Spat Recruitment Research Articles

Evaluation of bivalve spat recruitment in artificial collectors to identify potential species for small-scale farming in the north Pacific coast of Colombia

Decreases in fish stocks have led to new resource research, particularly in the Colombian Pacific where only a few species have traditionally been exploited. Among commercial species, bivalves are commonly implemented in small-scale aquaculture and their success and sustainability depend on consistent larval recruitment. Therefore, we evaluated the spat recruitment of some bivalves species and their potential for marine aquaculture in the north Colombian Pacific. To assess their potential, artificial substrates were exposed to different depths (3, 6, 9, and 12 m) during three immersion times (two, four, and six months) in five collecting stations along Bahía Cupica (Chocó department). Only Pinctada mazatlanica (Hanley, 1856) spat were recruited over the entire period, reaching up to 3.70 ± 5.76 individuals/collector (mean ± SD) on the external stations. Considering immersion times and depths, the highest recruitments were recorded after two months at 6 m depth. Also, two other species with potential commercial interest were recruited, Pinna rugosa Sowerby I, 1835 and Isognomon janus Carpenter, 1857. The densities and distributions of P. rugosa were very similar to P. mazatlanica; in turn, I. janus was the dominant species among the bivalve community. Hence, we highlight the potential of P. mazatlanica as an alternative resource in the north Colombian Pacific due to their continuous recruitment, as well as the potential exploitation of P. rugosa and I. janus due to their simultaneous recruitment. Furthermore, we highlight the benefits of cultivating these species, and particularly P. mazatlanica, as could significantly improve the economy and food security of local communities.

CONSTRUCTED OYSTER REEFS AS SEDIMENT STABILISERS AND ECOLOGICAL ENGINEERS: A DUTCH CASE STUDY

Global degradation and the collapse of valuable coastal ecosystems has resulted in major efforts to reestablish ecosystem engineering species that provide valuable services like ecosystem-based coastal defense (EBCD). However, conditional outcomes of ecosystem engineering effects make it hard to predict the services provided by such restored systems. In this study we focused on reefs constructed with Crassostrea gigas shells on a sand nourishment at the Oesterdam, in the Oosterschelde tidal bay in the Netherlands. We investigated how the environmental setting, waves and currents, influence sediment stabilisation, as well as oyster spat recruitment and the development of associated biodiversity.

Bivalve Spat (Anadara granosa) recruitment in rehabilitation mangrove ecosystem of Rangsang Island, Riau province

Southeast Asia's mangrove areas are inhabited by several bivalves, such as the blood clam (Anadara granosa), which are widely distributed in intertidal areas. The importance of economic value of bivalves causes the availability of seeds to be very important. Knowing the abundance and life cycle of bivalves (Anadara granosa) is the right step in estimating the ideal time to collect bivalves in an ecosystem. This study aimed to determine the abundance and time of attachment of bivalves (Anadara granosa) seeds in the rehabilitation mangrove ecosystem on Rangsang Island, Riau. The sampling method used is purposive sampling, consisting of two subzones, and each subzone is located in the intertidal zone, namely at the point of the highest tide and the highest low tide in the mangrove forest area. The results showed that A. granosa was more common in December (79100 ind/100 m2) with an average length of 7.67 (±3.94). The relationship between mangrove density and abundance of A. granosa has a strong relationship in December and January, with the length range of A. granosa being influenced (strong category) by pH and temperature.

Localized Placement of Breakwater Reefs Influences Oyster Populations and Their Resilience after Hurricane Harvey

Populations of the eastern oyster (Crassostrea virginica) have been historically declining due to both natural and anthropogenic stressors. In response, oyster reefs have been created with many different approaches. This study utilized intertidal reefs constructed with oyster shells recycled from local restaurants to provide oyster settlement substrate, reef-associated faunal habitat, and a barrier to prevent marsh erosion. The objective of this study was to determine how oyster population characteristics changed over four years (2016–2019) on five different reefs within Sweetwater Lake, Galveston Bay, Texas, with a secondary objective to examine how oyster populations responded after Hurricane Harvey. Over the study period, five different reefs were sampled each summer by removing five bags per reef to determine oyster abundance and size demography. For the three years of the study (2017–2019), we also quantified oyster spat recruitment to the reefs. Oyster abundance and size (shell height) varied interactively by year and reef number, whereas oyster recruitment was significantly lower following Hurricane Harvey and then returned to pre-storm levels. Our results further highlight the importance of reef placement for breakwater-style reefs, as it appears the hydrodynamics within Sweetwater Lake influenced both oyster abundance and size among individual reefs. While the created reefs receive limited larval influx due to the narrow opening between Sweetwater Lake and Galveston Bay proper, this limited connectivity seemed to prevent mass mortality from the freshwater influx from Hurricane Harvey. Therefore, projects creating oyster reefs should consider local and regional landscape factors for the long-term success of oyster populations and robustness to natural disasters.

Predictive biophysical models of bivalve larvae dispersal in Scotland

In Scotland, bivalves are widely distributed. However, their larvae dispersion is still largely unknown and difficult to assess in situ. And, while Mytilus spp. dominate shellfish production, it is mostly dependent on natural spat recruitment from wild populations. Understanding the larval distribution pattern would safeguard natural resources while also ensuring sustainable farming practises. The feasibility of a model that simulates biophysical interactions between larval behaviour and ocean motions was investigated. We employed an unstructured tri-dimensional hydrodynamic model (finite volume coastal ocean model) to drive a particle tracking model, where prediction of larval movement and dispersal at defined locations might aid in population monitoring and spat recruitment. Our findings reveal a strong link between larval distribution and meteorological factors such as wind forces and currents velocity. The model, also, depicts a fast and considerable larval movement, resulting in a substantial mix of plankton and bivalve larvae, forming a large connection between the southern and northern regions of Scotland’s West coast. This enables us to forecast the breeding grounds of any area of interest, potentially charting connectivity between cultivated and wild populations. These results have significant implications for the dynamics of ecologically and economically important species, such as population growth and loss, harvesting and agricultural management in the context of climate change, and sustainable shellfish fisheries management. Furthermore, the observations on Scottish water flow suggest that tracking particles with similar behaviour to bivalve larvae, such as other pelagic larval stages of keystone species and potential pathogens such as sea lice, may have policy and farming implications, as well as disease control amid global warming issues.

Investigation on Suitable Spat Collectiors and Culture Sites for Edible Oyster in the Coast of Bay of Bengal, Bangladesh

Potential spat collectors and suitable culture sites were investigated for the development of edible oyster culture from June to December 2019 at three study sites (Moheshkhali, the Jeti of Nuniarchora, and Sonadia) of Cox’s Bazar coast of Bangladesh. Four types of collectors such as oyster shell, earthen pot, kortal (windowpane oyster shell) and tiles were investigated. On site sampling of water quality parameters and number of spats on each collector were done at 15-days interval following standard methods. Results indicated insignificant difference (P > 0.05) in temperature, salinity, dissolved oxygen and pH, while significant difference (P < 0.05) in total dissolved solids, total suspended solids and Chl-a content of the water among the study locations. However, these parameters were in suitable range for growth and spawning of oyster. Results also indicated spat recruitment was significantly influenced by the types of collectors and study locations with significantly (P < 0.05) higher spat were recruited in Tiles. Tiles were also found to facilitate with an advantage of recycling of this collector. The location in interaction with polluting materials such as total dissolved solids and total suspended solids had a significant effect on spat recruitment rate and therefore, Sonadia was the most suitable location for spat recruitment. This study site can also be used as a suitable location for the development of oyster culture in the cost of Bay of Bengal, Bangladesh based on its environmental characteristics. Bangladesh J. Zool. 49 (2): 257-265, 2021

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.

Sink before you settle: Settlement behaviour of Eastern oyster (Crassostrea virginica) larvae on artificial spat collectors and natural substrate

Eastern oysters (Crassostrea virginica) are ecosystem engineers that are important to the ecological and economic sustainability of Atlantic Canada’s estuarine resources. Recently, there has been an increased industry demand for oyster spat (i.e., newly-settled larvae), which is often collected using artificial spat collectors suspended in the water column. Little is known, however, about the interactions between artificial spat collectors and naturally occurring substrates, and whether or not such collectors can affect oyster recruitment to wild beds which are simultaneously fished. In the laboratory, we mimicked the typical set-up of artificial spat collectors used in Atlantic Canada to measure differences in spat recruitment between locally-used artificial collectors and natural shell substrate under real-life spat-collection scenarios. Larvae were allowed to settle on various substrates where they occur in a natural system and were subsequently counted. In both single substrate and choice experiments, results indicated that oyster larvae recruited in higher numbers to natural shell substrate located on the benthic surface compared to suspended shell; and there were no significant differences among suspended substrates. This experiment provides evidence supporting existing theories around recruitment behaviour by oyster larvae, mainly that settling oysters tend to sink before they settle, suggesting that spat collectors in the wild may have little effect on wild recruitment. With increasing densities of artificial collectors in estuarine systems to meet system demands, however, further research is needed to investigate the potential draw of oyster larvae away from benthic oyster beds under more realistic natural conditions before broad conclusions regarding spat collector effects on wild oyster populations can be achieved.

The effects of a stressed inshore urban reef on coral recruitment in Suva Harbour, Fiji.

A relic inshore reef ecosystem adjacent to the Fijian capital of Suva and another remote inshore reef were monitored monthly from July 2014 to July 2015 for coral recruitment, sedimentation rates, coral cover, temperature, and light intensity. Despite a major sewage spill in Suva Harbour in December 2014, the municipal inshore site exposed to constant anthropogenic activity, recorded no significant differences in coral spat abundance (except for the family Poritidae) on artificial substrata compared to the remote inshore site. Total yearly spat abundance was 106 on municipal reef and 132 on remote reef, while average daily sediment trap collection rates (g cm2/day) were significantly higher in the municipal site for the entire duration of monitoring. Total annual particulate organic matter content in sediment was also significantly higher in the municipal site (107.51 g cm2), compared to the remote site (43.37 g cm2). Mean light intensity was significantly lower for the municipal site (69.81 lum/ft2) compared to the remote site (239.26 lum/ft2), with Photosynthetically Active Radiation also lower for the former (800–1,066.66 µmol m−2 s−1) compared to the latter (3,266.66–3,600 µmol m−2 s−1). The lack of significant differences in coral spat recruitment rates suggests that settling larvae may be unable to distinguish between sub‐optimal and optimal sites probably as a consequence of interference with coral settlement cues arising from anthropogenic development.

Studies on the Spat Recruitment and Age Structure in the Population of the Mussel, Mytilus galloprovincialis LAMARCK, with Special Reference to the Cause of the Extinction of Population

Studies on the Spat Recruitment and Age Structure in the Population of the Mussel, Mytilus galloprovincialis LAMARCK, with Special Reference to the Cause of the Extinction of Population

Spat Settlement of the Smooth ScallopFlexopecten glaber(Linnaeus, 1758) and Variegated ScallopChlamys varia(Linnaeus, 1758) in Amvrakikos Gulf, Ionian Sea (Northwestern Greece)

ABSTRACT The seasonal variation and spat recruitment pattern of the scallops Flexopecten glaber and Chlamys varia in the protected aquatic ecosystem of the northwestern Amvrakikos Gulf (Natura, 2000) were examined by using a combination of plankton sampling and spat collection techniques during the spring and summer of 2007. The presence of the larvae was reported in all samples from the beginning of May to the end of August. Peak numbers were obtained at the beginning of June and in mid-July. The highest settlement density was recorded at a depth of 8 m below the surface, indicating the most suitable placement for the spat collectors despite the hypoxic bottom layer underneath.

SCLERACTINIAN CORAL RECRUITMENT DENSITY IN COASTAL WATER OF BALOK, PAHANG, MALAYSIA

Study on scleractinian coral recruitment is important in understanding the mechanisms that regulate their population and the resilience of coral reef communities to disturbance. This study aims to investigate temporal recruitment density of scleractinian coral at selected remote area in Balok, Pahang. Two types of settlement plates, which are terra-cotta tiles and artificial reef, were deployed at three stations to determine the recruitment density. The retrieval of the settlement plate was done at every three months interval started from March to September 2014. A total of 159 coral recruits were counted with mean recruitment densities on both terracotta tiles was 1.52 ± 0.65 and artificial reef plate was 4.37 ± 1.84 respectively. Recruitment was dominated by Platygyra (36%) followed by Porites (32%), Fungia (17%), Turbinaria (7%), Acropora (2%), Stylopora (2%), Montipora (1%), Leptoria (1%), Favites (1%) and Echinophyllia (1%). Kruskal - Wallis ANOVA test shown that recruitment densities varied significantly with plate’s orientation (p < 0.05), but not with sampling stations, type of substrates and month retrieval. Artificial reef plate has better recruitment densities compared to terra-cotta tiles. Coral spat settlement and recruitment patterns were consistent with adult coral distributions. The percentage cover of adult coral varied within the three stations. A total of 33 coral genera from 13 families were recorded during coral video transect survey with Station 3 showed the highest H’ (2.35). Meanwhile, Station 2 showed higher EH’ indexes with 0.82. Therefore, results of this study is important because coral recruitment pattern reflect its adult coral population, and if it closely monitored and harvested sustainably, the survival of parent population could be increased for successful breeding.

Oyster reef restoration: effect of alternative substrates on oyster recruitment and nekton habitat use

Eastern oysters (Crassostrea virginica) in Gulf of Mexico estuaries create complex reefs and provide important habitat for fish and crustaceans. Oyster reefs have suffered historic losses due to overharvest, disease, and degraded water quality, and recent efforts have focused on restoring reefs to benefit nekton populations. Oyster shell is the preferred substrate for oyster reef restoration, but as a consequence of its limited supply, a variety of alternative substrates are being used. We used field experiments to quantify the effects of substrate type (concrete, porcelain, limestone, river rock, and oyster shell) on oyster recruitment, growth, and nekton habitat use in St. Charles Bay, TX. After 4 months, oyster spat recruitment density, nekton density and community structure were similar across substrate types—and analogous to those on natural reefs—but differed from samples collected on bare sediment. To determine refuge value of the alternative substrates, we tested mud crab (Panopeidae) prey mortality with and pinfish (Lagodon rhomboides) or blue crab (Callinectes sapidus) predators. Prey mortality was similar across substrate types for both predators, and was significantly lower than no substrate and bare sand controls. Alternative substrates can provide important structural materials to support the development of oyster populations and nekton assemblages, and may be used to promote sustainable management of oyster reef resources via restoration.

Spat availability of commercial bivalve species recruited on artificial collectors from the northern Gulf of California. Seasonal changes in species composition

This study reports a year-round recruitment of spat of four commercial bivalve species; Pteria sterna, Euvola vogdesi, Pinctada mazatlanica and Pinna rugosa collected in the region of Puerto Peñasco, north-eastern coast of the Gulf of California. Bimonthly recruitment of commercial bivalve spat on netlon® collectors was evaluated for six sites from June 2007 to August 2008. To describe spat recruitment abundances with environmental parameters, sea surface temperature (°C) and surface chlorophyll a concentration (mg m−3) were characterized by means of monthly Aqua/MODIS satellite data. For each species a repeated measures anova was used to evaluate differences in the number of spat between months, sites and depths. Maximum sea surface temperature was recorded in August–September (~31.5°C) and the minimum in January–February (~15°C), while the minimum surface chlorophyll a was observed in June–September (mean range = 1.5–2 mg m−3) and the maximum in January–March (mean range = 2–5 mg m−3). Spat recruitment showed distinct patterns; P. sterna can be characterized as having a Winter–Spring pattern, E. vogdesi a winter pattern, while P. mazatlanica and P. rugosa a summer spat recruitment pattern. This information constitutes part of the fundamental data needed for the development of aquaculture and conservation initiatives in the region based on wild spat supply.

64. Comparative cryopreservation study of trochophore larvae from two species of bivalves: Pacific oyster (Crassostrea gigas) and blue mussel (Mytilus galloprovinciallis)

The Pacific oyster Crassostrea gigas is among the most farmed aquaculture species worldwide. The most farmed bivalve species in Spain is the mussel, Mytilus galloprovinciallis (FAO). Due to the variability of spat recruitment from year to year, and in response to the economic importance of these two bivalve species, there is an increasing interest in developing hatchery spat production. Cryopreservation of shellfish embryos and larvae can improve aquaculture management and enhance breeding design flexibility. The aim of this study was to develop a cryopreservation for trochophore larvae of Pacific oysters and blue mussels larvae for future aquaculture purposes. Gametes from mature Pacific oysters were obtained during the natural breeding season by gentle stripping of the gonad (Marlborough Sounds, New Zealand). Blue mussel gametes were obtained by thermal cycling mature broodstock ( Ria de Vigo Spain). Oocytes were fertilized and after 16–20 h of incubation, trochophores were collected by gently siphoning onto a mesh screen held in seawater. For each experiment, at least three pools of trochophores were produced. The ability of trochophores to develop to the D-larval stage following treatment was assessed against a control. Experiment 1: Five ethylene glycol (EG) concentrations in combination with trehalose (TRE) and/or polyvinylpyrrolidone (PVP) were tested for toxicity for both species. Experiment 2: Based on experiment 1, selected cryoprotectant (CPA) concentrations were then used to evaluate two cooling regimes for both species. Trochophores diluted with CPAs were aspirated into 0.25 mL straws and loaded into temperature controlled freezers that were programmed to hold at 0 °C for 5 min, then cool to −10 °C at 1 °C min−1, hold for 10 min, then cool at either 0.5 or 1 °C min−1 to −35 °C, after which, straws were plunged into liquid nitrogen. For thawing, straws were thawed at 35 °C and 0.1% Bovine Serum Albumin (BSA) included in the thawing medium. Experiment 3: A final extra experiment was performed to compare the % of normal D-larvae resulting from cooling mussel trochophores at 0.5 or 1 °C min−1, and also the variation of larvae size after 48, 72 and 96 h incubation. 10% EG + 0.2 M TRE was used. For trochophores of both species, the no observed effect concentration (NOEC) was 15% EG and the lowest observed effect concentration (LOEC) was 20% EG. Development of thawed oyster trochophores through to D-larval stage was highest (60 ± 6.7%) when trochophores were frozen in 10% EG at a rate of 0.5 °C min−1. For mussels, there was large variation between replicate pools with several treatments producing ∼50% normal D-larvae from thawed trochophores and one pool producing 80% normal D-larvae when frozen in 10% EG + 0.2 M TRE at a cooling rate of 0.5 °C min−1. For both species measurements of D-larvae size were performed along the experiments. Extended research must be done to study the long-term viability of resulting D-larvae by examining their ability to develop to the eyed-larval stage and scale-up issues for application in selective breeding and hatcheries.

Recruitment of catarina scallop (Argopecten ventricosus) larvae on artificial collectors off the NE coast of the Gulf of California

We evaluated recruitment of larvae of catarina scallop, Argopecten ventricosus, in the area of Puerto Penasco, NE Gulf of California. We moored artificial collectors in six sites from June 2007 to August 2008 and replaced them every 2 months. We used monthly (July 2002-September 2011) sea surface temperature (SST, °C) and surface chlorophyll-a concentration (SSChl, mg m � 3 ) Aqua/MODIS satellite data to describe seasonal environmental behaviour study area. Also, we recorded bottom temperature at each site every 4 h, and every 2 months measured sea surface salinity, temperature and dissolved oxygen. We used a repeated measures ANOVA to evaluate differ- ences in the number of recruited spat between main factors, and analysed the presence of multi- modal spat shell size frequency distributions. Over- all, spat recruitment was negatively correlated with seawater temperature and showed higher spat recruitment abundances throughout winter, which is the season with the highest surface chlo- rophyll a concentration. We estimated multimodal shell size frequency distributions characterized by more than one modal size. The natural collection of A. ventricosus spat on artificial collectors in the area can be successfully performed over a pro- tracted period (November-December to May-June). Our results extend the area where collection of A. ventricosus spat can be successful.

Influence of depth and diameter of rope collectors on settlement density of Mytilus galloprovincialis spat in Baie de M’diq (Alboran Sea)

The dependence of wild seed to replenish mussel culture plots is a limiting factor in areas where spat recruitment is poor. One way to maximize recruitment of mussel spat is to optimize the artificial substrates used as collectors. This study compares the performance of two 5 m long rope collectors with different diameters (14 and 32 mm) for recruiting planktonic spat in Baie de M’diq (Tétouan), an embayed area of high potential for marine aquaculture in the Alboran Sea. Multiple collectors of both diameters were suspended from a long-line system settled in this bay during the main spawning season. Each metre of the 5 m collectors was treated as a different depth grouping and the settled mussels were counted with a microscope. The mean settlement was greater on the thick collector (179.7 ± 62.5 spat m−1) than on the thin collector (34.7 ± 11.6 spat m−1). Significant differences were found in spat abundance between depth samples on thick collectors but not so on thin collectors. Spat abundance on the deepest metre of the thick collector (259.3 ± 14.9) was twice that on the shallowest metre (107.7 ± 11.30). These results are interpreted in terms of aggregation behaviour of mussels that seems to be influenced by length and surface of collectors placed well above the thermocline. We provide recommendations on how to maximize the artificial collection of juveniles in turbulent areas of high mussel spawning but low recruitment.

Seasonal Changes in Recruitment ofPteria penguinin North Queensland, Australia

Spat recruitment of the winged pearl oyster Pteria penguin, in relation to season, substrate type, and depth was investigated at Orpheus Island in north Queensland for 27 mo, from February 2008 to April 2010. Two substrate types (70% shade cloth and open-weave polypropylene mesh bags) were deployed at 2 depths (4 m and 6 m) and checked every 6 wk for 3 spawning seasons to determine any differences in quantity of spatfall between these factors. No significant difference was found in spat recruitment between substrate types (P = 0.158) or depth (P = 0.349), although there was a significant seasonal effect on spat recruitment (P < 0.001), with a peak in the quantity of spatfall in late summer, from February to March, and no spat collected in the winter to spring (July to October). Maximum settlement of spat was 10.2 spat per mesh bag collector in February 2008. Recruitment was significantly reduced (P < 0.001) during the 2010 spawning season as a result of disturbance from severe storms generated by tropical cyclone Olga in late January.

Larval abundance and spat collection of the lion’s paw scallop Nodipecten subnodosus in Ojo de Liebre Lagoon, Baja California Sur, Mexico

Large numbers of spat of giant lion’s paw scallop Nodipecten subnodosus are required for the development of the scallop aquaculture industry. Despite the large adult populations of this species in Ojo de Liebre Lagoon, Baja California Sur, Mexico, attempts to collect spat with onion bag collectors during the reproductive season (September–November) have not been successful. We assessed lion’s paw spatfall at three sites (La Ventana, El Conchalito, and El Borbollón) within the lagoon, where high recruitment was previously recorded. Netlon collectors instead of onion bags were used and they were deployed at each site at a depth of 1 m on two occasions (October and November 2007) when pediveliger larvae were more abundant. Collectors were retrieved and evaluated in February 2008, after being submerged for 118 or 82 days. Pediveliger larvae were present from late September to late November at all three sites. Densities peaked at 1 m in mid-November and were significantly higher at La Ventana, accounting for 12,400 larvae m–3. Collectors installed in October at El Conchalito showed higher (P &lt; 0.05) mean recruitment (1.7 ± 0.2 spat per collector) than collectors set in November (0.4 ± 0.3 spat per collector). Collectors installed in October and November at La Ventana had 0.6 ± 0.3 and 0.9 ± 0.2 spat per collector, respectively. No significant differences were observed in the growth rates of the juveniles collected. High densities of larvae in the plankton during November indicated that high reproductive activity occurred earlier that month or in late October. La Ventana showed the highest potential for spat collection based on larval abundance, followed by El Borbollón and El Conchalito; however, El Conchalito showed the highest spat recruitment, followed by La Ventana and El Borbollón. Since spat collection was relatively low at all sites, more efforts to determine better collection sites and techniques, as well as appropriate deployment times are required.

Gametogenic stages in triploid oysters Crassostrea gigas: Irregular locking of gonial proliferation and subsequent reproductive effort

Although triploid oysters Crassostrea gigas have generally been considered to be sterile, gametogenesis events are sometimes recorded. We aimed to establish a new classification adapted for the description of gametogenesis in triploid oysters and their comparison with diploid animals. From stage I to stage III, two types of gametogenic pattern were identified: α-pattern, corresponding to animals displaying numerous proliferating gonia (PCNA labelling at stage I), resulting in abundant gametes at stage III and β-pattern, which was associated with locked gametogenesis (only few mature gametes at sexual maturity) with accumulation of abnormal gonia from stage I to III. The granular aspect of TUNEL labelling in the perinuclear area of stage Iα animals suggests either the occurrence of apoptotic events or the possibility of chromosome number regulation (chromosome extrusion). Reproductive effort was evaluated by quantitative approaches in order to evaluate the possible contribution of triploid oysters to recruitment in the natural environment. For mature α triploid animals, the ratio of gonadal area over total area on histological slide preparations reached almost 50% that of diploid counterparts. Moreover, the gonadal area contained numerous mature germinal cells as in diploids. Future ecological studies should consider the involvement of triploids in spat recruitment in the case of spawning by these animals.