Understanding marine larval dispersal in a broadcast-spawning invertebrate: A dispersal modelling approach for optimising spat collection of the Fijian black-lip pearl oyster Pinctada margaritifera

Identifying the source populations supplying a vital economic marine species for the New Zealand aquaculture industry

Aquaculture of New Zealand's endemic green-lipped mussel (Perna canaliculus) is an industry valued at NZ$ 336 M per annum and is ~ 80% reliant on the natural supply of wild mussel spat harvested at a single location-Te Oneroa-a-Tōhē-Ninety Mile Beach (NMB)-in northern New Zealand. Despite the economic and ecological importance of this spat supply, little is known about the population connectivity of green-lipped mussels in this region or the location of the source population(s). In this study, we used a biophysical model to simulate the two-stage dispersal process of P. canaliculus. A combination of backward and forward tracking experiments was used to identify primary settlement areas and putative source populations. The model was then used to estimate the local connectivity, revealing two geographic regions of connectivity in northern New Zealand, with limited larval exchange between them. Although secondary dispersal can double the dispersal distance, our simulations show that spat collected at NMB originate from neighbouring mussel beds, with large contributions from beds located at Ahipara (southern end of NMB). These results provide information that may be used to help monitor and protect these important source populations to ensure the ongoing success of the New Zealand mussel aquaculture industry.

Reproductive condition of the black-lip pearl oyster Pinctada margaritifera during the lunar phase

This study analyzed the relationship between the lunar phase and the reproductive cycle of Pinctada margaritifera inhabiting Weno Island, Chuuk Lagoon, Micronesia. We measured indicators of maturity (gonadosomatic index [GSI] and sexual maturation-related genes) and investigated changes in the gonadal maturity stages (GMS) of P. margaritifera over lunar cycle. GSI was higher around the full moon. GMS of P. margaritifera were classified as the early gametogenesis stage, ripe and spawning stage, and spent and degenerating stage. A large percentage of oysters was observed in the ripe and spawning stage at the first quarter moon in female and the full moon in male as well as in the spent and degenerating stages at the third quarter moon in both sexes. In addition, the expression of doublesex- and mab-3-related transcription factor 2 (DMRT2) in the male P. margaritifera black-lip pearl oyster was the highest during the full and third quarter moon phases, whereas no difference in expression was observed with the lunar phase in females. In contrast, the expression of vitellogenin (VTG) was the highest in female P. margaritifera during the first and third quarters. No difference in expression was observed according to the lunar phase in males. The results suggest that the lunar phase directly affects the expression of sexually mature gonads in P. margaritifera black-lip pearl oyster.

Genetic and particle modelling approaches to assessing population connectivity in a deep sea lobster

The emergence of high resolution population genetic techniques, such as genotyping-by-sequencing (GBS), in combination with recent advances in particle modelling of larval dispersal in marine organisms, can deliver powerful new insights to support fisheries conservation and management. In this study, we used this combination to investigate the population connectivity of a commercial deep sea lobster species, the New Zealand scampi, Metanephrops challengeri, which ranges across a vast area of seafloor around New Zealand. This species has limited dispersal capabilities, including larvae with weak swimming abilities and short pelagic duration, while the reptant juvenile/adult stages of the lifecycle are obligate burrow dwellers with limited home ranges. Ninety-one individuals, collected from five scampi fishery management areas around New Zealand, were genotyped using GBS. Using 983 haplotypic genomic loci, three genetically distinct groups were identified: eastern, southern and western. These groups showed significant genetic differentiation with clear source-sink dynamics. The direction of gene flow inferred from the genomic data largely reflected the hydrodynamic particle modelling of ocean current flow around New Zealand. The modelled dispersal during pelagic larval phase highlights the strong connectivity among eastern sampling locations and explains the low genetic differentiation detected among these sampled areas. Our results highlight the value of using a transdisciplinary approach in the inference of connectivity among populations for informing conservation and fishery management.

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.

Screening of pharmaceuticals in coastal waters of the southern coast of Viti Levu in Fiji, South Pacific

The global reliance on pharmaceuticals coupled with the lack of effective treatment methods has resulted in pseudo-persistence of pharmaceuticals within the environment. Globally, efforts to quantify and monitor pharmaceuticals within the environment have been well underway, however few studies have been made within small Pacific Islands. This study aims at screening for the occurrence and concentration of pharmaceutical residues within the southern coastal waters of Fiji's main island, Viti Levu. Water samples were collected from a depth of ca. 0.6 m from seven sites and were analyzed for 80 pharmaceuticals via a combination of chromatography and heated electrospray ionization. Seventy-two pharmaceuticals were quantified at least once with average concentrations ranging between 0.04 ng/L (diltiazem) and 19 ng/L (ketoconazole), and with all but two pharmaceuticals (trimethoprim and biperiden) being present in less than 50% of the samples. Findings suggest that even though the release of pharmaceuticals into the marine environment is sporadic and pharmaceuticals are diluted via turbulent mixing, there are measurable concentrations of pharmaceuticals in Fiji and these pollutants are not necessarily restricted to highly populated areas.