Elsevier

Ocean & Coastal Management

Volume 198, 1 December 2020, 105381
Ocean & Coastal Management

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

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Highlights

  • Sediment composition and distribution .

  • Mean carbonate sediment grain size of 1.5 mm.

  • More than 50% of sediment grains are made of coral fragments.

  • The non-protected fringing reef is slowly filled with brown algae and most corals are dead.

  • The Marine Protected Area has high living coral cover compared to non-protected fringing reef .

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.

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

References (89)

  • T.C. Hoffmann

    Coral reef health and effects of socio-economic factors in Fiji and Cook Islands

    Mar. Pollut. Bull.

    (2002)
  • M. Lockwood et al.

    Marine biodiversity conservation governance and management: regime requirements for global environmental change

    Ocean Coast Manag.

    (2012)
  • H. McKoy et al.

    Sand cay evolution on reef platforms, Mamanuca Islands, Fiji

    Mar. Geol.

    (2010)
  • J. Sloan et al.

    An analysis of property rights in the Fijian qoliqoli

    Mar. Pol.

    (2016)
  • M.S. Srinivasan et al.

    Neogene planktonic foraminiferal biostratigraphy and evolution: equatorial to subantarctic, South Pacific

    Mar. Micropaleontol.

    (1981)
  • E. Tyllianakis et al.

    Policy options to achieve culturally-aware and environmentally-sustainable tourism in Fiji

    Mar. Pollut. Bull.

    (2019)
  • R. Varea et al.

    Knowledge gaps in ecotoxicology studies of marine environments in Pacific Island Countries and Territories – a systematic review

    Mar. Pollut. Bull.

    (2020)
  • S.A. Wooldridge et al.

    Excess seawater nutrients, enlarged algal symbiont densities and bleaching sensitive reef locations: 2. A regional-scale predictive model for the Great Barrier Reef, Australia

    Mar. Pollut. Bull.

    (2017)
  • L.P. Zann

    The status of coral reefs in south western Pacific islands

    Mar. Pollut. Bull.

    (1994)
  • R.G. Baker et al.

    An oscillating Holocene sea-level? Revisiting rottnest island, western Australia, and the fairbridge eustatic hypothesis

    J. Coast Res.

    (2005)
  • J.D. Bell et al.

    Adaptations to maintain the contributions of small-scale fisheries to food security in the Pacific Islands

    Marine Policy

    (2017)
  • B.J.F. Biggs

    Eutrophication of streams and rivers: Dissolved nutrient-chlorophyll relationships for benthic algae

    J. North Am. Benthol. Soc.

    (2000)
  • S.J. Blott et al.

    GRADISTAT: a grain size distribution and statistics package for the analysis of unconsolidated sediments

    Earth Surf. Process. Landforms

    (2001)
  • R.M. Bonaldo et al.

    Small marine protected areas in Fiji provide refuge for reef fish assemblages, feeding groups, and corals

    PloS One

    (2017)
  • C. Bosserelle et al.

    Wave inundation on the coral coast of Fiji

  • C. Bosserelle et al.

    Maui Bay (Fiji), Bathymetric and Topographic Data Collection

    (2016)
  • T.M. Bowron et al.
    (2009)
  • C.J. Brown et al.

    Tracing the influence of land-use change on water quality and coral reefs using a Bayesian model

    Sci. Rep.

    (2017)
  • L. Burke et al.

    Reefs at Risk Revisited

    (2011)
  • A. Cakacaka

    Effects before and after Closure of a Marine Protected Area: Case Study of Navakavu, Suva, Fiji Islands

    (2008)
  • A. Chin et al.

    Status of Coral Reefs of the Pacific and Outlook: 2011

    (2011)
  • P. Clarke et al.

    Law, custom and community-based natural resource management in Kubulau District (Fiji)

    Environ. Conserv.

    (2010)
  • C. Clements et al.

    Effects of small, Fijian community-based marine protected areas on exploited reef fishes

    Mar. Ecol. Prog. Ser.

    (2012)
  • R.L. Cumming et al.

    Mass bleaching in the Fiji islands

    (2000)
  • R. Cumming et al.

    Coral Reefs of the Fiji Islands: Current Issue

    (2002)
  • R.J. Dunham

    Classification of carbonate rocks according to depositional textures

  • L.X.C. Dutra et al.

    Impacts of climate change on corals relevant to the Pacific Islands

  • J.B. Elsner et al.

    The increasing intensity of the strongest tropical cyclones

    Nature

    (2008)
  • C. Folke et al.

    The problem of fit between ecosystems and institutions: ten years later

    Ecol. Soc.

    (2007)
  • S. Gelcich et al.

    Public awareness, concerns, and priorities about anthropogenic impacts on marine environments

    Proc. Natl. Acad. Sci. Unit. States Am.

    (2014)
  • G. Guannel et al.

    The power of three: coral reefs, seagrasses and mangroves protect coastal regions and increase their resilience

    PloS One

    (2016)
  • N. Guillemot et al.

    Cyclone effects on coral reef habitats in New Caledonia (South Pacific)

    Coral Reefs

    (2010)
  • P. Hallock et al.

    Foraminifera as bioindicators in coral reef assessment and monitoring: the FORAM index

    Environ. Monit. Assess.

    (2003)
  • J.N. Harney et al.

    Age and composition of carbonate shoreface sediments, Kailua Bay, Oahu, Hawaii

    Coral Reefs

    (2000)
  • 1

    Present address: United Graduate School of Agricultural Sciences, Kagoshima University, 1-21-24 Korimoto, Kagoshima, 890–0056, Japan.

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