Citation: | East, Holly K., Perry, Chris T., Kench, Paul S., and Liang, Yiqing. (2016). Atoll-scale comparisons of the sedimentary structure of coral reef rim islands, Huvadhu Atoll, Maldives |
Abstract: | Coral reef islands are low-lying (typically <5 m above mean
sea level, MSL) accumulations of wave deposited bioclastic
sediments. These sediments are produced within the surrounding
coral reef habitats and reef islands are therefore intrinsically
linked to reef ecology (Perry et al. 2011). As a result of their
dependence upon locally generated sediment, low elevations and
largely unconsolidated structure, reef islands are regarded as
extremely vulnerable to environmental change, particularly to
sea-level rise. This is of concern given their high ecological and
socioeconomic value, not least because they offer the only
habitable land in regions including the Maldives, Kiribati and
the Marshall Islands. However, assertions of vulnerability are
largely made without a full understanding of how and when
islands formed, the processes controlling island formation and
inter- and intra-regional variations in island-building processes.
Understanding reef island accretionary histories and the
controls on island development is thus crucial for assessing their
morphological stability and future resilience. To date, research
has focused largely upon a few discrete localities in the Pacific
and within the Great Barrier Reef Shelf/Torres Strait region (e.g.
Kench et al., 2014; Woodroffe et al., 2007; Yamano et al.,
2014). In other major reef island regions such as the Maldives (a
nation comprised of >1,200 reef islands inhabited by a
population of ~345,000), our knowledge of island building
processes is far more limited. Maldivian reef islands may be
divided into two key types: (i) rim islands, which form around
the atoll perimeters; and (ii) interior islands, which are located on the reef platforms within atoll lagoons. However, research of
reef island sedimentology and the modes of island-building in
the Maldives is restricted to two main datasets developed for
interior islands within just one atoll (South Maalhosmadulu
Atoll in the northern-central part of the archipelago – Kench et
al., 2005; Perry et al., 2013). Knowledge of rim island
stratigraphy is even more limited and based on qualitative
descriptions of one pit in the centre of Feydhoo island, Addu
Atoll (Woodroffe, 1992). However, it is the rim islands that
dominate spatially (82.4% of land area), host the majority of the
population (88.93%), and therefore support the nation’s key
infrastructure (all regional administrative capitals, hospitals, and
designated ‘safe islands’). Here, we present the first detailed
sedimentary study of Maldivian rim islands. Textural,
compositional and topographical datasets are used to infer the
major sources of reef island sediment, the key controls upon
island building, and the degree of intra-regional (at the atollscale)
variability in island building.
Study Site
Two sites were selected on the rim of Huvadhu atoll – a
leeward site, with respect to wave energy, in the north-east
(Galamadhoo and Baavanadhoo islands), and a windward site in
the south-west (Mainadhoo, Boduhini and Kudahini islands;
Figure 1). |