Temporal Changes in Physiological Responses of Bay Scallop: Performance of Antioxidant Mechanism in Argopecten irradians in Response to Sudden Changes in Habitat Salinity

Changes to habitat salinity may induce oxidative stress in aquatic organisms. The effect of salinity on the antioxidant function of bay scallops was investigated at 55, 70, 85 and 120% of seawater salinity (SW), with 100% SW as the control. The scallops were sampled 0, 6, 12, 24, 48 and 72 h after the salinity change to measure superoxide dismutase (SOD), catalase (CAT), hydrogen peroxide (H2O2), and lipid peroxidation (LPO) levels, as well as apoptosis in the digestive diverticula and/or hemolymph. The SOD immunohistochemistry and apoptotic response were assessed at 55% and 120% SW at 12 h. Antioxidant expressions at 55% and 70% SW peaked at 24 h or 48 h, and then decreased. At 120% SW, they increased with exposure time. The H2O2 and LPO levels at each SW increased significantly with time. A comet assay also revealed that changes in salinity increased the rate of nuclear DNA damage in all the salinity groups. Thus, variations in salinity result in significant physiological responses in bay scallops. A change in habitat salinity of 15% or more produces oxidative stress that cannot be resolved by the body’s antioxidant mechanism, suggesting that excessive generation of reactive oxygen species can lead to cell death.

Characterization of Wnt Genes in Argopecten Scallops and Their Involvement in Responses to Different Temperature Stresses in Bohai Red Scallops

Background: Bohai Red, a new Argopecten scallop strain selected from the hybrids between the Peruvian scallop, Argopecten purpuratus and the bay scallop northern subspecies, A. irradians irradians, is now one of the most cultured scallop strains in northern China. As one of a series of studies focusing on adaptation of Bohai Red scallops to fluctuations in environmental factors, this study aimed to examine the expression profile of Wnt genes in response to different temperature stresses in Bohai Red. Results: As Bohai Red scallops were originated from the hybrids between the Peruvian scallop and the bay scallop northern subspecies, we first identified all Wnt genes from the genomes of the Peruvian scallop and the bay scallop northern subspecies, as well as the bay scallop southern subspecies, A. i. concentricus. Twelve Wnt members were identified from the two subspecies of bay scallop, and 13 Wnt genes were found in the genome of the Peruvian scallop. Protein structure analyses showed that most Wnt genes poses all 5 conserved motifs except Wnt 1, Wnt 2, Wnt 6 and Wnt 9 in the bay scallops and Wnt2 and Wnt9 in the Peruvian scallop. Unexpectedly, Wnt8 gene was present while Wnt3 was absent in both the bay scallops and the Peruvian scallop. Phylogenetic analysis revealed that Wnt3 may have disappeared in the early evolution of mollusks. The expression profile of Wnt genes in Bohai Red exposed to different temperatures were examined by qRT-PCR. The results showed that expression of Wnt genes responded differentially to temperature changes. The Wnt genes such as Wnt1, Wnt6, Wnt7, Wnt11 and WntA that responded slowly to low and high temperature stresses may be related to the maintenance of basic homeostasis. Other Wnt genes such as Wnt4, Wnt9, Wnt5 and Wnt2 that responded rapidly to low temperature may play an important role in organismal protection against low temperature stress. And yet some Wnt genes including Wnt10, Wnt16, and Wnt8 that responded quickly to high temperature stress may play key roles in response to organismal stress provoked by high temperature stress. Conclusions: Wnt genes are well conserved in Argopecten scallops, as in other bivalves. Wnt genes may play important roles in adaptation of Bohai Red scallops to changing temperatures. The results in this study will provide new insights into the evolution and function of Wnt genes in bivalves and eventually benefit culture of Bohai Red scallops.

Predation on Planted and Wild Bay Scallops (Argopecten Irradians Irradians) by Busyconine Whelks: Studies of Behavior Incorporating Acoustic Telemetry

Quantifying predator-prey interactions and gaining insights into predator behavior are crucial for optimizing restoration strategies; yet, such knowledge is often lacking for marine invertebrates. We examined potential impacts of predation by channeled (Busycotypus canaliculatus) and knobbed whelks (Busycon carica) on natural and planted populations of bay scallops in the Peconic Bays, New York, through laboratory and field investigations. Mean rates of predation by small channeled whelks were low: 0.06 and 0.005 scallops d-1 for adult and juvenile scallops; respective lab predation rates of small knobbed whelks on juvenile scallops were 24x higher. Channeled whelks usually did not damage shells of scallop prey (86%), but knobbed whelks typically notched the ventral shell margin (73%). In field plots where scallop densities were manipulated via removals/plantings, whelks consumed ~2% of ~19,100 planted juveniles; crabs and presumably finfish consumed over 40% in all trials overall. Acoustic telemetry revealed that tagged channeled whelks moved shorter distances and spent more time in plots planted with scallops versus those without scallops. Unexpectedly, whelks spent more time in low vs. high density plots, but consumed far more scallops in the latter. In trials without scallops, whelk movement rates were 5x higher, presumably due to increased exploratory behavior. Overall, whelks were most active during crepuscular hours and during periods of increasing wind speeds. Our results, combined with population abundance data, suggest that whelks (especially B. carica) are drawn to high density scallop plantings and may be important causes of bay scallop mortality in the context of restoration efforts.

Genome-Wide Association Study Reveals PC4 as the Candidate Gene for Thermal Tolerance in Bay Scallop (Argopecten irradians irradians)

The increasing sea temperature caused by global warming has resulted in severe mortalities in maricultural scallops. Therefore, improving thermal tolerance has become an active research area in the scallop farming industry. Bay scallop (Argopecten irradians irradians) was introduced into China in 1982 and has developed into a vast aquaculture industry in northern China. To date, genetic studies on thermal tolerance in bay scallops are limited, and no systematic screening of thermal tolerance-related loci or genes has been conducted in this species. In the present study, we conducted a genome-wide association study (GWAS) for thermal tolerance using the Arrhenius break temperature (ABT) indicators of 435 bay scallops and 38,011 single nucleotide polymorphism (SNP) markers. The GWAS identified 1,906 significant thermal tolerance-associated SNPs located in 16 chromosomes of bay scallop. Gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses showed that 638 genes were enriched in 42 GO terms, while 549 annotated genes were enriched in aggregation pathways. Additionally, the SNP (15-5091-20379557-1) with the lowest P value was located in the transcriptional coactivator p15 (PC4) gene, which is involved in regulating DNA damage repair and stabilizing genome functions. Further analysis in another population identified two new thermal tolerance-associated SNPs in the first coding sequence of PC4 in bay scallops (AiPC4). Moreover, AiPC4 expression levels were significantly correlated (r = 0.675–0.962; P < 0.05) with the ABT values of the examined bay scallops. Our data suggest that AiPC4 might be a positive regulator of thermal tolerance and a potential candidate gene for molecular breeding in bay scallop aiming at thermal tolerance improvement.

Restoration of seagrass habitat leads to rapid recovery of coastal ecosystem services

There have been increasing attempts to reverse habitat degradation through active restoration, but few large-scale successes are reported to guide these efforts. Here, we report outcomes from a unique and very successful seagrass restoration project: Since 1999, over 70 million seeds of a marine angiosperm, eelgrass (Zostera marina), have been broadcast into mid-western Atlantic coastal lagoons, leading to recovery of 3612 ha of seagrass. Well-developed meadows now foster productive and diverse animal communities, sequester substantial stocks of carbon and nitrogen, and have prompted a parallel restoration for bay scallops (Argopecten irradians). Restored ecosystem services are approaching historic levels, but we also note that managers value services differently today than they did nine decades ago, emphasizing regulating in addition to provisioning services. Thus, this study serves as a blueprint for restoring and maintaining healthy ecosystems to safeguard multiple benefits, including co-benefits that may emerge as management priorities over time.

Assessment of the presence of lipophilic phycotoxins in scallops (Argopecten purpuratus) farmed along Peruvian coastal waters

Harmful algal blooms (HABs) are known to produce lipophilic marine biotoxins (LMTs) such as okadaic acid (OA) (and its analogues dinophysistoxins (DTXs)), yessotoxins (YTXs), pectenotoxins (PTXs), and azaspiracids (AZAs), all of which can accumulate in bivalve mollusks and exert noxious effects on humans. Health regulations indicate a limit up to 160 µg/kg for OA/DTXs, PTXs or AZAs, and 3.75 mg/kg for YTXs.Argopecten purpuratus is one of the most important commercial marine products exploited in Perú. Despite its importance and the periodic reports of the presence of HABs in Peruvian coastal waters, the lack of information regarding potential contamination by LMTs is noteworthy.In this work, we report a study performed with 115 samples of A. purpuratus collected between November 2013 and March 2015 from 18 scallop production areas distributed along the Peruvian coast in search of LMTs. To magnify positive results, the hepatopancreas tissue was analyzed by an LC-MS/MS method implemented to quantify OA, YTX, AZA-1, and PTX-2. Baseline separation was achieved in 19 min. The method showed satisfactory linearity (R 2 > 0.997), precision (coefficient of variation < 15 %), and limit of quantification (0.155-0.479 ng/mL). The study revealed the presence of YTX in 72 samples and of PTX-2 in 17 samples, with both biotoxins found at concentrations below the regulatory limits. Free OA and AZA-1 were not detected in any scallop sample. This atypical profile, presence of PTX-2 in the absence of OA, has been previously reported and may be linked to presence of the dinoflagellate D. acuminata . The production of YTX could be associated to the phytoplankton G. spinifera and P. reticulatum .This is the first systematic assessment of the four groups of LMTs in shellfish from Peruvian coastal waters. The results attained suggest low prevalence of marine biotoxins in Peruvian bay scallops yet support the necessity of future surveillance and analysis of LMTs in Perú.