Comparison of in situ black-lipped oyster spat collection and larval dispersal modelling results in semi-closed pearl-farming lagoons of the Tuamotu Archipelago.

Spat collection of the pearl oyster Pinctada margaritifera in atoll lagoons of French Polynesia is the fundamental sustain of black pearl farming. Spat collection has always yielded variable results in space and time, but obvious signs of steady decreases, even collapses, have emerged in several lagoons. Spat collection materializes the ecological connectivity pathways between wild spawning populations and the location of artificial larval settlement substrates. To assess if oyster larval dispersal modelling could capture such pathways, we compared four six-week long spat collector deployment periods with dispersal simulations in two different lagoons. Spat collectors displayed wide spatial and temporal variations. Numerical modelling and field experiments were generally not in agreement. Although both methods have limitations, they can still approximate each other. But the accuracy of model simulations cannot be ascertained with spat collection data only. Using a SWOT (Strength-Weakness-Opportunities-Threats) analysis, we emphasize the complementarity of both approaches for management decisions.

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.

Mismatch between the ecological processes driving early life-stage dynamics of bivalves at two contrasting French Polynesian lagoons.

The pearl-farming industry depends mostly on the natural recruitment of pearl oysters. Little is known about the relative influence of different ecological processes on the natural recruitment of pearl oysters across biogeographical scales. Spatio-temporal dynamics of bivalve larvae and spats were described at Ahe and Mangareva, 1500 km apart across French Polynesia. We quantified the effect of candidate environmental predictors on the dynamics of larvae. Both lagoons showed similar temporal dynamics with twice more larvae and 6 times more spat in Ahe. Pinctada maculata spat were more abundant than for P. margaritifera at both lagoons. While the temporal dynamics in larvae abundance were best explained by a positive effect of temperature in Ahe, the dynamics in Mangareva were poorly predicted by the environmental variables, meaning bivalve early-life stages perform better in Ahe than Mangareva suggesting a mismatch between the relevant environmental forces driving larval dynamics at these two contrasting lagoons.

Understanding connectivity of pearl oyster populations within Tuamotu atoll semi-closed lagoons: Cumulative insight from genetics and biophysical modelling approaches.

Connectivity affects species demography, (meta)population dynamics, evolution, phylogeny and biogeography. Various methodological approaches are applied to measure connectivity. Biophysical modelling can explore systematically the influence of atmospheric, oceanic and ecological forcing, while genetics measures connectivity patterns within the sampling strategy limit. In the Pacific Ocean pearl farming lagoons, the activity relies on spat collecting of the black lipped pearl oyster Pinctada margaritifera occurring after the larval dispersal phase, which follows spawning from wild or farmed populations. Biophysical 3D modelling and genomic studies have both separately brought insights on within-lagoon connectivity and on the origin of spats. Here, we combined previous genetics results with new realistic biophysical modelling scenarios to elucidate connectivity in Ahe Atoll lagoon. When combined, we identified the weather sequence likely explaining the realized connectivity observations. We discuss the strengths, weaknesses, opportunities and threats of combining these two approaches considering specific pearl farming demographic connectivity questions.

Dynamic Energy Budget model suggests feeding constraints and physiological stress in black-lip pearl oysters, 5 years post mass-mortality event.

Mass-mortality events of marine species can disturb the structure of communities. While identifying the causes of mass-mortality events is crucial for implementing recovery strategies, monitoring is challenging in remote locations. Black-lip pearl oysters (Pinctada margaritifera) are farmed for producing black pearls within remote atolls of French Polynesia. Previous mass-mortality events have resulted in the collapse of oysters and other species; however, the causes and conditions that favour recovery are unclear. We investigated the potential for oyster population recovery 5 years after a mortality event at Takaroa Atoll (Tuamotu Archipelago). Temperature, food availability (total chlorophyll-a), growth and reproduction were monitored. Growth was also simulated using a Dynamic Energy Budget model. Despite favourable conditions, reduced growth and reproduction signalled an energetic deficit. The model overpredicted growth, and supported the hypotheses that individuals are unable to profit from the phytoplankton available and maintenance costs are high in Takaroa, ultimately explaining their poor physiological condition.

Correction: Reisser, C.M.O. et al. Population Connectivity and Genetic Assessment of Exploited and Natural Populations of Pearl Oysters within a French Polynesian Atoll Lagoon. Genes 2020, 11, 426.

The authors wish to make the following corrections to this paper [...].

Population Connectivity and Genetic Assessment of Exploited and Natural Populations of Pearl Oysters within a French Polynesian Atoll Lagoon.

In French Polynesia, the production and exportation of black pearls through the aquaculture of the black-lip pearl oyster Pinctada margaritifera provide the second largest economic income for the country after tourism. This industry entirely relies on the collection of natural spats from few highly recruiting lagoons. In recent years, pearl oyster producers have experienced variable success rates in spat collection, with significant spatial and temporal variability in spat supply, driving uncertainty in the future of pearl production. This study combines, for the first time in a farmed lagoon, genetic (SNPs), demographic (sex ratio, age), and biophysical data (larval dispersal modelling) to shed new light on population dynamics, connectivity, and spat recruitment in Ahe Atoll, a well-studied pearl farming site. Our results indicate that the geographical structuring of the natural populations and the contribution of both natural and exploited stocks to the production of spats result from the interaction of hydrodynamic features, life history traits and demographic parameters: the northeastern natural populations are older, not well connected to the southwestern natural populations and are not replenished by larvae produced by adjacent exploited populations. Moreover, we observe that the exploited populations did not contribute to larval production during our experiment, despite a sampling period set during the most productive season for spat collection. This is likely the result of a strong male bias in the exploited populations, coupled with a sweepstakes reproductive strategy of the species. Our results warrant further investigations over the future of the northeastern older natural populations and a reflection on the current perliculture techniques.