Vairao (Tahiti), November 2025 – The MaHeWa project has reached an important milestone with the completion of the first experimental simulation of marine heatwaves applied to the orbicular batfish Platax orbicularis, locally known as Paraha peue. This species is emblematic of Polynesian lagoons and holds aquaculture interest for the fenua. The experimental setup was designed and implemented during the mission of Benjamin Geffroy (Ifremer – UMR MARBEC, Montpellier), who supported the Ifremer team in Vairao in preparing the system and launching the trials.
As part of the MaHeWa project, a team from the Louis Malardé Institute (ILM) is currently conducting fieldwork in the Gambier Islands, French Polynesia. This mission is part of Work Package 2 – Task 2.2, which focuses on studying the impacts of harmful algal blooms (HAB), particularly those related to ciguatera, a marine foodborne intoxication caused by microalgae of the genus Gambierdiscus.
The objective of this mission is to understand how marine heatwaves influence the presence, growth, and toxicity of these microalgae in Polynesian lagoons. The research conducted will contribute to assessing the physiological costs associated with thermal tolerance and the functions affected during these extreme warming events.
In the field, researchers monitor the genetic composition of natural Gambierdiscus populations as well as their toxicity levels. Two environmental monitoring stations have been installed: one in Rikitea Bay and the other in Gatavake Bay. These stations will make it possible to examine how temperature, light, and salinity shape the dynamics of these toxic microorganisms. The collected data will support efforts to anticipate ciguatera risks, which represent a major public health concern and a key ecological resilience issue in the Pacific region.
This mission is led by Mireille Chinain (ILM, EIO). The Municipality of the Gambier Islands has encouraged residents not to handle the monitoring instruments, as the data gathered will be valuable for all the islands and will contribute to protecting Polynesian lagoons in the face of climate change.
Māuruuru to the ILM team for its commitment to advancing science and safeguarding marine life.
As part of WP2 of the MaHeWa project — and specifically Task 2.2, which focuses on the impacts of harmful algal blooms (HAB), including ciguatera — a major new study has just been published in the journal Harmful Algae. Entitled “Gambierdiscus polynesiensis from New Caledonia (South West Pacific Ocean): Morpho-molecular characterization, toxin profile and response to light intensity”, this article includes contributions from two MaHeWa researchers: Thierry Jauffrais and Manoella Sibat.
The study focuses on Gambierdiscus polynesiensis, a dinoflagellate known for producing neurotoxins involved in ciguatera fish poisoning. In New Caledonia, where knowledge gaps persist regarding the phenomenon and the microalgae responsible, the authors describe a newly identified strain of G. polynesiensis — the first recorded outside the Polynesian archipelago. They also provide its toxin profile and its response to different light intensities.
This work directly supports the objectives of WP2, coordinated by G. Mitta (Ifremer, French Polynesia), which seeks to understand the effects of marine heatwaves on coral ecosystems and biosafety, particularly through the lens of ciguatera. The results offer critical insights into the environmental conditions that enhance the toxicity of these microalgae, contributing valuable elements for anticipating and managing public health risks.
This discovery marks an important step for New Caledonia, where ciguatera represents a major health challenge. By clarifying the behaviour and toxin production of G. polynesiensis, this study strengthens the scientific foundation needed for improved prevention and protection of both communities and marine ecosystems.
The article is available online:
— Publisher’s version: https://doi.org/10.1016/j.hal.2025.102859
— Open Access version: https://archimer.ifremer.fr/doc/00948/105952/
This research was also presented at the International Symposium on Ciguatera Poisoning in the Pacific Islands, held from 19 to 22 May 2025 in Nelson, New Zealand.
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