Aldabra
Aldabra is a significant coral atoll located in the Seychelles, part of the western Indian Ocean, and is recognized as a UNESCO World Heritage Site due to its unique biodiversity and high degree of endemism. Covering an area of approximately 174 square miles (450 square kilometers), it comprises four large coral islands that encircle a shallow lagoon, creating a pristine environment largely untouched by human activity. The atoll is characterized by its rocky terrain, minimal freshwater sources, and a climate that experiences seasonal variations, with warm temperatures and a monsoon season contributing to annual rainfall.
Aldabra is home to a remarkable array of flora and fauna, including the famous Aldabra giant tortoise, which boasts the largest population of its kind on Earth. Additionally, the atoll supports numerous endemic species, including various birds, a unique lizard, and a fruit bat species. The marine ecosystem surrounding Aldabra is rich with coral, fish, and invertebrates, although the area has been relatively understudied compared to its terrestrial environments.
Conservation efforts are paramount in Aldabra, which has successfully maintained its ecological integrity due to its isolation and strict regulations against human settlement and exploitation. However, challenges such as invasive species, climate change, and rising sea levels threaten its delicate ecosystem. Scientific research on Aldabra continues to be vital for understanding evolutionary processes and monitoring environmental changes, ensuring that this unique biome remains a focus of global conservation efforts.
Aldabra
- Category: Marine and Oceanic Biomes.
- Geographic Location: Africa.
- Summary: Aldabra is a pristine atoll with a high degree of endemism that makes it a United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage Site and a prize for scientists and naturalists.
Aldabra is among the very largest coral atolls in the world, with an area of approximately 174 square miles (450 square kilometers). It is part of the Seychelles island group in the western Indian Ocean, and is located 684 miles (1,100 kilometers) southwest of Mahé, the main island, and 261 miles (420 kilometers) north of Madagascar. The atoll is actually four large coral islands that enclose a shallow lagoon. These islands formed in the late Quaternary and now are surrounded by coral reefs. Climate can vary throughout the year, with maximum mean temperatures of 88 degrees F (31 degrees C) in December and minimum temperatures of 72 degrees F (22 degrees C) in August. An average 43 inches (1,100 millimeters) of rainfall occurs each year, with the northwest monsoon winds bringing the heaviest rainfall from November to March. The terrain is rocky, with little soil, and freshwater is virtually absent, so native organisms have adapted to the abundant ocean water. The tides have major influences on all life, especially within the lagoon, which drains regularly.
The Aldabra atoll is one of the most isolated and pristine biomes on Earth. Its location and environment have kept it from much human disturbance. These factors have also contributed to the extreme degree of endemism (evolution of unique species that fit an isolated biome) across many taxonomic levels on Aldabra.
Flora and Fauna
The atoll is home to large seabird colonies; breeding sea turtles, including the threatened green sea turtle (Chelonia mydas) and hawksbill sea turtle (Eretmochelys imbricate); the last Western Indian Ocean flightless-bird species, the white-throated rail (Dryolimnas cuvieri); and the largest population of giant tortoises on Earth. The atoll is a refuge for 13 endemic bird taxa, including two species—the Aldabra brush warbler (Nessilas aldabrana) and the Aldabra drongo (Dicrurus aldabranus)—and 11 subspecies. An endemic lizard race (Phelsuma abbotti abbotti) and an endemic fruit bat race, the Aldabra Flying Fox (Pteropus seychellensis aldabrensis), also inhabit the atoll. The most widely known of the endemic species is the Aldabra giant tortoise (Dipsochelys dussumieri), which has a healthy population of more than 100,000 individuals.
Offshore reefs house many species of corals, fish, and marine invertebrates. Mangroves and seagrass beds grow along the shoreline. The land supports around 180 species of flowering plants, with 20 percent being endemic.
Conservation and Management
Overall, Aldabra has been spared the fate of many other island environments and is relatively intact. The atoll is not conducive to human presence, which has deterred settlement and exploitation. Development was briefly considered in the 1960s, however, when the British government considered constructing an air-staging outpost until international outcry from scientists caused the proposed development to be abandoned.
The Royal Society of London began a full inventory of the atoll's features that lasted until 1979. At that point, management was handed over to the Seychelles government and, specifically, to the Seychelles Island Foundation (SIF), which has been successful in conserving the biome through consistent monitoring and management. Tourism is strictly regulated, and the logistics of visiting the atoll have deterred most prospective visitors. The largest threats to this biome are invasive species (including cats, rats, and goats), global climate change, and oil spills from increasing energy development in the Indian Ocean region.
Aldabra's conservation was further ensured by its designation as a UNESCO World Heritage Site in 1982 and as an endemic bird area by BirdLife International. International support has also come from the Global Environment Facility of the World Bank. Funding to renovate the research station and to provide the resources for a complete management, science, and conservation plan has been influential in establishing Aldabra as a location of immense scientific activity.
Perhaps the gravest threat on the horizon is global warming; with much of the atoll no more than 6 or 7 feet (about 2 meters) above sea level—the highest ground is just 26 feet (8 meters)—this danger is very real in light of sea-level rise as well as the increase in cyclone intensity due to higher ambient water temperatures. Indeed, sea-level rise is cited as a major threat in various studies of endangered species on Aldabra, in particular for those biota that inhabit either the intertidal realm or even the more inland niches that in the case of Aldabra are extremely close to the sea's direct influence. Among such fauna are the snail species Kaliella aldabra and Cyathopoma picardense.
Scientific Studies
The biome is well suited to scientific investigations, especially of evolution. In fact, Aldabra was described by the US Academy of Sciences as “an ideal location for the scientific study of evolutionary processes in a relatively closed environment.” Indeed, a large amount of research has been done on the evolution of the endemic species and populations of this atoll. Most research has focused on the terrestrial environment—specifically the birds, giant tortoises, and invertebrate communities. With the worry over climate change, scientific studies have also begun to examine the changes in climate by studying coastal lines and shifting weather patterns on the island. One study revealed that despite rising sea levels, the coastal line of the island remained relatively stable for fifty years.
The unique marine environment has been comparatively understudied, with only about 25 percent of the published scientific work involving these ecosystems. This shortcoming is minor, however, compared with the conservation concerns of many other imperiled biomes worldwide. No doubt the Aldabra atoll will persist into the future, due to its conservation designation and its importance to scientific inquiry.
Bibliography
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