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Maldives Reef Survey - June 13-30 th 2008

  • Marine Conservation Society
Maldives Reef Survey - June 13-30
Jean-Luc Solandt, Biodiversity Policy Officer
Chris Wood, Seasearch Co-ordinator
Wolf Business Park
Alton Rd
Ross on Wye
Tel: 01989 566 017
Innovation House
Boldero Rd
Bury St Edmunds
Suffolk IP32 7BS
Tel: 01284 748010
1. Introduction
The Maldives archipelago lies in the heart of the Indian Ocean approximately 300nm SSW
of the southern tip of India. The archipelago comprises approximately 1190 islands lying on
a raised oceanic ridge, which is approximately 900km long, and straddles the equator
between 00
S (Addu atoll) to approximately 07 06.00
N (Ihavandhippolhu atoll). The
chain of atolls is relatively narrow (approximately 150km wide), with the capital Male
situated in the centre of the archipelago at N 04 10.00
; E 073 32.00
The reefs and islands of the Maldives are entirely comprised of raised reef limestone, built
over thousands of years by billions of tiny corals laying down of calcium carbonate. There
are 26 major atolls comprising a total of some 1190 islands – all entirely built by corals.
Figure 1. Location of the Maldives in the central Indian Ocean (left), and Ari atoll (right)
showing the variety of coral reefs found within any one atoll. (Maps by Steve
The structures these corals have created can broadly be divided into three geo-
morphological features:
i. Inner atoll reefs – (Thillas, Faros and Giris)
Thillas are submerged reefs found in the middle of the atolls – which reach depths of around
80m in the largest lagoons, and rise to between 15 and 5m of the surface. Giris are simply
small thillas which reach the surface, whilst Faros are larger thillas, usually assuming the
shape of a small atoll within the atoll (fig. 1).
A common feature of thillas is a cave or overhang system at 15-20m depth. The various
changes in sea level over thousands of years has contributed to these features. The last ice
age finished between 8 and 10,000 years ago whereupon large volumes of water were
released relatively quickly into the oceans. Prior to the melting of the huge amount of ice,
sea level used to be at current depth of the Maldives caves and overhangs, which is
remarkably consistent (15-20m). The increase in sea level rise was then accompanied by
an increase in the vertical growth of the corals on top of the reefs over the ensuing 10,000
years, creating a further layer of reef above these overhangs. Some of the overhangs are
precarious, with many periodically collapsing under the weight of corals on the tops of reefs,
combined with storm surges.
The overhangs attract cave-dwelling species such as soldierfish and glass fish. Large sea
whips, Tubastrea corals, and sponges also dominate these overhangs. As such, they
provide their own micro-community to the coral reefs of the Maldives.
ii. Outer reefs
Outer exposed reefs usually feature a large reef flat which grows horizontally over
thousands of years to dominate the outer rim of the atoll (see the west-facing outer reef ring
of Ari atoll in figure 1). Reef flats and reef crests absorb energy from oceanic swells, and are
therefore dominated by small stubby growth forms such as coralline algae, and robust coral
species (eg. digitate Acropora). The outer deeper reefs are generally comprised of a
number of ledges after which the reef plummets to deep waters (over 1,000m) at the outer
edge of the archipelago.
iii. Channels between outer reefs and inner atolls.
Channel mouths to lagoons tend to be where large apex predators congregate where large
numbers of their fish prey can feed on plankton passed into and out of the reef by immense
currents. The reason as to why currents are so great is related to the structure of the atolls.
Channels lie on the outer edge of the atolls, where the deep wide oceanic water is
continuously either entering or leaving the atoll with the tide. The channels effectively act as
a bottleneck through which millions of tones of seawater pass during each tidal cycle
between the relatively shallow waters of the inner atoll basin to the open ocean outside the
atoll plate. The restricted channel mouths (which usually measure between 500-1000m wide
by 30-70m deep (such as at Guraidhoo Channel, South Male atoll) funnels all this water,
and therefore the currents pick up the nearer one dives to the channel entrance.
2. Marine Resource Use in the Maldives
i. Reef fish for artisinal use and tourist resorts
The fishery for reef fish is thought to be relatively sustainable. Biomass estimates of
predatory (target) reef fish such as grouper, snapper and scrombids from most Maldivian
reefs are broadly high relative to other Indo-Pacific reefs. The massive development of
the tourist industry since the 1970s, coupled with the demand for reef fish may have led
to a change in reef fish assemblages on some reefs close to tourist resorts and near to
the more populated atolls. As such, the Maldivian government introduced 10 Marine
Protected Areas in 1995 and a further 10 in 1999 to stop all reef fishing (whilst fishing for
bait fish such as caesionids is still permitted). However, efforts to enforce these
protection measures are weak, with limited government support available to fund patrols,
or appropriate infrastructure to accommodate and supply rangers near to the sites.
ii. Bait fish fishery on inner atoll reefs.
The Maldivian baitfish fishery use small-mesh nets to capture Caesionidae (fusiliers),
Apagonids (cardinalfish) and Clupeids (spreats) to use as bait for the offshore tuna
fishery (fig 2).
Figure 2. Live baitfish (caesionids) in a holding pen at Male harbour beside the fish market
iii. Offshore tuna fishery
The tuna fishery is (along with the tourist industry) the primary source of GDP for the
Maldives. Tuna are caught in many places close to offshore Fish Aggregation Devices
(FADs), which are used to attract principally yellowfin tuna, but bluefin tuna are also
captured. Yellowfin tuna are graded depending on freshness and quality. Those of the
highest grade are flown to Japan for sale as sashimi. Lower grade (b and c) are sold to
Europe (including the UK), for restaurants and supermarkets. Skipjack tuna are also
caught within and outside of atolls for the canning industry, and for supply to the local
population (Fig. 2).
Figure 2. Skipjack tuna (left) and low-grade yellowfin tuna and marlin fillets (right) on sale in
Male fish market.
Figure 3. A yellowfin tuna aboard a tuna-fishing vessel in Male harbour, adjacent to the fish
Figure 4. The deck of a Maldivian tuna fishing boat. Vessels can be out to sea for a week. Note the
large freezer containers for storing the fish.
iv. Long-lining for pelagic species
The Maldives currently sells licenses to other states, which allows foreign fishing vessels
to fish within its 200nm EEZ waters. Unfortunately this results in many long-lining
vessels operating adjacent to the atolls. These vessels often target hotspots for pelagic
species, and sharks constitute a considerable proportion of the catch. The main
economic demand for the shark fishery comes from the sale of shark fins to Fareast Asia
for the shark fin soup trade. One estimate is that between 400 and 800kg of shark fins
are exported per week from the Maldives (Tim Davies, pers. comm.). This has prompted
the Maldives Fishermen Union on July 24
2008 to call for a ban on shark fishing in
Maldivian waters.
Figure 5. Beruwela fish market, Sri Lanka with finned sharks – a common site amongst tropical
developing country fish markets. The provenance of the sharks in these photos is
unknown, but could quite feasibly be from the Maldives.
3. Aims and background of MCS/MST surveys
The Marine Conservation Society and Maldives Scuba Tours have surveyed the atolls of the
central Maldives since 2005. The first survey trip using the Reef Check method was carried
out in July 2005, with subsequent survey visits in Jan 2006, Jan 2007 and June 2008.
The first Reef Check survey of the reefs in 2005 was carried out in order to set up
permanent monitoring stations at popular dive sites regularly visited by Maldives Scuba
Tours, and in areas where the coral reefs appear to be relatively healthy and diverse. The
site chosen was Rasdhoo. The June 2005 survey trip also monitored the impacts of the
Asian Tsunami (of 24.12.04) on the reefs of the Maldives, where little impact was recorded
(Solandt and Wood, 2005).
The Marine Conservation Society has been the Reef Check Co-ordinator for the Maldives
since 2006, and co-ordinates the activities of other survey teams, ensuring that data is
quality assessed, and regularly passed on to the ReefCheck HQ in California.
Since 2004, there has been limited published data from reef monitoring carried out in the
Maldives (Table 1) although the Maldives government Marine Research Centre is carrying
on with subtidal reef monitoring (Liz Wood, pers comm.). The work carried out between
1998 and 2004 recorded the recovery of Maldivian reefs at different locations to the impact
of the global coral bleaching event of 1998.
Figure 6: Bleached Galaxea fascicularis coral colony.
The bleaching event was caused by unusually high water temperatures in the region –
where monthly mean Sea Surface Temperature was 1.2 – 4 degrees Celsius above the
1950-1999 average for the region (Edwards et al., 2001). The greatest temperatures were
recorded in May 1998, reaching +2.1
C above mean SST. The El-Nino Southern
drove temperatures up in many other coral reef regions of the world in 1997-998
(NOAA, Fig 9). The recovery of reefs to the bleaching event of 1998 has been variable both
across the Indian Ocean and within the Maldives (Fig. 6). It appears that southern reefs of
the atoll chain were less affected than northern reefs (Table 1).
El Nino leads to warm surface water conditions in central - western Pacific regions, a slowing down or
cessation of the cold Humboldt Current in Peru, floods in Pacific South American states, and drought in the
western Pacific Rim because of the eventual reversal, or slowing down of the westerly equatorial currents.
Figure 7. Survey sites carried out to
investigate the effects of the 1998
bleaching event on Maldivian coral
reefs. (Results are in Table 1)
Table 1: Percent cover of live coral from 19
Maldives reefs between 1998 and
2004. (Source: Wilkinson et al
(2005), Status of the coral reefs of
the World, Global Coral Reef
Monitoring Program).
Figure 8: Location of the Maldives in the
Indian Ocean. (Map by Steve
Figure 9. NOAA satellite image of the Sea Surface Temperature temperatures above the
seasonal averages from the Indian Ocean in April, May and June 1998. This shows a
significant anomaly of warm water directly over the Maldives.
Table 2: Summary of MCS Reef Check surveys of coral reef live coral cover (%) 2005-2008.
(N/m – Not monitored) (See fig. 10 for a map of the sites).
Site June
Rasdhoo (14m) 34.4 16.25 33.1 18.75 33
HP reef (14m) N/m 17.5 36.9 N/m 19
Niumath (15m) N/m 10 N/m 10.75 N/m
Dega Giri (2m) N/m N/m N/m N/m 66.9
Adhureys Rock (10m) 12.5 N/m N/m N/m N/m
The aim of the June 2008 survey was to:
1. Survey Dega Giri shallow waters to gather baseline data on the coral cover and
species composition of a relatively mature growth coral reef.
2. To carry out a quantitative assessment of predatory reef fish between different dive
4. Methods
4.1 Reefcheck
Reef Check was carried out at one site at Dega Giri on 8 June 2008 (World Oceans Day).
International reef check protocol methods and results can be found at
The site was chosen for its exceptional coral cover in shallow waters, first noticed by JL
Solandt in January 2007, however it wasn’t possible to survey it that year due to low water
(the site is inaccessible at low water). It also wasn’t accessible at this shallow depth in
January 2008, because of heavy wave action over the top of the reef making the snorkel
surveys impossible to carry out.
Normally Reefcheck is carried out at between 5 and 8m for the shallow transect, and 10-
15m for the deep transect to record reef health in the most productive, shallow habitats of
coral reefs. A further reason to carry out the surveys in relatively shallow water is to ensure
that surveyors can accomplish lengthy surveys within the safety margins of SCUBA diving.
However, with regard to Dega giri, an exception to this rule was made because of the
exceptional coral colony size and cover in shallow water (1-3m).
Reef Check survey methods were taught to the volunteer surveyors aboard the MV
SeaSpirit and carried out on June 8
2008. An introduction talk to Reef Check results and
the Global Coral Reef Monitoring programme was given on June 3
. A practice in-water
survey was carried out with the survey team on June 4
in order to get volunteers
accustomed to the methodology, and carrying out data collection in the field for the first
time. Further ID presentations were given on Reefcheck on June 7
and 8
Ali Naseer carried out Benthic surveys, fish counts by Rob Andrews and Kim Bonham, with
invertebrates recorded by Judy England. JL Solandt (team leader) and Judy England
provided movie and stills footage. The remaining divers were used to lay out the transect
line, and attach marker buoys for the start and end of the transects.
Data have already been validated by JL Solandt and sent to Reef Check headquaters in the
4.2 Fish surveys
Fish surveys aimed to gather detailed information on the density and biomass of predatory
fish species (higher trophic level) (listed in table 3), and an estimate of the abundance and
biomass of non-predatory fish families (listed in table 4). Fish were recorded onto
underwater sheets with the species and family list, within 10cm size ranges (11-20; 21-30;
21-30 etc.).
Fish were recorded along 50m transect laid out at between 10 and 14m depth. Divers
recorded fish at 5m intervals - 0; 5; 10; 15; 20; 25; 30; 35; 40; 45; 50. Each 5m recording
interval was effectively a volume of 5m (length) x 5m (width) x 5m (height) = 125m
blocks –
the whole transect thus covering an area of 1250m
. Divers made sure that individual fish
recorded in each 125m
block weren’t recounted in subsequent blocks. Fish surveys were
carried out by JL Solandt (recording predatory fish species and size) and Judy England
(other families).
Table 3. Predatory species recorded in the
fish surveys.
phareus furca
smalltooth jobfish
prio viriscens
green jobfish
Lutjanus bohar
red snapper
Lutjanus gibbus
Lutjanus monostigma
one spot
Ltjanus kasmira
blue lined
Macolor macularis
Lutjanus fulvus
Macolor niger
black and white
Lethrinus conchyliatus
redaxil emperor
Lethrinus erythracanthus
Lehtrinus microdon
Letrhinus olivaceus
Lethrinus miniatus
red spotcheeck
Lethrinus xanthochilus
Monotaxis grandoculis
bigeye bream
Gnathodentex aurolineatus
goldspot emperor
ethaloperca rogaa
nyperodon leucogramma
slender grouper
Cephalophis argus
Cephalophis miniata
coral hind
Epinephalus spp.
Plecropomus laevis
Plectropomus pessuliferus
coral trout
Varoila louti
lunar tail
Caranx sexcfasciatus
bigeye trevally
Carangoides fulvoguttatus
yellowspot trevally
Caranx ignobilis
giant trevally
Caranx melampygus
bluefin jack
other jack
Carchahinus albimarginatus
Carchahinus amblyrhinchus
grey reef
Triaenodon obesus
whitetip reef
Euthynnus affinis
mackeral tuna
Gymnosorda unicolor
dogtooth tuna
Thunnus albacores
yellowfin tuna
Diagrama pictum
painted sweetlips
Plectorhinchus vittatus
oriental sweetlips
Plectorhinchus chaetodonoide
harlequin sweetlips
Table 4. Non-predatory fish (recorded by
other species
moray eels
planktivorous balistidae triggerfish
other balistidae triggerfish
planktivorous acanthuridae surgeonfishes
other acanthuridae surgeonfishes
planktivor Chaetodontidae butterflyfish
other chaetodontidae butterflyfish
Sphyraena barracuda
great barracuda
Sphyraena jello
Tylosaurus crocodilus
Cheilinus undulatus
humphead wrasse
other labridae wrasse
Siganidae rabbit fish
Other anthias
Habitat surveys were carried out using the
Line Intercept Transect (LIT) methodology
at 0.5m intervals (Table 5).
Table 5. Benthic categories recorded on LIT
surveys at each fish survey site.
Hard coral
Soft coral
Recently killed coral
Nutrient impact algae
5. Survey sites:
5.1 Reefcheck survey sites (2005-2008)
Sites are all located within the central atolls of the Maldives (Fig 10). Reefs surveyed using
Reef Check methodology varied from outer atoll reefs (Rasdhoo); inner Giris (Dega giri);
thillas (Adhureys Rock and Niumath), and channel reefs (HP).
Dega giri*
Adhureys Rock
(Kahanbu thila)
Niumath thila
Figure 10: Location of Reefcheck permanent monitoring sites of central Maldives reefs. Sites
were surveyed between June 2005 and June 2008. (* only site surveyed in June
2008 – Dega Giri). (Map by Steve Frampton).
5.2 Fish Survey sites
In June 2008, nine fish surveys were carried out to record the individual abundance, size
and species of predatory reef fish, and the size and abundance of other reef fish families
(Fig. 11). Sites were at 3 inner atoll thillas (Maya; Okobe and Angaga); 3 outer channel
reefs (HP; Bodhu hithi; Kudarah); and 3 outer reef walls (Aquarium; Rasdhoo; Bathaalaa
5. Rasdhoo
1. Okobe thila
3. A
2. HP
4. Bodu hithi thila
7. Maya
6. Bathalaa Maagaa
9. Kudarah thila
8. Angaga thila
Figure 11. Fish survey sites: 1 Okobe thila; 2 HP reef; 3 Aquarium; 4 Bodhu hithi thila; 5
Rasdhoo; 6 Bathalaa Maagaa thila; 7 Maya thila; 8; Angaga thila; 9 Kudarah thila.
(Map by Steve Frampton).
6. Results:
6.1 Reefcheck at Dega thila
6.1.1 Fish populations
Fish recorded at Dega were dominated by butterflyfish and parrotfish species. The other
families observed on the survey were acanthurids (surgeonfish), siganids (rabbitfish) and
mullids (goatfish), which exploited the rapid ephemeral algal growth on the reef top, whilst
the mullids were found in the shallow sand patches in the centre of the giri (Fig. 12).
Humphead w
Bumphead pa
Moray eel
Mean Abundance +- SE
Figure 12: Fish recorded at Dega Giri using the ReefCheck methodology.
6.1.2 Invertebrate populations
Invertebrates at the site were dominated by sea cucumbers and giant clams. The complex
nature of the reef flat would mean that many crevice-dwelling invertebrates such as
Diadema echinoids wouldn’t be easily recorded, as they were likely to be found deep within
the coral framework (Fig. 13).
Diadema Pencil
Giant clam Triton Lobster
Mean Abundance +- SE
Figure 13: Invertebrates recorded out at Dega Giri using the ReefCheck methodology.
6.1.3 Giant clam size
The surveys recorded relatively small giant clams, with 3 animals recoded in the 10-20cm
range, with one below and one above this size class (Fig 14).
<10 10-20 20-30 30-40 40-50 >50
Size Classes (cm)
Mean Abundance +- SE
Figure 14. Clam sizes recorded at Dega Giri.
6.1.4 Damage recorded at the site
There was very little damage. A single patch on the transect could have been damaged by
anchor, but this was inconclusive (Fig. 15).
Boat/Anchor Dynamite Other coral
Fish nets Trash
Impact rank +-SE
0 = None
1 = Low
2 = Medium
3 = High
Figure 15. Damage recorded at Dega Giri.
6.1.5 Substrate cover at Dega Giri.
The substrate was dominated by mature colonies of fast-growing table Acropora coral (Fig
16 and 17). The survey was laid from the outer edge of the giri (in 3m water) to the inner
central area of the giri, adjacent to a sand patch. Coral cover decreases with distance along
the transect from the outer edge of the giri towards the centre. Coral cover over the first
20m section was 87.5% the second section was 62.5, the third 57.5, with the lowest cover
at the centre of the giri of 60% which was linked to the fall in table Acropora cover from the
outer to inner area of the giri over the transect (Fig. 18).
Mean Percent Cover + - SE
Figure 16. Relative substrate cover recorded at Dega Giri using the ReefCheck methodology.
Acropora (table)
Acropora (digitate)
Acropora (staghorn)
Acropora (encrusting)
Acropora (submassive)
Non-Acropora (encrusting)
Non- Acropora (submassive)
Non-Acropora (massive)
Figure 17. Relative representivity of different coral lifeforms and benthic features recorded at
Dega Giri.
0-20 25-45 50-70 75-95
distance from giri edge
percent cover
Acropora (table)
Acropora (digitate)
Acropora (staghorn)
Figure 18. Relative change in the most dominant coral lifeforms and substrate with increasing
distance from the outer edge of Dega Giri.
0m 100m
Figure 19. Schematic cross-section of the reef from the outer edge (left) to centre (far right).
Coral species identified at Dega giri by Professor Doug Fenner (Department of Marine and
Wildlife Resources, American Samoa) were Acropora nobilis, A. cytherea, A. muricata
(formosa), A palifera and Gardineroseris planulata.
6.2 Fish surveys
Fish were randomly distributed by site. There was no significant difference in predatory fish
family or species density between sites surveyed (Fig. 19). Two of the MPs surveyed –
Maya thila in Ari atoll and HP reef in North Male atoll had a higher abundance of carangids
(jacks) than in other locations. Other MPAs such as Kudarah in SE Ari atoll channel had
considerable number of dogtooth tuna (Gymnosorda unicolor). Most sites surveyed had one
or more individual humphead wrasse (Chelinus undulatus).
Figure 20. Relative abundance of predator fish families at nine sites around the central Maldives.
(Map by Steve Frampton).
Table 6. Summary of fish family abundance at each site
Species / common name
Mean number of
fish / 1250m
lutjanidae (snapper) 149.1 383.0
lethrinidae (emperor) 50.9 61.4
serranidae (grouper) 9.6 5.3
carangidae (jacks) 6.1 10.5
carchahinidae (sharks) 1.0 1.0
haemulidae (sweetlips) 1.1 2.3
murainidae (morays) 0.9 1.7
Sphyraena (great barracuda) 0.1 0.3
Sphyraena jello (picklehandle barracuda) 0.0 0.0
Tylosaurus crocodiles
0.0 0.0
Cheilinus undulates (humphead wrasse) 0.6 0.5
scaridae (parrotfish) 11.7 8.2
planktivorous balistidae (triggerfish) 164.9 325.1
other balistidae 8.9 4.4
planktivorous acanthuridae (surgeonfish) 30.1 23.8
other acanthuridae 45.1 25.2
planktivorous chaetodontidae (butterflyfish) 12.7 8.3
other chaetodontidae 13.0 8.6
caesionidae (fusiliers) 75.7 42.2
mullidae (goatfish) 5.6 6.7
ommacanthidae (angelfish) 5.0 3.1
ommacentridae (damselfish) 83.9 105.4
holocentridae (soldierfish) 40.4 47.7
labridae (wrasse) 18.4 27.8
siganidae (rabbitfish) 12.3 26.4
other 84.3 148.4
Figure 21. Mean relative abundance of fish per trophic level from all nine sites.
(Clockwise from top left: herbivores; planktivores; omnivores; predators).
7. Discussion
7.1 Maldives Reef Health
An estimated 80% of Maldives reefs werekilled by the 1998 bleaching event (Wilkinson,
2004). The Global Coral Reef Monitoring Network (GCRMN) carries out an assessment of
the health of Indian Ocean reefs every four years. The report is currently being compiled
whilst a recent report has proved that the world’s coral reefs are currently at a highly
vulnerable stage, with a considerable threat of local extinction of some species (Carpenter
et al., 2008). The next GCRMN report is due to out in 2008, which will put much of the data
from the Maldives into a regional and global perspective. The average coral cover of
Maldivian reefs visited by MCS/MST since 2005 of 25.7% is within the category of ‘poor-fair’
condition according to the GCRMN
. The data derived from MCS/MST surveys carried out
in central atolls between 2005 and 2008, compared to that available between 1998 and
2004 would suggest that these central reefs continue to recover from the bleaching event of
7.1.1 Coral species diversity
Most deeper reefs (>15m deep) are dominated by mature colonies of Tubastrea micranthata
in deeper reef waters, and acoporid and pocilloporid colonies in shallow waters (<15m),
which grow to about 40cm diameter. The latter two families do not significantly contribute to
the structural architecture of the reef, and cannot be described as ‘reef building’ corals such
as those species within the massive Porites, Pavona and Faviid families. The recovery of
reef-building species is very much slower, evinced by the common occurrence of small
(<30cm diameter) Porites colonies present on many shallower (10-20m deep) reefs. Larger
colonies of this family are probably survivors from the initial 1998 bleaching event (fig. 23).
Clearly it is important to survey sites with slightly higher coral cover where species diversity
is greater. Dega giri fits this description, as it is a site of higher diversity, and more mature
Figure 22. Mature (over 100cm diameter) reef-building corals such as Porites are rare on
Maldives reefs (left), and tend to be less than 50cm diameter (right), indicating that
most colonies completely died-off, or were partially bleached in 1998.
GCRMN coral health categories: excellent = >75%; good = 50-75%; fair = 25-50%; poor = <25%
Figure 23. A large Acropora cytherea colony on the reef flat at Dega giri.
7.2 Fish families and trophic levels.
7.2.1 Planktivores:
A large number and biomass of planktivorous fish dominate Maldives reefs, including the
red-toothed triggerfish, the chaetodontid pennant bannerfish, fusiliers and numerous small
damselfish species. Fusiliers in particular are very commonly caught in reef areas for the
live fish trade, along with apogonids (cardinalfish) and clupeidae (principally silver sprats).
The planktivorous fish dominate the outer walls of thillas and atoll outer rim reefs. The red-
tooth triggerfish feed between 2 and 10m above the reef and tend to be fairly site attached,
being faithful to a particular stretch of reef measuring less than 500m
. Fusiliers, however
have a more fusiform shape, and are a wider-ranging species and may move to where
plankton feeding conditions are better.
7.2.2 Herbivores:
Herbivorous families were dominated by scarids, acanthurids and siganids. As observed
with the planktivorous families, different species and families occupied different niches on
the reef, with acanthurids feeding on floating zooplankton and phytoplankton in the water
column, and foraging on the bottom amongst attached algae in shallow reef areas. Mixed
herbivore schools commonly occur in and around Maldives reefs, where siganids,
acanthurids and scarids along with wrasses and other families roam over expanses of reef
flat, targeting areas rich in algal growth (fig 24). Occasionally these schools were observed
feeding in areas of damselfish territories, where large standing crops of algae were present.
Scarids were ever present on shallow fore and back reefs, with a number of species
commonly represented on the surveys, at different growth / morphological stages.
Figure 24. Mixed herbivore school of parrotfish, rabbitfish and surgeonfish.
The relatively common recording of ‘terminal phase’ parrotfish in Maldives reefs indicates
that their population is in reasonable health (fig 25). The 1997-2001 Reef Check global
assessment of Indo-Pacific coral reefs recorded an average abundance of 2
(Hodgson and Liebler, 2002). Our study recorded a mean parrotfish
abundance of 0.94 individuals /100m
from the nine reefs surveyed, less than half the Indo-
Pacific average from the 1997-2001 Reef Check report. We also recorded a mean of 3.6
herbivorous acanthurids/100m
at the survey sites. Parrotfish have recently been proved to
be essential in maintaining ecosystem equilibrium in coral reefs in order to maintain hard
coral dominance (Mumby et al., 2003), as they graze significant quantities of algal turfs and
macroalgae. Furthermore, the importance of maintaining a suite of different herbivorous
species is imperative to keep the standing crop of most algal species in check. The
abundance and total biomass of these fish herbivores is particularly relevant in reef areas
where the bleaching event of 1998 led to the creation of considerable free space after the
die-off of most corals. If it weren’t for the activity of large numbers, diversity and biomass of
grazers clearing ephemeral algae from the surface of the corals, the regeneration of the
reefs which we are currently recording, would be significantly hampered by algal
Figure 25. Terminal phase female bicolour parrotfish (Cetoscarus bicolor) at HP reef (January
Figure 26. Sailfish surgeonfish (Zebrasoma desjardinii).
Another abundant reef fish family was the damselfish family, including territorial benthic
omnivorous, planktivorous and herbivorous species. Territorial damselfish species were
often found in aggregations of up to 15 individuals occupying areas of up to 100m
of reef.
They can radically alter the natural ecological community of the reef by allowing space for
algae to grow, which in turn provides habitat for invertebrates to occupy interstitial spaces
between the algal fronds. They spend a considerable amount of time nurturing certain algal
species to both provide a food source, and in order (in the case of territorial males) to make
their patch more attractive to females, in which the females will lay their eggs on the
substrate within the territories of the males. Successful males fertilize the eggs by swimming
over them, releasing sperm, and guarding them (for approximately 1-2 weeks) before they
hatch, and are released into the plankton.
The bleaching event of 1998 may have allowed many species to dominate areas of reef
which they would otherwise not have had access to prior to the loss of healthy live coral
cover. For example, the territorial damselfish species which dominates expose areas of
loose reef and rubble, which would otherwise be dominated by widespred Acropora growth
similar to that found at Dega Giri.
7.2.3 Predators:
Predatory fish species are dominated by omnivorous species such as L monostigma and L.
kasmira, rather than large members of the grouper family. Some sites did however have
large numbers of piscivores such as jacks, red snapper (L bohar) and grouper which were
abundant or common at HP reef, Kudarah and Rasdhoo, which are also Marine Protected
There is concern that the increasingly expanding tourism sector (measured at 30% of GDP
in 1997) and the indigenous population are combining to overfish some species of reef fish.
Furthermore, a grouper fishery has was initiated in 1993 which targets the family not only for
the Maldivian market, but for export to the far east, as a commercial fishery.
Sharks were not common on the dives, with the whitetip reef shark Traeinodon obesus the
most commonly observed individual. Sites visited during the surveys were not the most
suitable habitat for the grey reef shark, which tends to occupy deep channel reefs in large
numbers, rather than the inner shallower patch reefs on which the surveys were carried out.
In July 2008, the Maldivian fisherman’s Union called for a complete cessation in the sale of
shark fins from the Maldives to foreign markets. The continuing exploitation of Maldives
waters by foreign vessels operating, under license, within the 200nm EEZ appears now to
be accounting for the reduction in reef-associated shark species which would otherwise be
available for consumption by local Maldives fishermen, but are of more value alive to the
dive-tourist sector which attracts divers to many sites because of the guarantee of seeing
sharks. If sharks aren’t present at many sites (as could be the case), the Maldives will
become less attractive to the dive-tourism market.
The reefs of southern atolls (over 300km south of Male) were less affected by the bleaching
event than the central and northern atolls (see Table 1), and also are less heavily populated
and developed (by the tourism industry) than the northern atolls. The population of
Huvadhoo atoll is approximately 20,000 with a total area (land and sea) of 3,200km
) whereas the population of North and South Male Atoll is approximately 120,000
with a surface area of 3,600 (33 people/km
. This would suggest that the reef fish
populations of southern atolls are less affected by fishing because there is more limited
exploitation, and the area of reef relative to local human population is high, and the level of
commercial resource extraction, is relatively low compared to the rest of the archipelago.
Research carried out at the relatively isolated Northwestern Hawaiian Islands in the central
Pacific has revealed a progression of increasing number of large predatory fish (principally
sharks and jacks) in isolated coral atolls away from centers of human population
(Friedlander and DeMartini, 2002), compared to near the heavily populated islands more
Population statistics from Maldives Ministry of Planning and Natural Development (2006). Total Maldivian population
estimated at 298,968.
familiar to the tourist industry (such as Oahu. Maui and Moloki). The density of predatory
fish in isolated regions relative to the main island group was 11-1 (fig. 27).
Figure 27. The northwest Hawaiian Islands (left) and the relative biomass of predatory and non-
predatory fish recorded in the heavily-populated Main Hawaiian islands (clear bars)
relative to the isolated Northwestern Hawaiian Islands (black bars). The number of
apex predators (jacks and sharks) is greater in the isolated areas where population
pressure is lower. (Reproduced from Friedlander and DeMartini, 2002).
8. Summary
8.1 Corals reefs
The reefs of the central parts of the Maldives are recovering from the coral bleaching
event of 1998, yet have not reached the coral cover, diversity and health of the reefs
prior to the 1998 bleaching event.
Reefs are mainly dominated by acropora and pocillopora families.
Most reefs have patchy coral populations, but in the top 10m are dominated by small
(average size 30-50cm) coral colonies.
Many of the old structural reef-building colonies are dead. These are being
succeeded by small isolated colonies, which have recruited since 1998.
Dega giri is an anomalous reef where growth of delicate fast-growing acroporids is
much more extensive (in coral cover and individual colony size) than was recorded at
many other dive sites.
The reefs from the southern atolls (principally Huvadhoo) are less affected by the
bleaching event in 1998, and resemble unimpacted healthy coral communities.
8.2 Fish
Fish surveys show relatively high numbers of apex predators in some MPAs
(particularly at HP; Rasdhoo; Kudarah) compared to other Indo-Pacific reef regions.
Predatory fish at MPAs are dominated by jacks (principally the bigeye jack Caranx
sexfasciatus), and snapper (principally the red snapper, lutjanus bohar), and blue-
striped snapper, Lutjanus kasmira.
There was no significant different in fish assemblage between the different types of
reef surveyed (inner reef thillas; channels and outer atoll walls).
There appeared to be no significant difference in the fish populations surveyed
between MPAs sites visited on the surveys and sites outside MPAs (t-test, P >
9. Recommendations
MCS recommends greater enforcement of MPAs by outposted rangers to islands and
communities adjacent to the sites trained in enforcement techniques.
MCS recommends that the MPAs are regularly monitored by Marine Research
Centre scientists in collaboration with the tourism sector (if there are no available
funds to sponsor research from government sources).
The survey and monitoring work carried out by the MCS in collaboration with the
MST should continue for the long-term to record any changes to fish populations or
coral health.
New surveys on fish populations need to be carried out in the relatively undeveloped
and lightly populated atoll of Huvadhoo as soon as possible before the tourist
industry becomes well established in this area.
10. References:
Anderson C (1997)The Maldivian tuna livebait industry – status and trends. In Workshop on
integrated reef resources management in the Maldives – Bay of Bengal Programme. FAO.
Edwards, AJ, Clark, S, Zahir, H, Rajawsuriya, A, Naseer A, Rubens, J (2001) Coral
bleaching and mortality on artificial and natural reefs in Maldives in 1998, sea surface
temperature anomalies and initial recovery. Marine Pollution Bulletin 42(1): 7-15.
Friedlander, AM and DeMartini EE (2002). Contrast in density, size and biomass of reef
fishes between the northwestern and main Hawaiian Islands: the effects of fishing down
apex predators. MEPS 230: 253-264
Hodgson, G and Liebeler J (2002). The global coral reef crisis: Trends and solutions (5
years of Reef Check). Reef Check, LA, California.
Mumby, PJ, CP Dahlgren, AR Harborne, CV Kappel, F Micheli, DR Brumbaugh, KE
Holmes, JM Mendes, K Broad, JN Sanchirico, K Buch, S Box, RW Stoffle and AB Gill
(2006). Fishing, trophic cascades, and the process of grazing on coral reefs. Science 311
(5757): 98-101.
Rajasuriya, A, Zahir H, Venkataramen K, Islam Z, Tamelander J (2004) In Status of coral
reefs in South Asia. In GCRMN status of coral reefs of the World 2004, Australian Institute
of Marine Science, Townsville, Australia.
Solandt, JL and Wood C (2005). Observations of reef conditions on central Maldives reefs,
2005. Unpublished report. The Marine Conservation Society, Ross on Wye, UK.
Full-text available
Stretching over almost 4 million ha the Myeik Archipelago and associated Moscos Islands along Myanmar’s most southern coastline is a biologically rich and diverse seascape abound with unique, rare and threatened flora and fauna and the lifeblood of many island and coastal communities. Over the past 30 years however this once unspoiled ecosystem has been slowly degraded from a number of anthropogenic impacts including destructive fishing gears such as dynamite and other illegal, unreported and unregulated (IUU) fishing, increased terrestrial runoff from forest clearing and coastal development, increased population and climate change. To prevent further destruction of the area and to aim towards sustainable use and management of the archipelago, surveys were initiated in 2013 to quantitatively understand the status of the habitats and species and identify priority areas for protection. In summary surveys have found: Coral reefs: Coral reefs in the survey area showed high levels of hard coral diversity, with 288 species observed, in 68 genera and 17 families. Species accumulation curves predicted a total of 309 species would be obtained with the same method of sampling. The status of hard coral cover varies greatly across the archipelago from 0% to 92% with an average of 48.9%. Coral communities were clearly structured by three main reef types: a) fringing reefs on relatively exposed boulder slopes of outer islands, from the surface to about 15 m depth where the boulders transitioned into sandy slopes; b) fringing reefs on relatively sheltered slopes of the inner islands with high turbidity and strong currents; and c) steepy sloping/vertical rock walls on small isolated rocks or outer island cliff faces, extending into deeper water over 20-30 m deep. Coral disease prevalence ranged from 0% to 15% across all sites surveyed, with a mean disease level of 4.9%. Levels of compromised coral health was very high across the archipelago, with a mean level of 23.3%. Overall condition of reefs in the Myeik Archipelago is average, as a result of diverse impacts, including thermal stress and coral bleaching, fishing for reef fish, and trawler/pelagic fishing on the banks surrounding the islands. Fish: The total reef fish fauna of the Islands of the Myeik Archipelago of Myanmar consists of 495 species belonging to 62 families. The Coral Fish Diversity Index (CFDI) for the Myeik Archipelago predicts a total of 618 species. Sharks and large rays were notably absent. Larger individuals of predatory species such as groupers (Epinephelus, Plectropomus), snappers (Lutjanus) and emperors (Lethrinus) were present but only in relatively small numbers. Results for the nine fish categories within the archipelago (including groupers, snappers, butterfly fish and parrotfish) indicate an ecosystem heavily impacted by overfishing. Biomass surveys noted many sites have relatively low estimates of fishable biomass (< 3 g/m2). Global estimates of biomass below 30 g/m2 present unhealthy and unstainable fishing states. Invertebrates: A total of 258 reef invertebrate fauna have been collected and of these only 127 could be identified to species level. The majority of the 258 invertebrates observed were decapods with 103 specimens and gastropods with 55. For sponges 36 unique species were collected during this expedition, with representatives from at least nine orders. Diadema were the most common of all the invertebrates recorded with 52.01 individuals per transect. Mean invertebrate numbers per transect were generally very low with all but banded coral shrimp, collector urchin and Diadema recording means under one. Sea cucumbers and lobsters have been heavily impacted by an unregulated fishery. No reefs exhibited high numbers or outbreaks of Crown of Thorns Starfish. Seagrass: Seven species of seagrasses were identified, with coverage ranging from 25.75-64.57% across ten sites surveyed. Seagrass beds face problems such as smothering by sand. This can arise from trawlers stirring up sediments or sediment run-off from where forest areas have been cleared. Fish life was found to be depauperate within these seagrass beds, with an average of only 1.7 fish observed across 51 baited video samples of 30 minutes each. There was a clear lack of abundance of top predatory fish from families such as trevally, grouper, snapper and sweetlips across all samples.
Full-text available
A comparison between the northwestern Hawaiian islands (NWHI), a large, remote, and lightly fished area, and the main Hawaiian islands (MHI), an urbanized, heavily fished area, revealed dramatic differences in the numerical density, size, and biomass of the shallow reef fish assemblages. Grand mean fish standing stock in the NWHI was more than 260% greater than in the MHI. The most striking difference was the abundance and size of large apex predators (primarily sharks and jacks) in the NWHI compared to the MHI. More than 54% of the total fish biomass in the NWHI consisted of apex predators, whereas this trophic level accounted for less than 3% of the fish biomass in the MHI. In contrast, fish biomass in the MHI was dominated by herbivores (55%) and small-bodied lower-level carnivores (42%). Most of the dominant species by weight in the NWHI were either rare or absent in the MHI and the target species that were present, regardless of trophic level, were nearly always larger in the NWHI, These differences represent both near-extirpation of apex predators and heavy exploitation of lower trophic levels in the MHI compared to the largely unfished NWHI. The reefs in the NWHI are among the few remaining large-scale, intact, predator-dominated reef ecosystems left in the world and offer an opportunity to understand how unaltered ecosystems are structured, how they function, and how they can most effectively be preserved. The differences in fish assemblage structure in this study are evidence of the high level of exploitation in the MHI and the pressing need for ecosystem-level management of reef systems in the MHI as well as the NWHI.
Full-text available
The major coral reefs in South Asia occur in the Maldives, Chagos, Lakshadweep and the Andaman and Nicobar Islands. There are also extensive reefs in the Gulf of Mannar, and fringing and patch reefs elsewhere in India and Sri Lanka. Limited coral communities occur around St. Martin's Island in Bangladesh and on the Balochistan coast of Pakistan. Coral reef recovery following the 1998 bleaching was variable. Some areas show relatively good recovery, such as the severely bleached Lakshadweep Islands, where coral cover has doubled from less than 10% after the bleaching to 20% on some atolls, whereas in other areas there are indications of a phase shift, with algal growth smothering corals. Minor coral bleaching was observed in 2003 and 2004 in the Maldives, Sri Lanka, on the Indian side of the Gulf of Mannar and on St. Martin's Island in Bangladesh, with almost 100% recovery within months. Several reef areas have been declared marine protected areas (MPAs) in India, the Maldives and Sri Lanka. However, with the exception of Chagos, reef management remains poor in the region, particularly in India and Sri Lanka, where the exploitation of reef resources is increasing. 100 Years ago: Most reefs in the region were in pristine condition although the reefs near human populations may have been showing the effects of some resource exploitation. For example, chanks and sea cucumber were heavily exploited in the Gulf of Mannar region in the 1920s.
Full-text available
Since the mass mortality of the urchin Diadema antillarum in 1983, parrotfishes have become the dominant grazer on Caribbean reefs. The grazing capacity of these fishes could be impaired if marine reserves achieve their long-term goal of restoring large consumers, several of which prey on parrotfishes. Here we compare the negative impacts of enhanced predation with the positive impacts of reduced fishing mortality on parrotfishes inside reserves. Because large-bodied parrotfishes escape the risk of predation from a large piscivore (the Nassau grouper), the predation effect reduced grazing by only 4 to 8%. This impact was overwhelmed by the increase in density of large parrotfishes, resulting in a net doubling of grazing. Increased grazing caused a fourfold reduction in the cover of macroalgae, which, because they are the principal competitors of corals, highlights the potential importance of reserves for coral reef resilience.
The bleaching and subsequent mortality of branching and massive corals on artificial and natural reefs in the central atolls of Maldives in 1998 are examined with respect to sea surface temperature (SST) anomalies. SST normally peaks in April–May in Maldives. The UK Meteorological Office's Global sea-Ice and SST data set version 2.3b shows that in 1998 monthly mean SST was 1.2–4 S.D. above the 1950–1999 average during the warmest months (March–June), with the greatest anomaly in May of +2.1°C. Bleaching was first reported in mid-April and was severe from late April to mid-May with some recovery evident by late-May. At least 98% of branching corals (Acroporidae, Pocilloporidae) on artificial structures deployed on a reef flat in 1990 died whereas the majority of massive corals (Poritidae, Faviidae, Agariciidae) survived the bleaching. The pre-bleaching coral community on the artificial reefs in 1994 was 95% branching corals and 5% massives (n=1589); the post-bleaching community was 3% branching corals and 97% massives (n=248). Significant reductions in live coral cover were seen at all natural reefs surveyed in the central atolls, with average live coral cover decreasing from about 42% to 2%, a 20-fold reduction from pre-bleaching levels. A survey of recruitment of juvenile corals to the artificial structures 10 months after the bleaching event showed that 67% of recruits (⩾0.5 cm diameter) were acroporids and pocilloporids and 33% were from massive families (n=202) compared to 94% and 6%, respectively, in 1990–1994 (n=3136). Similar post-bleaching dominance of recruitment by branching corals was seen on nearby natural reef (78% acroporids and pocilloporids; 22% massives). A linear regression of April mean monthly SST against year was highly significant (p<0.001) and suggests a rise of 0.16°C per decade. If this trend continues, by 2030 mean April SST in the central atolls will normally exceed the anomaly level at which corals appear there are susceptible to mass bleaching.
The Maldivian tuna livebait industry -status and trends
  • C Anderson
Anderson C (1997)The Maldivian tuna livebait industry -status and trends. In Workshop on integrated reef resources management in the Maldives -Bay of Bengal Programme. FAO.
Observations of reef conditions on central Maldives reefs
  • J L Solandt
  • C Wood
Solandt, JL and Wood C (2005). Observations of reef conditions on central Maldives reefs, 2005. Unpublished report. The Marine Conservation Society, Ross on Wye, UK.
The global coral reef crisis: Trends and solutions (5 years of Reef Check)
  • G Hodgson
  • J Liebeler
Hodgson, G and Liebeler J (2002). The global coral reef crisis: Trends and solutions (5 years of Reef Check). Reef Check, LA, California.