Strategies for Successful Scallops Spat Collection on Artificial Collectors in the Taranto Gulf (Mediterranean Sea)

The high variability in natural recruitment of Pectinidae is a common feature of many marine invertebrates with a pelagic larval stage, but may negatively affect aquaculture activities. Detailed information on settlement patterns and spat availability is required to reduce costs and labor. In this regard, we attempted to establish the precise immersion time and the deployment dates for spat collectors in the Taranto Gulf (Mediterranean Sea, Italy). The first experiment was carried out from June to October 2013, deploying collectors every 15 days and retrieving them after 4, 6, 8, and 10 weeks. Results from the first experiment allowed us to select 8 weeks as the best immersion time for spat collection. The second experiment was carried out from June 2013 to July 2014 when we deployed spat collectors every 15 days and recovered them after 8 weeks to detect the favorable periods to place the collectors in water to obtain the highest scallop spat harvest rate. Mimachlamys varia was the most abundant pectinid (greater than 90%), whose recruits were collected during most of the year studied, followed by Flexopecten glaber with the highest rates in July (87%) and Pecten jacobaeus, which never exceeded 17% of collected spat. M. varia had a long recruitment period (from October to early June), F. glaber showed a high number of spat during autumn months and from June to July while P. jacobaeus showed a restricted period of spawning. Our experiments provide useful insights into strategies for establishing scallop aquaculture in order to promote these mollusks as alternative candidates for aquaculture farming in the area.

Feeding and growth coupling during different development larvae phases of the Mediterranean mussel Mytilus galloprovincialis L. from Amsa Bay

Spat supply for mussel farming in Morocco is essentially based on seed capture and collection from natural beds. However, natural irregularity recruitment in exploited areas and encountered difficulties during spat collection operations have led to develop and improve reproduction techniques under controlled conditions in hatcheries. The present study focused on the larvae phase aiming at assessing growth rate varies between different development stages. Trocophore larva stage had a size of 63.25 μm and reached the pedivilegere stage with a size of 272.56 μm in 18 culture days. Length growth was more significant than width growth for both H-batch and T-batch. For instance, larvae grew in terms of length quickly in H-batch than T-batch (11.10± 1.30 and 9.67 ± 1.17 μm day-1), and the same pattern was observed for T-batch larvae. Inversely, the total biomass consumed was higher during T-batch larvae rearing than H-batch ones. In contrast, the effect of feeding on growth was observed more significantly for H-batch larvae (t=7.55, df=23, p<0.001) than T-batch ones (t=4.13, df=23, p<0.001). However, the specific feeding effect was revealed higher for I. galbana for both batches rather than C. calcitrans and T. suecica. However, the larvae growth reduction is linked to the beginning of tissue synthesis.

Evaluating the effectiveness of local materials for the wild oyster (Crassostrea tulipa Lamarck, 1819) spat collection in four coastal waterbodies in Ghana

The West African mangrove oyster, Crassostrea tulipa (Lamarck, 1819), has the potential to improve global shellfish food production and is being considered for commercial farming in many countries in West Africa. The current background information to support this venture is, however, inadequate especially with respect to identification of suitable materials for optimal collection of spat for large-scale production. We assessed the effectiveness of five locally available materials (coconut shell, oyster shell, nylon mesh, PVC, and ceramic tile) for harvesting C. tulipa spat from the Densu Delta, Narkwa Lagoon, Benya Lagoon and Whin Estuary, along the coast of Ghana from November 2017 to October 2018. Ceramic tile had the highest mean monthly spat settlement in the Narkwa Lagoon (3451 ± 206 spat m-2), Benya Lagoon (1769 ± 145 spat m-2) and Whin Estuary (373.1 ± 52.4 spat m-2). This settlement was not significantly different from settlement on PVC slats (P > 0.05). Coconut shell consistently had the least C. tulipa spatfall in all four coastal water bodies (P < 0.05). The under-horizontal surfaces of collectors, [mean (S.E.); 2523.7 ± 66.9 spat m-2] had significantly more C. tulipa spatfall than upper-horizontal surfaces [mean (S.E.); 775.2 ± 33.4 spat m-2] in the main experiment (P = 0.000). In a separate experiment, a change of orientation from “Face down”/0° to “Face up”/180° did not change the observed profuse under-horizontal settlement of C. tulipa spat on the collectors, suggesting that under-horizontal surfaces were more attractive to C. tulipa spat. Larger-sized C. tulipa spat on under-horizontal surfaces, mean (S.E.) 9.88 ± 0.5 mm, compared to upper-horizontal surfaces, mean (S.E.) 5.99 ± 0.5 mm, of the collectors suggest earlier settlement on the undersides. Ceramic tiles and PVC slats were the most effective materials for C. tulipa spat collection, hence, their use recommended for large-scale C. tulipa farming.

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.

Recruitment of oyster in artificial collectors on the Amazon macrotidal mangrove coast

ABSTRACT: The purpose of this study was to determine the moment of the year for the oyster recruitment and define the type of collector and environmental conditions that maximize recruitment. Collections were conducted, during 12 months, on Amazon Macrotidal Mangrove at two different sites: raft (point I) and mangrove (point II). In each location three types of collectors were used (1) transparent PET bottles, (2) green PET bottles, and (3) PVC sheets, each with three replicates. Spats were counted and measured at 45-day intervals, while the environmental data were measured every two weeks. Identification of oyster species occurred by genetic testing (multiplex PCR) by randomly selecting individuals by sampling. Results indicated spat capturing was significantly influenced by the collector type, location and period of collection (P<0.05, MANOVA) with significantly higher recruitment in the PVC collector (P<0.05, Tukey test). Oyster recruitment occurred throughout the year, suggesting that these individuals reproduce during all months; however, months with less rain and greater salinity were the best for spat collection, while the rainy period with lower salinity proved to be the best for individuals growth. The location in interaction with the environmental variables, mainly salinity, has a significant effect on the recruitment rate of spat and on their size, so that point II (mangrove) had the best results for recruitment and point I (raft) provided the spats of the largest size. Genetic identification verified two native oysters species (Crassostrea gasar and Crassostrea rhizophorae) in both points (I and II).

Evaluation of reproduction for mussel Mytilus trossulus (Bivalvia: Mytilidae) in the Veselaya Bay (Tauiskaya Guba Bay, Okhotsk Sea)

Abundance, size composition, and terms of plankton stage were investigated for the larvae of pacific mussel in the Veselaya Bay (Okhotsk Sea) in two years with different oceanographic regime. The first larvae (density 8-30 ind./m³, shell length 75–150 μm) appeared in late June in the year with relatively high water temperature (2016) and in early July in the year with lowered temperature (2011), then their number had increased to 1750 ind./m³ in early August of 2016 and to 1320 ind./m³ in late August of 2011. Density and size composition of the spat and young mussels were examined in hanging collectors and nurseries. The growth rate change in dependence on shell length was noted. There is concluded that the hanging collectors are more effective for spat collection, while the nurseries are better for growing of littoral mussels.