Year-class strength regulation in plaice (Pleuronectes platessa L.) on the Swedish west coast

Year-class strength of plaice (Pleuronectes platessa) has been studied over periods of 10 and 35 years, respectively, in two shallow sandy areas on the Swedish west coast. In one area, Gullmar Bay (N 58 ° 19 – W 11 ° 33), 0-group plaice were sampled quantitatively with a drop trap at 0–0.7 m depth and densities between 0.2 and 3.8 ind./m² were recorded in early summer. In the other area, Laholm Bay (N 56 ° 30 – W 12 ° 55), 0-group plaice were sampled semi-quantitatively in August with young-fish trawl at 1.5 m depths. Densities between 0.001 and 0.28 ind./m² were assessed.The effects of temperature and wind (in the winter and early spring) and predation (in early summer), on the recruitment of 0-group plaice were investigated. In Gullmar Bay high recruitment occurred after severe winters and in years when on-shore winds dominated during spring. No such correlations were found in Laholm Bay. In Gullmar Bay a significant inverse relationship was found between the density of O-group plaice in early summer and the biomass of brown shrimp (Crangon crangon) and the shore crab (Carcinus maenas), the main predators in the nursery area.The importance of physical and biological factors regulating recruitment in plaice are discussed.     

Density Dynamics and Size Composition of Bivalve Mollusk Larvae of the Genus Mya in Peter the Great Bay (Sea of Japan)

The seasonal population size of planktonic larvae of mollusks of the soft-shell clam genus Mya were studied in Vostok Bay. The larvae occurred in plankton from the first third of June to early September. The highest density of larvae (279.7 ± 98.7 specimens/m³) was found in late June. In early July, larval numbers decreased sharply, and at the end of the first third of July, only single Mya larvae were found in the plankton. Another increase in larval population was observed in early and late August. The larvae varied in length from 175 to 325 m in June–July and from 150 to 250 m in August. It is likely that the larvae of two species of Mya, M. arenaria and M. uzenensis, are present in the plankton of Vostok Bay.     

Fungal biomass and decomposition in Spartina maritima leaves in the Mondego salt marsh (Portugal)

Spartina maritima (Curtis) Fernald is a dominant species in the Mondego salt marsh on the western coast of Portugal, and it plays a significant role in estuarine productivity. In this work, leaf litter production dynamics and fungal importance for leaf decomposition processes in Spartina maritima were studied. Leaf fall was highly seasonal, being significantly higher during dry months. It ranged from 42 g m^-2 in June to less than 6 g m^-2 during the winter. Fungal biomass, measured as ergosterol content, did not differ significantly between standing-decaying leaves and naturally detached leaves. Fungal biomass increased in wet months, with a maximum of 614 g g^-1 of ergosterol in January in standing-decaying leaves, and 1077 g g^-1 in December, in naturally detached leaves, decreasing greatly in summer. Seasonal pattern of fungal colonization was similar in leaves placed in litterbags on the marsh-sediment surface. However, ergosterol concentrations associated with standing-decaying and naturally detached leaves were always much higher than in litterbagged leaves, suggesting that fungal activity was more important before leaf fall. Dry mass of litterbagged leaves declined rapidly after 1 month (about 50%), mostly due to leaching of soluble organic compounds. After 13 months, Spartina leaves had lost 88% of their original dry weight. The decomposition rate constant (k) for Spartina maritima leaves was 0.151 month^-1.     

Seasonal cycles of zooplankton from San Francisco Bay

The two estuarine systems composing San Francisco Bay have distinct zooplankton communities and seasonal population dynamics. In the South Bay, a shallow lagoon-type estuary, the copepods Acartia spp. and Oithona davisae dominate. As in estuaries along the northeast coast of the U.S., there is a seasonal succession involving the replacement of a cold-season Acartia species (A. clausi s.l.) by a warm-season species (A. californiensis), presumably resulting from the differential production and hatching of dormant eggs. Oithona davisae is most abundant during the fall. Copepods of northern San Francisco Bay, a partially-mixed estuary of the Sacramento-San Joaquin Rivers, organize into discrete populations according to salinity distribution: Sinocalanus doerrii (a recently introduced species) at the riverine boundary, Eurytemora affinis in the oligohaline mixing zone, Acartia spp. in polyhaline waters (18–30\%), and neritic species (e.g., Paracalanus parvus) at the seaward boundary. Sinocalanus doerrii and E. affinis are present year-round. Acartia clausi s.l. is present almost year-round in the northern reach, and A. californiensis occurs only briefly there in summer-fall. The difference in succession of Acartia species between the two regions of San Francisco Bay may reflect differences in the seasonal temperature cycle (the South Bay warms earlier), and the perennial transport of A. clausi s.l. into the northern reach from the seaward boundary by nontidal advection.Large numbers (>10⁶ m^–3) of net microzooplankton (>64 µm), in cluding the rotifer Synchaeta sp. and three species of tintinnid ciliates, occur in the South Bay and in the seaward northern reach where salinity exceeds about 5–10 Maximum densities of these microzooplankton are associated with high concentrations of chlorophyll. Meroplankton (of gastropods, bivalves, barnacles, and polychaetes) constitute a large fraction of zooplankton biomass in the South Bay during winter-spring and in the northern reach during summer-fall.Seasonal cycles of zooplankton abundance appear to be constant among years (1978–1981) and are similar in the deep (>10 m) channels and lateral shoals (<3 m). The seasonal zooplankton community dynamics are discussed in relation to: (1) river discharge which alters salinity distribution and residence time of plankton; (2) temperature which induces production and hatching of dormant copepod eggs; (3) coastal hydrography which brings neritic copepods of different zoogeographic affinities into the bay; and (4) seasonal cycles of phytoplankton.     

Stable isotope evidence of benthic microalgae-based growth and secondary production in the suspension feeder Cerastoderma edule (Mollusca,Bivalvia) in the Marennes-Oléron Bay

The contribution of natural food sources to the growth and secondary production of the suspension feeding bivalve Cerastoderma edule (L.) was estimated under field conditions in the Marennes-Oléron Bay (Atlantic coast, France). Monthly estimates of abundance, biomass and cockle growth were combined with seasonal analyses of ¹³C and ¹⁵N ratios of juvenile and adult cockles, together with their potential food sources [i.e. suspended particulate organic matter (POM), microphytobenthos, macroalgae and seagrass] sampled at mid-tide level in a muddy sandflat. Adult cockles grew mainly in spring, whereas juveniles grew in summer and autumn, following spat recruitment in early summer. Total annual production and elimination of cockles were estimated to be 32.5 and 34.7 g AFDW m^–2 yr^–1. Relative contributions of each year class to production were ca 40, 41, 11 and 6% for 0-group, 1-, 3- and 4-yr-old cockles in 1995, respectively. Quantitative assessment of proportions of food sources to the annual secondary production of cockles was obtained by using a simple carbon isotope-mixing model with microphytobenthos (¹³C = –16.0±0.6) and POM (¹³C = –22.2±1.1) as end-members. On average, more than 70% of the total annual cockle production originated from microphytobenthos, with a much higher contribution for the 0-group (88%) than for adult cockles (60%). The between-age difference was induced mainly by changes in the availability of food resources (benthic versus planktonic) during the non-synchronous growing seasons of juvenile and adult cockles.     

Dynamics of the phycotoxin domoic acid: accumulation and excretion in two commercially important bivalves

Batch cultures of the toxigenic diatomNitzschia pungens Grunow f.multiseries Hasle were fed to blue mussels (Mytilus edulis) and deep sea Atlantic scallops (Placopecten magellanicus) to elucidate conditions under which domoic acid (DA) was accumulated and excreted (depurated). Mussels accumulated the toxin to a maximum level of 13 g g^-1, at rates of 0.21 to 3.7 g h^-1 g^-1, dry weight. Accumulation efficiency (the proportion of accumulated DA to estimated net uptake) ranged from 1–5%. The highest filtration rate of 1.71 h^-1 occurred at concentrations of 4–8 × 10⁶ Nitzschia cells 1^-1 with no formation of pseudofeces. Depuration rates between fed and starved mussels over a 2 h test period were the same. The depuration rate of domoic acid was about 17% d^-1 and did not account for the low uptake efficiencies, so it is suggested that most of the DA is lost from mussels in the solution during the feeding process. Domoic acid accumulation in mussels was dependent on the amount of toxin available, which in turn was a function of the density and growth phase of theNitzschia population. Changes in filtration rate withNitzschia concentration and depuration rate with time can account for the DA levels of mussels collected during toxic episodes in Cardigan Bay, Prince Edward Island, Canada in 1988 and 1989.Scallops accumulated DA (0.39–1.3 g h^-1 g^-1, more slowly than mussels, however, accumulation efficiencies ranged from 5–100%. Filtration rates remained relatively low and constant at 0.081 h^-1. Scallops retained domoic acid longer than mussels, a fact which must be considered in the marketing of whole scallops for human consumption.     

Planktonic chlorophyll a and eutrophication in two Mediterranean littoral systems (Mallorca Island,Spain)

Two Mediterranean littoral systems of Mallorca Island have been studied using planktonic chlorophyll a (total concentration and seasonal variations) as trophic indicator. The studied systems are quite different in geomorphology, physicochemical trends and anthropic incidence. S'Albufera-Alcudia Bay is the drainage outlet of a coastal marsh, with a salt wedge estuarine regime. Andratx Harbour is a narrow bay affected by a high anthropic incidence due to the presence of a small fishing port and mainly a large leisure harbour. Both systems are affected by a typical Mediterranean climate and a negligible tide incidence. The present work is based on several year monitoring of physical, chemical and biological water parameters. In S'Albufera-Alcudia Bay, Chl a concentration ranged from 0.01 to 17.10 mg m^–3, the values dropping from the inland site to the sea. The phytoplankton biomass gradient takes its origin in physical and chemical differences. The variance is mainly related to the inland-sea water axis. Nitrogen and silica enriched inland waters are the main source of eutrophication, hence their relation with Chl a. These nutrients entering the Albufera are mainly derived from leaching from farmed soils. The transition from an inland eutrophic system to an oligotrophic marine one show the filter character of these coastal marshes. In Andratx Harbour, Chl a ranged from a non detectable concentration to 6.36 mg m^–3. The ultraplankton (<5 m) was the most important contributor to total concentration. The ultraplankton in this system is related to influence of more oligotrophic open seawater. A greater proportion of microplankton (>20 m) is related both to higher nutrient concentrations and a higher water column stability. In Andratx Harbour, the enclosure state seems very important for development of phytoplankton blooms.     

Regulation of aplanospore germination in Vaucheria

Germination of aplanospores in Vaucheria longicaulis Hoppaugh var. macounii Blum proceeds through three stages of development. Stage I begins with the initiation of germination and lasts approx. 2 h. During this stage germinating filaments grow at an accelerated rate (266 ± 12 m · h^–1). Stage II is characterized by a sharp decline in the growth rate of germinating filaments (96 ± 4 m · h^–1) and lasts 4 h. This is followed, during the next 4 h, by a recovery in the growth rate (168 ± 8 m · h^–1) of germinating filaments, stage III. Growth rates stabilize and remain unchanged during subsequent development (Oliveira and Fitch, 1988, J. Submicrosc. Cytol. Pathol. 20, 397–406). The Ca²⁺-influx modulators LaCl₃, nifedipine and methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4 (2-trifluoromethylphenyl)-pyridine-5-carboxylate (Bay K-8644), the ionophore calcimycin (A23187), the intracellular Ca²⁺-release antagonist 8-N-N'-(diethylamino)-octyl-3,4, 5-trimethoxybenzoate (TMB-8), the Ca²⁺-uptake inhibitor ruthenium red and the phosphoinositide-cycle modulators LiCl and myo-inositol show that the events required for the initiation are distinct from those required for the completion of each stage of germination. These studies in conjunction with microinjection of germinating filaments with inositol 1,4,5-trisphosphate, the natural ligand for Ca²⁺ release from Ca-storing organelles (endoplasmic reticulum, vacuole), and treatment with chlorotetracycline (CTC), to visualize the distribution of membrane-bound Ca²⁺ reveal that both the initiation and completion of each stage of germination are controlled by Ca²⁺ signals which are restricted to well-defined time intervals and are modulated by the origin (source) of Ca²⁺.Abbreviations BAPTA 1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid - Bay K-8644 methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4(2-trifluoromethylphenyl)-pyridine-5-carboxylate - CTC chlorotetracycline - InsP₃ inositol 1,4,5-trisphosphate - RR ruthenium red - TMB-8 8-N-N-(diethylamino)-octyl-3,4,5-trimethoxybenzoate The author wishes to express his gratitude to the technical group of the Immunocytochemistry Unit for their help with the microinjection studies. This work was supported by a grant from the Natural Sciences and Engineering Research Council of Canada (grant A-7844).     

An assessment of soil enrichment by actinorhizal N2 fixation using δ15N values in a chronosequence of deglaciation at Glacier Bay,Alaska

The extent of transfer of fixed N between N₂-fixing and non-N₂-fixing plant species is largely unknown in successional studies. In order to redress this deficiency at a locale intensively studied ecologically, leaf tissue samples were collected from actinorhizal N₂-fixing (Alnus, Shepherdia, and Dryas) and two non-N₂-fixing (Salix) woody species within research plots located along a chronosequence of deglaciated fjord in Glacier Bay National Park, Alaska. The tissue samples were analyzed for ¹⁵N content, and the resulting data analyzed for trends in plant tissue N. Among the non-N₂-fixing Salix species, ¹⁵N values increased from the most recently deglaciated sites to converge with the temporally more-stable values for the symbiotic N₂-fixing species on sites at about 40 years after deglaciation. The lower ¹⁵N values of sequestered N in plant tissues suggested that N derived from N₂-fixing plants accounts for the major portion of N in associated plants up to 40 years after deglaciation. The ¹⁵N isotopic data also suggested that Shepherdia canadensis depends least on soil N, D. drummondii the most, and A. viridis ssp. sinuata somewhere between those two species. The presence of a sere dominated by dense thickets of A. viridis ssp. sinuata at the convergence of ¹⁵N values for the N₂-fixing and non-N₂-fixing species indicated that this species is most responsible for accumulation of fixed N in soil at Glacier Bay. This paper is dedicated to the memory of Steven J. Kohls who died prior to publication of this research.     

Importance of Shallow Water Habitats for Demersal Fishes and Decapod Crustaceans in Penobscot Bay, Maine

We characterized demersal fish and decapod crustacean habitats in 14 shallow (< 12m) areas in Penobscot Bay, Maine, by mapping the distribution of subtidal substrata with an acoustic sea bottom profiler. We identified the aquatic vegetation and the fishes and decapods associated with these habitats. Samples of fishes and decapods in each habitat were collected with a small beam trawl. The seabed at most of the stations sampled was composed of a mosaic of substrata. More species of fishes tow^-1 and higher abundances of fishes and decapods were found in stations with vegetation present, particularly eelgrass, Zostera marina. Decapod species richness tow^-1 was similar between vegetated and unvegetated habitats. Shallow habitats in Penobscot Bay were dominated by juvenile fishes and function as nursery areas. The greater species diversity and higher abundances of epibenthic fishes and decapod crustaceans observed in vegetated habitats, particularly beds of Zostera marina, compared with unvegetated areas in Penobscot Bay conform to the hypothesis that increased habitat complexity results in increased species richness and abundance.The first author is also senior author     

Antifouling activity of seaweed extracts on the green alga Enteromorpha prolifera and the mussel Mytilus edulis

Twenty-seven species of common seaweeds from the coast of Korea havebeen screened for antifouling activity. The seaweed extracts were tested inlaboratory assays against the marine fouling green alga Enteromorphaprolifera and the blue mussel Mytilus edulis. Tissue growth, sporesettlement, zygote formation and germlings of the E. prolifera wereinhibited by methanol extracts of the seaweed Ishige sinicola (= I. foliacea) and Sargassum horneri. Spore settlement was stronglyinhibited by using extract concentrations as low as 30 g mL^-1with I. sinicola and 120 g mL^-1 with S. horneri. The repulsive activity of the foot of the mussel was completely inhibited bymethanol extracts of I. sinicola and Scytosiphon lomentaria atconcentrations of 40 g per 10 L drop supplied to eachmussel. These extracts also showed strong antifouling activities onlarval settlement with, respectively, no or only 6% of the spat settlingwhen a test concentration of 0.8 mg mL^-1 was used. This work isthe first stage towards the development of novel antifouling agents frommarine macroalgae.     

The effect of organic calcium channel modulators on the germination ofVaucheria longicaulis aplanospores

Summary InVaucheria longicaulis var.macounii aplanospore germination and filament growth are severely inhibited by the Ca²⁺-channel antagonists (–)202–791, diltiazem, nifedipine and verapamil, whereas the agonists (+)202–791, Bay K-8644 and CGP-28392 stimulate those processes. Both antagonist and agonist actions suggest that voltage-controlled Ca²⁺ influx plays a major role in the regulation of the initial events of germination and filament growth. Increases in⁴⁵Ca²⁺ influx are observed after pretreatment of the aplanospores with low temperature shocks of brief duration or FCCP. Both agents are known to depolarize the surface membrane.⁴⁵Ca²⁺ influx is reduced in material treated with FC, an agent known to hyperpolarize cell membranes. The results indicate that Ca²⁺ influx takes place through voltage-sensitive Ca-channels.Abbreviations Bay K-8644 methyl 1,4-dihydro-2,6-dimethy1-3-nitro-4-(2-trifluoromethylphenyl)-pyridine-5-carboxylate - CGP CGP-28392 - CTC chlorotetracycline - dil diltiazem - DMSO dimethyl sulphoxide - DTE dithioerythritol - EGTA ethyleneglycol-bis-(-aminoethylether) N,N¹-tetraacetic acid - FC fusicoccin - FCCP p-fluoromethoxy-(carbonylcyanide)phenylhydrazone - nif nifedipine - PCMB p-chloromercuribenzoate - ver verapamil     

Developmental Change in CO2 Compensation Concentrations in Spartina alterniflora Results from Sigmoidal Photosynthetic CO2 Responses

We investigated seasonal patterns of photosynthetic responses to CO₂ concentrations in Spartina alterniflora Loisel, an aerenchymous halophyte grass, from a salt marsh of the Bay of Fundy (NB, Canada), and from plants grown from rhizome in controlled-environment chambers. From late May to August, CO₂ compensation concentrations () of field-grown leaves varied between 2.5–10.7 cm³(CO₂) m^–3, with a mean of 5.4 cm³(CO₂) m^–3. From September onwards field leaves showed CO₂ compensation concentrations from 6.6–21.1 cm³(CO₂) m^–3, with a mean of 13.1 cm³ m^–3 well into the C₃–C₄ intermediate range. The seasonal variability in did not result from changing respiration, but rather from a sigmoidal response of net photosynthetic rate (P _N) to applied CO₂ concentration, found in all tested leaves but which became more pronounced late in the season. One explanation for the sigmoidal response of P _N to external CO₂ concentration could be internal delivery of CO₂ from roots and rhizomes to bundle sheath cells via the aerenchyma, but the sigmoidal responses in S. alterniflora persisted out to the tips of leaves, while the aerenchyma extend only to mid-leaf. The sigmoidicity persisted when CO₂ response curves were measured from low to high CO₂, or from high to low CO₂, and even when prolonged acclimation times were used at each CO₂ concentration.     

Low salinities adversely affect photosynthetic performance of the mangrove,Avicennia marina

Photosynthetic performance of the highly salt tolerant mangrove, Avicennia marina, was compared at two sites differing insubstrate soil salinities. Carbon dioxide exchange and chlorophyll fluorescence weremonitored at a high salinity site in Durban Bay (35) and at a low salinitysite in Beachwood (< 12). Mean CO₂ exchange, conductanceand transpiration were consistently higher at the high salinity site. Carbondioxide response curves indicated that carboxylation efficiency was higherand stomatal limitation lower at the Durban Bay site. PSII quantum yield,electron transport rates (ETR) and intrinsic PSII efficiency(F_v/F_m) were significantly higher at the high salinity site.Quenching analysis indicated a higher degree ofphotoinhibition/photoprotection in leaves at the low salinity site. Predawnand midday leaf water potentials were –1.6 and –3.1 MPa at Beachwood,compared to –2.6 and –3.8 MPa, respectively, at Durban Bay. Leafconcentrations of Na⁺, K⁺, Ca²⁺, Mg²⁺,Cl^- and N were significantly higher at Durban Bay. Photosyntheticperformance is apparently impaired at the low salinity site in Beachwood asa result of K⁺ and N deficiencies in the leaves.     

Detection of a 65 kDaras binding protein in rat and sheep brain cytosol using a chemical cross linking agent

The ability of aras protein to associate with proteins present in rat brain cytosolin vitro was investigated using chemical cross-linking agents and the¹²⁵I-labelled v-H-ras protein. Two iodinated protein complexes with apparent molecular weights of 40 and 85 kDa were observed when a mixture of rat brain cytosol and [¹²⁵I]ras was treated with the cross-linking agent disuccinimidyl suberate and subjected to SDS-PAGE. Formation of the [¹²⁵I] 85 kDa complex was enhanced by a high concentration of EDTA while generation of the 40 kDa species was abolished by this treatment. Formation of the [¹²⁵I] 85 kDa complex was inhibited by unlabelledras protein, GTP, GTPS, and GDP but not by ATPS and GMP.Chromatography of the cross-linked brain cytosol-[¹²⁵I]ras mixture on DEAE cellulose partially resolved the [¹²⁵I] 85 kDa complex from the [¹²⁵I]ras protein. The [¹²⁵I] 85 kDa complex (formed using ethyleneglycolbis (succinimidylsuccinate) as the cross-linking agent) could be immunoprecipitated using a rabbit anti-ras polyclonal antibody. Treatment of the immunoprecipitate with hydroxylamine to cleave the cross-link yielded [¹²⁵I]-labelledras. A substantial enrichment of the proportion of the [¹²⁵I] 85 kDa complex in the cross-linked extract was achieved by preparative SDS-PAGE. It is concluded that thein vitro chemical cross-linking approach employed here has detected tworas binding proteins in rat brain cytosol: a 65 kDa heat-sensitive and a 20 kDa heat-stable protein. The possibility that the 65 kDaras binding protein is aras regulatory orras effector protein which has not so far been characterised is briefly discussed.Abbreviations DSS disuccinimidyl suberate - EGS ethyleneglycolbis (succinimidylsuccinate) - GTPS guanosine 5-[-thio] triphosphate - ATPS adenosine 5-[-thio] triphosphate     

Use of the GUS gene as a selectable marker for Agrobacterium-mediated transformation of Rubus

A transformation system was established for red raspberry, blackberry and blackberry x raspberry hybrids, utilizing the binary vector system of Agrobacterium tumefaciens. Leaf discs or internodal stem segments were inoculated with Agrobacterium strain LBA4404 containing the binary vectors PBI121.X, which has the -glucuronidase (GUS) marker gene, or Bin 19, which has the neomycin phosphotransferase II (NPT II) gene. Regenerants were produced on media containing MS salts, 20 gl^-1 sucrose, 7 gl^-1 agar, 100 mgl^-1 inositol, 0.5 mgl^-1 nicotinic acid, 0.5 mgl^-1 pyridoxine-HCl, 0.1 mgl^-1 thiamine, and either 0.1 mgl^-1 IBA and 2 mgl^-1 BAP for leaf discs, or 0.2 mgl^-1 BAP and 0.2 mgl^-1 2,4-D for stem segments. Kanamycin sulphate, which was used as a selective agent for the NPT II gene, inhibited organogenesis at 50 mgl^-1 and was therefore unsuitable for use as a selectable marker gene in Rubus. All regenerants were assayed utilizing the fluorogenic assay procedure to determine if the GUS gene had been transferred into the material and could therefore cleave the substrate 4-methyl-umbelliferyl--D-glucuronide. Seven GUS-positive plantlets were obtained which confirmed that this marker gene had been transferred into Rubus. A dot blot assay was carried out on GUS-positive plant material to establish if the NPT II gene had also been transferred to the plant material.     

Distribution and toxicity of a new colonial Microcystis aeruginosa bloom in the San Francisco Bay Estuary,California

The first distribution, biomass and toxicity study of a newly established bloom of the colonial cyanobacteria Microcystis aeruginosa was conducted on October 15, 2003 in the upper San Francisco Bay Estuary. Microcystis aeruginosa was widely distributed throughout 180 km of waterways in the upper San Francisco Bay Estuary from freshwater to brackish water environments and contained hepatotoxic microcystins at all stations. Other cyanobacteria toxins were absent or only present in trace amounts. The composition of the microcystins among stations was similar and dominated by demethyl microcystin-LR followed by microcystin-LR. In situ toxicity computed for the >75 m cell diameter size fraction was well below the 1 g l^–1 advisory level set by the World Health Organization for water quality, but the toxicity of the full population is unknown. The toxicity may have been greater earlier in the year when biomass was visibly higher. Toxicity was highest at low water temperature, water transparency and salinity. Microcystins from the bloom entered the food web and were present in both total zooplankton and clam tissue. Initial laboratory feeding tests suggested the cyanobacteria was not consumed by the adult copepod Eurytemora affinis, an important fishery food source in the estuary.     

Growth,biomass, mortality,production and potential yield of the West African clam,Egeria radiata (Lamarck) (Lamellibranchia,Donacidae) in the Cross River system,Nigeria

An important fishery for the West African hemi-estuarine clam, Egeria radiata exists in the lower reaches of the Cross River (CR) system. The stock is heavily exploited but its productivity and potential yield have not been studied. This paper discusses the distribution and ecology of, and presents data on growth, abundance, mortality, biological production and potential yield of the CR stock of E. radiata based principally on length structured relative age. Growth was exponential and conformed to the von Bertalanffy's growth model (VBGM), with the parameters L = 9.3 cm, K = 0.36 and T _o = –0.10 year. The instantaneous total mortality coefficient (Z) by the catch curve method was 0.82 yr^–1; natural mortality coefficient (M) was estimated at 0.32 yr^–1. Total mean biomass computed from data obtained in two month's grab sample surveys in the area of occurrence of E. radiata was 1923 kg ha^–1 for total (i.e. flesh + shell) and 628 kg ha^–1 for flesh (i.e. shell-free) production units. The production-to-mean-biomass (or P/B ratio, R) were 0.31 and 0.52 for total and shell-free production units respectively. The maximum sustainable yield (Y _max) was estimated at 398.4 kg ha^–1 for total and 112.2 kg ha^–1 for shell-free production units. With an exploitation ratio (E) of 0.61 and an estimated present catch rate of 1970 tonnes(t) yr^–1 total weight (or about 82% of Y _max) the Egeria stock of the CR is currently being fished above the level of its optimum yield. Much of the fishing pressure is on the very young clams, thus lowering the age at first capture (T _c) to 1 year. This is an unhealthy situation for a species with limited area of distribution and low (< 1.0) P/B ratio; it can lead to rapid extinction of the stock if for some reason there is a substantial reduction in annual recruitment. It is recommended that in order to conserve this valuable resource and keep it at a level of sustained optimum yield, there should be a regulation prohibiting the landing of young clams (< 6.0 cm shell length). Furthermore the fishermen should learn to cultivate the animal by transplanting the young clams to new beds upstream to give them time to grow larger before harvesting. This type of management has been practised in Ghana for a long time and has helped to conserve the Egeria stock of the Volta River. The need for a continuous monitoring of the effluents from the Nigerian Newsprint Manufacturing Company's factory located at the bank of the CR in the centre of the clam industry is stressed; such monitoring would ensure that dangerous toxic chemicals are not discharged into the river to damage the Egeria industry.     

Short term spatial — temporal distribution patterns of zooplankton in Admiralty Bay (Antarctica)

The present work analyses the abundance and species composition of mesozooplankton in relation to different patterns of wind speed and tides in Admiralty Bay. The plankton was sampled on 12, 13 and 15 March 1989 with a 385 m mesh size conical-cylindrical net by R.V. Barão de Teffé. In Martel Inlet, the zooplankton standing stock reached 25,223 individuals 100 m^–3 during the high tide. Under north-west winds, the abundance of the dominant species Ctenocalanus citer and Fritillaria borealis followed the tidal cycle. Weak south-west winds promoted the input of plankton even during low tide. Throughout the Bay, the highest densities of plankton (446–2,899 individuals 100 m^–3) were observed in surface waters flowing towards the Bransfield Strait. Surface waters flowing through the Bay and the inlets showed different species composition to surface waters flowing towards the Bransfield Strait.     

Structure and function of the yeast vacuolar membrane proton ATPase

Our current work on a vacuolar membrane proton ATPase in the yeastSaccharomyces cerevisiae has revealed that it is a third type of H⁺-translocating ATPase in the organism. A three-subunit ATPase, which has been purified to near homogeneity from vacuolar membrane vesicles, shares with the native, membrane-bound enzyme common enzymological properties of substrate specificities and inhibitor sensitivities and are clearly distinct from two established types of proton ATPase, the mitochondrial F₀F₁-type ATP synthase and the plasma membrane E₁E₂-type H⁺-ATPase. The vacuolar membrane H⁺-ATPase is composed of three major subunits, subunita (M _r =67 kDa),b (57kDa), andc (20 kDa). Subunita is the catalytic site and subunitc functions as a channel for proton translocation in the enzyme complex. The function of subunitb has not yet been identified. The functional molecular masses of the H⁺-ATPase under two kinetic conditions have been determined to be 0.9–1.1×10⁵ daltons for single-cycle hydrolysis of ATP and 4.1–5.3×10⁵ daltons for multicycle hydrolysis of ATP, respectively.N,N-Dicyclohexylcarbodiimide does not inhibit the former reaction but strongly inhibits the latter reaction. The kinetics of single-cycle hydrolysis of ATP indicates the formation of an enzyme-ATP complex and subsequent hydrolysis of the bound ATP to ADP and Pi at a 7-chloro-4-nitrobenzo-2-oxa-1,3-diazolesensitive catalytic site. Cloning of structural genes for the three subunits of the H⁺-ATPase (VMA1, VMA2, andVMA3) and their nucleotide sequence determination have been accomplished, which provide greater advantages for molecular biological studies on the structure-function relationship and biogenesis of the enzyme complex. Bioenergetic aspects of the vacuole as a main, acidic compartment ensuring ionic homeostasis in the cytosol have been described.Abbreviations CCCP carbonyl cyanidem-chlorophenyl hydrazone - DCCD N,N-dicyclohexylcarbondiimide - DES diethylstilbestrol - DIDS 4,4-diisothiocyano-2,2-stilbene disulfonic acid - NBD-Cl 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole - Pi inorganic phosphate - SDS sodium dodecylsulfate - SF6847 3,5-di-tert-butyl-4-hydroxybenzylidenemalononitrile - SITS 4-acetamide-4-isothiocyanatostilbene-2,2-disulfonic acid - ZW3-14 N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate