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Reintroduction of giant tortoises in Aride recorded rapid effects on vegetation, soil, and native seed dispersal, according to researchers who observed ecological processes not seen on the island for almost two centuries.
The reintroduction of 10 Aldabra giant tortoises on the island of Aride, in the Seychelles, restored in six months ecological functions that had been absent for over 180 years, according to an international study published in the scientific journal Restoration Ecology and released on April 16, 2026, by the Doñana Biological Station, linked to the Spanish National Research Council.
During the monitoring of the animals after their release, the research identified effects on vegetation, soil, and native seed dispersal, with records that helped scientists measure the resumption of ecological processes on the island.
In two months, the tortoises spread more than 11,000 seeds, of which 89.5% belonged to native species, in addition to consuming 54 species of introduced plants, according to the data released by the team responsible for the study.
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The result was highlighted by the researchers because Aride had lost these ecological interactions almost two centuries ago, when the tortoises disappeared from the island and ceased to play a role in the natural dynamics of the vegetation.
Without these large herbivores, processes related to plant control, nutrient circulation, and local species regeneration ceased to occur at the same pace, according to the interpretation presented by the scientific team.
Giant tortoises and the impact on the island of Aride
The giant tortoises are classified by researchers as “ecosystem engineers” because they modify the environment while feeding, moving, and eliminating seeds in their feces, influencing different stages of plant regeneration.
This behavior, according to the study, helps connect areas of the island and favors the circulation of seeds of species adapted to the local environment, a process considered relevant for the recovery of lost ecological functions.
In field observations, the animals acted on three main fronts: reduction of exotic plants, acceleration of plant matter decomposition, and transport of native seeds to different points on the island.
With these interactions, scientists recorded conditions associated with the resumption of natural processes that had been interrupted or reduced after the disappearance of the tortoises from the region.
Aride is an island reserve of the Seychelles, an archipelago located in the Indian Ocean, where changes in fauna can have significant effects due to isolation and the smaller number of species compared to continental environments.
On small islands, according to conservation specialists, few species can concentrate important functions for the balance of vegetation and soil, making the loss or reintroduction of animals an ecological impact factor.
The study was conducted by researchers from the Doñana Biological Station, the National Museum of Natural Sciences, the Royal Botanical Garden, all linked to the CSIC, and the University of Exeter, in the United Kingdom.
To identify what each tortoise consumed, the team combined field observations, feces analysis, and DNA techniques, which allowed them to associate individual behavior with the effects recorded in the environment.
Seed dispersal showed differences between the animals
The research also pointed out behavioral differences among the reintroduced individuals, a fact considered relevant to assess how each animal contributed to the ecological restoration of Aride Island.
Only three of the ten tortoises accounted for more than 80% of the native seed dispersal in two months, while others had a greater role in the consumption of exotic plants or in nutrient recycling.
This result indicates, according to the researchers, that restoration programs do not only depend on the number of animals returned to the environment but also on the functions performed by each reintroduced individual.
For this reason, the team advocates that conservation projects evaluate which animals play broader ecological roles, as individuals of the same species can generate different effects in the ecosystem’s recomposition.
The case of the tortoise identified as T08 was used by the scientists to exemplify this variation in behavior observed during monitoring conducted after reintroduction on the island.
According to the study, this individual demonstrated greater efficiency in consuming exotic flora, strong native seed dispersal, and balanced ingestion of native and introduced plant matter compared to other monitored tortoises.
The finding led the researchers to highlight behavioral diversity within the same species as an element to be considered in ecological restoration actions.
On small islands, where the loss of an animal can affect different natural interactions, conserving individuals with varied habits can contribute to maintaining ecological functions, according to specialists involved in the study.
Species reintroduction and ecological restoration
The research data indicate that the reintroduction of a reduced number of turtles can restore ecological processes on islands affected by local extinctions, provided the action is scientifically planned and monitored.
This practice is known as rewilding, a term used for initiatives that aim to return species to areas where they performed relevant ecological functions before disappearing or having their populations reduced.
In the case of Aride, scientists observed that the turtles helped control exotic vegetation without relying solely on mechanical removal, a method that usually requires continuous work and prolonged maintenance.
When well monitored, biological restoration can reduce part of this operational demand, according to researchers, although it does not eliminate the need for technical monitoring and environmental risk assessment.
The study does not claim that any release of animals will produce the same result, nor does it indicate that reintroduction can be done without planning in other island ecosystems.
For this type of action, experts consider it necessary to evaluate species, environment, ecological history, health risks, and subsequent monitoring, especially on islands, where imbalances can spread quickly.
The Aldabra giant tortoise, whose scientific name is Aldabrachelys gigantea, is a species associated with the Seychelles and recognized for playing the role of a large terrestrial herbivore.
By consuming fruits, leaves, and plant matter, this species influences the structure of the landscape and the distribution of plants, mainly through feeding, movement, and seed dispersal.
Researchers advocate that future restoration initiatives consider the so-called effective number of individuals capable of sustaining ecological functions, and not just the total number of animals reintroduced.
This concept broadens the traditional analysis, which usually prioritizes the genetic viability of a reintroduced population, by also including the individuals’ ability to recover natural processes in the environment.
Numbers recorded in Aride draw attention
The data recorded in Aride show that the recovery of ecological interactions can begin in a short period when a key species returns to occupy a space from which it had disappeared.
The six-month interval does not represent complete restoration of the island, but indicates, according to the study, that functions previously absent were measurably resumed after the reintroduction of the turtles.
The dispersal of more than 11,000 seeds in two months helps to gauge the extent of the process recorded by scientists during the initial monitoring of the animals.
As nearly nine out of ten seeds belonged to native species, the movement of the turtles may favor the regeneration of original vegetation in areas where introduced plants have gained space.
The consumption of 54 exotic species was also recorded as relevant data because invasive plants can compete with local flora for light, water, and nutrients.
By feeding on these species, the turtles reduce some of the pressure on native vegetation and alter the growth dynamics in the territory, according to the researchers’ assessment.
The research in Aride can serve as a reference for studies on other islands, including archipelagos where giant turtles perform similar functions, although they belong to different evolutionary lineages.
The comparison between environments allows for the evaluation of conditions under which the reintroduction of large herbivores can accelerate natural restoration processes, without replacing the need for long-term scientific monitoring.
For scientists, the return of a species should not be measured only by the survival of released animals, but also by the recovery of ecological interactions associated with the functioning of the environment.
In the case of Aride, records indicate that the turtles moved seeds, influenced vegetation, participated in nutrient recycling, and restored ecological functions that had been absent for over 180 years.
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