Large-scale oyster farming accelerates the removal of dissolved inorganic carbon from seawater in Sanggou Bay.

While the direct impact of oyster calcification and respiration on the seawater inorganic carbon system is well-acknowledged, their indirect effect through filter feeding activities remains unclear. Here we studied the impact of large-scale oyster farming on the removal of dissolved inorganic carbon (DIC) from seawater. Field investigations showed that the DIC level in the oyster farming area in Sanggou Bay, China were significantly lower than that in the non-farming area. In-lab incubation showed that regardless of whether incubated in high or low-transparent environments, the DIC removal rate of seawater from the oyster farming area was significantly higher than that of the non-farming area. These results indicate that cultivated oysters facilitate the removal of seawater DIC in the farming area. To reveal the indirect effect of filter feeding activities on DIC removal, we used 6-m3 ponds to simulate the oyster-farming environment. Results showed that the average DIC level of the oyster-cultivating groups was 105.83 µmol/kg lower than that of the control groups (without of oyster) after a six-day cultivation. Surprisingly, the average concentration of Chl-a in oyster-cultivating groups was significantly higher than that of the control group at the end of the experiment. Similarly, DIC level declined faster while Chl-a concentration increased faster in seawater that previously experienced 12～20 h of oyster cultivation than that in the control seawater. It was noticed that the transparency of seawater within 6-m3 ponds increased significantly just after hours of oyster cultivation. This enhanced transparency created a favorable light environment that supported phytoplankton photosynthesis and simultaneously accelerated the DIC removal rate. Overall, oysters not only remove the inorganic carbon in the seawater through calcification but also create a suitable environment for phytoplankton photosynthesis through their filtering activity, and subsequently accelerating the removal of inorganic carbon in the seawater of the oyster farming area.

Biogenic silica in sediment core indicates the historical development of off-bottom oyster farming.

Sediment cores are commonly used for reconstructing historical events by determining the biogenic elements in sediment vertical profiles. The vertical flux of biogenic silica (BSi) can be enhanced by bivalve mollusks through biodeposition and can be subsequently recorded in the sediment core. However, whether BSi in sediment core can indicate the interactions between aquaculture farms and the ecosystem is unclear. In this study, sediment cores were collected from a typical off-bottom oyster farm in Sanggou Bay, China. Based on 210Pb chronology analysis of the sediment vertical profile, BSi content was determined to reflect the BSi burial flux during the farming history. The BSi biodeposition fluxes were estimated based on the biodeposition model, to identify the correspondence among BSi burial flux, BSi biodeposition flux, and annual oyster production during the historical development of the farm. The results show that the BSi density in the sediment increased obviously after 1980 when intensive oyster farming began, and reduced after 2000 when farming began to decline. Moreover, BSi burial flux had a corresponding relationship with oyster production and the simulated biodeposition rate, except for 1997-2001 when oyster production peaked. Our finding supported that the variation of BSi from biodeposition can be preserved and then recorded in the sediment, suggesting that BSi could be considered as an indicator to reconstruct the historical development of the oyster farm.

A food-web model as a tool for the ecosystem-level management of bivalves in an Atlantic coastal lagoon.

The Ria de Aveiro is an important coastal lagoon for wildlife in Portugal, where the production of bivalves reaches approximately 2700 tons annually. However, the illegal overfishing of bivalves is frequent in this lagoon, which causes critical changes in the ecosystem. In this study, using a developed food-web model (Ecopath model), the ecological carrying capacity (ECC) and maximum sustained yield (MSY) of the Manila clam, Ruditapes philippinarum were estimated, and the effects of further increases in clam biomass on other species were investigated. The results showed that 1) the current biomass and legal catch of R. philippinarum do not yet exceed the ECC (172.40 tons km-2) or the MSY (86.20 tons km-2 year-1) in Ria de Aveiro; 2) the harvested Manila clams of the MSY represent removing from the ecosystem âˆ¼ 581 tons carbon (C) and ∼83 tons nitrogen (N) annually, with substantial ecological and economic implications; and 3) a further increase in the biomass levels of this species may cause the ecotrophic efficiency of other groups to become unrealistic, potentially leading to decreases in ecosystem transfer efficiency, biodiversity and health. The results here are expected to guide the sustainable development and management of bivalve aquaculture in Ria de Aveiro and the protection of the local environment.

The Application of the Generalized Additive Model to Represent Macrobenthos near Xiaoqing Estuary, Laizhou Bay.

Macrobenthos is widely used as an indicator of ecological health in marine monitoring and assessment. The present study aimed to characterize the interrelationships between the distribution of the macrobenthos community and environmental factors near Xiaoqing Estuary, Laizhou Bay. Responses of species richness to environmental factors were studied using the generalized additive model (GAM) and the Margalef diversity index (dM) as indicators of species diversity instead of individual indicator species. Six factors were selected in the optimal model by stepwise regression: sediment factors (organic matter, phosphate, nitrate nitrogen, and ammonium nitrogen) and water factors (salinity, and ammonium nitrogen). The response curves generated by the GAM showed a unimodal relationship among taxa diversity, salinity in water, and sediment organic matter. dM was positively correlated with ammonium nitrogen in water and was negatively correlated with phosphate in the sediment. The model optimized by forward stepwise optimization explained 92.6% of the Margalef diversity index with a small residual (2.67). The model showed good performance, with the measured dM strongly correlated with the predicted dM (Pearson R2 = 0.845, p < 0.05). The current study examined the combined influence of multiple eco-factors on macrobenthos, and the Margalef diversity index of macrobenthos was predicted by the GAM model in a salinity-stressed estuary.

CO2-Induced Ocean Acidification Alters the Burrowing Behavior of Manila Clam Ruditapes philippinarum by Reversing GABAA Receptor Function.

Biological burrowing behavior is an important driver shaping ecosystems that is being threatened by CO2-induced ocean acidification; however, the effects of ocean acidification on burrowing behavior and its neurological mechanism remain unclear. This study showed that elevated pCO2 significantly affected the burrowing behaviors of the Manila clam Ruditapes philippinarum, such as increased foot contraction, burrowing time, and intrabottom movement and decreased burrowing depth. Delving deeper into the mechanism, exposure to elevated pCO2 significantly decreased extracellular pH and increased [HCO3-]. Moreover, an indicator GABAA receptor, a neuroinhibitor for movement, was found to be closely associated with behavioral changes. In situ hybridization confirmed that the GABAA receptor was widely distributed in ganglia and foot muscles, and elevated pCO2 significantly increased the mRNA level and GABA concentration. However, the increase in GABAA receptor and its ligand did not suppress the foot movement, but rather sent "excitatory" signals for foot contraction. The destabilization of acid-base homeostasis was demonstrated to induce an increase in the reversal potential for GABAA receptor and an alteration in GABAA receptor function under elevated pCO2. This study revealed that elevated pCO2 affects the burrowing behavior of Manila clams by altering GABAA receptor function from inhibitory to excitatory.

Comparison of macrofaunal assemblages in temperate seagrass meadows and neighboring seabeds along the southeastern coast of Shandong Peninsula, China.

Comparative study of macrofaunal assemblages in seagrass meadows and neighboring seabeds along the southeastern coast of Shandong Peninsula, China were performed. A total of 136 species were identified, including polychaetes (49 species), crustaceans (28), molluscs (58), and echinoderms (1). Species numbers of macrofauna in seagrass meadows and the neighboring seabeds were 52 and 65, respectively, whereas those in autumn were 90 and 56, respectively. Average macrofaunal abundances in spring in seagrass and neighboring seabeds were 2388.9 and 2516.7 ind./m2, respectively, whereas those in autumn were 11,689.0 and 1733.3 ind./m2, respectively. Ranges of species richness index, evenness index, and Shannon-Wiener index in seagrass meadows and the neighboring seabeds were 1.3-2.7, 0.7-0.9, 2.8-3.8, and 1.04-2.4, 0.5-0.9, 1.6-3.4 during spring, whereas those in autumn were 0.1-4.2, 0.3-0.8, 0.8-3.6 and 1.4-3.5, 0.5-0.9, 2.2-4.5. Bottom water temperature, salinity, sediment chlorophyll a concentration, and water content were the most important environmental factors influencing macrofaunal assemblages.

Microplastics influence physiological processes, growth and reproduction in the Manila clam, Ruditapes philippinarum.

Microplastics (<5 mm) are widely distributed in marine environments and pose a serious threat to bivalves. Here, the ingestion and accumulation of polystyrene microplastics (PS microplastics, diameters 5 and 10 µm) by the Manila clam, Ruditapes philippinarum, and their impacts on physiological processes, growth and reproduction were studied. The results showed that both PS microplastics were ingested by the Manila clam and accumulated in their gills, hepatopancreases and intestines. Furthermore, the accumulation of 5 and 10 µm PS microplastics significantly increased the rates of respiration and excretion while significantly decreasing feeding and absorption efficiency (AE), leading to a dramatically reduced amount of energy available for growth (SfG) and ultimately led to slower growth. The dynamic energy budget (DEB) model predicts that PS microplastic exposure for 200 days would cause lower shell/flesh growth rates and reproductive potentiality. Transcriptomic profiles support these results, as carbon and protein metabolism and oxytocin and insulin-related signaling pathways were significantly altered in clams in response to PS microplastics. This study provides evidence that microplastics strongly affect the physiological activities, energy allocation, growth and reproduction of filter-feeding bivalves.

How efficient is graphene-based nanocomposite to adsorb Hg from seawater. A laboratory assay to assess the toxicological impacts induced by remediated water towards marine bivalves.

Advanced investigations on the use of graphene based nanomaterials have highlighted the capacity of these materials for wastewater treatment. Research on this topic revealed the efficiency of the nanocomposite synthetized by graphene oxide functionalized with polyethyleneimine (GO-PEI) to adsorb mercury (Hg) from contaminated seawater. However, information on the environmental risks associated with these approaches are still lacking. The focus of this study was to evaluate the effects of Hg in contaminated seawater and seawater remediated by GO-PEI, using the species Ruditapes philippinarum, maintained at two different warming scenarios: control (17 °C) and increased (22 °C) temperatures. The results obtained showed that organisms exposed to non-contaminated and remediated seawaters at control temperature presented similar biological patterns, with no considerable differences expressed in terms of biochemical and histopathological alterations. Moreover, the present findings revealed increased toxicological effects in clams under remediated seawater at 22 °C in comparison to those subjected to the equivalent treatment at 17 °C. These results confirm the capability of GO-PEI to adsorb Hg from water with no noticeable toxic effects, although temperature could alter the responses of mussels to remediated seawater. These materials seem to be a promise eco-friendly approach to remediate wastewater, with low toxicity evidenced by remediated seawater and high regenerative capacity of this nanomaterial, keeping its high removal performance after successive sorption-desorption cycles.

Integrated transcriptomics and metabolomics analyses reveal benzo[a]pyrene enhances the toxicity of mercury to the Manila clam, Ruditapes philippinarum.

Mercury (Hg2+) and benzo[a]pyrene (BaP) are ubiquitous and persistent pollutants with multiple toxicities in bivalve molluscs. Here, the toxicological responses in the gills of Manila clams, Ruditapes philippinarum, to Hg2+ (10 µg L-1), BaP (3 µg L-1), and their mixture were analysed using transcriptomics and metabolomics approaches. Comparisons of the transcriptomes and metabolomes of Hg2+-and/or BaP-treated clams with control animals revealed the involvement of the detoxification metabolism, immune defence, energy-related pathways, and osmotic regulation in the stress response of R. philippinarum. Exposure to Hg2+ alone primarily enhanced the detoxification and energy metabolic pathways by significantly increasing the expression of genes associated with heat-shock proteins and oxidative phosphorylation. However, co-exposure to Hg2+ and BaP caused greater immunotoxicity and disrupted detoxification metabolism, the TCA cycle, glycolysis, and ATP generation. The expression levels of cytochrome P450 1A1 (CYP1A1), multidrug resistance-associated protein 1 (MRP1), and myosin (MYO), and the activity of electron transport system (ETS) in gills were detected, supporting the underlying toxic mechanisms of Hg2+ and BaP. We suggest that the presence of BaP enhances the toxicity of Hg2+ by 1) hampering the detoxification of Hg2+, 2) increasing the immunotoxicity of Hg2+, and 3) constraining energy availability for clams.

Effect of large-scale kelp and bivalve farming on seawater carbonate system variations in the semi-enclosed Sanggou Bay.

Although cultured algae and shellfish can be the dominant species in some localized coastal waters, research on the effect of large-scale mariculture on the carbonate system variations in these local waters is still lacking. We conducted five cruises from May to September and studied spatiotemporal variations in the seawater carbonate system in the semi-closed Sanggou Bay, which is famous for its large-scale mariculture. Our results showed that both kelp and bivalve farming induced significant spatiotemporal variations in the carbonate system within the bay. When cultured kelp reached its highest biomass in May, the maximum ΔDIC, ΔpCO2 and ΔpHT between the seawater from the kelp farming area and the non-farming outer bay area was -156 µmol kg-1, -102 µatm and 0.15 pH units, respectively. However, no significant effect of kelp farming on seawater total alkalinity (TA) was observed. Kelp farming also caused the carbonate system variations of seawater from the bivalve farming area. Assuming no kelp was farmed in May, the average pH and pCO2 would reduce by 0.12 pH units and increase by 179 µatm, respectively, in the bivalve farming area. Bivalve farming significantly reduced seawater TA, indicating that fast deposition of calcium carbonate occurred in the bivalve farming area. Although bivalve respiration released CO2 into seawater and elevated seawater pCO2 level and reduced seawater pHT, surprisingly, seawater dissolved inorganic carbon (DIC) reduced significantly in the bivalve farming area. These results indicated that bivalves fixed a larger amount of inorganic carbon by calcification than that released into seawater by respiration. Overall, large-scale kelp and bivalve farming are important biological drivers of variations in the carbonate system within the semi-enclosed Sanggou Bay. Altered carbonate systems by kelp farming may favour calcification of farmed bivalves and provide an essential refuge for these species during the future ocean acidification.

Biomarkers responses in Manila clam, Ruditapes philippinarum after single and combined exposure to mercury and benzo[a]pyrene.

Physiological and biochemical responses in bivalves exposed to pollutants have proved a valuable tool to assess the health of organisms in aquatic ecosystems. The single and combined effects of mercury (Hg2+, 2 and 10 µg/L) and benzo[a]pyrene (BaP, 3 µg/L) on physiological and biochemical biomarkers in Manila clam, Ruditapes philippinarum were evaluated. Results showed that significant higher oxygen consumption (OR) and ammonia-N excretion rates (NR) together with significant lower ingestion rates (IR) were observed for the 10 µg/L Hg2+ or 3 µg/L BaP treatments compared to controls (P < 0.05). However, clam NR decreased significantly in response to the binary mixtures of 10 µg/L Hg2+ and 3 µg/L BaP (P < 0.05). Moreover, the levels of superoxide dismutase (SOD), catalase (CAT), glutathione-s-transferases (GSTs), glutathione (GSH), acetylcholinesterase (AChE) and malondialdehyde (MDA) in the hepatopancreas of clams were induced substantially, whereas glycogen (GLY) contents were suppressed dramatically after Hg2+ and BaP exposure. Additionally, the integrated biomarker response (IBR) values measured showed significant increases in combination treatments and they were much higher than that in the Hg2+ treatment. This study will provide further information on the defense mechanism in the Manila clam after exposure to marine pollutants and may help evaluate the quality of the aquatic environment.

Metabolic responses to elevated pCO2 in the gills of the Pacific oyster (Crassostrea gigas) using a GC-TOF-MS-based metabolomics approach.

Rising atmospheric carbon dioxide (CO2), primarily from anthropogenic emissions, are resulting in increasing absorption of CO2 by the oceans, leading to a decline in oceanic pH in a process known as ocean acidification (OA). There is a growing body of evidence demonstrating the potential effect of OA on the energetics/physiology and consequently life-history traits of commensally important marine organisms. However, despite this little is known of how fundamental metabolic pathways that underpin changes in organismal physiology are affected by OA. Consequently, a gas chromatography time-of-flight mass spectrometry (GC-TOF-MS) based metabolic profiling approach was applied to examine the metabolic responses of Crassostrea gigas to elevated pCO2 levels, under otherwise natural field conditions. Oysters were exposed natural environmental pCO2 (~625.40 µatm) and elevated pCO2 (~1432.94 µatm) levels for 30 days. Results indicated that 36 differential metabolites were identified. Differential metabolites were mapped in the Kyoto Encyclopedia of Genes and Genomes (KEGG) database to search for the related metabolic pathways. Pathway enrichment analysis indicates that alanine, aspartate and glutamate metabolism and glycine, serine and threonine metabolism were the most statistically enriched pathways. Further analysis suggested that elevated pCO2 disturb the TCA cycle via succinate accumulation and C. gigas most likely adjust their energy metabolic via alanine and GABA accumulation accordingly to cope with elevated pCO2. These findings provide an understanding of the molecular mechanisms involved in modulating C. gigas metabolism under elevated pCO2.

Transcriptome analysis of the Yesso scallop, Patinopecten yessoensis gills in response to water temperature fluctuations.

Water temperature fluctuations are considered to be a major factor affecting the immune functions and metabolic processes of scallops. To better understand the immune defense mechanisms of Yesso scallop, Patinopecten yessoensis following exposure to water temperature fluctuations, transcriptomic profiles in the gills from high-frequency fluctuations (HF_G), low-frequency fluctuations (LF_G), and no fluctuations (NF_G) groups were obtained using HiSeq™ 2500 (Illumina). For HF_G, scallops were transferred directly between 18 and 8 °C every 4 h and for 10 fluctuations, while scallops in LF_G were transferred between 18 and 13 °C every 12 h, for a total of 4 fluctuations. A total of 442,922,590 clean reads were generated in 9 libraries and then assembled into 210,780 unigenes with an average length of 705 bp and an N50 of 1253 bp. Based on sequence similarity, 54,529 unigenes (25.87%) were annotated in at least one database. Comparative analysis revealed that 696 unigenes differentially expressed in temperature stressed groups compared with the control, including 229 unigenes between HF_G and NF_G, and 548 unigenes between LF_G and NF_G, respectively. Additionally, among these differentially expressed genes (DEGs), there were 41 immune-related unigenes and 16 protein metabolism-related unigenes. These results provide fundamental information on the molecular defense mechanisms in the Yesso scallop gills after exposure to water temperature fluctuations.

Two novel calreticulin-related molecules with microbial binding and phagocytosis enhancing capacity in the half-smooth tongue sole, Cynoglossus semilaevis.

Calreticulin (CRT) is highly conserved chaperone located in the endoplasmic reticulum. It plays important roles in innate immunity. Although various immune-related functions of CRT have been reported in vertebrates and invertebrates, information on the potential functions of teleost CRT is very limited. In the present study, we characterized two calreticulin-related molecules from tongue sole (Cynoglossus semilaevis), calreticulin-like1 and calreticulin-like2 (CsCRTL1 and CsCRTL2). CsCRTL1and CsCRTL2 contain signature CRT motifs that are highly conserved in different species. CsCRTL1and CsCRTL2 were expressed in liver, head kidney, brain, spleen, heart, muscle, skin, intestine and gills. The expression levels of CsCRTL1and CsCRTL2 were highest in liver and spleen, respectively. After stimulation by Vibrio anguillarum and Streptococcus agalactiae, CsCRTL1 and CsCRTL2 were significantly up-regulated. The expression patterns depended on the tissue type, pathogen type, and infection time. The recombinant proteins rCsCRTL1and rCsCRTL2 bound to different pathogen-associated molecular patterns (PAMPs) including LPS and PGN, and to different bacteria, such as Gram-negative bacteria V. anguillarum and Gram-positive bacteria Staphylococcus aureus. Moreover, rCsCRTL1and rCsCRTL2 significantly enhanced the killing of V. anguillarum by tongue sole macrophages. Our results indicate that CsCRTL1and CsCRTL2 play important roles in antibacterial immunity of tongue sole.

Identification and characterization of a novel calreticulin involved in the immune response of the Zhikong scallop, Chlamys farreri.

Calreticulin (CRT) is a multifunctional calcium-binding chaperone shared among vertebrates and invertebrates. In this study, a novel CRT (CfCRT) was identified in the Zhikong scallop Chlamys farreri by rapid amplification of cDNA ends. The full-length cDNA was composed of 1345 bp, which included a 1158 bp open reading frame, a 25 bp 5'-untranslated region (UTR) and a 162 bp 3'-UTR. The predicted molecular mass of CfCRT was 44.8 kDa. CfCRT contained three highly conserved domains (N-, P- and C-domains) essential to the function of CRT. BLAST analysis revealed significant sequence similarity (73%-92%) with CRT proteins from other mollusks. The mRNA transcripts of CfCRT were present in all the tested tissues of Zhikong scallops, with the higher expression level in the hemocytes and mantle. After stimulation by Vibrio anguillarum, the mRNA transcript of CfCRT in hemocytes was significantly upregulated. Recombinant plasmid pBCRT was successfully expressed in Escherichia coli BL21 (DE3). The recombinant (r)CfCRT protein could bind to the surface of several bacteria including the Gram-negative bacteria V. anguillarum, E. coli, and the Gram-positive bacterium Staphylococcus aureus. Moreover, rCfCRT was able to suppress their growth significantly. These results indicate that CfCRT might act as an immune effector in Zhikong scallop innate immunity.

Identification of a new calreticulin homolog from Yesso scallop (Patinopecten yessoensis) and its role in innate immunity.

Calreticulin (CRT) is a multifunctional and highly conserved Ca2+-binding protein shared among vertebrates and invertebrates. In this study, we cloned and characterized a CRT gene, PyCRT, from Yesso scallop, Patinopecten yessoensis. The full-length cDNA of PyCRT was 1830 bp, including a 1242 bp open reading frame (ORF), a 29 bp 5'-untranslated region and a 559 bp 3'-untranslated region. PyCRT was consisted of three distinct structural and functional domains (N-, P- and C-domains), a signal peptide and an endoplasmic reticulum (ER) retrieval signal sequence (HDEL). Tissue specific expression analysis showed that PyCRT was distributed widely in Yesso scallop, and was highly expressed in the mantle and hemocytes. After Vibrio anguillarum challenge, the expression of PyCRT in hemocytes had a significant increase and reached the maximum level at 12 h post-infection. We also demonstrated for the first time in mollusc that the recombinant PyCRT (rPyCRT) could bind to the Gram-negative bacterium V. anguillarum, Escherichia coli and the Gram-positive bacterium Staphylococcus aureus. Our results suggested that the CRT gene from Yesso scallop possessed immune-related regulatory functions in the innate immune system in scallops.

[Distribution, seasonal variation and influence factors of dissolved inorganic arsenic in the Sanggou Bay].

The biogeochemical behavior of arsenic in the aquatic environment has already captured the attentions of scientists due to its complex forms and toxicity. Four cruises were carried out in April, August, October 2011 and January 2012 in the Sanggou Bay. The concentrations of total dissolved inorganic arsenic (TDIAs, TDIAs = [ As(5+] + [As(3+)]) and arsenite (As(3+)) were measured by Hydride Generation-Atomic Fluorescence Spectrometry (HG-AFS). The concentrations of TDIAs ranged from 3.4-12.4 nmol x L(-1) in April, 8.9-16.9 nmol x L(-1) in August, 14.7-21.3 nmol x L(-1) in October and 13.8-21.9 nmol x L(-1) in January. The concentrations of arsenite ranged from 0.3-2.1 nmol x L(-1), 0.4-3.8 nmol x L(-1), 1.8-4.0 nmol x L(-1) and 0.3-2.9 nmol x L(-1) during four cruises, respectively. The concentrations of TDIAs in spring and summer were lower than those in autumn and winter, and high values of TDIAs appeared in the bay-mouth and the coastal estuary. The concentrations of arsenite in spring and winter were lower than those in summer and autumn. The maximum As(3+)/TDIAs ratios appeared in summer. The mean value of TDIAs in the Sanggou Bay was (13.9 +/- 4.7) nmol x L(-1), which was lower than the national primary drinking in water Standards from USEPA and met the first grade water quality based on the environmental quality standards for surface water of China. It indicates that there is no obvious anthropogenic pollution. The concentrations of TDIAs in the Sanggou Bay were lower than those in the Ailian Bay and the Lidao Bay in spring and summer due to the different hydrological environments and terrestrial inputs. Riverine input, incursion of Yellow Sea and biological activities were the three main factors impacting the distribution of TDIAs in the Sanggou Bay, and the influence of aquaculture activities was particularly significant. The enrichment of arsenic by aquaculture may lead to potential ecological crisis and food safety problems, and need to be paid more attentions to ensure the sustainable development of aquaculture in the Sanggou Bay.

Detrimental effects of reduced seawater pH on the early development of the Pacific abalone.

The hatching process of the Pacific abalone Haliotis discus hannai was prolonged at a pH of 7.6 and pH 7.3, and the embryonic developmental success was reduced. The hatching rate at pH 7.3 was significantly (10.8%) lower than that of the control (pH 8.2). The malformation rates at pH 7.9 and pH 8.2 were less than 20% but were 53.8% and 77.3% at pH 7.6 and pH 7.3, respectively. When newly hatched larvae were incubated for 48 h at pH 7.3, only 2.7% of the larvae settled, while more than 70% of the larvae completed settlement in the other three pH treatments. However, most 24 h old larvae could complete metamorphosis in all four pH treatments. Overall, a 0.3-unit reduction in water pH will produce no negative effect on the early development of the Pacific abalone, but further reduction in pH to the values predicted for seawater by the end of this century will have strong detrimental effects.

Relationship between differential retention of Escherichia coli and Enterococcus faecalis and variations in enzyme activity in the scallop Patinopecten yessoensis.

Uptake of Escherichia coli and Enterococcus faecalis and variations of trypsin amylase activity acid phosphatase and superoxide dismutase in tissue of the scallop Patinopecten yessoensis were detected. The results showed that P. yessoensis accumulated E. faecalis in larger numbers and more rapidly than E. coli, both with the highest concentration in the digestive tract and lowest in hemolymph. Compared to E. coli, all scallops exposed to E. faecalis showed significantly higher trypsin and AMS activity. SOD activity in hemocytes and ACP activity in hemolymph was significantly higher in the treatments with 5 log(10)CFU/ml E. coli than with E. faecalis. But no significant differences in ACP activity of P. yessoensis exposed to a 3 log(10)CFU/ml inoculum of both bacteria were recorded. In conclusion, the mass retention of gut microflora in P. yessoensis is positively correlated with digestive enzymes activity and negatively correlated with ACP activity in the hemocyte.

[Phosphate adsorption characteristics onto surface sediments from aquaculture area in Sungo bay].

Phosphate adsorption characteristics onto surface sediments from aquaculture area in Sungo bay were studied in laboratory simulating condition, and phosphate adsorption-desorption equilibrium mass concentration was also analyzed. The results showed that the process of phosphate adsorption onto sediments mainly occurred within 0.5 h, and attended to dynamic equilibrium after 6 h. Adsorption kinetics were fitted to modified Elovich model which can be expressed by Q = 85.536 + 35.512 lnt (R2 = 0.9602). Under low initial phosphate concentration condition, the adsorption isotherm curves were fitted to linear equation Q = 265.04c(e) - 7.46 (R2 = 0.965), while under high initial phosphate concentration condition, the adsorption isotherm curves were fitted to Langmuir equation (R2 = 0.989). The native adsorbed phosphorus was 7.46 microg/g and the maximum adsorption capacity was 769.23 microg/g. The phosphate adsorption-desorption equilibrium mass concentration was 0.028 mg/L, which indicated that the sediments played the source role in most time in this area based on the phosphate concentration in water body.