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Try out PMC Labs and tell us what you think. Learn More. BoxMayaguez, PR BOXMombasaKenya. The Chagos Archipelago was deated a no-take marine protected area MPA in ; it covers km 2with more than 60 km 2 shallow limestone platform and reefs. This has doubled the global cover of such MPAs. It has suffered from warming episodes, but after the most severe mortality event ofcoral cover was restored after 10 years.
Coral reef fishes are orders of magnitude more abundant than in other Indian Ocean locations, regardless of whether the latter are fished or protected. The no-take MPA extends to the nm boundary, and. On the larger islands, native plants, coconut crabs, bird and turtle colonies were largely destroyed in plantation times, but several smaller islands are in relatively undamaged state. Pollutant monitoring shows it to be the least polluted inhabited atoll in the world. Today, strict environmental regulations are enforced. Shoreline erosion is ificant in many places. Its economic cost in the inhabited part of Diego Garcia is very high, but all islands are vulnerable.
Chagos is ideally situated for several monitoring programmes, and use is increasingly being made of the archipelago for this purpose. It is a large group of atolls and submerged banks in the central Indian Ocean, lying at the southernmost end of the Lakshadweep—Maldives—Chagos ridge. The area within the total BIOT nm zone is about km 2. The Chagos Archipelago. Inset shows location and MPA boundary circular shape with flattened northern border.
Main map: the five atolls with land are shown in bold, the islands on Great Chagos Bank and submerged reefs and atolls are not bold. All are located in the central area of the MPA. During recent decades, most of the tropical ocean has been heavily affected by pollution, over-exploitation and various unwise forms of development Millennium Ecosystem Assessment, All reefs are highly vulnerable to increasing intensity of human exploitation, which reduces both biomass and productivity, and consequences of reef deterioration may be greater than ly anticipated Mora et al.
Most conventional forms of marine management are failing to arrest the decline, so many marine science bodies, conservation organizations and international conventions have called for more and larger marine protected areas MPAs that have effective levels of protection United Nations, ; Wood et al. MPAs remain one of the only extensive tools being used directly for conservation purposes Spalding et al. A recent assessment Toropova et al. Recently their median size was only 5 km 2 Wood et al. The small proportion of ocean covered by MPAs must be compared with estimated need. Most targets will manifestly fail, and participating parties would need to create over 19 million of the median size MPAs to achieve these targets.
Chagos was occupied from the 18th century, during which time most of its native vegetation was converted to coconut plantations. This industry lasted until the s. Two of the five atolls were abandoned for economic reasons and social problems in the s, and in the early s the plantations on the remaining three atolls were closed due to the establishment of a military facility.
The people were moved to various countries, notably Mauritius and the Seychelles, and some eventually to Europe, especially England Edis, The remaining plantations were already in some decline given diminishing world demand for coconuts and the ascendency of palm oil from elsewhere, but nevertheless political issues surrounding the forced removal of the last inhabitants has been mired in controversy ever since.
For the last 40 years the islands have been uninhabited except for the southernmost atoll of Diego Garcia, the western arm of which contains the military facility and at least Asian contractors and others. That facility does not depend on local food resources but is provisioned and supported entirely from outside the archipelago. It has become clear during this period when coral reefs in most of the Indian Ocean have become seriously degraded that those of Chagos persist in an exceptionally good state.
This led increasingly to calls to extend its conservation, and data to support the concept came from over papers arising from both those scientific expeditions and, to a lesser extent, from unpublished information, from regional data and from modelling.
Existing environmental laws are currently being revised and consolidated to accommodate this status. Diego Garcia atoll to its 3 nm boundary is excluded from the MPA. Monitoring and enforcement are undertaken in large part by a patrol vessel which serves as a mobile base for both the military and civilian research expeditions.
Figure 2 a shows the areas of islands and reefs. Diego Garcia contains half the total land area, the rest being split among over 50 small islands, the varying to some degree with tidal height and shifts of sand banks. All islands are very low lying, and are typical coral cays constructed of limestone. Beneath these lie freshwater lenses sustained by high rainfall. The largest islands are named. In contrast to the small island areas, sublittoral substrate in the photic zone is calculated to be approximately 60 km 2 Figure 2 b Dumbraveanu and Sheppard, There is enormous opportunity for new discoveries: as recently as an expedition discovered many hectares of seagrass and a ly unknown 3 km 2 mangrove forest.
Other parts of Chagos have been mapped using bathymetric or satellite data-based modelling Yesson et al. There were no quantitative studies of reef condition on Chagos reefs before the s, although descriptive studies, notably Stoddart and Taylordescribed land and reef flat in Diego Garcia. From the s, episodic visits enabled a series of coral cover measurements to be taken on reef slopes. Coral cover declined between the first survey in Sheppard, a and the next in Sheppard, a Figure 3. This was mainly due to loss of shallow and mid-depth branching species, particularly Acropora palifera and table corals including Acropora cythereaand causes were only speculated upon at the time Sheppard, a.
Later, after much work globally and more surveys in Chagos, the cause was suggested to be several warming events. This modest decline occurred in many Indian Ocean islands groups over this period Ateweberhan et al. Percentage coral on reefs by the main coral types in 4 years, for the major live identifiable by snorkelling in Arrows along the top are dates and approximate relative severity arrow thickness of warming events from Sheppard, a. Severe warming in then caused severe mortality on all Chagos reefs Sheppard, b ; Sheppard et al.
Coral and soft coral mortality was almost total on several Chagos ocean-facing reefs to clearly defined depths, below which corals provided much higher cover. This killed zone extended deeper in southern atolls, and in Diego Garcia for example was greater than 40 m depth, while in more northern atolls it extended to only about 10—15 m depth Sheppard et al. Such variability was mirrored in the Indian Ocean as a whole Sheppard, Lagoon reefs of Chagos atolls were much less affected than ocean facing reefs Figure S1 in Supplementary Materialwith many retaining high coral cover, including stands of Acropora.
Post, coral species diversity was greatest in deep lagoon areas. Several ocean-facing transects around the atolls have been monitored repeatedly from onwards Figure 4. Increase in coral cover became evident byespecially in shallow water Harris and Sheppard, ; Sheppard et al. Deeper recovery has been slower. Coral cover in reached values recorded in in a few transects in Diego Garcia, but most atolls were not surveyed during that year. Coral cover in depths to 25 m on ocean-facing slopes in different years Sheppard aab ; Sheppard et al.
Data are of all ocean-facing transects in this series measured on each date. Bars are error bars error data lost for Inextensive video surveys were taken and archived, showing mean percentage cover of several benthic Bayley, Figures 5 and S3, S4 in Supplementary Material. These showed no ificant differences that year in hard coral cover in pooled data between atolls, although ificant differences existed at depth and site levels between ocean-facing reefs. Hard coral cover was ificantly higher in lagoons Soft coral was higher on ocean-facing slopes Hard coral cover decreased between 6 and 25 m, but sponge and soft corals showed an increase with depth.
Structural complexity was reduced to 15 m in the outer atolls, and to deeper zones on the Great Chagos Bank and Diego Garcia atoll. Furthermore, deep lagoonal areas exhibited the highest s of small, juvenile coral colonies. Modelling studies indicate that such deep reef areas could be responsible for relatively rapid recolonization of denuded shallow reefs Riegl and Piller, Bars are error bars. The past decade has seen further coral bleaching events in Chagos, in,and a mild one in None were sufficient to cause mass mortality, although species-specific coral mortality was recorded of many Acropora cytherea tables in Pratchett et al.
Given that warming episodes sufficient to kill corals are predicted to increase Sheppard, ; Hoegh-Guldberg et al. However, models based on recruit availability scaled to the present coral cover, suggest that Chagos reefs will long be able to withstand recurring strong mortality events — even each decade — and still maintain high coral cover. ificant declines in cover are expected only if both larval supply decreases and coral mortality events increase in intensity and frequency. Pre- and post studies have also revealed some changes in the soft coral component.
The principal octocorals before and after the ENSO shared many common taxa Reinicke and van Ofwegen, ; Schleyer and Benayahu,but a few discontinuities in their biodiversity indicate subtle changes in more persistent genera Lobophytum, Sarcophyton. Cespitularia, Efflatounaria, Heteroxenia disappeared after the ENSO-related coral bleaching Reinicke and van Ofwegen, ; Schleyer and Benayahu,suggesting that such transient fugitives might be eliminated from soft coral communities on isolated reef systems by bleaching disturbance of this nature.
Carijoa riseiia species often considered a fouling organism, and even an invasive in some places Concepcion et al. The observed post-ENSO recovery gives cause for hope for soft coral survival in the face of climate change. Biomass of reef fish around the northern atolls of Chagos was quantified for the first time inusing underwater visual census Graham, Biomass estimates for Chagos exceed values from both fished and protected reefs elsewhere in the region, such as Kenya, Seychelles, Madagascar and even the Maldives, by several orders of magnitude McClanahan et al.
The Chagos biomass estimates are matched only by some remote, unfished locations in the Pacific Ocean Sandin et al. With recent declines in coral cover globally Ateweberhan et al.
Much work has followed the bleaching event around the world in trying to document changes to reef fish populations. However, subsequent studies have shown that longer term effects of coral loss and reef structural collapse on fish are much wider reaching, with a large portion of the fish community affected, including reductions in species richness, reduced abundance of many groups and changes in the size structure of the community Jones et al. Reef fish surveys in Chagos conducted in were repeated in using identical methodology. This was part of a study across seven Indian Ocean nations. One of the groups of fish most affected by coral loss is coral-feeding butterflyfishes, but a comparison between Chagos and Seychelles demonstrated that, although both specialized and generalist coral feeding butterflyfishes showed declines in abundance in the Seychelles through the bleaching event, there was no detectable difference in Chagos Graham et al.
In contrast, the populations of Chagos remained remarkably stable Figure 6. Changes in fish species richness for Chagos were extremely small and either side of zero, compared with the regional decline. This highlights the temporal stability of Chagos fish assemblages in response to a large-scale disturbance, despite substantial negative responses elsewhere in the ocean, and accords with findings of Mora et al. Change in reef fish species richness across seven countries in the Indian Ocean following the coral mortality event.
Chagos sites represented by filled circles. Adapted from Graham et al.
Also of note are some different fish behaviours that are very rarely seen elsewhere around the world where human exploitation, coastal development, and other impacts have changed abundances, ecological interactions, and behaviour. One such example is the daytime feeding behaviour of the moray eel, Gymnothorax pictuson shore crabs, leaping clear of the water to capture their prey Graham et al. Behaviours like this, and the exceptional stability and abundance of the reef fish communities, make Chagos a very important reference area with which scientists can understand ecological and behavioural changes elsewhere in the world.
In a survey assessed corals along 37 transects at eight sites across the archipelago Figure 7.Sexy mature Coral Harbour
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Reefs and islands of the Chagos Archipelago, Indian Ocean: why it is the world’s largest no-take marine protected area