Terrestrial environment

D’Arros and the islands of the St Joseph Atoll are flat and entirely sandy. Scattered throughout the interior of the larger islands, a rocky layer of fossilised guano lies beneath the surface of the sand, giving testament to bygone seabird colonies. The beaches consist of uninterrupted soft white sand and are fringed by gently lapping waves on one side and coconut palms on the other. Although coconuts are indigenous to the region, they are normally restricted to the beach crests of islands as they are unable to penetrate existing tropical forests. However, when the interior is denuded of native vegetation, coconut palms quickly occupy the open space to form a dense jungle devoid of other plant species. Unfortunately, by the late 1900s this fate had overcome most of the Seychelles’ Outer Islands. D’Arros and the seven largest islands of the St Joseph Atoll were no exception and today 90% of the vegetation on them is dominated by coconut palms. The remaining 10% comprises casuarina trees and small patches of indigenous broad-leaved forest interspersed along the beach crest and among the coconut palms.

While a jungle of coconut palms may seem aesthetically pleasing, it is extremely low in biodiversity. This quickly becomes evident when you attempt to slash your way into the dense jungle on D’Arros – apart from a few skinks, spiders and several million mosquitoes, there is very little life! If the natural forest had been left undisturbed, you would probably have encountered several species of land birds feeding on a diversity of insects and fruits; giant tortoises lumbering around on the open forest floor; crabs and skinks scuttling about; and seabirds nesting in the leafy canopy overhead. Fortunately there is a very strong conservation ethic in the Seychelles and several vegetation rehabilitation projects are currently under way. The D’Arros Research Centre has taken a leading role in this initiative (link to What we do > Ecosystem rehabilitation > Forest rehabilitation) as it implements the most extensive forest rehabilitation programme in the region using an innovative, low-cost and effective technique that was devised on the island. Encouragingly, large numbers of seabirds have already begun nesting and roosting in the rehabilitated areas, raining down the nutrient-rich guano that is required to kick-start natural ecosystem processes.

In the south-east of the atoll, along the inner shore of St Joseph Island, there is a series of muddy channels flowing between rocky shelves of fossilised corals. Small stands of mangroves grow in these channels and along the inner rim of most of the other islands in the atoll. In the past, mangroves were heavily exploited for their bark, and thus it is believed that they were once far more common in the atoll than they are today. Although these remnant mangrove stands are expanding again, the D’Arros Research Centre is accelerating this process by planting propagated mangrove seedlings in strategic areas. Mangroves are a vital component of lagoon ecosystems as they provide food and shelter for a diversity of marine creatures; act as a nursery for fish, sharks and rays; provide nesting habitat for seabirds; trap nutrients; offer a valuable food source for many species; and reduce coastal erosion.

Of the five land bird species on D’Arros and St Joseph today, the turtle dove and the Seychelles fody are believed to be native while the house sparrow, Madagascar fody and zebra dove were probably introduced by humans. However, once a significant portion of the vegetation has been rehabilitated, certain land bird species that are endemic to the Seychelles will be reintroduced.

Three heron species occur, of which grey and green-backed herons are breeding residents. No fewer than 15 migrant wader species have been recorded, of which the most common are ruddy turnstone and crab plover.

More than 1,000 greater and lesser frigatebirds and 1,500 lesser noddies roost on the islands at any one time. These birds breed at other locations and use D’Arros and St Joseph as a convenient stopover or as a routine perch from which to go on daily fishing forays.

At least seven seabird species breed on the islands: approximately 23,000 pairs of wedge-tailed shearwaters, 2,000 pairs of fairy terns, 500 pairs of roseate terns, 300 pairs of lesser noddies, 50 pairs of common noddies, 15 pairs of black-naped terns and 10 pairs of white-tailed tropicbirds. The roseate tern and shearwater colonies are of particular importance as they are the second largest in the Seychelles. The roseate terns usually arrive in June and settle in a single noisy colony somewhere along a remote beach crest in the atoll. A pair usually produces one or two chicks, but breeding success is strongly dependent on the rate of predation by grey herons and hermit crabs. More than 90% of the wedge-tailed shearwaters breed on Fouquet Island in the atoll. Shearwaters mate for life, separating only if they have had no breeding success after several successive seasons. They lay only one egg per season in a meticulously excavated burrow. At sunset, when shearwaters return to the island after a full day of fishing, they face two obstacles before arriving safely at their burrows. Firstly, they must avoid hordes of frigatebirds that specialise in stealing their food by chasing them down relentlessly until they regurgitate. Secondly, the pecking order on the island is fierce and shearwaters residing in the interior must choose whether to land on the beach and make a run for it through a colony of sharp beaks or attempt a death-defying flight through the dense coconut palm canopy.

Three gecko and one skink species are ubiquitous around the islands and a small reproductive population of Aldabra giant tortoises lives in the open grasslands adjacent to the village and gardens. Aldabra giant tortoises are very similar in shape and size to their Galapagos cousins and can reach enormous proportions. The largest tortoise on D’Arros is Petifour, named after the local pastry that is his favourite treat. He is approximately 100 years old, weighs in excess of 250 kilograms and has a head height of 1.5 metres! Petifour and about five other tortoises arrived at D’Arros roughly 40 years ago after a one-week boat journey from their home island, Aldabra. By the 1900s giant tortoises had gone extinct on all the Outer Islands except remote Aldabra Atoll, where more than 100,000 of them persist to this day. In the 1970s the Seychelles government initiated an admirable conservation project in which several hundred tortoises from Aldabra were reintroduced to D’Arros and other Outer Islands.

Giant tortoises are a vital component of the island ecosystem as their voracious appetite ensures that the herbaceous layer does not grow out of control. Possessing comical charisma and prehistoric fierceness in equal measure, these tortoises are very interesting to observe and interact with. Petifour in particular appears to enjoy human interaction and will approach anyone within sight, hissing and gaping his sharp beak belligerently. Fortunately, scratching his leathery neck or feeding him a treat easily subdues him. His other favourite pastimes include crushing bicycles, lying in the sprinkler and mating. The last is his favourite occupation and has resulted in the gradual growth of the tortoise community.

Massive land crabs are common along the beaches of the atoll and raise their pincers threateningly at passers-by. Hermit crabs hide in the shady forest by day, but at night millions of them migrate to the beach to feed on anything that the tide has washed up. Ghost crabs are also especially abundant, scuttling along the beach and building elaborate holes. Despite going extinct in the Amirantes several decades ago, the giant robber crab is slowly making a reappearance.