Aldabra, One of the Great Wonders of the World

Across an open ocean birds begin to flock circling high above in the clouds. The water turns in cycles bringing schools of baitfish and shrimp to the surface. A pod of bottlenose dolphins feeds on the sandy bottom of the fringing reef, a passing Wahoo. From the water you cast your eyes upon a shore in the distance. Turtles wander up the beach to nest; sunbirds jump from branch to branch. Mangroves feed of the tides and crabs scavenge at night. The cold wind comes with the southerly breeze; the clouds are turquoise and the lagoon vast and magnificent. Welcome to paradise.

Aldabra has the title of being the world’s largest atoll and a refuge for rare forms of fauna. Oval   the coral atoll is 31 km (19 mi) long and 13 km (8 mi) wide, and consists of four main islands Picard, Grande Terre (Main), Polymnie, and Malbar that together surround a large lagoon as well as several smaller coral islands. Aldabra is a dependency of the Seychelles in the Indian Ocean.

The isolation that has allowed Aldabra to develop in such a magnificent manner is so extreme, with much of the coral atoll being covered by masses of jaggered, sharp outcropping. It is possibly this factor more than any other that has helped save it.  Situated about 1,100 km (684 mi) southwest of Mahé and 420 km (260 mi) northwest of Madagascar. The islands are volcanic in origin and rise from a seabed about 4,000 m (13,120 ft) deep to no more than 10 m (33 ft) above sea level.

Being one of the great wonders of the planet; it has become so due to its isolation and remoteness. This isolation has allowed the development of a unique environment harbouring a diverse range of both plant and animal species. One of its feats of nature is to host an undisturbed ecosystem. It is the last remaining habitat of both the Aldabran giant land tortoise and the white-throated rail, a flightless bird. Aldabra is also the sole breeding habitat for greater and lesser frigate birds.  It is also a nesting ground to a great number of seabirds such as the boobies and tropicbirds. Regularly throughout the year a spectacular event of nesting sea turtles grace the white sand beaches and swim amongst the tranquillity of the lagoon. Among the 200 species of plants found on Aldabra, some 20% are endemic.

The Portuguese visited Aldabra (then uninhabited) in 1511 but did not settle. It became a French dependency in the 18th century, and then was held by the British in 1810 during the Napoleonic Wars. Aldabra was part of the British Indian Ocean Territory from 1965 to 1976 During this time there were controversial but unrealized plans to develop the atoll as a military base, this was condemned by conversationalist who saw the development as being catastrophic to the survival of the islands species.

It was fortunate that in this case nature won and later in 1976 the island was handed over to the Seychelles, with the Seychelles Island Foundation (SIF) as its protector. The SIF was established primarily to protect, conserve and monitor the atoll. As an independent organization the SIF is mainly self-financing and prides itself in putting nature at the top of the list and not the other way around. 

Seychelles Islands Foundation
P 0 Box 853,
Victoria, Seychelles
Tel : (+248) 321 735
Fax : (+248) 324 884
Email : sif@seychelles.net

The foundation was established as a public trust in 1979, with the President of Seychelles as patron. The Board of trustees, appointed by the President, has 14 members, including not less than five representing organizations concerned with the conservation of wildlife and natural history or national academics of science. In 1982 the atoll was declared a World Heritage listed site and further protection of its existence has occurred. There are no permanent residents, and the fragility of the ecosystem has meant that few visitors are permitted.

Life on Aldabra relies on the change of the tides. Twice a day the water surges through the narrow channels with tremendous force, it breathes new life into the lagoon, bringing with it a host of fish and other sea creature, humpbacks have been seen basking in the mouth of main channel, dolphins regularly parade the outer reef. Virtually un-spoilt by man the environment has become one of total inspiration. It is a virgin land where plants and animals can live in harmony on a fragile yet present equilibrium. We could easily upset this balance if we didn’t monitor the effects human impact is having on the daily life of the existing species.

In order to maintain the balance the SIF has introduced a management team of rangers, research officers, boat staff and a warden. It is there job to watch, or act as guardians to the atoll and it’s inhabitants. Monitoring of the islands species occurs on monthly bases, controlled tourist access to limited parts of the environment also aid in its protection. Zones are defined by the access allowed due to the ecological sensitivity of nature. Breeding, nesting, and critical habitat areas are included in the zone management.

Many parts of the island have been classified as restricted zones which limits the visitors in one area at any given time extreme caution is taken at all time to limit the interaction and impact visits to these zones have. In the restricted zones people numbers are limited to 6 at any given moment. This hopefully plays a role in limiting the impact of people on the island. In reality people will still visit Aldabra and to accommodate this zones have been set aside particularly for this use. The areas are selected for their richness in biodiversity and scenic value but most importantly their ability to support limited, well-managed nature conservation and educational tourism. Due to the physical limitations of the environment these areas can only support low numbers of people. It is therefore even more of an amazing experience if you receive the chance or opportunity to visit this wilderness.

Within the zones of the atoll much monitoring occurs ranging from rainfall to species distribution. There are six base camps on Aldabra which act as stations from which more in-depth study can occur over the period of a couple of days. Rainfall monitoring for example provides extremely important data in all aspects of science and conservation on Aldabra. It can help explain population cycles, animal behavioural patterns and more of the dynamics of life on Aldabra. The island has 13 rain gauges from which manual readings can be taken.

Over time Aldabra did have a higher rainfall and plants species developed endemic to the island. Today some of these species are restricted to small parts of the atoll due to the lower precipitation levels recorded recently. These species are quite unique in that nowhere else will you find them, many of them stem from other species and what you find are now subspecies. Atolls, and isolated Island groups have long been realized to host a microcosm of evolution; the giant land tortoise is a prime example.

As early as the 70’s studies began on the land tortoise delving into their history and their evolution cycles, including their survival as a species today. Aldabra host the healthiest population of giant land tortoises in the numbers of around 113,000. In 1997 The ERGO (Environmental Research Group Oxford) conducted a survey of the population and reviewed the monitoring process, the primary goal being the protection and survival of the species.  Conclusions were made that the monitoring techniques being used were satisfactory and providing a stable amount of information.

The population faces many predators’ birds preying on the young, lack of food and water. Although there is a more immediate threat to the population on Grande Terre. At the end of the nineteenth century goats where introduced to the Aldabran Islands to breed and create a source of meat. It is undeniable that this once introduced species is now having a detrimental impact on the ecosystem on Grande Terre. This is the only of the four islands in the toll that they still exist.

The land tortoise forages on the leaves of trees that have fallen to the ground. Initially the threat of the goats was not apparent, yet know it is becoming visible that the increase in the goat population is linked with the decline in available food because goats choose to cause destruction of anything in their path. Some parts of the vegetation show clear lines of destruction at their maximum feeding height of 2m. Eradication of the species and thus removing the threat on the giant land tortoise is essential to return the balance to that of which nature intended.

It is not only the giant tortoise which relies on the habitat for survival an entangled niche exists and provides homes for many other species. Land birds are particular special on Aldabra in particular the Flightless rail the last of it’s species in the Indian Ocean. There are 13 species of land birds and 6 shore birds. The lack of interference by man and the predators is one of the reasons these species are so unique to the island. The Rail is now only found in four places on the Atoll, it is believed that in the past feral cats another introduction could be responsible for the limited distribution. Where in the past there was no natural predator the species thrived and became specifically land based, thus easy prey for the introduced cats. Fortunately they have since been controlled and the population is able to slowly increase and return to normal. This species is yet another aspect of the atolls importance.

Charles Darwin noted that remote islands and atolls are prime examples of subspecies development and he viewed such occurrences on Galapagos, an environment similar to Aldabra in its isolation and development of unique species. Each bird species contribute to the food web in a particular way, which possibly a conclusion to the equilibrium found within the species, as they are not all competing for the same food source. The blue pigeons feed on fruit trees while the nightjar and the brush warbler are insect eater, and of course the flamingo which draws its fabulous colouration from feeding on plankton. The balance is an essential part of the ecosystems survival. Lets not forget the significance birds play in relation to plant pollination and seed dispersal.

Aldabra is also one of the most important breeding sites in the Indian Ocean for five species of sea birds. Great and lesser frigates red-tailed and white-tailed tropicbirds, and the red-footed bobby. The lagoon provides a sheltered and protected breeding site away from predators. This is important in Species like the frigates and bobbies whom feed and harbour their young for up to a year. This is also one of the reasons why the birds do not often breed every year, as they require time to recover. This results in the population of breeding birds being only a portion of the entire population of each species.

Of the breeding sites of the frigates and the Boobies only two are open to visitors and monitoring of the disturbance is recorded each time a boat enters the site. The rangers look at how many birds are disturbed from their nest, not including those already in the air. This gives them and idea of the impact of the visits. With frigates once they leave the nest you will notice they each scavenge twigs from the others nest or inhabit the nest themselves. So by influencing the birds to fly we are possibly changing the natural cycle of their selection.

There is yet another unique element to life on Aldabra the sea turtles. In the past sea turtles in particular Hawksbills and Greens fell to the hands of poaches after thee meat and shell of the delicate animal with no stringent control the impact on the population began to show and numbers of green turtles dropped as low as 200. Today Aldabra is the refugee and home to a flourishing population of turtles and an indication of the increase is the number of untagged individuals that have begun making it ashore in the last few years.

On Aldabra turtle monitoring covers a ranges of beaches both inside and outside the lagoon. The lagoon has been observed to be a more preferred nesting site of the hawksbills as well as a haven and growing habitat for juvenile of both species. The greens are noted to nest on the beaches on the outside of the atoll. Whether it has been by choice or selection, the two species have developed to be able to share the habitat and both prosper from it.

Unique to Aldabra they have also been recorded to mate the whole year round. More common is a mating season of approximately 3 months with variables, although this seems irrelevant to the turtle population on Aldabra, yet a peek season is evident between June and Oct with hatchlings in November.

Apart from the thriving population of turtles Aldabra also host a teeming biodiversity of marine life and studies of the coral reef ecosystem are beginning to follow in the footsteps of the land tortoises. In 1999 a survey of benthic and reef fish communities and coral diversity and abundance with a side-glance at the improvements since a survey was taken just after the bleaching in 1998. Results from the survey showed a high diversity of reef fish at the atoll an indication that the overall productivity of the ecosystem has not yet been significantly affected from the bleaching. Although there is a correlation between the reef fish species and the live coral habitats remaining suggesting distribution and numbers will be effected by the further loss of coral habitats. On a positive note regardless of the fact that shallow coral reefs suffered a great deal, the deeper water habitats have shown substantial regeneration. This is a positive sign for the future and another of the reasons why preservation of the atoll is essential.

The focus is not only on the animal life but the ecosystem on a whole, which includes an extensive range of flora endemic to the islands. The first collection of plant specimens was carried out in the late 19th century. It wasn’t however until the 1960’s that an extensive study was carried out. It still lacked a little, in the access to some parts of the atoll were near impossible considering some of the more treacherous terrain, some data was collected from aerial photographs. Many species of plants found on the island once relied on a suitable source of plant material for dispersal and colonization.

Aldabra’s plant life is extremely diverse and rich for such a remote area. There are three major types that exist. The mangroves around the edge of the lagoon, grasslands covering much of the coastal areas as well as dense woodlands around the main island. The unique aspect of all of these areas is the role that their existence plays in the survival of many of the animal species. A prime example is in the land tortoises diet and well as providing shelter in the dry season when water is sparse.

With such an extreme diversity of species which appear to prosper in the some what uninhabitable environment, it is difficult not to assume in man ways it is nature way of marking the atoll and one of the main reasons why the SIF is working to ensure it’s ultimate survival as one of natures untouched wonders.

Untouched and untarnished is how this pristine environment should remain as a symbol of biodiversity existing in such perfect harmony. If there has ever been such a place that offers just the slightest glimpse of paradise Aldabra is such a place. It is one of Nature masterpieces and a perfect example of life the way Mother Nature intended. It allows people the opportunity to learn about the pure essence of a natural environment and the ability it has to shine, today tomorrow and forever.

Lou Oliver

References
Anna Liljevik, Research Officer, Aldabra station
Brian Betsy, Ranger, Aldabra Station
A.J. Seaton, K.Beaver and M.Afif, Editors (1991) A Focus on Aldabra, Seychelles Island Foundation (SIF), Ministry of Education, Seychelles No 3.