Population differences in nerve resistance to paralytic shellfish toxins in softshell clam, <Emphasis Type="Italic">Mya arenaria</Emphasis>, associated with sodium channel mutations

The softshell clam, Mya arenaria, is a commercially important bivalve with wide latitudinal distribution in North America. Populations of clams with a history of repeated exposure to toxic Alexandrium spp. have developed a natural resistance to the paralytic shellfish toxins (PSTs) produced by these algae. An association between PST resistance in individual clams and a single mutation in the saxitoxin (STX) binding region of the α-subunit of the voltage-gated sodium (Na⁺) channel gene was previously identified. Here we establish that more than one mutation associated with nerve resistance to STX occurred at this locus. Both cDNA from mRNA and genomic DNA sequences from individual clams are identical demonstrating that both alleles are expressed simultaneously. In addition, one resistant allele per individual is sufficient to confer neural resistance to STX even though heterozygous individuals show an intermediate level of resistance to STX in in vitro nerve trunk assays.     

Transfer of brevetoxins to a tellinid bivalve by suspension- and deposit-feeding and its implications for clay mitigation of <Emphasis Type="Italic">Karenia brevis</Emphasis> blooms

Blooms of the brevetoxin-producing Karenia brevis in the Gulf of Mexico cause massive fish kills, food poisoning and adverse respiratory effects in humans. Sedimentation of toxic cells following inert clay application could reduce toxin incorporation by commercially important suspension-feeding bivalves and thus prevent direct public health impacts, but could potentially lead to brevetoxin (PbTx) accumulation by benthic deposit-feeders. The goal of this study was therefore to compare suspension- and deposit-feeding as pathways for brevetoxins. We investigated: (1) the effect of toxic K. brevis on both feeding modes using a facultative deposit-suspension feeding tellinid bivalve, the clam Macoma balthica, as a model species and (2) the relative effectiveness of brevetoxin transfer via suspension- and deposit-feeding over 24-h exposure. Sedimentation of K. brevis was achieved by treatment with 0.25 g phosphatic clay l⁻¹ and brevetoxin concentrations were measured by ELISA. Karenia brevis reduced both suspension- and deposit-feeding activity. This study demonstrates that brevetoxins can be rapidly accumulated by a surface deposit-feeding bivalve from sedimented K. brevis cells and that comparable toxin levels can be attained by both suspension- and deposit-feeding modes [1.2–1.6 μg PbTx (g tissue wet weight)⁻¹]. Deposit-feeding clams generally do not pose a direct threat to humans but may provide a pathway for brevetoxin food web transfer.     

Differential effects of Aureococcus anophagefferens isolates ("brown tide") in unialgal and mixed suspensions on bivalve feeding

Picoplanktonic brown tides of Aureococcus anophagefferens have had devastating effects on production of commercially exploited bivalve populations in shallow, mid-Atlantic estuaries in the United States. The toxin produced by this alga has not been chemically characterized. This study develops a bioassay using juvenile mussels, Mytilus edulis, based on the inhibitory effect of brown tide on bivalve suspension-feeding, to compare the cellular toxicity of three Long Island, New York, clonal isolates of A. anophagefferens. Two recent (1995) isolates (CCMP 1707 and 1708) from Peconic Bay proved highly toxic and caused greater than 100-fold reduction in clearance rates (CR) of juvenile mussels in unialgal and mixed suspensions with a nutritious alga, Isochrysis galbana (clone T-iso), relative to controls. A third 1986 isolate from Great South Bay (CCMP 1784) showed no detectable toxicity in 24-h trials, and may have lost its initial potency over more than a decade of laboratory culture. Identification of a non-toxic strain provides a useful tool for future research. Cultures of the toxic isolate CCMP 1708 in late-stationary growth phase were significantly more toxic than those in early-exponential phase. The threshold concentration of toxic A. anophagefferens cells that inhibits clearance on co-occurring phytoplankton species was determined for juvenile (10-mm) hard clams, Mercenaria mercenaria. Relatively low concentrations (⣃᎒³ to 50᎒³ cells ml^-1) of isolate CCMP 1708 were sufficient to sharply reduce clam CR of I. galbana. Calculations based on these results suggest that, at peak historical densities of M. mercenaria in Great South Bay, removal of A. anophagefferens at low cell densities by suspension-feeding benthos could provide an effective top-down grazing control mechanism to prevent the initiation of brown tide in shallow, inner bays.     

粉煤灰对烟气中CO2的吸收特性及矿物相演变机理研究

粉煤灰矿化CO₂是一种极具前景的减少燃煤电厂CO₂排放的技术.然而,目前还缺乏从矿物学角度对碳酸化反应机理的详细认识.本研究选取了3种粉煤灰开展碳酸化实验和矿物学研究,考察碳酸化过程中温度对碳酸化能力及粉煤灰矿物学变化的影响.结果表明,在任一温度下,BJ粉煤灰的碳酸化率均高于YA和LY粉煤灰,这是由于BJ粉煤灰中硬石膏、钙铁石和无定形相等活性矿物相含量较高,LY粉煤灰缺少高活性的钙、镁结晶相.对YA粉煤灰而言,升高温度可显著提高透辉石、尖晶石、黑钙铁矿和方镁石的转化率.在碳酸化YA粉煤灰中同时检测出碳酸钙和碳酸镁/铁,说明除含钙相其他活性元素(Mg和Fe)也参与了碳酸化过程.因此,需要对每个粉煤灰原始材料的矿物学和操作温度进行具体的个案优化,以最大限度地提高固定CO₂能力和碳酸化率.结果还表明温度对不同晶型碳酸钙的形成具有重要作用.方解石在低温(40和80℃)下形成,而文石在高温(180和220℃)下形成.     

Resource allocation and population genetics of the bay scallop,Argopecten irradians irradians: effects of age and allozyme heterozygosity on reproductive output

The relationships among multiple-locus heterozygosity, age, reproduction and growth were examined over the ca. 2-yr lifespan of a cohort of northern bay scallops, Argopecten irradians irradians (Lamarck), from the Niantic River estuary, Connecticut, USA. Electrophoretic analyses revealed a relatively low proportion of polymorphic loci (=0.35) and low level of heterozygote deficiency ( D. across 6 loci=-0.05) in this population. Allele frequency distributions showed a high degree of temporal stability within and among cohorts. No significant correlation was found between multiple-locus heterozygosity and either somatic or reproductive growth. Our results lend support to the postulated linkage between low heterozygote deficit and lack of a heterozygosity/growth association in marine bivalves, and in the pectinid group in particular. Partial reproductive senility occurs in these scallops in their second year of life. Somatic tissue weight increased exponentially with increasing shell height, whereas pre-spawning gonad mass attained asymptotic values in 2-yr-old scallops. Thus, weight-specific reproductive effort was significantly lower in second- than first-year scallops (24 and 33% respectively). This pattern could be generated if high individual reproductive effort in the first year were correlated with accelerated (early) post-reproductive senescence. This kind of resource allocation, in which somatic growth is given precedence over reproductive growth in older individuals, has been previously reported in only one other bivalve, a pectinid (Chlamys islandica), in which the decline in reproductive effort occurs only after the scallops reach an age of ca. 20 yr.     

Ontogenetic changes in gill morphology and potential significance for food acquisition in the scallop <Emphasis Type="Italic">Placopecten</Emphasis><Emphasis Type="Italic">magellanicus</Emphasis>

Sources of mortality in both wild and cultured populations of marine bivalves during postlarval stages remain largely unknown, but may be partly associated with the inability to meet energetic demands during intense morphogenesis. The development of the gills in postsettlement scallops (Placopecten magellanicus) from 0.35 to 14 mm in shell height (SH) was investigated using scanning electron microscopy to determine the degree of size-specific differentiation of the gills and evaluate potential ontogenetic constraints in food acquisition. Key transitional stages in morphogenesis, likely to exert pronounced effects on feeding function, were identified and correlated with scallop size. The gill was initially homorhabdic, with unreflected inner demibranchs forming a basket-like structure maintained by ciliary junctions. Gill reflection, immediately followed by accelerated proliferation of gill filaments and formation of outer demibranchs, occurred at ~1 mm SH. Outer demibranchs were fully formed at ~2 mm SH. Suspension-feeding is probably rather inefficient prior to attaining 1-2 mm sizes. The onset of the heterorhabdic, adult form of the gill, which allows bidirectional particle transport and the potential for selection and for volume regulation of ingested material on the gill, occurred fairly late in development, at ~3.3-5.0 mm SH. Full development of gill plication was delayed until scallops attained ~7 mm. Gill differentiation in this species is thus relatively protracted and punctuated by critical transitional stages, which may be important in determining feeding and growth capacity of postlarval wild and cultured populations.     

Influence of algal and suspended sediment concentrations on the feeding physiology of the hard clam Mercenaria mercenaria

Short-term laboratory feeding experiments were conducted to determine the response of the hard clam Mercenaria mercenaria (L.) (32 mm in mean shell length) to increasing sediment concentrations. Clams were fed mixed suspensions of Pseudoisochrysis paradoxa (50 and 150 cells l^-1) and bottom sediments (0 to 44 mg l^-1). Algal ingestion rate deelined with increasing sediment loads. This resulted primarily from a reduction in clearance rate, which declined by 0.08 l h^-1 g^-1 (1.3%) for every 1 mg l^-1 increase in sediment load. This reduction was of similar magnitude for juvenile (13 mm) clams. At the algal concentrations tested, pseudofaeces production was intermittent and inconspicuous below about 10 mg silt l^-1. Loss of algae in pseudofaeces increased with increasing sediment loads; however, even at the highest silt and algal concentrations, clams lost a maximum of only 18% of the algae cleared from suspension. Thus, pseudofaeces production is not expected to cause significant loss of algal food at the sediment concentrations normally encountered in the natural environment ( ca 40 mg silt l^-1). Absorption rate of total organic matter remained constant, at least up to silt concentrations of 20 mg l^-1. Experiments using dual ⁵¹Cr:¹⁴C-formaldehyde-labelled sediment indicated that clams were able to counteract the dilution of algae by absorbing a considerable fraction (21 to 22%) of detrital sedimentary organics. Absorption efficiency of pure P. paradoxa ranged from 82% at 50 cells l^-1 to 58% at 150 cells l^-1. Integration of physiological rate measurements suggests that at moderate to high algal concentrations (300 g Cl^-1), growth improvement by the addition of silt, documented in mussels, surf clams and oysters, is unlikely to occur in M. mercenaria. It is suggested that a suspension-feeding bivalve's success in maximizing its energy gain in a turbid environment depends on the combination of two features: a high selection efficiency and a high rate of pseudofaeces production. It is proposed that species which regulate ingestion primarily by producing pseudofaeces are better adapted to cope with high suspended sediment loads than species such as M. mercenaria, which control ingestion mainly by reducing clearance rate.Contribution No. 451 from the Marine Sciences Research Center, State University of New York at Stony Brook, USA     

Toxicity of fluoranthene and its biodegradation metabolites to aquatic organisms

The toxicity of nine stable products of the biodegradation of fluoranthene with the pure bacterial strain Pasteurella sp. IFA was studied. For their quantification, an improved analytical procedure with two-step liquid-liquid extraction, derivatisation and gas chromatographic-mass spectrometric detection was used. Growth inhibition and immobility tests for fluoranthene and its metabolites were carried out using algae (Scenedesmus subspicatus), bacteria (Pseudomonas putida) and crustaceans (Daphnia magna and Thamnocephalus platyurus). Tests using the alga S. subspicatus revealed that with the exception of 9-hydroxyfluorene, which was only four times less toxic than fluoranthene, all the other metabolites were 37 to approximately 3000 times less toxic than the parent material. P. putida cells were resistant to fluoranthene and its primary metabolites, but were inhibited by low molecular weight intermediates, especially benzoic acid. Fluoranthene was not toxic to T. Platyurus, but was toxic to D. magna. Its primary metabolites (including 9-fluorenone and 9-hydroxyfluorene) were toxic to D. magna, and a low molecular weight metabolite (2-carboxybenzaldehyde) was highly toxic to T. platyurus.     

Gpi genotypic effect on quantitative traits in the northern bay scallop,Argopecten irradians irradians

The relationships between glucose-6-phosphate isomerase (Gpi) genotype and quantitative variation related to reproduction and growth were explored over the lifespan of a single cohort of northern bay scallops, Argopecten irradians irradians (Lamarck), from September 1986 to April 1988 in the Niantic River estuary, Connecticut, USA. Analyses revealed that Gpi genotype explained an increasingly significant proportion of variation in scallop size (up to 15%) as the cohort aged. The genotype-specific effects were consistent across sampling dates and among measured traits. There was no evidence for heterosis with respect to size at this locus; however, rare genotypes contributed substantially to the relationship and showed some tendency to fall on the extremes of the phenotypic distribution. The strength and consistency of the genotypic effect on scallop size suggest that genetic variation for Gpi, or some locus in linkage disequilibrium with Gpi, may translate into biochemical and/or physiological variation and affect fitness in this species.