Bivalve Larvae Research Articles

Expression of calcification-related ion transporters during blue mussel larval development.

The physiological processes driving the rapid rates of calcification in larval bivalves are poorly understood. Here, we use a calcification substrate‐limited approach (low dissolved inorganic carbon, C T) and mRNA sequencing to identify proteins involved in bicarbonate acquisition during shell formation. As a secondary approach, we examined expression of ion transport and shell matrix proteins (SMPs) over the course of larval development and shell formation. We reared four families of Mytilus edulis under ambient (ca. 1865 µmol/kg) and low C T (ca. 941 µmol/kg) conditions and compared expression patterns at six developmental time points. Larvae reared under low C T exhibited a developmental delay, and a small subset of contigs was differentially regulated between ambient and low C T conditions. Of particular note was the identification of one contig encoding an anion transporter (SLC26) which was strongly upregulated (2.3–2.9 fold) under low C T conditions. By analyzing gene expression profiles over the course of larval development, we are able to isolate sequences encoding ion transport and SMPs to enhance our understanding of cellular pathways underlying larval calcification processes. In particular, we observe the differential expression of contigs encoding SLC4 family members (sodium bicarbonate cotransporters, anion exchangers), calcium‐transporting ATPases, sodium/calcium exchangers, and SMPs such as nacrein, tyrosinase, and transcripts related to chitin production. With a range of candidate genes, this work identifies ion transport pathways in bivalve larvae and by applying comparative genomics to investigate temporal expression patterns, provides a foundation for further studies to functionally characterize the proteins involved in larval calcification.

Temporal variability in zooplankton community in the western Yellow Sea and its possible links to green tides.

Large-scale macro-algal blooms of Ulva prolifera (also called green tides) have appeared each summer since 2008 in the western Yellow Sea. In this study, we investigated the temporal variability in zooplankton community in the western Yellow Sea and its possible links to green tides using data from a long-term plankton survey off the coast of Qingdao, China. Environmental conditions observed in the study area during the green tide period (GTP: June–August, 2008–2013) were compared to the non-green tide period (NGTP: June–August, 2005–2007), to support the contention that variations observed in zooplankton community may be attributed to the green tides, as opposed to natural climatic or environmental variations. Zooplankton assemblage structure observed during the GTP was then compared to the NGTP. Significant variations were detected both in zooplankton abundance and assemblage structure between the two defined periods. The abundance of zooplankton, mainly copepods, was significantly decreased during the GTP. Meanwhile, the relative abundance of copepods decreased by approximately 10% and that of gelatinous zooplankton, including appendicularians, chaetognaths, and medusae, almost doubled (ca. increased by 6.4%). The dominant species of meroplankton completely changed, specifically, polychaeta, and echinoderm larvae were more dominant than decapod and bivalve larvae. With regard to zooplankton size structure, the NGTP showed a higher size diversity with more small-sized organisms, while the GTP showed a lower size diversity in the community. According to general linear models, the interannual variation in summer zooplankton abundance was significantly correlated with green tides. These results indicate that the temporal changes in zooplankton community may have a close link to the green tides.

The harmful algae, Cochlodinium polykrikoides and Aureococcus anophagefferens, elicit stronger transcriptomic and mortality response in larval bivalves (Argopecten irradians) than climate change stressors.

Global ocean change threatens marine life, yet a mechanistic understanding of how organisms are affected by specific stressors is poorly understood. Here, we identify and compare the unique and common transcriptomic responses of an organism experiencing widespread fisheries declines, Argopecten irradians (bay scallop) exposed to multiple stressors including high pCO2, elevated temperature, and two species of harmful algae, Cochlodinium (aka Margalefidinium) polykrikoides and Aureococcus anophagefferens using high‐throughput sequencing (RNA‐seq). After 48 hr of exposure, scallop transcriptomes revealed distinct expression profiles with larvae exposed to harmful algae (C. polykrikoides and A. anophagefferens) displaying broader responses in terms of significantly and differentially expressed (DE) transcripts (44,922 and 4,973; respectively) than larvae exposed to low pH or elevated temperature (559 and 467; respectively). Patterns of expression between larvae exposed to each harmful algal treatment were, however, strikingly different with larvae exposed to A. anophagefferens displaying large, significant declines in the expression of transcripts (n = 3,615; 87% of DE transcripts) whereas exposure to C. polykrikoides increased the abundance of transcripts, more than all other treatments combined (n = 43,668; 97% of DE transcripts). Larvae exposed to each stressor up‐regulated a common set of 21 genes associated with protein synthesis, cellular metabolism, shell growth, and membrane transport. Larvae exposed to C. polykrikoides displayed large increases in antioxidant‐associated transcripts, whereas acidification‐exposed larvae increased abundance of transcripts associated with shell formation. After 10 days of exposure, each harmful algae caused declines in survival that were significantly greater than all other treatments. Collectively, this study reveals the common and unique transcriptional responses of bivalve larvae to stressors that promote population declines within coastal zones, providing insight into the means by which they promote mortality as well as traits possessed by bay scallops that enable potential resistance.

Temporal and ontogenetic variation in the diet of three small pelagic fish in the Black Sea of Turkey

In the South Eastern Black Sea, anchovy (Engraulis encrasicolus), sprat (Sprattus sprattus), and horse mackerel (Trachurus mediterraneus) are the most important small pelagic fish both ecologically and economically. The stomach contents of 1485 fish, including anchovy, sprat, and horse mackerel, were examined. Fish fed on 35 prey taxa, and there were dietary differences among predators. Anchovies predominantly consumed calanoid copepods and bivalves; sprats had a diet dominated by calanoid copepods and Chaetognatha (Parasagitta setosa); horse mackerel consumed mainly decapods and calanoid copepods. Copepods in the stomachs of sprat were more abundant and more frequent than in the stomachs of anchovy or horse mackerel during all year. As the anchovies and horse mackerel grew, their copepod consumption increased, but despite their size, sprats consumed a similar amount of copepods. Seasonal shifts in diet were observed in all three species. In winter and autumn months, all small pelagic fish consumed copepod species. The bivalve larvae were mostly consumed in summer by anchovies (N%: 72.98) and in spring by sprats and horse mackerel (N%: 88.59 and 81.08, respectively). Decapod species were preferred in spring months by horse mackerel. P. setosa was mostly consumed in autumn and winter by sprat. Anchovy showed a low dietary overlap with sprat but had a high dietary overlap with horse mackerel. The feeding strategy of anchovy seems to be mixed, while horse mackerel is a generalist at the individual level, and sprat is a specialist at the population level.

Complex Relationships between the Blue Pigment Marennine and Marine Bacteria of the Genus Vibrio.

Marennine, the water-soluble blue pigment produced by the marine diatom Haslea ostrearia, is known to display antibacterial activities. Previous studies have demonstrated a prophylactic effect of marennine on bivalve larvae challenged with a pathogenic Vibrio splendidus, suggesting that the blue Haslea is a good candidate for applications in aquaculture as a source of a natural antimicrobial agent. Indeed, the genus Vibrio is ubiquitous in aquaculture ecosystems, and regular events of pathogenic invasion cause some of the biggest losses worldwide. To better characterize the effects of marennine on Vibrios, a panel of 30 Vibrio strains belonging to 10 different species was tested, including bivalve pathogenic species (e.g., Vibrio crassostreae and Vibrio harveyi). Vibrio strains were first exposed to 10 and 25 µg mL−1 of Blue Water (BW), a concentrated culture supernatant of H. ostrearia containing marennine. This screening evidenced a great diversity in responses, from growth stimulation to a total inhibition, at both the interspecific or intraspecific level. In a second series of experiments, 10 Vibrio strains were exposed to BW at concentrations ranging from 5 to 80 µg mL−1. The highest concentrations of BW did not systematically result in the highest growth inhibition as hormetic responses—opposite effects regarding the concentration—were occasionally evidenced. The relationships between marennine and Vibrio strains appear more complex than expected and justify further study—in particular, on the mechanisms of action—before considering applications as a natural prophylactic or antibiotic agent in aquaculture.

Composition, abundance and biomass of mesozooplankton in the southwestern Black Sea along the coast of İğneada, Turkey

The qualitative and quantitative structure of mesozooplankton assemblages in the southwestern Black Sea region along the coast of Igneada, Kirklareli Province were assessed and described. The study was conducted on 22 November 2012, 17 May 2013, 13 July 2013 and 4 October 2013. Samples were collected from nine stations using a plankton net via vertical boat hauls. In total, 30 mesozooplankton taxa were identified. The mean mesozooplankton abundance values ranged from 3890.84 ± 2250.04 to 13643.40 ± 1660.55 individuals (ind.) m−3, whereas the biomass values ranged from 26.91 ± 5.4 to 95.76 ± 29.31 mg m−3. The most abundant taxa were Oithona davisae (2871.20 ± 436.24 ind. m−3 in November 2012 and 1310.83 ± 157.222 ind. m−3 in October 2013), Copepoda nauplii (4007.08 ± 3513.07 ind. m−3 in May 2013) and Bivalvia larvae (11118.41 ± 4798.74 ind. m−3 in July 2013). The taxa with the highest biomass were Parasagitta setosa (7.43 ± 2.32 mg m−3 in November 2012 and 33.52 ± 9.45 mg m−3 in October 2013), Polychaeta larvae (20.87 ± 9.63 mg m−3 in May 2013) and Bivalvia larvae (55.59 ± 23.99 mg m−3 in July 2013). Abundance and biomass of the species/groups of mesozooplankton are presented as mean ± standard error of the mean (SEM). There were no significant differences among the seasons and stations for either total abundance or biomass; however, there was a significant monthly variation in the mesozooplankton assemblages. Changes in the abundance and biomass of mesozooplankton were dependent on the physical environment.

Harmful or harmless: Biological effects of marennine on marine organisms

Marennine is a water-soluble blue-green pigment produced by the marine diatom Haslea ostrearia. The diatom and its pigment are well known from oyster farming areas as the source of the greening of oyster gills, a natural process increasing their market value in Western France. Blooms of blue Haslea are also present outside oyster ponds and hence marine organisms can be exposed, periodically and locally, to significant amounts of marennine in natural environments. Due to its demonstrated antibacterial activities against marine pathogenic bacteria (e.g. Vibrio) and possible prophylactic effects toward bivalve larvae, marennine is of special interest for the aquaculture industry, especially bivalve hatcheries. The present study aimed to provide new insights into the effects of marennine on a large spectrum of marine organisms belonging to different phyla, including species of aquaculture interest and organisms frequently employed in standardised ecotoxicological assays. Different active solutions containing marennine were tested: partially purified Extracellular Marennine (EMn), and concentrated solutions of marennine present in H. ostrearia culture supernatant; the Blue Water (BW) and a new process called Concentrated Supernatant (CS). Biological effects were meanwhile demonstrated in invertebrate species for the three marennine-based solutions at the highest concentrations tested (e.g., decrease of fertilization success, delay of embryonic developmental stages or larval mortality). Exposure to low concentrations did not impact larval survival or development and even tended to enhance larval physiological state. Furthermore, no effects of marennine were observed on the fish gill cell line tested. Marennine could be viewed as a Jekyll and Hyde molecule, which possibly affects the earliest stages of development of some organisms but with no direct impacts on adults. Our results emphasize the need to determine dosages that optimize beneficial effects and critical concentrations not to be exceeded before considering the use of marennine in bivalve or fish hatcheries.

Differential toxicity of functionalized polystyrene microplastics to clams (Meretrix meretrix) at three key development stages of life history

Little knowledge is available on impact of microplastics (MPs) on the bivalve larvae at different developmental stages throughout their life history, especially for metamorphic stage. Therefore, this study aims to evaluate the toxic responses of carboxylated (PS-COOH) and amino (PS-NH2) polystyrene MPs on the developing clam larvae at three key life stages, i.e., fertilized eggs, D-veliger larvae, and umbo larvae. PS-COOH and PS-NH2 significantly decreased the hatching rates by 5.79–39.5% and developmental rates by 4.78–7.86% of the clam larvae relative to the unexposed clam larvae. The toxicity of MPs followed the order: hatching stage > metamorphosis > D-veliger larvae stage, showing stage-dependent toxic effects. Moreover, PS-NH2 with a smaller hydrodynamic diameter showed a greater toxicity to the developing larvae compared to PS-COOH. Our study highlighted the stage-dependent toxic effects of MPs on the developing clam larvae, thus posing ecological risks to population succession of marine bivalves and aquatic ecosystems.

Ocean pH fluctuations affect mussel larvae at key developmental transitions.

Coastal marine ecosystems experience dynamic fluctuations in seawater carbonate chemistry. The importance of this variation in the context of ocean acidification requires knowing what aspect of variability biological processes respond to. We conducted four experiments (ranging from 3 to 22 days) with different variability regimes (pHT 7.4–8.1) assessing the impact of diel fluctuations in carbonate chemistry on the early development of the mussel Mytilus galloprovincialis. Larval shell growth was consistently correlated to mean exposures, regardless of variability regimes, indicating that calcification responds instantaneously to seawater chemistry. Larval development was impacted by timing of exposure, revealing sensitivity of two developmental processes: development of the shell field, and transition from the first to the second larval shell. Fluorescent staining revealed developmental delay of the shell field at low pH, and abnormal development thereof was correlated with hinge defects in D-veligers. This study shows, for the first time, that ocean acidification affects larval soft-tissue development, independent from calcification. Multiple developmental processes additively underpin the teratogenic effect of ocean acidification on bivalve larvae. These results explain why trochophores are the most sensitive life-history stage in marine bivalves and suggest that short-term variability in carbonate chemistry can impact early larval development.

Features of plankton community in the Chukchi Sea in August-September, 2017

Zooplankton in the eastern Chukchi Sea is described on the data of summer observa­tions in 2017. The northern part of the surveyed area was occupied by the cold water masses from the Arctic Ocean and Beaufort Sea. Large-sized zooplankton dominated here, including copepods Calanus glacialis , C. hyperboreus (this species is an indicator of Atlantic waters) and cold-water hyperiids Themisto libellula. In the southern part of the surveyed area, small-sized zooplankton dominated by biomass and abundance and species belonged to the Bering Sea community, as copepods Calanus glacialis + Calanus marshallae , Eucalanus bungii , and Metridia pacifica , were presented in the large-sized fraction. In the western part of the sur­veyed area and in the coastal waters, small-sized copepods Pseudocalanus spp. and Oithona similis prevailed, and biomass and abundance of neritic species as Centropages abdominalis and Acartia longiremis were high, too. Besides, some species typical for desalinated water were observed here ( Eurytemora herdmani , Podon sp., and Epilabidocera amphitrites ), as well as larval forms of benthic invertebrates (larvae of polychaetes, bivalves, gastropods, and echinoderms). Arrowworms Sagitta elegans were abundant everywhere that was caused by this species reproduction. The observed structure of plankton community corresponded to feeding demands of arctic cod juveniles, but the zooplankton biomass was rather low. These features of community could be interpreted as early summer state, when its biomass does not reach the maximum yet, as it was observed, for example, in September 2007.

Isochrysis affinis galbana ve Phaeodactylum tricornutum Kültürlerinde Kuru Madde Tahminlerinin Karşılaştırılması

Isochrysis affinis galbana tek hücreli denizel bir mikroalg türü olup yüksek miktarda uzun zincirli doymamış yağ asitleri (PUFA) içermesinden dolayı akuakültürde özellikle bivalvia larvalarının beslenmesinde canlı yem kaynağı olarak kullanılmaktadır. Phaeodactylum tricornutum ise oval ve fusiform hücre şekilleri olan tek hücreli pennat bir diyatom türüdür. Phaeodactylum tricornutum %30-45 arasında uzun zincirli doymamış yağ asitlerini (PUFA) içermekte ve bu oranın da %20-40‘ını eikosapentaenoik asit (EPA) oluşturmaktadır. Esansiyel yağ asitlerinden eikosapentaenoik asit'in önemli potansiyel kaynağı olarak düşünülen mikroalgler insan gıdası olarak ve akuakültürde hayvan beslenmesinde kullanılmaktadır. Çalışmada, Isochrysis affinis galbana ve Phaeodactylum tricornutum kültürlerine ait kuru madde miktarlarının çoklu regresyon analizi yöntemi kullanılarak tahmin edilmesi amaçlanmıştır. Türler, F/2 besi ortamında %20 aşılama oranı ile kontrol grubu ve %50 oranında azotun eksiltildiği besi ortamı kullanılarak, laboratuvar ortamında kültüre alınmıştır. Deneme süresince optik yoğunluk, kuru madde ve klorofil a günlük olarak ölçülmüştür. Türlere ait kontrol grubu ve %50 oranında azotun eksiltildiği gruplarda optik yoğunluk ve klorofil a kullanılarak matematiksel bir model oluşturulmuştur. Bu modellerin önem testleri yapılıp, R2 ve HKO bulunmuştur.

Transport of bivalve larvae in the James River, Virginia

Transport of bivalve larvae in the James River, Virginia

Tidal shifts in the vertical distribution of bivalve larvae: Vertical advection vs. active behavior

AbstractSome previous studies, though not all, have reported that vertical distributions of bivalve larvae shift upward in the water column on flood tides and downward on ebb tides. When observed, such shifts have been interpreted as reflecting the vertical migration of larvae (i.e., an active behavioral process). This interpretation assumes that tidally driven vertical advection is insignificant compared to larval swimming speeds, but that assumption may not be valid in all regions. We demonstrated that the vertical distribution of mussel (Mytilus edulis) larvae shifted upward on flood tides on all surveyed dates at sites in the eastern Gulf of Maine. We then used a high‐resolution coastal circulation model to predict the vertical distribution of passive particles at one site on four sample dates. The modeled distribution shifts explained 99% of the variance in the larval vertical distribution. Finally, we conducted a multipart meta‐analysis of published papers on tidal shifts to assess whether variation in the results among studies could be explained by tidal vertical advection via two proxies—tidal range and shelf slope. For well‐replicated studies that could be analyzed with a paired t‐test, tidal range explained 78% of the variance in the test statistic. A multiple regression approach applied to distributional shifts from a broader set of studies indicated significant effects of tidal range and interactions between tidal range, slope, and slope heterogeneity. Our results demonstrate the importance of considering passive processes when evaluating how the vertical distribution of weakly swimming meroplankton varies between tidal phases.

Preface: Identification of Larval and Post-Larval Bivalve Molluscs

Preface: Identification of Larval and Post-Larval Bivalve Molluscs

Optical Imaging and Molecular Sequencing of a Preserved Collection of Bivalve Larvae

From the 1980s through 1995, scientists at numerous marine, coastal, estuarine, and freshwater laboratories spawned bivalves to provide larvae for use in identifying species based on larval hinge structures and gross shell morphometry. These larvae were preserved in 95% ethanol and stored in sample vials, many of which dried out over the years. Advantage was taken of 50 of 56 species from this collection (and two additional species that were not in the collection for a total of 52 species) to explore the use of optical techniques (polarized light and a full-wave compensation plate) to highlight birefringence patterns of larval shells to discriminate individual species. Representative images of various developmental stages of 77% (40/52) of the larval bivalve species in the collection were successfully imaged. Similarities across birefringence patterns were observed at the taxonomic ordinal and familial level. Molecular polymerase chain reaction techniques were used in an effort to sequence many of the dried-out specimens and they successfully identified 19% (10/52) of the larval bivalve species with matches in GenBank. Here it has been demonstrated that optical techniques are efficient for imaging dried-out larval bivalve shells for classification purposes and we present successful sequences of 10 species of bivalve larvae from the preserved collection.

Scanning Electron Microscopic Aids for Identification of Larval and Post-Larval Bivalves

The identification of bivalve larvae and early postlarvae in plankton and benthic samples has long been a challenge, hampering both basic and applied research efforts in marine, estuarine, and freshwater environments. The usefulness of published optical micrographs of the early life-history stages of bivalves is limited because of the great morphological similarity of the imaged articulated shells, particularly at the early (straight-hinge) developmental stages. While a number of techniques have been refined in recent years and show promise for use in routine identifications of larval and post-larval bivalves (e.g., single-step nested multiplex polymerase chain reaction; in situ hybridization protocols through color coding with taxon-specific, dye-labeled DNA probes; coupled fluorescence in situ hybridization and cell sorting; and image analysis techniques using species-specific shell birefringence patterns under polarized light), no adequate comprehensive reference source exists that accurately depicts the morphology and morphometry of the shells of larval and post-larval stages of target bivalve species in a consistent format to assist in identification of such stages. To this end, scanning electron micrograph (SEM) sequences are presented of the disarticulated shell valves of laboratory-reared larval and post-larval stages of 56 species of bivalve molluscs from a wide spectrum of marine, estuarine, and freshwater habitats. Emphasis is placed on the usefulness of the morphology and morphometrics of consistently-oriented, disarticulated shell valves and associated hinge structures in discriminating the early life-history stages of these various bivalve species. Although the scanning electron micrograph sequences presented accurately depict the gross morphologies/ morphometrics and hinge structures of the disarticulated shell valves of the larvae and/or postlarvae of the 56 species of bivalves, it is important to emphasize that a scanning electron microscope is not necessary to observe even fine hinge structures associated with the early ontogenetic stages of these species. Such structures are readily visible using a wide range of optical compound microscopes equipped with high-intensity reflected light sources, although the disarticulated shell valves must be viewed in several planes of focus to discern the often subtle details seen clearly in the scanning electron micrographs. These morphological characters provide researchers with invaluable aids for the routine identification of the early life-history stages of these species isolated from plankton and benthic samples.

The hydro-environmental conditions and zooplankton of the light house creek, Lagos, Nigeria

The hydro-environmental characteristics and zooplankton diversity at the Light-house creek were investigated for six months. Variations in water quality parameters were linked with tidal sea water incursion and rainfall/floodwater dynamics. Water and air temperatures were high (>25.8⁰C; >28 ⁰C) and Transparency decreased in the wet months. Salinity values were high (>19 ‰) all through, while the water remained alkaline (≥6.68). Biochemical oxygen demand (4.0-18.0 mg/L), chemical oxygen demand (1.0 and 2.0 mg/L) phosphate (0.06 and 8.40 mg/L) and nitrate showed variations (0.80 mg/L). On the other hand, minimum sulphate value was 224.0 mg/L while silicate values ranged from 2.10 to 4.60 mg/L. Zinc (<0.047 mg/L), Iron (<0.28 mg/L) and copper values (<0.014 mg/L) also varied. The zooplankton spectrum comprised 62.36% Arthropoda, 0.78% Chordata, 0.71% Cnidaria, 35.9%, juvenile stages and 0.95% were from other groups. A total of 49 zooplankton taxa from five different phyla and 18 juvenile stages were identified. Zooplankton biomass in terms of individuals per ml was higher in the dry than wet months. The copepod nauplii, bivalve and zoea larvae were the dorminant juvenile forms. Species richness indices (d) and similarity index were higher in the dry months than the wet months. Key Words : Phytoplankton, juvenile stages, Lagos habour, lagoon, water chemistry, mangrove creek

RFLP pattern determination for the invasive bivalves Limnoperna fortunei (Dunker, 1857) and Corbicula fluminea (Muller, 1774)

The golden mussel (Limnoperna fortunei) and Corbicula fluminea are considered well-established invasive species in the rivers of Brazil and South America. In addition to the environmental problems resulting from this invasion process, the economic issue, especially in hydroelectric dams, is very worrisome and has mobilized several types of studies on these invasive bivalves. The detection and identification of these organisms in their adult phase in the rivers is not a problem; however, the identification of bivalve larvae by usual morphological methods is difficult due to high similarity conserved in these stages. The use of PCR-RFLP has proven to be an efficient and agile molecular method that allowed the detection of different patterns in the agarose gel for the two bivalves tested. The gel pattern showed a 100 bp band for L. fortunei not detected for C. fluminea. Thus, it is possible to detect larvae of these species from water samples, which can be a powerful tool for environmental monitoring programs on aquatic invasive species.

Mechanisms to Explain the Elemental Composition of the Initial Aragonite Shell of Larval Oysters

AbstractCalcifying organisms face increasing stress from the changing carbonate chemistry of an acidifying ocean, particularly bivalve larvae that live in upwelling regions of the world, such as the coastal and estuarine waters of Oregon (USA). Arguably the first and most significant developmental hurdle faced by larval oysters is formation of their initial prodissoconch I (PDI) shell, upon which further ontological development depends. We measured the minor metal compositions (Sr/Ca, Mg/Ca) of this aragonitic PDI shell and of post‐PDI larval Crassostrea gigas shell, as well as the water they were reared in, over ∼20 days for a May and an August cohort in 2011, during which time there was no period of carbonate under‐saturation. After testing various methods, we successfully isolated the shell from organic tissue using a 5% active chlorine bleach solution. Elemental compositions (Sr, Mg, C, N) of the shells post‐treatment showed that shell Sr/Ca ranged from 1.55 to 1.82 mmol/mol; Mg/Ca from 0.60 to 1.11 mmol/mol, similar to the few comparable published data for larval oyster aragonite compositions. We compare these data in light of possible biomineralization mechanisms: an amorphous calcium carbonate (ACC) path, an intercellular path, and a direct‐from‐seawater path to shell formation via biologically induced inorganic precipitation of aragonite. The last option provides a mechanistic explanation for: (1) the accelerated precipitation rates of biogenic calcification in the absence of a calcifying fluid; (2) consistently elevated precipitation rates at varying ambient‐water saturation states; and (3) the high Ca‐selectivity of the early larval calcification despite rapid precipitation rates.

Planktonic bivalve larvae identification and quantification in Gomso Bay, South Korea, using next-generation sequencing analysis and microscopic observations

Planktonic larval stages of bivalves are notoriously difficult to identify due to their similar morphology. To evaluate changed patterns in the presented planktonic bivalve larvae within Gomso Bay (Yellow Sea, South Korea), three sites were sampled twice a month from June to October 2015 and were analysed using next-generation sequencing (NGS) and light microscopy. Bivalve larvae revealed different patterns, and at least five bivalve taxa were only detected by the NGS. According to the NGS results, most bivalve larvae were Crassostrea gigas (37%), followed by Ruditapes philippinarum (26%), and Solen strictus (23%); Mactra chinensis and M. veneriformis accounted for <1% of the bivalve larvae. C. gigas and S. strictus were most abundant in late June, but rare in the other investigated periods, while R. philippinarum was more abundant in June and late September. Microscopic observations showed a similar trend to the NGS in terms of bivalve larvae presence, although they were difficult to identify the exact species. Thus, morphological and molecular approaches should be combined in future studies to provide accurate sequences of correctly identified specimens to develop NGS libraries.