Tide and wave driven flow across the rim reef of the atoll of Raroia (Tuamotu, French Polynesia)

A multivariate approach to synthetize large amount of connectivity matrices for management decisions: Application to oyster population restocking in the pearl farming context of Tuamotu Archipelago semi-closed atolls

In applied ecology, numerical biophysical modelling allows running numerous simulations of spatial connectivity between source and destination locations. To characterize population connectivity, larval dispersal and resulting connectivity matrices can be computed for various forcing conditions of wind, density of spawners, or pelagic larval durations. Here, we investigate a methodology to synthetize meaningfully all numerical experiments performed for three atoll lagoons in the Tuamotu Archipelago pearl farming context. The objective is to identify the best restocking locations that consistently maximize the spread of pearl oyster larval dispersal, considering all forcing conditions. A multivariate generic approach is used to process and synthesize time-series of connectivity matrices and identify afterward with contextual criteria the spawning locations that match a variety of specific connectivity, logistical and ecological criteria. Similar synthesis of large volume of connectivity matrices will likely gain momentum considering the increasing use of numerical models for applied science and population management.

Periodicity of wave-driven flows and lagoon water renewal for 74 Central Pacific Ocean atolls

French Polynesia atolls are spread on a vast 2300 by 1200 km Central Pacific Ocean area exposed to spatially and temporally dependent wave forcing. They also have a wide range of closed to open morphologies and several have been suitable to develop from black-lipped pearl oysters a substantial pearl farming activity in the past 30 years, representing nowadays the 2nd source of income for French Polynesia. Considering here only the component of lagoon renewal that is driven by waves, we investigate for 74 atolls different lagoon renewal metrics using 20 years of wave model data at 0.05° spatial resolution. Wavelet spectral analyses highlight that atolls, even in close vicinity, can be exposed to different and characteristic periodicities in wave-driven flows and water renewal. These characteristics are discussed in relation to pearl farming atolls, including atolls known to be efficient oyster spat producers, a critical activity for pearl farming sustainability.

The MANA (MANagement of Atolls, 2017-2022) project for pearl oyster aquaculture management in the Central Pacific Ocean using modelling approaches: Overview of first results

This editorial presents results of the MANA (MANagement of Atolls) project compiled in the form of a Marine Pollution Bulletin collection of 14 articles. MANA is a project funded by the French Agence National pour la Recherche that specifically addresses the development of knowledge and management tools for pearl farming atolls, with a focus on the spat collecting activity in French Polynesia. The 14 papers cover the range of thematic tasks described in the initial project, including atoll geomorphology and bathymetry, climate forcing, atoll lagoon and rim hydrodynamics, typology of atolls, evaluation of remote sensing data for monitoring atoll lagoons, and development of numerical models and spatially-explicit tools that altogether have contributed to the applied objectives. In addition, this editorial draws an update on the pearl farming industry in French Polynesia with the latest statistics, and discusses the next targeted priorities for research programs focusing on pearl farming atolls.

A systematic prioritization approach for identifying suitable pearl oyster restocking zones following a mass mortality event in Takaroa Atoll, French Polynesia

Oyster farming for black pearl production is central in French Polynesia. It is the second source of national income and provides substantial job opportunities, notably in remote atolls. However, this sector has been undermined by successive crises, such as mass-mortalities of wild and farmed oyster stocks that have impacted entire lagoons. An option to revive the activity consists of reintroducing oysters in strategic benthic locations selected to maximize reproduction and dispersal of larvae throughout the lagoon, hence promoting recolonization and spat collection for farming. For Takaroa, a Tuamotu atoll recently impacted by mortalities, a systematic prioritization approach identified these restocking sites, using environmental and socio-economic criteria such as: location of suitable habitats for oyster settlement, larval connectivity estimated from hydrodynamic circulation model, farming waste accumulation, and opportunity cost to fishers and farmers who lose access to restocking areas. This approach provides managers with a portfolio of restocking options.