Carbonate sediments from Maui bay (coral coast, Fiji) reflect importance of coral reef conservation
Graphical abstract
Section snippets
INTRODUCTION
Sediment analyses help elucidate sources and fate of sediments generated in terrestrial, coastal and marine areas. Such analyses support a broad understanding about risks and vulnerability of coastal ecosystems such as coral reefs to erosion and accretion processes, and changes in energy patterns of residual waves over the reef flat (Milliman, 1974). Current threats to coral reefs include a mix of direct anthropogenic and climate change effects that work synergistically (Wooldridge et al., 2017
Study area and sample criteria
Maui Bay is located on the South Western side of Viti Levu, Nadroga-Navosa province, Fiji (Fig. 1). Maui Bay is a development site with holiday villas at the Coral Coast, which is bordered seawards by fringing coral reefs which extend 600–800 m seawards and stretch from East to West over 2400 m. The shallow fringing coral reef complex is terminated by a narrow 40 m wide passage to the East and a wide 150 m wide passage to the West; all is included within the MPA (Bosserelle et al., 2016). The
Sediment grain size
Half of the sediments from Maui Bay MPA are characterized as coarse sand (Table.1), whereby the mean sediment grain size is 1.5 mm (blue line in Fig. 2). Coarse sand (1 mm) made up 35% of the sediments while gravel contributes 15% to the overall sediments from the Maui Bay MPA (Fig. 2). On average, at 350 m from the shoreline a larger grain size is found (approximately 1.8 mm) while towards shoreline and the reef crest, the average grain size is reduced to coarse sand size (>1.0 mm) (Fig. 4a
Sediment grain size
Finer carbonate sediments are generated from the outer part of the reef and transported to nearshore area (Fig. 4a and b), where they settle due to a low energy environment favoured by the barrier provided by the reef crest. Finer siliciclastic sediments are transported into the beach system by creeks and currents (Fig. 1); similarly, McLaren and Bowles (1985) observed that sediment grain sizes decrease with the direction of the current flow from the source. The combination of coral fragments
Conclusion
The mean sediments of Maui Bay are very coarse sand (1.5 mm) and are predominantly coral fragments (>50%). Other calcareous organisms including foraminifera and molluscs also contribute to sediments in Maui Bay. Larger grains are more abundant where corals abound. The siliciclastic sediments are more abundant where the river enters the lagoon, between benchmarks 4 and 8, and at 500 m east of benchmark 10. Real estate development and land clearing further upstream may be contributing to
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This study is part of the RSS postgraduate diploma and was supported by USP-ACIAR (grant number FFIS/2012/074). We acknowledge the following people for their help during the research: Cybrien Bosserelle, for providing support with funding and field work; Robert Jimmy and Chris Barlow (ACIAR project manager) for supporting the postgraduate study; Viliamu Powell, for facilitating the financial processes until the end of this study. We also extend our acknowledgement to European Union for funding
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Present address: United Graduate School of Agricultural Sciences, Kagoshima University, 1-21-24 Korimoto, Kagoshima, 890–0056, Japan.