Larval Dispersal Modeling of Pearl Oyster Pinctada margaritifera following Realistic Environmental and Biological Forcing in Ahe Atoll Lagoon

Abstract

Studying the larval dispersal of bottom-dwelling species is necessary to understand their population dynamics and optimize their management. The black-lip pearl oyster (Pinctada margaritifera) is cultured extensively to produce black pearls, especially in French Polynesia's atoll lagoons. This aquaculture relies on spat collection, a process that can be optimized by understanding which factors influence larval dispersal. Here, we investigate the sensitivity of P. margaritifera larval dispersal kernel to both physical and biological factors in the lagoon of Ahe atoll. Specifically, using a validated 3D larval dispersal model, the variability of lagoon-scale connectivity is investigated against wind forcing, depth and location of larval release, destination location, vertical swimming behavior and pelagic larval duration (PLD) factors. The potential connectivity was spatially weighted according to both the natural and cultivated broodstock densities to provide a realistic view of connectivity. We found that the mean pattern of potential connectivity was driven by the southwest and northeast main barotropic circulation structures, with high retention levels in both. Destination locations, spawning sites and PLD were the main drivers of potential connectivity, explaining respectively 26%, 59% and 5% of the variance. Differences between potential and realistic connectivity showed the significant contribution of the pearl oyster broodstock location to its own dynamics. Realistic connectivity showed larger larval supply in the western destination locations, which are preferentially used by farmers for spat collection. In addition, larval supply in the same sectors was enhanced during summer wind conditions. These results provide new cues to understanding the dynamics of bottom-dwelling populations in atoll lagoons, and show how to take advantage of numerical models for pearl oyster management.

A Parallel Population Genomic and Hydrodynamic Approach to Fishery Management of Highly-Dispersive Marine Invertebrates: The Case of the Fijian Black-Lip Pearl Oyster Pinctada margaritifera

“…Work by Thomas et al [107] in French Polynesia on connectivity between populations discovered that larval sink and source locations for P . margaritifera accounted for 26% and 59% of the variation observed respectively, underscoring its importance for larval supply and management of farmed and wild pearl oysters.…”

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

“…Our results seem to indicate that the northeastern samples are not well connected to the rest of the lagoon: they are made of larger, older individuals, mostly females (up to 86%), all with a specific "northeastern" genetic signature, meaning they are not replenished by larval recruitment from either the exploited stock, or the southwestern natural stock. Previous research using modelling of larval dispersal showed the existence of two hydrodynamic systems in Ahe, separating the northeastern lagoon from the southwestern lagoon [7]. The model showed that wind and resource distribution patterns averaged over the years favored two dominant dispersal dynamics: (i) self-recruitment within each hydrodynamic system and (ii) east to west transfers, but very rarely west to east transfers [7,8].…”

“…Among the six sets of collectors deployed in the lagoon, the set #6 could not be located in May and was considered lost. From the five collectors left, we collected a total of 41 individuals (21,8,7,4 and 1 individual from C3, C5, C1, C4 and C2 respectively).…”

“…), including in Ahe, a well-studied and historically highly successful collecting lagoon. There, larval dispersal has previously been modeled in an attempt to identify dispersal routes and their correlation with various environmental drivers [6][7][8]. This research allowed for a better prediction of "sink" locations, where larvae would accumulate under particular wind regimes and environmental conditions and contributed to make spat collection more efficient throughout the year.…”

“…Nowadays, multiple techniques can be used to characterize the geographical and demographical origin of individuals: direct tagging of individuals using fluorochromes, dispersal modelling, [7,[12][13][14][15][16] or parentage analysis through the use of genetic markers [17,18]. Genetic markers also have the advantages to inform about the putative genetic diversity of the parental populations as well as demographic parameters such as the estimated number of adults reproducing in a population.…”