lines and analysed in the laboratory through drying process and sieving to fractional sizes. The results show that sediments from Maui Bay MPA are composed of very coarse sand (mean sediment size of 1.5 mm) mostly constituted of coral fragments (e.g. Seriatopora spp. and Porites spp.; coral fragments in ≥50% of grains) followed by other smaller particles of calcareous organisms (foraminifera and molluscs, 10–36% of the grains). As expected, siliciclastic sediments are most abundant near the mouth of a creek which brings in sediments from the mountainous hinterland. A comparison of Maui Bay with a non-protected fringing reef with very similar bathymetry at Tabua Sands (qualitative data) along the Coral Coast shows that the non-protected site is rich in brown algae with mostly dead corals. The darkish colour and smell of rotten eggs emanating from sediments collected at Tabua Sands suggests anoxic conditions at shallow sediment depth. This is in contrast to the clean white sediments encountered at Maui Bay indicating healthier coral reefs, which shows the importance and success of protection measures implemented here.