Genotypic diversity, antimicrobial resistance and screening of Vibrio cholerae molecular virulence markers in Vibrio alginolyticus strains recovered from a Tunisian Ruditapes decussatus hatchery

In this study, a total of 54 Vibrio alginolyticus strains were analyzed. The isolates were recovered from different compartments of the Ruditapes decussatus hatchery in the National Institute of Marine Sciences and Technologies, Monastir, Tunisia. All isolates were biochemically identified (API 20E and API ZYM strips), characterized by amplification of the Hsp-40 gene polymerase chain reaction (PCR) and analyzed by enterobacterial repetitive intergenic consensus (ERIC)-based genotyping to evaluate genetic relationship between the isolated strains. We also looked for the presence of ten V cholera virulence genes (toxRS, toxR, toxT toxS, tcpP, tcpA, ace, vpi, zot and ctxA) in the genomes of Vibrio isolates. The antibiotics susceptibility, exoenzymes production and in vitro cytotoxic activitiy against HeLa cell line were also carried out for all tested bacteria. Most of V alginolyticus isolates showed significant antimicrobial resistance rates to at least ten antibacterial agents. For most isolates, the minimum inhibitory concentration (MIC) data showed that tetracydclin and streptomycin were the most effective antibiotics. Construction of the phylogenetic dendogram showed that studied isolates were in general genetically heterogeneous; however some Vibrio strains were present in different structures of the R. decussatus hatchery. The V cholerae virulence genes investigation showed a wild distribution of toxS (49/54), toxaR (45/54) and toxT (22/54) genes among V alginolyticus strains isolated from the R. decussatus rearing system. Cytotoxic effects of several Vibrio extracellular products (28154) were also observed on HeLa cells.

Effects of glucose and probiotic supplementation in nursing juvenile clam, Meretrix lyrata

This study was conducted to evaluate the effects of different glucose concentration on the survival and growth rate of juvenile hard clam, Meretrix lyrata. Juvenile clams M lyrata were cultured with algae from a tilapia-greenwater system and different concentrations of glucose (0, 35, and 70microg.l-1). After 70 days of culture, highest survival rate was obtained with 35microg.l-1 glucose supplementation (99.5-100%). However, in highest concentration of glucose, weight gain and shell length of clams reached highest values (p<0.05). Our findings showed that supplementation of probiotics and suitable glucose concentration in the nursery period could increase survival and growth rate of clams.

Across-shelf transport of bivalve larvae: can the interface between a coastal current and inshore waters act as an ecological barrier to larval dispersal?

Using an integrated physical and biological approach, we examined across-shelf advection and exchange and the associated transport of bivalve larvae in the presence of a strong coastal current separated from the coast by a stratified inshore environment. We tested the hypothesis that the interface of the coastal current and inshore waters can act as an ecological barrier to across-shelf transport of larvae but can be overcome by wind- or tidally-induced transport. Our study region in the Gulf of Maine encompasses a coastal current that diverges from the coast as it moves downshelf. The region inshore of this current is home to several species that exhibit limited recruitment in spite of extensive upshelf larval sources. Analysis of surface water temperatures and wind velocities revealed episodic decreases in temperature along the coast correlated with alongshelf (but not upwelling) winds, indicating wind-forced onshore movement of the cold coastal current. Such wind-driven onshore migrations are more common along the northern portion of the study region where the coastal current is near the coast, tidal currents are strong, and wind directions are more conducive to onshore migration, but rarer further south where the interface between inshore waters and the coastal current is further offshore and suitable wind events are less common. The distribution of bivalve larvae was consistent with the physical measurements. There was little across-shelf variation in larval abundance where the current abuts the coast, indicating strong across-shelf exchange of larvae, but strong across-shelf variation in larval density where the stratified inshore waters separate the current from the coast, indicating weak across-shelf transport of larvae. Our results suggest that the interface between the coastal current and inshore waters may constitute a major ecological barrier to larval dispersal in the southern part of the region that may only be overcome by rare, strong wind-forced events.

First measurements of the scope for growth (SFG) in mussels from a large scale survey in the North-Atlantic Spanish coast

SFG and physiological rates were measured in wild mussels from the Spanish Marine Pollution monitoring program (SMP) in order to determine seawater quality. It consists of 41 stations, covering almost 2500 km of coast, making the SMP the widest-ranging monitoring network in the Iberian Peninsula's Atlantic region. Results of the 2007 and 2008 surveys when 39 sites were sampled: (20 in 2007 and 19 in 2008, being 8 sites sampled both years) were presented. Chemical analyses were carried out to determine the relationships between physiological rates and the accumulation of toxic compounds. Data presented are the first to become available on the use of SFG as a biomarker of the marine environment on a large spatial scale (>1000 km) along Spain's Atlantic seaboard. SFG values enable significant differences to be established between the areas sampled and between the two years surveyed. The integration of biological and chemical data suggests that certain organochlorine compounds, namely chlordanes and DDTs, may have a negative effect on SFG, although such an effect is of a lesser magnitude than that associated with certain biological parameters such as condition index and mussel age. These variables act as confounding factors when attempting to determine the effect of chemical compounds present in the marine environment on mussel SFG. Further research is therefore needed on the relation between these confounding factors and SFG in order to apply the relevant corrective strategies to enable this index to be used in monitoring programs. The effect of these confounding factors is more clearly revealed in studies that cover a wide-ranging spatial and time scale, such as those carried out within the SMP. These results do not invalidate the use of biological data in monitoring programs, but rather point to the need to analyze all the factors affecting each biological process.

Single nucleotide polymorphisms in i-type lysozyme gene and their correlation with vibrio-resistance and growth of clam Meretrix meretrix based on the selected resistance stocks

I-type lysozyme is considered to play crucial roles in both anti-bacteria and digestion function of the bivalve, which signifies that it is related to both immunity and growth. In this study, based on the principle of case-control association analysis, using the stock materials with different vibrio-resistance profile obtained by selective breeding, single nucleotide polymorphisms (SNPs) in the DNA partial sequence of an i-type lysozyme of Meretrix meretrix (MmeLys) were discovered and examined for their association with vibrio-resistance and growth. Twenty-seven SNPs were detected and fifteen of them were genotyped in clam stocks with different resistance to Vibrio harveyi (09-C and 09-R) and to Vibrio parahaemolyticus (11-S and 11-R). Allele frequency distribution among different stocks was compared. And wet weight of clams with different genotype at each SNP locus was compared. The results indicated that SNP locus 9 was associated with V. harveyi and V. parahaemolyticus resistance and growth of M. meretrix. Loci 12 and 14 were associated with both V. parahaemolyticus-resistance and growth, and also have the potential to be related with V. harveyi-resistance of M. meretrix. Therefore these three SNPs especially locus 9 were the potential markers which may be involved in assisting resistance selective breeding. In addition, this study showed evidence that improvements in clam resistance to vibriosis could be achieved through selective breeding. All results provided encouragement for the continuation of the selective breeding program for vibrio-resistance gain in clam M. meretrix and the application of polymorphisms in MmeLys to the future marker assisted selection.

Evaluation of sampling sizes on the intertidal macroinfauna assessment in a subtropical mudflat of Hong Kong

In this study, two types of sediment cores with different diameters were used to collect sediment samples from an intertidal mudflat in Hong Kong to investigate the influence of sampling unit on the quantitative assessment of benthic macroinfaunal communities. Both univariate and multivariate analyses were employed to detect differences in sampling efficiencies by the two samplers through total abundance and biomass, species richness and diversity, community structure, relative abundance of major taxa of the infaunal community. The species-area curves were further compared to find out the influence of the sampling units. Results showed that the two sampling devices provided similar information on the estimates of species diversity, density and species composition of the benthos in main part of the mudflat where the sediment was fine and homogenous; but at the station which contained coarse sand and gravels, the significant differences were detected between the quantitative assessments of macrobenthic infauna by the two samplers. Most importantly, the species-area curves indicated that more and smaller samples were better in capturing more species than less large ones when comparing an equal sampling area. Therefore, the efficiency of the sampler largely depended on the sediment properties, and sampling devices must be chosen based on the physical conditions and desired levels of precision on the organisms of the sampling program.

Toxic effects of benzo[a]pyrene (Bap) and Aroclor1254 on embryogenesis, larval growth, survival and metamorphosis of the bivalve Meretrix meretrix

To assess the potential toxicity of polycyclic aromatic hydrocarbons and polychlorinated biphenyls on the early development of Meretrix meretrix, the effects of benzo[a]pyrene (Bap) and Aroclor1254 on embryogenesis and larval development were investigated using static laboratory toxicity tests at nominal concentrations of 6.25-1,600 μg/L. Even at 1,600 μg/L, Bap and Aroclor1254 only caused minor reductions in embryo development rates. The 96 h LC(50) values for D-shaped larvae were 156 μg/L for Bap and 132 μg/L for Aroclor1254, respectively. The most sensitive toxicity endpoint in this study was metamorphosis, with an EC(50) value of 20 μg/L for Bap and 35 μg/L for Aroclor1254. Aroclor1254 was more toxic than Bap to embryos and larvae. Our results indicate that Bap and Aroclor1254 do not show extreme toxicity to M. meretrix embryos and larvae. These data provide information for evaluating the toxicity of Bap and Aroclor1254 on bivalve embryos, especially over the entire larval stages.

Ecotoxicological evaluation of tributyltin toxicity to the equilateral venus clam, Gomphina veneriformis (Bivalvia: Veneridae)

Tributyltin (TBT) is the most common pesticide in marine and freshwater environments. To evaluate the potential ecological risk posed by TBT, we measured biological responses such as growth rate, gonad index, sex ratio, the percentage of intersex gonads, filtration rate, and gill abnormalities in the equilateral venus clam (Gomphina veneriformis). Additionally, the biochemical and molecular responses were evaluated in G. veneriformis exposed to various concentrations of TBT. The growth of G. veneriformis was significantly delayed in a dose-dependent manner after exposure to all tested TBT concentrations. After TBT was administered to G. veneriformis, the gonad index decreased and the sex balance was altered. The percentage of intersex gonads also increased significantly in treated females, whereas no intersex gonads were detected in the solvent control group. Additionally, intersex gonads were detected in male G. veneriformis specimens exposed to relatively high TBT concentrations (20 μg L⁻¹). The filtration rate was also reduced in a dose-dependent manner in TBT-exposed G. veneriformis. We also noted abnormal gill morphology in TBT-exposed G. veneriformis. Furthermore, increases in antioxidant enzyme activities were observed in TBT-exposed G. veneriformis clams, regardless of dosage. Vitellogenin gene expression also increased significantly in a dose-dependent manner in G. veneriformis exposed to TBT. These results provide valuable information regarding our understanding of the toxicology of TBT in G. veneriformis. Moreover, the responses of biological and molecular factors could be utilized as information for risk assessments and marine monitoring of TBT toxicity.

Transcriptomic analysis of the clam Meretrix meretrix on different larval stages

The clam Meretrix meretrix (Mollusca: Bivalvia) is an important commercial species in China. The deficiency of genomic and transcriptomic data is becoming the bottleneck of further researches on its complex and unique developmental processes. To improve this situation, in this study, a large-scale RNA sequencing was conducted on M. meretrix on larval stages. In particular, mRNAs of trochophore, D-veliger, pediveliger, and postlarva were purified, reverse transcribed, and sequenced through 454 sequencing technology. A total of 704,671 reads were obtained and assembled into 124,737 unique sequences (35,205 contigs and 89,532 singletons). Further analysis showed that 118,075 (94.66%) of these sequences were low-expression-level transcripts. Fifteen thousand two hundred fifteen (12.20%) of the unique sequences were annotated by searching against Uniprot Protein Knowledgebase, while the others (109,522, 87.80%) were left as novel sequences. Gene ontology analysis of the annotated sequences showed that most of them were assigned to certain gene ontology terms. By analyzing the depth of each unique sequence, a preliminary quantification analysis was conducted. An amount of sequences that showed a dramatic transcript discrepancy among the four larval stages were screened, which were related to development, growth, shell formation, and immune responses etc. As the first attempt on large-scale RNA sequencing of marine bivalve larvae, this work would enrich the knowledge of larval development of marine bivalves and provide fundamental support for further researches.

Induction of settlement in mussel (Perna canaliculus) larvae by vessel noise

Underwater sound plays an important role in the settlement behaviour of many coastal organisms. Large steel-hulled vessels are known to be a major source of underwater sound in the marine environment. The possibility that underwater sound from vessels may promote biofouling of hulls through triggering natural larval settlement cues was investigated for the mussel, Perna canaliculus. The mussel larvae showed significantly faster settlement when exposed to the underwater noise produced by a 125-m long steel-hulled passenger and freight ferry. Median time to attachment on the substrata (ie settlement) was reduced by 22% and the time taken for all experimental larvae to settle was reduced by 40% relative to a silent control. There was no difference in the survival of the mussel larvae among the various noise treatments. The decrease in settlement time of the mussel larvae appeared to correlate with the intensity of the vessel sound, suggesting that underwater sound emanating from vessels may be an important factor in exacerbating hull fouling by mussels.

Effects of elevated temperature and carbon dioxide on the growth and survival of larvae and juveniles of three species of northwest Atlantic bivalves

Rising CO₂ concentrations and water temperatures this century are likely to have transformative effects on many coastal marine organisms. Here, we compared the responses of two life history stages (larval, juvenile) of three species of calcifying bivalves (Mercenaria mercenaria, Crassostrea virginica, and Argopecten irradians) to temperatures (24 and 28°C) and CO₂ concentrations (∼250, 390, and 750 ppm) representative of past, present, and future summer conditions in temperate estuaries. Results demonstrated that increases in temperature and CO₂ each significantly depressed survival, development, growth, and lipid synthesis of M. mercenaria and A. irradians larvae and that the effects were additive. Juvenile M. mercenaria and A. irradians were negatively impacted by higher temperatures while C. virginica juveniles were not. C. virginica and A. irradians juveniles were negatively affected by higher CO₂ concentrations, while M. mercenaria was not. Larvae were substantially more vulnerable to elevated CO₂ than juvenile stages. These findings suggest that current and future increases in temperature and CO₂ are likely to have negative consequences for coastal bivalve populations.

Molecular cloning and copy number variation of a ferritin subunit (Fth1) and its association with growth in freshwater pearl mussel Hyriopsis cumingii

Iron is one of the most important minor elements in the shells of bivalves. This study was designed to investigate the involvement of ferritin, the principal protein for iron storage, in shell growth. A novel ferritin subunit (Fth1) cDNA from the freshwater pearl mussel (Hyriopsis cumingii) was isolated and characterized. The complete cDNA contained 822 bp, with an open reading frame (ORF) of 525 bp, a 153 bp 5′ untranslated region (UTR) and a 144 bp 3′ UTR. The complete genomic DNA was 4125 bp, containing four exons and three introns. The ORF encoded a protein of 174 amino acids without a signal sequence. The deduced ferritin contained a highly conserved motif for the ferroxidase center comprising seven residues of a typical vertebrate heavy-chain ferritin. It contained one conserved iron associated residue (Try27) and iron-binding region signature 1 residues. The mRNA contained a 27 bp iron-responsive element with a typical stem-loop structure in the 5′-UTR position. Copy number variants (CNVs) of Fth1 in two populations (PY and JH) were detected using quantitative real-time PCR. Associations between CNVs and growth were also analyzed. The results showed that the copy number of the ferritin gene of in the diploid genome ranged from two to 12 in PY, and from two to six in JH. The copy number variation in PY was higher than that in JH. In terms of shell length, mussels with four copies of the ferritin gene grew faster than those with three copies (P<0.05), suggesting that CNVs in the ferritin gene are associated with growth in shell length and might be a useful molecular marker in selective breeding of H. cumingii.

Bioindicative potential of shell abnormalities occurring in the clam Macoma balthica (L.) from the Baltic Sea

This study reports the occurrence of shell deformities in the Baltic clam Macoma balthica from the Northern Baltic Sea (Trösa Archipelago, Sweden). The functional significance and the bioindicative potential of observed exoskeleton' anomalies was assessed using a suite of physiological and morphological biomarkers. Analyzed shell deformations (SD) included damages of the dorsal margin visible as shell excavations, destruction of the beak, umbo and hinge ligament and decreased shell' transparency. Deformed clams exhibited worse physiological conditions and increased frequency of micronuclei. Skewed sex ratio towards male domination was observed in all studied populations. Spatial differences in the occurrence of deformed clams are reported, with more than 50% of deformed clams inhabiting polluted locations and 8% the reference station. These results are encouraging for the use of described SDs as initial and cost effective indicators of environmental health.

Aquaculture fouling: Efficacy of potassium monopersulphonate triple salt based disinfectant (Virkon® Aquatic) against Ciona intestinalis

With the increasing spread of invasive marine species and their detrimental effects on aquaculture operations globally, mitigation strategies need to be optimized to mitigate economic impacts. The efficacy of a potassium monopersulphonate triple salt based disinfectant used in the aquaculture industry (Virkon® Aquatic at 0.5-5%) was evaluated against the solitary tunicate Ciona intestinalis, as well as the susceptibility of three different age groups of C. intestinalis to the treatment and the effect of the disinfectant on mussel mortality. Younger C. intestinalis were most affected by all treatments, and almost all immersion applications significantly decreased the biomass of C. intestinalis compared to untreated plates. Disinfectant solutions of ≥ 1% reduced biomass below pre-treatment levels. Mussel mortality was low, especially for solutions <3%. C. intestinalis should be treated 4 weeks post-settlement to maximize antifouling treatment effects. Immersion in 3% disinfectant for 30 s reduced the biomass of C. intestinalis by up to 89% and would be feasible in field applications using existing treatment equipment.

Long-term response of an arctic fiord system to lead-zinc mining and submarine disposal of mine waste (Maarmorilik, West Greenland)

Contamination by lead (Pb) and zinc (Zn) was studied in seawater, sediments, seaweeds and blue mussels near the former Black Angel Pb-Zn Mine in Maarmorilik, West Greenland. The mine operated during the period 1973-90 when mine waste (tailings and later waste rock) was discharged directly into the sea. Metal concentrations peaked during the mining period and Pb and Zn in seawater within the discharge area were measured up to 440 and 790 μg L⁻¹, respectively. Pb in fiord sediments, seaweeds and blue mussels just outside the discharge area were measured in concentrations up to 190, 84 and 2650 and Zn up to 300, 360 and 1190 μg g⁻¹ dry wt., respectively. Within the discharge area, seawater metal concentrations (especially Pb) decreased abruptly after mine closure. Metals concentrations in sediments and biota, however, decreased more slowly and two decades after mine closure seaweeds and blue mussels were still contaminated 12 km from the mine.

Seasonal nitrogen and phosphorus dynamics during benthic clam and suspended mussel cultivation

Effects of suspended mussel and infaunal clam cultivation on sediment characteristics, and benthic organic and inorganic nitrogen and phosphorus fluxes were compared in a shallow coastal lagoon. The two species had different impacts on sediment features, but both created "hotspots" of nutrient fluxes with annual N and P regeneration rates being 4.9 and 13.5 (mussel) and 4.5 and 14.9 (clams) fold greater than those of unfarmed control sediments. Mussel farming also caused considerable nutrient regeneration within the water column with the mussel ropes contributing ∼25% of total inorganic N and P production and at times dominating the sediments (e.g. 95% of SRP production in summer and 45% of DIN production in winter). Such nutrient regeneration rates seriously question the proposal that suspension-feeding bivalves act as a eutrophication buffer, especially during summer when nutrient regeneration rates are maximal, but other nutrient sources (freshwater run-off and unfarmed sediments) are at their lowest.

Ecology of twelve species of Thyasiridae (Mollusca: Bivalvia)

Benthic samples from coastal locations off Southwestern Norway were examined and the specimens of Thyasiridae were identified to species. A multivariate analysis based on 13 parameters was carried out and the environmental preferences of all thyasirid species present were determined. The potential of the Thyasiridae as indicators of organic enrichment was investigated by using direct canonical correspondence analyses to identify correlations between selected environmental parameters and the collected biological data. The presence of Thyasira sarsi together with a low biodiversity is a good indicator of organic enrichment. High thyasirid species diversity seems to indicate good environmental conditions, and single thyasirid species that lack symbiotic bacteria might also be useful as indicators of good environmental conditions.

[Self-pollution in Ruditapes philippinarum bottom-cultured area of Zhuanghe coast]

By using sediment trap and closed respirator, a year-round in situ investigation was made on the bio-deposition rate, ammonia excretion rate, and phosphate excretion rate in the Ruditapes philippinarum bottom-cultured area of Zhuanghe coast. The three test rates of R. philippinarum all showed obvious seasonal variability, with the bio-deposition rate ranged in 0.15-1.47 g x ind(-1) x d(-1) (annual average 0.61 g x ind(-1) x d(-1)), ammonia excretion rate ranged in 0.02-0.40 mg x ind(-1) x d(-1) (annual average 0.17 mg x ind(-1) x d(-1)), and phosphate excretion rate ranged in 0.01-0.39 mg x ind(-1) x d(-1)(annual average 0. 13 mg x ind(-1) x d(-1)). Based on these, it was estimated that the annual bio-deposit production by the bottom-cultured R. philippinarum in Zhuanghe coast could reach as high as 5.46 x 10(7) t dry mass, amounting to 9.07 x 10(6) t organic matter (OM), 1.00 x 10(6) t organic carbon (OC), or 1.18 x 10(5) t organic nitrogen (ON), and the annual NH4+ -N and PO4(3-)-P productions were 1.49 x 10(4) t and 1.15 x 10(4) t, respectively. Our results suggested that for the large scale and high density bivalve culture in China coasts, the potential impacts of self-pollutants by filter-feeding bivalves on the environment should not be neglected.

Spikey bivalves: intra-periostracal crystal growth in anomalodesmatans

The external shell surfaces of most anomalodesmatan bivalves are studded with small spikes, particularly at the posterior end. We have studied the morphology, mode of growth, and distribution among taxa of these spikes. In this study we found that spikes vary widely in morphology, from acute spikes to flat plaques. Optical and electron microscopy has revealed that the periostraca of Laternula, Myadora, and Thraciopsis consist of an outer dense layer and an inner translucent layer. The dense layer grows at the expense of the inner layer as it progresses toward the shell edge. The spikes begin to grow in the free periostracum, within the translucent periostracal layer, immediately below the dense layer. With growth, they push the dense periostracal layer upward but without penetrating it. Those parts of the spike in contact with this layer cease to grow, which explains the typical conical shape of spikes. When fully grown, spikes reach the base of the translucent layer, becoming incorporated into the outer shell layer. Scanning electron microscopy and electron backscatter diffraction analysis reveal that the spikes of Lyonsia norwegica and Lyonsiella abyssicola are prisms of aragonite composed of twinned crystals, with the c-axis vertical. A survey of the occurrence of spikes within the anomalodesmatans shows that they are present in all but a few families. Elsewhere within the closely related palaeoheterodonts, intra-periostracal calcification is also known in Neotrigonia and unionids, which indicates that this character may be plesiomorphic for these bivalves. The present data do not support the homology of spikes in other bivalve groups (e.g., veneroids) or in the aplacophorans or polyplacophorans.

Analysis of metallotionein expression and antioxidant enzyme activities in Meretrix meretrix larvae under sublethal cadmium exposure

To investigate the possible role of metallothioneins (MTs) and antioxidant enzymes in cadmium (Cd) tolerance in Meretrix meretrix larvae, a new MT (designated MmMT) gene was identified and cloned from M. meretrix. The full-length cDNA of MmMT consisted of an open reading frame (ORF) of 231bp encoding a protein of 76 amino acids, with 21 cysteine residues and a conserved structural pattern Cys-x-Cys-x(3)-Cys-Tyr-Gly-x(3)-Cys-x-Cys-x(3)-Cys-x-Cys-Lys at the C-terminus. The deduced amino acid sequence of MmMT showed about 57-84% identity with previously published MT sequences of mussels and oysters. Real-time PCR was used to analyze the expression level of MmMT mRNA at different M. meretrix larval stages under Cd exposure (25μgL⁻¹). Results showed that Cd could induce the expression of MmMT mRNA in the larvae, and the expression level increased 5.04-fold and 3.99-fold in D-shaped larvae and pediveligers, respectively. Immunolocalization of MmMT in the stressed larvae revealed that MmMT was synthesized in almost all of the soft parts at the trochophore and postlarva stages, whereas it was only synthesized in the velum and epidermis at the D-shaped larva and pediveliger stages. The activities of three antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), also were measured in larvae at different developmental stages. Increased enzymatic activities were detected mainly in D-shaped larvae and pediveligers under Cd stress, suggesting that these enzymes respond synchronously with MT. Our results indicate that MmMT and antioxidant enzymes played important roles in counteracting Cd stress in M. meretrix larvae.

Effects of past, present, and future ocean carbon dioxide concentrations on the growth and survival of larval shellfish

The combustion of fossil fuels has enriched levels of CO(2) in the world's oceans and decreased ocean pH. Although the continuation of these processes may alter the growth, survival, and diversity of marine organisms that synthesize CaCO(3) shells, the effects of ocean acidification since the dawn of the industrial revolution are not clear. Here we present experiments that examined the effects of the ocean's past, present, and future (21st and 22nd centuries) CO(2) concentrations on the growth, survival, and condition of larvae of two species of commercially and ecologically valuable bivalve shellfish (Mercenaria mercenaria and Argopecten irradians). Larvae grown under near preindustrial CO(2) concentrations (250 ppm) displayed significantly faster growth and metamorphosis as well as higher survival and lipid accumulation rates compared with individuals reared under modern day CO(2) levels. Bivalves grown under near preindustrial CO(2) levels displayed thicker, more robust shells than individuals grown at present CO(2) concentrations, whereas bivalves exposed to CO(2) levels expected later this century had shells that were malformed and eroded. These results suggest that the ocean acidification that has occurred during the past two centuries may be inhibiting the development and survival of larval shellfish and contributing to global declines of some bivalve populations.

Recurrent, thermally-induced shifts in species distribution range in the Humboldt current upwelling system

El Niño-Southern Oscillation (ENSO) is a global climate variablility, which fundamentally influences environmental patterns of the Humboldt Current System (HCS) off Chile and Peru. The surf clams Donax obesulus and Mesodesma donacium are dominant and highly productive bivalves of exposed sandy beaches of the HCS. Existing knowledge indicates that El Niño (EN, warm phase of ENSO) and La Niña (LN, cold phase of ENSO) affect populations of both species in a different way, although understanding of the mechanisms underlying these effects is still lacking. The aim of this study was to test hypotheses attempting to explain field observations on the effect of strong EN or LN events by using controlled experimental conditions. Growth and mortality rates of both species were registered during a four-week experiment under EN temperature conditions, normal temperature conditions and LN temperature conditions. While D. obesulus exhibited reduced growth and higher mortality under LN conditions, M. donacium showed reduced growth and higher mortality under EN conditions. The results clearly indicate different temperature tolerance windows for each species, possibly reflecting the evolutionary origins of the Donacidae and Mesodesmatidae in regions with contrasting temperature regimes. These results provide experimental support for previous hypotheses suggesting that thermal tolerance is the driving factor behind observed changes in the species distributions of D. obesulus and M. donacium during the extreme phases of ENSO.

Bivalve population health: multistress to identify hot spots

This study investigated some stress (metals, parasites) and response (immunity, metallothionein) factors in two cockle and two Manila clam populations. Data from eight seasons were averaged to obtain global baseline values. Stress/response characteristics of each population were compared to population health status that was determined through population dynamics parameters. Four different scenarios were discussed: (1) a lightly stressed cockle population with correct population health but with a risk of deterioration (hot spot); (2) a lightly stressed introduced cockle population threatened of extinction. In this case ecological factors were suspected; (3) a moderately stressed clam population with moderate adaptative response. The population was sustainable but the level of stress should not increase (hotspot); and (4) a stressed clam population and unfavourable ecological conditions preventing clam settlement. This monitoring highlighted that the discrepancy between population health and stress levels could be due to insufficient response by bivalves and/or by unfavourable ecological factors.

Environmental occurrence and reproductive effects of the pharmaceutical fluoxetine in native freshwater mussels

The present study measured the occurrence, distribution, and bioaccumulation of fluoxetine in samples of water, polar organic chemical integrative sampler (POCIS), sediment, and caged freshwater mussels at stream sites near a municipal wastewater treatment facility effluent discharge. We assessed the relation of the environmental concentrations to reproductive endpoints in mussels in acute laboratory tests. Concentrations of fluoxetine in water and POCIS samples were similar (<20% difference) within each site and were greatest in the effluent channel (104-119 ng/L), and decreased at 50 m and 100 m downstream. Likewise, concentrations of fluoxetine in sediment and mussel (Elliptio complanata) tissue were greatest in the effluent channel (17.4 ng/g wet wt for sediment and 79.1 ng/g wet wt for mussels). In 96-h lab tests, fluoxetine significantly induced parturition of nonviable larvae from female E. complanata exposed to 300 microg/L (p = 0.0118) and 3,000 microg/L (p < 0.0001) compared to controls. Fluoxetine exposure at 300 microg/L (p = 0.0075) and 3,000 microg/L (p = 0.0001) also resulted in stimulation of lure display behavior in female Lampsilis fasciola and Lampsilis cardium, respectively. In male E. complanata, 3,000 microg fluoxetine/L significantly induced release of spermatozeugmata during a 48-h exposure. These results suggest that fluoxetine accumulates in mussel tissue and has the potential to disrupt several aspects of reproduction in freshwater mussels, a faunal group recognized as one of the most imperiled in the world. Despite the disparity between measured environmental concentrations of fluoxetine and effects concentrations in our short-term tests with these long-lived animals, additional tests are warranted to evaluate the effects of long-term exposure to environmentally relevant concentrations and critical lifestages (e.g., juveniles).