The alteration of ecosystem functioning following the introduction of invasive alien species is particularly damaging, both for the environment and for economic activities. This project aims to characterize the effects of three introduced species on biodiversity and ecosystem functioning across many islands of French Polynesia. Using the Tetiaroa Atoll as a natural laboratory, we will focus on the coconut palm Cocos nucifera, which is the target of a management plan on the atoll; the mosquito Aedes polynesiensis, which is the target of a future eradication program on Tetiaroa; and the Western honey bee Apis mellifera, whose ecological functions on atolls remain poorly understood.
This PhD project will investigate the effects of these species on terrestrial crabs, soil fauna, seabird communities, and pollinating insect communities, as well as on a set of key ecosystem functions (nutrient fluxes, litter decomposition, and pollination). The project will thereby support informed decision-making regarding the management of introduced species by anticipating the likely indirect effects of management actions.
Developed for and with Michael Demortier, a student aiming to pursue an academic career in French Polynesia, and in collaboration with Hervé Bossin (ILM), this PhD project will build a bridge between three ongoing projects led by institutions with complementary expertise: the InvEcoF project, led by IRD and UPF and funded by the ANR; the TAME project, led by ILM and Pacific Beachcomber; and the TARP project, led by the Tetiaroa Society FP.
Summary of field activities
A survey of brown booby (Sula leucogaster) nests was conducted on the three islets (motu) hosting the largest breeding colonies, namely Horoatera, Tiarauunu, and Tahuna Iti. This activity aimed to assess the impact of mosquitoes on the species’ reproductive success.
Mosquito trapping campaigns were conducted simultaneously within the colonies. Cameras were installed near nests to document potential irritation or stress-related behaviors associated with high mosquito densities.
Several parameters were measured, including the distance of nests from the vegetation line, the size of laid eggs, and the monitoring of hatched eggs from hatching through to the fledging stage.
Mosquitoes were captured within the colonies on the three motu in triplicate using BG-Pro traps provided by Hervé Bossin’s team (ILM, Paea). Targeted collections were also conducted directly at individual nests using adhesive devices.
Two main missions were carried out in July and late August 2025, bringing together three researchers in the field. These campaigns aimed to ensure post-eradication monitoring of crabs, seabirds and vegetation on several motu of the atoll.
In July, the team conducted capture-mark-recapture sessions of crabs on six beaches to estimate population sizes and analyze the morphology of the different species. These surveys, initiated before the 2022 eradication, now make it possible to measure the changes observed since the disappearance of the rats, particularly among ghost crabs. At the same time, the vegetation was characterized along 25 kilometers of coastal transects used since 2021 for monitoring seabirds.
The researchers also carried out maintenance on the camera traps—replacing batteries and SD cards—used to monitor the reproduction of the main seabird species, including red-footed boobies, lesser and Pacific frigatebirds, gray-backed terns, brown noddies, sooty terns, masked boobies, and great crested terns.
Camera traps were also installed on the sampled beaches, and acoustic recordings were made for two species of ghost crabs. During the late August mission, vegetation characterization was completed along the last ten kilometers of coastal transects. The researchers recovered the camera traps installed in July and continued monitoring brown booby nests, in collaboration with the team of B. Gardner and S. Converse from the University of Washington. Sites were selected for the ATTRACT program, and several nighttime capture sessions documented the morphology of ghost crabs on two beaches, including one at Tiaraunu, to expand the comparative database. These observations complete a coherent set of ecological monitoring designed to measure the rapid response of terrestrial fauna to the disappearance of introduced predators.
Impacts and preliminary results
Over the period from January to July 2025, a total of 590 brown booby (Sula leucogaster) nests were recorded. Nest distribution varied among the study sites, with 176 nests on Tahuna Iti, 265 nests on Horoatera, and 149 nests on Tiarauunu.
Initial results confirm a very positive evolution of terrestrial communities on motu cleared of rats. The diversity and abundance of crabs have increased significantly, particularly on islets where black rats were previously present. This rapid recolonization illustrates the central role of crabs in soil rehabilitation and the resumption of natural ecological cycles. Among seabirds, several encouraging signs have been observed. A pair of masked boobies successfully bred again, and the chick observed in August was healthy and about to fledge. This reproductive success demonstrates a gradual return to favorable nesting conditions and supports the idea that restoring terrestrial ecosystems directly benefits the marine species that depend on them. These preliminary results suggest that the eradication of rats on Tetiaroa has already led to a significant revitalization of terrestrial ecological networks, and that prolonged monitoring will allow us to better quantify the magnitude and stability of these changes.
Perspectives / Next steps
The next phases of the project will focus on in-depth analysis of the collected data and on linking nest inventory results with mosquito trapping data, in order to assess their potential influence on the reproductive success of the brown booby (Sula leucogaster). This analytical phase will be carried out in scientific collaboration with the teams of Beth Gardner and Sarah Converse, with the aim of integrating field-measured ecological parameters with indicators of reproductive success.
In addition, a new field campaign is planned for the October–November period, in connection with the study of Tahinu phenology, in order to incorporate seasonal vegetation dynamics into the interpretation of interactions between habitat, mosquitoes, and brown booby reproduction.
