Razor Clam Research Articles

Diet of eiders and body condition change from the late 1980s to the mid 2010s

Food and foraging decisions are fundamental drivers of the population dynamics of bird species. Eider Somateria mollissima was sampled in Danish marine waters during the non-breeding season in 1986–1990 and in 2010–2017 in order to analyze changes in diet and body condition between the two periods. The food items found were among those commonly consumed by eiders. Between the late 1980s and the mid 2010s there was a decrease in the number of blue mussels Mytilus edulis, cockles Cerastoderma edule and common whelks Buccinum undatum in the diet, and an increase in the number of razor clam Ensis directus. Blue mussel was the most abundant prey. When present, this prey item occurred almost exclusively in the eiders' digestive tract and was negatively correlated with the numbers of other prey items. Eiders with blue mussels, other bivalves and shore crabs in the gizzard had better body condition than eiders with other food items. Blue mussel was a preferred food item and is important for the build-up of body condition. Body condition increased between the late 1980s and the mid 2010s. We assume that this increase in body condition has occurred in parallel with a decrease in the size of the population of the Baltic/Wadden Sea flyway.

Melatonin in razor clam Sinonovacula constricta: Examination of metabolic pathways, tissue distribution, and daily rhythms

Melatonin affects physiological processes that have circadian and seasonal cycles and causes behavioural changes in nearly all organisms, ranging from bacteria to mammals. However, no studies have focused on the presence, biosynthetic pathway, and rhythms of melatonin in bivalves, which are considered as the class of molluscs with the highest economic value. Here, the metabolic pathway and tissue distribution of melatonin, tissue transcription profiles of melatonin-related genes [key synthases arylalkylamine N-acetyltransferase type 2 and 5 (aanat2, aanat5), N-acetylserotonin methyltransferase (asmt), and melatonin receptor type 1 A1 and C3 (MTNR1A1, MTNR1C3)], daily changes in melatonin, transcripts of genes, and effects of four lights (blue, cyan, orange, and red) during the night on melatonin secretion were studied in a bivalve species, razor clam Sinonovacula constricta. Our results showed the presence of complete metabolic and circadian entrainment pathways of melatonin. The melatonin content in the lymphocytes and labial palp was higher than that in the other studied tissues, and aanat2, aanat5, asmt, MTNR1A1, and MTNR1C3 mRNA levels were the highest in the labial palp. Melatonin fluctuated rhythmically in lymphocytes and labial palps and increased at night. Similarly, aanat2, aanat5, asmt, MTNR1A1, and MTNR1C3 mRNA levels were rhythmic in the labial palp, peaking at night. In addition, blue light effectively inhibited the nocturnal secretion of melatonin in the clam. In summary, our results suggest that melatonin plays a role in light signal transduction and the circadian system in S. constricta.

Genome Wide Identification and Expression Profiling Indicate Expansion of Family I84 Protease Inhibitor via Gene Tandem Duplication and Divergence in Razor Clam Sinonovacula constricta.

Family I84 protease inhibitors represent a novel family in the MEROPS peptidase database and are likely unique for molluscan host defense. Two Family I84 members, scSI-1 and scSI-2, were reported from the razor clam Sinonovacula constricta in a previous research. In the present study, 12 additional genes, named scSI-3 to scSI-14, were identified via genome wide sequence analyses. Among them, 10 genes were predicted to have a signal sequence, but one (scSI-7) was not. Besides, one sequence (scSI-14) was likely to encode a prematurely terminated peptide. The predicted mature peptides shared characteristics including 12 conserved cysteine residues, isoelectric points of 4.98 to 6.11, and molecular weights of 7.1 to 9.3 kDa with previously reported family members. Four motifs were characterized in 13 predicted mature peptides (with exception of scSI-14), which shared two to four conserved cysteine residues, are possibly to form two functional domain comprised 6 cysteine residues, respectively. At genomic level, all the 14 razor clam Family I84 genes were organized into 3 exons and 2 introns; 13 of them clustered in 3 regions of 100 kb on 3 separate chromosomes, suggesting tandem duplications of related genes. The promoter region of all the 14 genes was predicted to share some transcription factor binding sites, in particular those responsive to pathological and physiological stimuli, but no shared motifs were identified. Analyses also revealed differences in expression patterns among the genes. One gene in a tandem duplicated gene pairs usually showed a higher expression level than the other whereas non-tandem duplicated genes exhibited a higher degree of correlation in expression level. In addition, 8 of the 14 genes demonstrated higher level of expression in Vibrio tolerant clams than in non-tolerant clams following challenges with Vibrio parahaemolyticus. These results generated important information about the evolution of Family I84 protease inhibitors in S. constricta.

Heritability estimation of high salt tolerance in razor clam (Sinonovacula constricta)

As an important marine mollusk, the growth and development of razor clams (Sinonovacula constricta) are affected by salinity. Genetic selection for salt tolerance is an imperative and effective approach to the improvement of growth and production. To examine whether the tolerance to high salt can be included in razor clam breeding programs, we conducted a genetic analysis of high salt tolerance using three phenotypes and four statistical models. The correlation between tolerance and growth traits was evaluated simultaneously. In this study, we used 9-day experimental stress data of 1005 individuals from 17 full-sib families (the offspring of 17 sires and 17 dams). The survival rate of the families ranged from 0% to 100%, suggesting that the viability of razor clams was different under diverse high salt stress. A positive Pearson and Spearman correlation existed between high salt tolerance and growth traits. A very high genetic correlation (0.886–0.999) was also observed between them, indicating indirect breeding was feasible. Heritabilities of tolerance to high salt were from low to high, with values of 0.55–0.64, 0.11, and 0.047–0.487 for trait TS (test survival), trait DD (day of death), and trait TDS (test-day survival), respectively. The Pearson correlation coefficients of families estimated breeding values between different models ranged from 0.921 to 0.998 which indicated a near-identical ranking of families. This study demonstrated that the salt tolerance of razor clams could be improved genetically through selective breeding. Overall, cross-sectional threshold and linear repeatability models were the most appropriate in estimating heritability for salt tolerance with trait TS and trait TDS in this species. Our study provides important information to guide the effective selection for salt tolerance in S. constricta.

Genetic parameters and genotype by environment interaction for growth traits of razor clam Sinonovacula constricta, from outdoor pond and semi-natural environment

The razor clam, Sinonovacula constricta, is a commercially important bivalve. To date, there have been very limited quantitative genetic studies of this species, especially in different aquaculture environments. This study is the first report of genotype by environment (G × E) interactions for growth traits of razor clams from outdoor pond (OP) and semi-natural environments (SNE). Over a 2-month period, the data for shell length (SL), shell height (SH), shell width (SW), and body weight (BW) of razor clams were recorded for 1 month, and marked as Data 1 and Data 2. Phenotypic data of 1627 individual clams from 17 full-sib families were used for the analysis. The overall heritabilities (h2) for all growth traits were from low to moderate, ranging from 0.127 to 0.230. The h2 of SNE was higher than that of OP (0.243–0.423 vs. 0.101–0.285). Heritabilities for growth traits indicated that these traits could be effectively selected in both aquaculture environments. Overall, both phenotypic (rp) and genetic (rg) characteristics showed high positive correlations among the growth traits. However, the rg and rp were highly variable in OP, ranging from 0.435 to 0.973 and from 0.597 to 0.874, respectively. The rg of SL, SH, SW, and BW between the two aquaculture environments for Data 1 were 0.867, 0.682, 0.651, and 0.844, respectively. The rg ranged from 0.274 to 0.619 for Date 2. These results indicated significant G × E interactions among families at different sites. This study therefore provided optimal guidelines to select breeding programs for razor clams reared in different aquaculture environments.

New bivalve burrows from the mid-Holocene of northeastern Buenos Aires Province (Argentina): ichnotaxonomy and ethology

Oblongichnus vulpesi n. isp. is herein described as amygdaloid, oval or cleft-shaped burrows with a lining of variable thickness and an oblong to quadrangular elongated shaft from the mid-Holocene of the Destacamento Río Salado Member. Valves of the solenid bivalve species Solen tehuelchus were found within the burrows, indicating that this razor clam is the tracemaker. This new finding corroborates the validity of Oblongichnus and previous interpretation that the burrow was produced by infaunal, filter feeding bivalves with a foot of very limited horizontal movements. We found that the origin of oblong elongate bivalves may be dated back to the Ordovician, while an infaunal radiation likely occurred during late Paleozoic. We interpret that O. vulpesi was made in a moderate energy subtidal marine setting during the last marine highstand.

Effects of light intensity on artificial breeding of Sinonovacula constricta

In the present study, we aimed to explore the optimal light intensity for the breeding of Sinonovacula constricta, and the effect of light intensity on the growth of S. constricta at different developmental stages was studied. Four developmental stages (spawning, fertilized eggs, planktonic larvae, and juveniles) and different light intensities were set up in our current experiments. The results showed that various light intensities had significantly different effects on spawning amount and initial spawning time, while it had little influence on the hatchability of fertilized eggs (P > 0.05). The spawning amount of the razor clam peaked at a light intensity of 44–250 lx (P < 0.05). In the planktonic larvae experiment, the highest survival rate appeared at 487 ± 31 lx (58.61 ± 4.0%).For juvenile S. constricta, two substratum thicknesses (1 and 5 mm) and four light intensities, including L1 (14 ± 11 lx), L2 (380 ± 145 lx), L3 (3792 ± 2105 lx), and L4 (12,244 ± 5290 lx), were set up in a 10-day experiment. When the substratum thickness of 1 mm was applied, the body length and survival rate of S. constricta juveniles (0.26 ± 0.02 mm) in the L2 group were found to be the largest, which were significantly different compared with the other groups. When the substratum thickness was changed to 5 mm, the body length and survival rate among those groups showed no significant difference. However, when the shellfish samples were changed to a larger size of razor clam (1.45 ± 0.16 mm), a more obvious effect of light intensity on the growth was observed in a 1-mm substratum group compared with the 5-mm group. These results indicated that light intensity exerted a significant effect on the growth of S. constricta at different stages, and each stage exhibited a distinct sensitivity to light intensity. Further study from the aspects of photoreceptors and relevant genes is currently in progress in our laboratory.

Characteristics of glutathione peroxidase gene and its responses to ammonia-N stress in razor clam Sinonovacula constricta

Glutathione peroxidase (GPX) is a crucial enzyme in the antioxidant defense system. However, the previous studies on the structure and functions of mollusk GPX genes are still very limited. Here, we investigated the GPX gene from Sinonovacula constricta (Sc-GPX), and its expression profiles, protein localization, gene function and association with ammonia tolerance. The full length of sequence of Sc-GPX was 1781 bp, containing an open reading frame (ORF) of 588 bp encoding 195 amino acids. Quantitative expression of seven adult tissues showed that Sc-GPX was most abundant in hepatopancreas, followed by gills. Furthermore, the enzyme activity of Sc-GPX in hepatopancreas increased significantly under different ammonia concentrations (100, 140, and 180 mg/L) (P < 0.01). Further, we explored the mRNA expression level, histological structure and histo-cellular localization in gills and hepatopancreas of Sc-GPX under 140 mg/L ammonia stress. The mRNA expression level in gills and hepatopancreas of Sc-GPX increased significantly (P < 0.05) and immunohistochemistry results suggested that the columnar cells of gills filaments and the endothelial cells of hepatopancreas were the major sites for the action of Sc-GPX protein. In addition, we performed western blotting (WB), RNA interference (RNAi) and single nucleotide polymorphisms (SNPs) in the hepatopancreas of Sc-GPX under ammonia stress (140 mg/L). WB results indicated that the protein expression of Sc-GPX increased significantly (P < 0.01) after ammonia challenge. In addition, expression of Sc-GPX mRNA were significantly downregulated at 24 and 48 h after RNAi (P < 0.01). The association analysis between ammonia-tolerance group and control group identified six SNPs in coding sequence (CDS) of Sc-GPX from 449 individuals. Among them, c.162A > C was missense mutation, which lead to the amino acid change from Lys to Asn. These findings revealed that Sc-GPX may play a critical role in clam ammonia detoxification.

Filter-Feeding Bivalve Weakens Food Competition Between Crustaceans (Portunus trituberculatus, Marsupenaeus japonicus) in Integrated Culture Ponds: Evidence From 18S rDNA Barcoding and Stable Isotope Analysis

In order to investigate the effects of razor clams (Sinonovacula constricta) on the food composition and isotopic niches of swimming crabs (Portunus trituberculatus) and kuruma shrimp (Marsupenaeus japonicus) in polyculture systems, this study analyzed 60 P. trituberculatus, 60 M. japonicus and 30 S. constricta to quantify the food sources, food source contributions, and isotopic niches of cultured organisms using 18S rDNA barcoding and stable isotope techniques. The results were as follows: (1) In the P. trituberculatus-M. japonicus (PM) polyculture system, the Sobs and Shannon-Wiener indices of the stomach contents of P. trituberculatus and M. japonicus were not significantly different (P &amp;gt; 0.05). In the P. trituberculatus-M. japonicus-S. constricta polyculture (PMS) system, the Sobs and Shannon-Wiener indices of the stomach contents of P. trituberculatus and M. japonicus were also not significantly different (P &amp;gt; 0.05), but the Sobs indices of P. trituberculatus in the PMS system were significantly higher than those in the PM system (P &amp;lt; 0.05), M. japonicus shows a similar pattern. (2) 18S rDNA barcoding analysis showed the dominant taxa in the stomach contents of both P. trituberculatus and M. japonicus in the PM system were Trebouxiophyceae, Embryophyta and Rotifera, and the food overlap between them was 0.8992, which was significant (Q &amp;gt; 0.6). In the PMS system, the dominant taxa in the stomach contents of P. trituberculatus were Chrysophyceae, Intramacronucleata, and Embryophyta, and in M. japonicus were Chrysophyceae, Embryophyta, and Bacillariophyceae, in this system the food overlap was 0.2061, which was not significant (Q &amp;lt; 0.6). (3) Stable isotope analysis suggested, in both systems, the main food sources of P. trituberculatus and M. japonicus were iced trash fish, zooplankton, phytoplankton, and organic particulate matter (POM). Iced trash fish accounted 77.67% of food sources for P. trituberculatus and 69.42% for M. japonicus in the PM system, and 60.82% and 57.60% in the PMS system. (4) The isotopic niche overlap between P. trituberculatus and M. japonicus was 5.69% in the PM system and 1.21% in the PMS system. These results suggested food competition between P. trituberculatus and M. japonicus, and S. constricta can reduce the competition and isotopic niche overlap, improve the contribution of food sources such as phytoplankton. Razor clams also serve to purify the water and improve the utilization of iced trash fish by filtering phytoplankton (51.10%), POM (32.25%), SOM (7.47%), and iced trash fish (9.18%). Thus, P. trituberculatus-M. japonicus-S. constricta is a healthy and sustainable culture model.

Metabolomics approach to assess the effect of siphonal autotomy on metabolic characteristics of razor clam Solen grandis

Autotomy appendages are fundamental evolutionary adaptations to escape predation. The siphon is an important foraging organ for bivalves. Here, we report the first demonstration of autotomy of the siphon in marine bivalves (razor clam Solen grandis) and the effect of siphonal autotomy in S. grandis on foraging and metabolic characteristics. In this study, the feeding rate and digestive enzyme activities upon siphonal autotomy in razor clams were investigated. Moreover, endogenous metabolites pre/post-autotomy of the siphon were investigated using liquid chromatography tandem-mass spectrometry (LC–MS). The feeding rate and digestive enzyme activities decreased significantly after siphonal autotomy in S. grandis (P < 0.05), suggesting that autotomy of the siphon negatively affected its foraging. These results might be related to the reduction in the foraging radius. Additionally, the effect of autotomy was investigated on a total of 34 differentially abundant metabolites, and pathway analysis indicated that 32 differentially enriched metabolic pathways were worthy of attention. Further integrated key metabolic pathway analysis showed that glycine, serine and threonine metabolism; taurine and hypotaurine metabolism; biotin metabolism; vitamin B6 and thiamine metabolism were significantly relevant pathways in S. grandis pre/post-autotomy of the siphon. The downregulation of glycine, taurine, and hypotaurine is expected to indicate a shortage of intermediate compounds and energy in S. grandis. Therefore, to provide the required energy and materials for siphon regeneration in S. grandis, we anticipated that it would be necessary to supplement these as exogenous metabolites from the daily diet.

Molecular Characterization of Aquaporins Genes from the Razor Clam Sinonovacula constricta and Their Potential Role in Salinity Tolerance

Aquaporins (AQPs) play crucial roles in osmoregulation, but the knowledge about the functions of AQPs in Sinonovacula constricta is unclear. In this study, Sc-AQP1, Sc-AQP8, and Sc-AQP11 were identified from S. constricta, and the three Sc-AQPs are highly conserved compared to the known AQPs. The qRT-PCR analysis revealed that the highest mRNA expressions of Sc-AQP1, Sc-AQP8, and Sc-AQP11 were detected in the gill, digestive gland, and adductor muscle, respectively. In addition, the highest mRNA expression of Sc-AQP1 and Sc-AQP11 was detected in the D-shaped larvae stage, whereas that of SC-AQP8 was observed in the umbo larvae stage. The mRNA expression of Sc-AQP1, Sc-AQP8, and Sc-AQP11 significantly increased to 12.45-, 12.36-, and 27.44-folds post-exposure of low salinity (3.5 psu), while only Sc-AQP1 and Sc-AQP11 significantly increased post-exposure of high salinity (35 psu) (p &lt; 0.01). The fluorescence in situ hybridization also showed that the salinity shift led to the boost of Sc-AQP1, Sc-AQP8, and Sc-AQP11 mRNA expression in gill filament, digestive gland, and adductor muscle, respectively. Knockdown of the Sc-AQP1 and Sc-AQP8 led to the decreased osmotic pressure in the hemolymph. Overall, these findings would contribute to the comprehension of the osmoregulation pattern of AQPs in S. constricta.

Comparative transcriptome analyses unravel the response to acute thermal stress in the razor clam, Sinonovacula constricta

The razor clam, Sinonovacula constricta, must have acquired adaptive mechanisms to defense thermal pressure during evolution as it’s an eurythermal bivalve. However, the specific mechanisms remain unclear. To identify thermal responsive genes and unravel adaptive mechanisms, the clams were subjected to acute thermal stress from 21 °C to 32 °C for 24 h. The transcriptomic profilings of gills and hepatopancreas from control and treatment groups were investigated. A total of 786 differentially expressed genes (DEGs) were identified in the hepatopancreas between both groups while 556 DEGs were identified in the gills. GO and KEGG analysis showed that these DEGs were significantly enriched in protein homeostasis, metabolisms, immune response, antioxidant response and cytoskeletal organization processes. Protein processing in endoplasmic reticulum was most enriched in the gills. Lipid metabolism pathway was mainly repressed in the hepatopancreas. Antigen processing and presentation and NOD-like receptor (NLR) signaling pathways were enriched in both tissues while C-type lectins (CTLs) and allograft inflammatory factor (AIF) were more significantly down-regulated in the hepatopancreas (P < 0.05). Besides, the cytoskeletal structure related genes showed opposite expression pattern in the gills and hepatopancreas after thermal stress, such as tubulin-related genes were up-regulated in the gills, while fibrillins (FBNs) were down-regulated in the hepatopancreas. These findings suggested gills and hepatopancreas have specific functions to thermal stress. Our results indicated that multiple-biological process adjustments have occurred in the razor clam after heat stress. This study will contribute to understanding the molecular adaptive mechanism to heat stress and provide candidate genes for genetic breeding with thermal resistant trait.

DEM study of the alteration of the stress state in granular media around a bio-inspired probe

Soil penetration is a ubiquitous energy-intensive process in geotechnical engineering that is typically accomplished by quasi-static pushing, impact driving, or excavating. In contrast, organisms such as marine and earthworms, razor clams, and plants have developed efficient penetration strategies. Using motion sequences inspired by these organisms, a probe that uses a self-contained anchor to generate the reaction force required to advance its tip to greater depths has been conceptualized. This study explores the interactions between this probe and coarse-grained soil using 3D discrete element modeling. Spatial distributions of soil effective stresses indicate that expansion of the anchor produces arching and rotation of principal effective stresses that facilitate penetration by inducing stress relaxation around the probe’s tip and stress increase around the anchor. Spatial strain maps highlight the volumetric deformations around the probe, while measurements of both stresses and strains show that the state of the soil around the anchor and tip evolves toward the critical state line. During subsequent tip advancement, the stresses and strains are similar to those during initial insertion, leading to the remobilization of the tip resistance. Longer anchor and shorter anchor-to-tip distance better facilitate tip advancement by producing greater stress relaxation ahead of the tip.

Assessing the potential for invasive species introductions and secondary spread using vessel movements in maritime ports

Global shipping facilitates the introduction of invasive species and parasites via ballast water and hull fouling. Regional management of invasives may be strengthened by identifying the major routes in a network, to allow for targeted ship inspections. This study used cargo shipping records to establish the connectivity of shipping routes between ports in Ireland and other nations. 9291 records were analysed, investigating vessel residence and journey times. On average, vessels spent up to five days in port and less than five days at sea. However, there was strong variation, with general cargo ships recording up to 13 days in port. A horizon scan for species likely to invade in Ireland was incorporated for five species and their associated parasites: American razor clam, Asian shore crab, Brush clawed shore crab, Chinese mitten crab and American slipper limpet. Routes of concern are highlighted and a general framework for effective management is outlined.

Effects of High Salinity Stress on the Survival, Gill Tissue, Enzyme Activity and Free Amino Acid Content in Razor Clam Sinonovacula constricta

Salinity can affect the physiological and productive characteristics of bivalves. The razor clam Sinonovacula constricta naturally distributing in intertidal zones and estuarine waters is extensively cultured in China. High-salinity is a serious threat to its culture, especially in pond culture model. Here, we investigated the effects of high-salinity on the survival, gill tissue, enzyme activity and free amino acid content of S. constricta. Individuals were randomly divided into six groups treated with different salinities of 20, 25, 30, 35, 40, and 45 ppt. The median lethal salinity calculated by linear regression and probit analysis methods were similar, with 46.61, 43.17, 36.99, 35.99, and 34.99 ppt by linear regression, while 44.63, 42.87, 38.45, 37.32, and 36.17 ppt by probit analysis at 72, 96, 120, 144, and 168 h, respectively. Furthermore, paraffin section revealed that the gill of razor clam shrunk quickly under high-salinity and dissolved at 48 h under salinity of 40 ppt, but not under 30 ppt. In addition, the activities of three enzymes including Na+-K+-ATPase, acid phosphatase and alkaline phosphatase changed significantly under high-salinity. Besides, the contents of total free amino acids (TFAAs) in the gill tissues were 61.25 ± 1.58, 89.36 ± 4.18, and 111.98 ± 1.46 mg⋅g–1 at salinity of 20, 30, and 40 ppt, respectively, indicating increasing TFAA contents with salinity. Notably, several amino acid species including taurine, alanine, proline, glycine and glutamic showed significantly changed contents in response to salinity variation, suggesting these amino acids might play an important role in razor clam’s adaptation to salinity stress. Combining all these results, it was referred that razor clams may adapt to moderately high-salinity of 30 ppt in a short time through osmotic adjustment. Although a small proportion of individuals could survive under the salinity of 35 ppt, the death of most individuals still suggested it can hardly be accepted in aquacultural production. Notably, living under a salinity of 40 ppt for more than 48 h could cause great damage to razor clams. Therefore, the seawater salinity is recommended to be lower than 30 ppt for S. constricta aquaculture. Overall, this study provides guidance for the culture and breeding of high-salinity tolerant razor clams.

Expression of p38MAPK and its regulation of apoptosis under high temperature stress in the razor clam Sinonovacula constricta

p38MAPK is a key branch of the MAPK (mitogen-activated protein kinase) pathway that plays an important role in physiological processes such as apoptosis, cell proliferation and growth. In this experiment, we screened and identified one p38MAPK gene in the razor clam Sinonovacula constricta, which encoded 359 amino acids and was widely expressed in various adult tissues. After 24 h of high temperature stress at 34 °C, the transcript expression of p38MAPK showed significant changes in all tested tissues. In particular in the gill and hepatopancreas tissues, where the expression increased 1.81 and 7.83 times compared with the control group, respectively (P < 0.01). Furthermore, we examined the expression of the apoptosis suppressor gene Bcl-2 and pro-apoptosis gene Bax by knock-down of p38MAPK with dsRNA interference in the gill and hepatopancreas tissues. The obvious up-regulation expression of Bcl-2 and significant suppression of Bax were observed, respectively (P < 0.01). Moreover, the TUNEL staining technique was used to detect apoptosis before and after interference. The degree of apoptosis in the gill and hepatopancreas tissues was reduced after interference with p38MAPK, and the ROS content was significantly reduced (P < 0.01). The results suggested that p38MAPK had a regulatory role in the heat tolerance of razor clams.

Transcriptomic Analysis of Gill and Hepatopancreas in Razor Clam (Sinonovacula constricta) Exposed to Acute Ammonia

Accumulation of excessive ammonia is a big threat to aquatic animals, which causes adverse effects on the health, production reduction, and even high mortality. The razor clam Sinonovacula constricta, a bivalve living in intertidal mudflat with a deep-burrowing lifestyle, often faces a high concentration of ambient ammonia. However, there is less available information concerning the toxic effects of ammonia on razor clam and its molecular mechanisms of adaptation to ammonia stress. The aim of this study was to investigate the effects of ammonia exposure on the gill and hepatopancreas of razor clam by transcriptome sequencing. The results showed that the median lethal concentration of ammonia was 244.55 mg/L for 96 h. A total of 1,415 and 306 differentially expressed genes (DEGs) were identified in the gill and hepatopancreas, respectively. The functional annotation showed that DEGs of the gill were mainly involved in the regulation of nitrogen compound metabolic process, nitrogen compound transport, and amide transport. The DEGs of the hepatopancreas were mostly enriched in oxidation-reduction process, response to stress, and amine metabolic process. The expression levels of NH3/NH4+ transporting channels and H+ excreting-related genes, including Rhesus glycoproteins (Rh), Na+/K+-ATPase (NKA), Na+/H+ exchanger, V-ATPase (VHA), and carbonic anhydrase (CA), were upregulated significantly in the gill (p &amp;lt; 0.05). In addition, the expression levels of glutamine and urea synthesis-related genes that played vital roles in ammonia detoxification, such as glutamine synthetase (GS), arginase (ARG), and argininosuccinate synthetase (ASS), were also increased obviously in the hepatopancreas (p &amp;lt; 0.05). Taken together, our results indicate that the synergistic action of ammonia excretion in the gill and ammonia metabolism in the hepatopancreas might be the mechanism through which the clams tolerate to environmental ammonia. This study provides a molecular basis for the better evaluation of the responding mechanism of ammonia tolerance.

Trial on artificial breeding and laviculture of giant razor clams (Cultellus maximus Gmelin, 1791)

The study was carried out with the aim of determining the reproductive parameters and performing the rearing of giant razor clams (Cultellus maximus Gmelin, 1791) at larval stage and postlarval stage with different diets. The results showed that the spawning rate was 62.22 ± 3.85%, the fecundity was 7.98 ± 0.67 million eggs/female, the relative fecundity was 48,081 ± 5,826 eggs/g female, the fertilization rate was 42.67 ± 4.47%, and the hatching rate was 44.19 ± 4.02%. The rearing at larval stage with different diets of algae was investigated ((T1.1): Nanochloropsis oculata + Isochrysis galbana; (T1.2): N. oculata + Chaetoceros muelleri; and (T1.3): N. oculata + Isochrysis galbana + C. muelleri). The results showed that T1.3 gave the survival rate, length and width of larvae, reaching 5.3 ± 0.91%; 1525.60 ± 48.90 μm and 918.20 ± 28.00 μm, respectively. The parameters obtained from T1.3 was significantly higher (P &lt; 0.05) than that of T1.1 and T1.2. The rearing at postlarval stage with different diets was also studied as follow: (T2.1): N. oculata + I. galbana + C. muelleri; (T2.2): using commercial feed (Lansy and Frippak); and (T2.3): combination of 50% of T2.1 + 50% of T2.2. The results showed that T2.1 gave the survival rate, growth in length and width of postlarvae, reaching 11.83 ± 3.89%; 5.72 ± 0.61 mm and 3.31 ± 0.14 mm respectively. Growth parameters of T2.1 were significantly higher (P &lt; 0.05) compared to that of T2.2 and T2.3.

Growth performance and ecological services evaluation of razor clams based on dynamic energy budget model

Bivalve shellfish aquaculture has been proposed to abate eutrophication and increase carbon sink in integrated multi-trophic aquaculture ecosystems. An individual growth model for razor clams Sinonovacula constricta in an integrated aquaculture pond of Portunus trituberculatus– Penaeus japonicus– S. constricta was constructed based on dynamic energy budget (DEB) theory after parameter measurement and model validation. Goodness-of-fit indices (R-squared, mean difference, and absolute and relative root mean square error) showed that the DEB model accurately reproduced razor clam growth. The growth performance evaluation of razor clams under different environmental conditions showed that warming climate and food shortages inhibited the razor clam growth. The quantification results of ecological service showed that individual razor clam have the potential for nutrient (nitrogen and phosphorus) removal and CO2 fixation, but exhibit a source of CO2 in individual month. The possible applications and contribution of this aquaculture model in China are also discussed, and the assessment results can provide important support for the low carbon bivalve integrated aquaculture.

Carbon dioxide uptake overrides methane emission at the air-water interface of algae-shellfish mariculture ponds: Evidence from eddy covariance observations

Mariculture ponds are widely distributed along the coastal regions and have been increasingly recognized as biogeochemical hotspots of air-water greenhouse gas (GHG) fluxes, but their source/sink dynamics and climate benefits have not been well understood. Due to strong temporal variations of GHG fluxes over mariculture ponds, previous studies based on short-term or discrete flux measurements have large uncertainty in assessing GHG budgets and their radiative effects. In this study, we examined the temporal variations of air-water GHG fluxes, net CO2 exchange (NEE) and net CH4 exchange (NME), and their environmental controls, based on one-year (2020) continuous eddy covariance (EC) measurements over algae-shellfish mariculture ponds (razor clam) in a subtropical estuary of Southeast China. The results showed that (a) annually the ponds acted as a strong CO2 sink of −227.7 g CO2-C m−2 and a weak CH4 source of 1.44 g CH4-C m−2, and thus the NME-induced warming effect offset 25.9% (12.1%) of the NEE-induced cooling effect at a 20-year (100-year) time horizon using the metric of sustained-flux global warming potential; (b) two GHG fluxes showed different diurnal and seasonal variations but both had stronger source/sink capacity in summer and more fluctuating fluxes in winter; (c) temporal variations of NEE and NME tended to be more regulated by photosynthetically active radiation and tidal salinity, respectively, but both of them were affected by water temperature and area proportion of algae ponds within the EC footprint. This is the first study to disentangle temporal variations of air-water GHG fluxes over mariculture ponds based on simultaneous EC measurements of CO2 and CH4 fluxes. This study highlights the climate benefits of algae-shellfish mariculture ponds as biogeochemical hotspots by exerting a net radiative cooling effect dominated by the CO2 sink.