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IAG Working Group REEForm – Reef and reef landform responses to environmental and climatic change

Report from Research Expedition, Maldives, 29th June to 13th July 2011

Participants:

Chris Perry (Manchester Metropolitan University, UK), Paul Kench (University of Auckland, NZ), Scott Smithers (James

Cook University, Australia), Hiroya Yamano (National Institute for Environmental Studies, Japan), Mick O’Leary (Notre

Dame University, Australia), Philipp Mandlier (University of Auckland)

Building upon the science priority areas identified at the REEForm Working Group meeting in 2010, the first REEForm

research expedition took place between 29th June to 13th July 2011 in The Maldives. The focus of the trip was to test

previously published ideas regarding the nature and timing of reef island development in the Maldives, to undertake an

assessment of the links between platform lagoon/faro infilling and island development, and to develop some of the first

data on rates and styles of faro and lagoon infilling in the region. Specific objectives of the trip were as follows:

1. To determine rates of lagoon infill in a number of platform lagoons/faro’s in the Maldives.

2. To establish the chronologies of island accumulation for a range of island types in the Maldives.

3. To document the morphology of islands and their surrounding reef platforms.

4. To examine the sedimentary relationships (grade and composition) between reef islands and the

surrounding reef flat sediment sources.

To address these objectives, field research was undertaken on 6 reef platforms within South Maalhosmadula (Baa) Atoll

that exhibit a gradient from partially filled faro’s to those where islands occupy a high proportion of the reef platform

surface. In order of increasing fill/island development these sites were:

Kamburu Faru

Boatu Urunu Faru

Velaa Faru

Dhakandhoo

Mendhoo

Funadhoo

At each site the research team collected a wide range of data including: the recovery of reef/lagoon and island cores; data

on contemporary sedimentary-ecological zonation patterns across the reef platforms to the platform top islands/lagoons;

and data on cross platform bathymetric and island profiles. The following is a brief account of the study sites and the

activities undertaken at each site.

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Kamburu Faru

Kamburu Faru is a reef platform with a relatively open lagoon that has not yet infilled to reach sea level across its entire

extent. Several deep (6-10 m) lagoonal basins are present and there is some evidence for the existence of an underlying

karstic control on the location of these. In addition to ecological and bathymetric datasets collected along both the long

and short axes of the islands, five cores were recovered along a SE – NW aligned transect perpendicular to the long axis

of the platform. Two cores were recovered from the reef rims and three from across the lagoon, including two cores from

the deeper basinal areas in water depths of ~7 m. These penetrated to a depth of ~10 m below present mean sea level

(MSL).

(A) Kamburu Faru showing the deeper unfilled areas of the lagoon, (B) Reef communities on the steeply sloping platform

margin, (C) In-situ (living and dead) Acropora stands which are a common feature of the shallower lagoon areas, (D)

Bioturbated, fine-grained carbonate sands and muds characteristic of the deeper lagoon basins.

A

B

C D

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Boatu Urunu Faru

Boatu Urunu Faru is a reef platform which has undergone a relatively high degree of infilling, only one deep basinal area

(reaching ~ 6 m below MSL) remaining in the SE region of the lagoon. There is an incipient sand cay developed on the SE

side of the platform close to the reef rim. Water depths are <1 m across most of the platform. In addition to ecological and

bathymetric datasets collected along both the long and short axes of the islands, seven cores were recovered along a SE

– NW aligned transect perpendicular to the platforms long axis. Two cores were recovered from each of the platforms reef

rims and three from across the lagoon, including a core from the deeper basinal area and one from the sloping flanks of

the basin. These penetrated to a depth of up to ~10 m below present mean sea level (MSL).

(A) Boatu Urunu Faro showing the largely filled nature of the platform, (B) View across the SE margins of the island, the

remaining unfilled area of the platform is visible top right, (C) View across the incipient sand cay on the SE margin of the

platform, (D) Acropora thickets colonising the shallow lagoon floor.

A

B

C D

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Velaa Faru

Velaa Faru is a reef platform which has undergone near complete infilling and has a small, incipient sand cay on its

southern flank. Water depths across the platform top are about 1-1.5 m relative to MSL. In addition to ecological and

bathymetric datasets collected along both the long and short axes of the islands, three cores were recovered along a SE –

NW aligned transect perpendicular to the platforms long axis. Cores were recovered from close to each of the platforms

reef rims and one from the central area of the platform, although coring was impeded by strong wave activity. Cores

penetrated to a depth of up to ~3 m below present mean sea level (MSL).

(A) View showing the near complete infilling of Velaa Faru, (B) View SE across the incipient sand cay, (C) Reef crest coral

communities, D) Coral rubble and Halimeda on the shallow platform top, both key constituents of the faro’s infill material.

A

B

C D

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Dhakandhoo

Dhakandhoo is a reef platform with a vegetated island about 350 m long. The island is located towards the eastern

margins of the reef platform and occupies ~25 % of the platform area. A sand moat surrounds the toe of the beach and

extends out to a reef flat which is up to 50-75 m wide round the island. In addition to ecological and bathymetric datasets

collected along both the long and short axes of the islands, four cores were recovered along an approximately E – W

aligned transect perpendicular to the platform and islands long axis. One core was recovered from the islands eastern reef

rim, two from the reef platform on the western side of the island, and one through the centre of the island. The island core

reached a depth of 3.6 m below the island and contained lagoonal sediments at its base.

(A) View showing the island of Dhakandhoo and its surrounding reef platform, (B) View westwards across an area of

extensive recently deposited sediment (the seasonally mobile portion of the island flanks, (C) View across the shallow reef

platform towards the reef rim, D) Coral communities along the margins of the reef rim.

A B

C D

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Mendhoo

Mendhoo is a reef platform with a vegetated island (approx 500 m long) developed upon it. The island is located towards

the SE margins of the reef platform and occupies ~50 % of the platform area. A sand moat surrounds the toe of the beach

and extends out to a reef flat 50-100 m wide round the island. In addition to ecological and bathymetric datasets collected

along both the long and short axes of the islands, six cores were recovered along a SE – NW aligned transect

perpendicular to the platform and islands long axis. Two cores were recovered from the islands SE reef rim, and three

from the wider NW area of the platform extending from close to the island shoreline to near the reef rim. In addition, a core

of 4.6 m length was taken through the centre of the island and contained lagoonal sediments at its base.

(A) View showing the island of Mendhoo and its surrounding reef platform, (B) View of the eastern side of Mendhoo, (C)

View across the shallow reef platform on the western side of the island with a field of Heliopora microatolls exposed on the

low tides, D) High coral cover along the margins of the reef rim.

A B

C D

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Funadhoo

Funadhoo is a reef platform with a vegetated island about 300m diameter that occupies a high proportion of the reef

platform surface. The island is relatively centrally located on the platform and occupies ~75 % of the platform area. In

addition to ecological and bathymetric datasets collected along both the long and short axes of the islands, four cores

were recovered along an E-W aligned transect perpendicular to the platform and islands long axis. One core was

recovered from the islands eastern reef rim, two from the reef platform on the western side of the island, and one through

the centre of the island. The island core reached a depth of 3.7 m below the island and contained lagoonal sediments at

its base.

(A) View showing the island of Funadhoo and its surrounding reef platform, (B) View of the eastern side of Funadhoo, (C)

View across exposed beachrock along the eastern side of the island, D) Reef flat coral communities at Funadhoo.

Data analysis An extensive sample set of both contemporary and core sediments, and coral material for radiometric

dating have been recovered and will be analysed by the research team to constrain: (1) the timing of lagoon infill and,

where relevant, of island evolution; and (2) to allow interpretations of modes, rates and styles of faro infilling and platform

evolution (and where relevant the temporal links with island initiation and growth). In addition, ecological survey data will

be used to delineate different habitat zones around each platform and to relate these to contemporary platform and island

margin sediments. Detailed island elevation (where relevant) and platform bathymetry datasets will provide a

structural/depth framework for subsequent data interpretations.

A B

C D

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Team and other photos

The expedition boat, the Noah Safari (and dive dhoni) Loading the dingy for a day of coring

The team enjoying an early breakfast Surveying island to reef rim elevations and profile

Coring in the middle of Dhakandhoo Island Coring logging and sample processing on the Noah Safari

Chris Perry, July 2011