Blooms of Pseudo-nitzschia and domoic acid in the San Pedro Channel and Los Angeles harbor areas of the Southern California Bight, 2003–2004

Abundances of Pseudo-nitzschia spp. and concentrations of particulate domoic acid (DA) were determined in the Southern California Bight (SCB) along the coasts of Los Angeles and Orange Counties during spring and summer of 2003 and 2004. At least 1500 km² were affected by a toxic event in May/June of 2003 when some of the highest particulate DA concentrations reported for US coastal waters were measured inside the Los Angeles harbor (12.7 μg DA L⁻¹). Particulate DA levels were an order of magnitude lower in spring of 2004 (February and March), but DA concentrations per cell at several sampling stations during 2004 exceeded previously reported maxima for natural populations of Pseudo-nitzschia (mean = 24 pg DA cell⁻¹, range = 0–117 pg DA cell⁻¹). Pseudo-nitzschia australis dominated the Pseudo-nitzschia assemblage in spring 2004. Overall, DA-poisoning was implicated in >1400 mammal stranding incidents within the SCB during 2003 and 2004. Ancillary physical and chemical data obtained during our regional surveys in 2004 revealed that Pseudo-nitzschia abundances, particulate DA and cellular DA concentrations were inversely correlated with concentrations of silicic acid, nitrogen and phosphate, and to specific nutrient ratios. Particulate DA was detected in sediment traps deployed at 550 and 800 m depth during spring of 2004 (0.29–7.6 μg DA (g sediment dry weight)⁻¹). The highest DA concentration in the traps was measured within 1 week of dramatic decreases in the abundances of Pseudo-nitzschia in surface waters. To our knowledge these are the deepest sediment trap collections from which DA has been detected. Sinking of the spring Pseudo-nitzschia bloom may constitute a potentially important link between DA production in surface waters and benthic communities in the coastal ocean near Los Angeles. Our study indicates that toxic blooms of Pseudo-nitzschia are a recurring phenomenon along one of the most densely populated coastal stretches of the SCB and that the severity and magnitude of these events can be comparable to or greater than these events in other geographical regions affected by domoic acid.     

Note on the occurrence of Pseudo-nitzschia australis and domoic acid in squid from Monterey Bay, CA (USA)

Over the past decade diatom blooms of domoic acid (DA)-producing Pseudo-nitzschia spp. have been responsible for numerous marine mammal and bird mortalities in Monterey Bay, CA. One possible toxin vector is the market squid, Loligo opalescens, a small pelagic mollusk that plays an important role in the near-shore food web of the California Current ecosystem as a favored vertebrate prey species. This study examined the trophic link between toxic Pseudo-nitzschia and L. opalescens using toxin and stomach content analyses of animals collected from Monterey Bay, CA in 2000. Receptor binding assay data (confirmed by tandem mass spectrometry), demonstrated the presence of DA in squid during a toxic Pseudo-nitzschia event, with P. australis frustules observed in stomach samples. Though DA levels were low (<0.5 μg DA g⁻¹ tissue) in L. opalescens during the study period, it is now clear that this potent neurotoxin can occur in squid and is likely delivered through its krill prey species, which are known to retain DA after feeding on toxic Pseudo-nitzschia. Our findings suggest that further study of the relationship between Pseudo-nitzschia blooms and DA contamination of squid is warranted to better evaluate the potential health risk to humans and wildlife associated with this major commercial seafood species and important prey item.     

Ecology and taxonomy of potentially toxic Pseudo-nitzschia species in Lim Bay (north-eastern Adriatic Sea)

The population dynamics of Pseudo-nitzschia in relation to environmental factors was investigated from March 2002 to July 2008 in Lim Bay, in the north-eastern Adriatic Sea. Domoic acid was monitored in the breeding population of Mytilus galloprovincialis from 2005 to 2008. The principal-component analysis of environmental parameters showed that the system is mostly temperature driven. The phytoplankton community was mainly composed of diatoms. Pseudo-nitzschia was the dominant diatom, present in 60% of samples, with a maximum (1.6 × 10⁶ cells L⁻¹) contribution up to 97% of the total diatom abundance. Morphological analysis revealed Pseudo-nitzschia manii and potentially toxic Pseudo-nitzschia pseudodelicatissima, Pseudo-nitzschia pungens, Pseudo-nitzschia fraudulenta and Pseudo-nitzschia calliantha as the dominant species in blooms. Pseudo-nitzschia abundance positively correlated to temperature, phosphate and ammonia in accordance with its maximal abundance in the summer/autumn period when fish farms had a maximum impact on the environment. Domoic acid was detected in M. galloprovincialis in concentrations below regulatory limits, ranging from 0.097 to 0.8721 μg g⁻¹ in five cases from April to October 2005 in Lim Bay, but so far it is not clear which of the species was responsible for DA production. This study is also the first record of P. manii, P pungens and P. fraudulenta species in the Adriatic Sea.     

Domoic acid exposure in pygmy and dwarf sperm whales (Kogia spp.) from southeastern and mid-Atlantic U.S. waters

The neurotoxin domoic acid (DA) was detected in urine and fecal samples recovered from pygmy sperm whales (Kogia breviceps) and dwarf sperm whales (Kogia sima) stranding along the U.S. Atlantic coast from 1997 to 2008. Of the 41 animals analyzed from Virginia, North Carolina, South Carolina and Florida, 24 (59%) tested positive for DA at concentrations of 0.4–1.8 ng/mL in urine and 12–13,566 ng/g in feces as determined by liquid chromatography–tandem mass spectrometry (LC–MS/MS). Feces appeared to be the best indicator of DA exposure in Kogia spp., with 87% of all fecal samples analyzed testing positive for this toxin. Additional stranded animals (n = 40) representing 11 other cetacean species were recovered from the same region between 2006 and 2008 and analyzed by LC–MS/MS, however DA was not detected in any of these individuals. DA is produced naturally by diatoms in the genus Pseudo-nitzschia. Although blooms of DA-producing Pseudo-nitzschia have been associated with repeated large-scale marine mammal mortalities on the west coast of the U.S., there is no documented history of similar blooms on the southeast U.S. coast, and there were no observed Pseudo-nitzschia blooms in the region associated with any of these strandings. The feeding habits of Kogia spp. are poorly documented; thus, the vector(s) for DA exposure to these deep-diving species remains to be identified. Toxin accumulation in these pelagic whale species may be an indication of cryptic harmful algal bloom activity in offshore areas not currently being monitored. This study highlights the need for a better understanding of the role of toxigenic algae in marine mammal morbidity and mortality globally.     

Factors controlling the production of domoic acid by Pseudo-nitzschia (Bacillariophyceae): A model study

A mechanistic model has been developed to explore the factors controlling the production of domoic acid (DA) by the pennate diatom Pseudo-nitzschia. The idealized model allows consideration of the uncoupling between photosynthesis and growth, while DA production has been set as a secondary metabolism sharing common precursors with growth. Under growth limitation, these precursors can accumulate, resulting in an increased DA production. The model was first evaluated based on its ability to simulate the observed DA production by either silicon (Si) or phosphorus (P) limited batch cultures of Pseudo-nitzschia available in the literature. Sensitivity tests were further performed to explore how the ambient nutrients and the light regime (intensity and photoperiod length) are possibly directing the Pseudo-nitzschia toxicity. The general pattern that emerged is that excess light, in combination with Si or P limitation, favours DA production, provided nitrogen (N) is sufficient. Model simulations with varying nutrient stocks supporting Pseudo-nitzschia blooms under non-limiting light suggest two potential ways for nutrients to control DA production. First, N excess in comparison to available Si and P relieves DA production from its limitation by N, an absolute requirement of the DA molecule. Second, increased nutrient stocks amplify the DA production phase of the blooms (in addition to enhancing Pseudo-nitzschia biomass) which leads to an even more toxigenic bloom. Simulations investigating the light regime suggest a light threshold below which an important delay in DA production could be expected in Pseudo-nitzschia cultures. In the natural environment, the monitoring of light conditions during Pseudo-nitzschia blooms might help to anticipate the magnitude of the toxic event. Pseudo-nitzschia toxicity is indeed linked to the excess of primary carbon that accumulates during photosynthesis under growth limitation by nutrients.     

Phytoplankton growth and krill grazing during spring in the Bransfield Strait,Antarctica — Implications from sediment trap collections

Summary Phytoplankton primary production, biomass, species composition and sedimentation of organic matter (using a moored and a free drifting sediment trap) were measured in eastern Bransfield Strait during spring 1983. Biomass and primary production increased from low levels in late November (1 mgChla m^-3 and 400 mgC m^-2 d^-1) to bloom levels by the end of December (5 mgChla m^-3 and 1000 mgC m^-2 d^-1). The moored trap was deployed at 323 m depth for 22.5 days, and collected 2968 mgC and 67.6 mg chlorophyll a and derivatives per m² (132 and 3.0 mg m^-2 d^-1), of which 90% was in the form of krill faeces. These figures are regarded as egestion of krill, and using ingestion: egestion ratios from the literature, grazing loss of phytoplankton by krill was estimated at 45% of the primary production during a period of 3 weeks. Large-scale surveys of phytoplankton standing stock indicate that the build-up of blooms during spring is apparently not controlled by krill grazing. It is therefore suggested that the intense grazing that must have occurred over the trap during the period of deployment was only of local importance.     

Seasonal occurrence of coccoliths in sediment traps from West Caroline Basin, equatorial West Pacific Ocean

Coccolith fluxes were investigated by sediment trap studies in the West Caroline Basin, which is located in the equatorial western Pacific. The investigation was conducted from June 1991 to March 1992 at two water depths, 1592 and 3902 m, as part of the Northwest Pacific Carbon Cycle Study (NOPACCS) program. Two seasonal maxima of coccolith fluxes were observed during September–early October and late December–January. The average coccolith and coccosphere fluxes at the depth of the shallow trap were 1800×10⁶ coccoliths m⁻² day⁻¹ and 1.9×10⁶ coccospheres m⁻² day⁻¹, respectively. The flux of coccoliths followed the same trend as the total flux, and was closely correlated with the flux of organic matter flux. Florisphaera profunda, Gladiolithus flabellatus, Gephyrocapsa oceanica, Umbilicosphaera sibogae var. sibogae, Emiliania huxleyi, and Oolithotus fragilis were the most abundant species together comprising more than 85% of the total flora. Observed seasonal changes of the species composition of coccolith flora, as well as analysis of the R-mode cluster, revealed that during the summer, the assemblage was marked by the dominance of G. oceanica and U. sibogae. However, during the winter, the assemblage was dominated by E. huxleyi and O. fragilis. These assemblage changes were influenced by monsoonal events, which were observed off the New Guinea coast. F. profunda dominated the community in the shallow trap throughout most of the year; peak values of this species were recorded during the winter. The coccosphere assemblage was dominated by G. oceanica at both water depths. In the deep trap, the sedimentation pattern was similar to that observed at the shallow depth. Mean coccolith and coccosphere fluxes at the deep trap were 2000×10⁶ coccolith m⁻² day⁻¹ and 0.08×10⁶ coccospheres m⁻² day⁻¹, respectively. The increase in coccolith flux with water depth suggests a lateral influx. The estimated average daily mass of CaCO₃ flux in coccoliths and coccospheres was 16.6 mg m⁻² day⁻¹ at the 1592 m trap and 17.9 mg m⁻² day⁻¹ at the 3902 m trap, respectively. These calculated values contributed only 23.3% to the total CaCO₃ flux at the shallow trap and 27.9% at the deep trap.     

Recent domoic acid closures of shellfish harvest areas in Washington State inland waterways

Several species of the toxigenic diatom Pseudo-nitzschia, together with low concentrations of domoic acid (DA) in shellfish have been observed in Puget Sound, Washington State, since 1991. However, for the first time in September 2003, high-density blooms of Pseudo-nitzschia forced the closure of recreational, commercial, and tribal subsistence shellfish harvesting in Puget Sound. Here we report on the environmental conditions associated with shellfish closures in two inland waterways of Washington State during the Fall 2005. In Sequim Bay, shellfish harvest losses occurred on September 12 following the measurement of elevated macronutrient levels on September 2, and a bloom of P. pseudodelicatissima (up to 13 million cells/L) on September 9. Ambient NH₄ concentrations >12 μM (measured on September 2) were likely due to anthropogenic sources, ostensibly from sewage inputs to Sequim Bay. The closure of a Penn Cove commercial shellfish farm on October 16 was caused by a bloom of P. australis that followed a period of sustained precipitation, elevated Skagit River flow, and persistent southeasterly winds. The relative importance of a number of environmental factors, including temperature, stratification caused by rivers, and nutrient inputs, whether natural or anthropogenic, must be carefully studied in order to better understand the recent appearance of massive blooms of toxigenic Pseudo-nitzschia in the inland waterways of Washington State.     

Large-scale patterns of Nodularia spumigena blooms in Pyramid Lake,Nevada, determined from Landsat imagery: 1972–1986

Magnitude and long-term periodicity of summer-autumn blooms of the nitrogen-fixing cyanobacterium, Nodularia spumigena, were characterized for hyposaline Pyramid Lake, Nevada, from Landsat MSS band 3 film negatives. Predicted lakewide mean chlorophyll a concentrations for Landsat overpasses during the July–October Nodularia bloom season ranged from 27 to 72 mg m^–3 with an overall average concentration of 32 ± 7 mg m^–3 between 1972 and 1986. Nodularia blooms were usually annual events. Blooms were not observed on Landsat images in only three of 15 years (1973, 1980, 1982) and midsummer calcium carbonate whitings occurred in two of these years (1973, 1980). Magnitude of Nodularia blooms was highly variable among years and very large blooms, where maximum mean chlorophyll a concentration exceeded one standard deviation of the 15 year overall mean (> 39 mg m^–3) appeared in 1974, 1975, 1977, 1979, 1984, 1985 and 1986. Very large early-July blooms always occurred during or following years of above average fluvial discharge to Pyramid Lake (1984–1986) and were associated with meromixis produced by the large influx of freshwater.Several problems arise using Landsat remote sensing to estimate magnitude and periodicity of scum-forming blue-green algal blooms. These complications may reduce accuracy and precision of phytoplankton biomass estimates made from Landsat images. Nevertheless, Landsat remote sensing enabled us to quantify relative bloom magnitude with limited collection of ground-based data and at a large-scale temporal and spatial resolution not possible using alternative methodologies.     

The influence of Procambarus clarkii (Cambaridae,Decapoda) on water quality and sediment characteristics in a Spanish floodplain wetland

This study describes the effects of the American red swamp crayfish, Procambarus clarkii Girard, on water quality and sediment characteristics in the Spanish floodplain wetland, Las Tablas de Daimiel National Park. Our short term enclosure study during a summer drawdown revealed that crayfish acted as a nutrient pump that transformed and translocated sediment bound nutrients to the water column. Water quality impoverishment was mainly due to the increase of dissolved inorganic nutrients (soluble reactive phosphorus and ammonia), and a significant increase of total suspended solids occurred likely as a result of crayfish associated bioturbation. At the same time, crayfish reduced the content of organic matter in the sediment and we observed a slight increase of total sediment phosphorus and nitrogen content as a result of crayfish benthic activity. P. clarkii effects, in terms of internal nutrient loading (229.91 mg TP m^–2 d^–1), were shown to be important on a local scale, indicating the significance of internal nutrient supply to water column primary producers particularly under low external supply (summer). Extrapolations to the whole ecosystem, however, revealed a negligible crayfish contribution (0.06%) to total internal nutrient loading (0.035 mg TP m^–2 d^–1). Hence, crayfish spatial heterogeneity patterns are important in global and local matter fluxes and nutrient cycles in wetlands.     

Nutrient (N,P, Si) fluxes between marine sediments and water column in coastal and open Adriatic

Nutrient benthic fluxes, as well as sediment phosphorus concentration at the open sea and coastal water stations of the Central and South Adriatic were studied during 1997–98. The fluxes were in the ranges: 0.16–2.67 mmol m^–2 d^–1 (silicate); –0.031–0.164 mmol m^–2 d^–1 (phosphate); –0.51–2.03 mmol m^–2 d^–1 (ammonia); and –1.32–1.62 mmol m^–2 d^–1 (nitrate + nitrite). Silicate flux showed a gradient from the coastal area to the open sea. Ammonia was the main nitrogen species in the flux at the estuary and bay stations, while the sum of nitrate and nitrite was predominant at the open sea stations. Relationships between phosphate and ammonia fluxes (r = 0.699, p<0.01) as well as phosphate and silicate (r = 0.529, p<0.01) were established.     

Phosphorus release from sediments in a treatment wetland: Contrast between DET and EPC0 methodologies

Wetlands are capable of reducing nutrient loadings to receiving water bodies, and hence many artificial wetlands have been constructed for wastewater nutrient removal. In this study, diffusive equilibrium in thin films (DETs) and equilibrium phosphorus concentration (EPC₀) analysis were used to examine the role of sediment as a nutrient source or sink in a constructed treatment wetland in summer. The effect of dredging on sediment-water nutrient exchange was also studied. Soluble reactive phosphorus (SRP), ammonium (NH₄⁺) and sulphate (SO₄²⁻) concentration profiles were measured by DET across the sediment-water interface (SWI) in both a settling pond and iris reed bed within the wetland. The SRP concentrations in the sediment pore-waters of the settling pond were extremely high (up to 29,500 μg l⁻¹) near the SWI. This is over an order of magnitude higher than the levels found in the water column, which in turn are over an order of magnitude higher than environmental levels proposed to limit eutrophication in rivers. The profiles demonstrated an average net release of SRP and NH₄⁺ from the settling pond sediment to the overlying water of 58 mg m⁻² d⁻¹ (±32 mg m⁻² d⁻¹ (1 sd)) and 16 mg m⁻² d⁻¹ (±25 mg m⁻² d⁻¹ (1 sd)), respectively. The DET SO₄²⁻ concentration profiles revealed that the sediment was anoxic within 2 cm of the SWI. Dredging of the reed bed made no significant difference to the P release characteristics across the SWI. The EPC₀s were much lower than the SRP concentration of the overlying water, indicating that the sediment had the potential to act as a phosphate sink. The apparent contradiction of the DET and EPC₀ results is attributed to the fact that DET measurements are made in situ, where as EPC₀ measurements are ex situ. These results show that substantial releases of P can occur from wetland sediments, and also highlight the need for caution when interpreting ex situ EPC₀ analytical results.     

Temporal and spatial variability in Pseudo-nitzschia spp. in Alabama coastal waters: A “hot spot” linked to submarine groundwater discharge?

The potentially toxic diatom Pseudo-nitzschia is common in the northern Gulf of Mexico. Seven sites along the Alabama Gulf Coast have been monitored weekly to bi-weekly for Pseudo-nitzschia spp., which were detected in 489 of 829 samples (59%) taken between November 2003 and July 2008. Mean population density peaked at 19.6 ± 3.2 °C but bloom densities (>10⁶ cells L⁻¹) occurred at 20–32 °C. Mean population density peaked at a salinity of 30.1 ± 3.2, with blooms occurring between salinities of 26 and 32. Peaks in abundance occurred in April–May, with secondary peaks in fall. A cluster analysis of the relative frequency distributions of abundance by site showed that Little Lagoon Pass had a strong dissimilarity compared to other sites, due to a higher frequency of bloom densities and a lower frequency of absences. Salinities at Little Lagoon Pass were higher and less variable than at other sites. Pseudo-nitzschia spp. were absent more frequently from sites at the mouths of Perdido and Mobile Bays, where salinity was lower and more variable. Freshwater transport from Baldwin County, which lies between these bays, has previously been shown to be primarily through submarine groundwater discharge into the Gulf of Mexico. Groundwater in Baldwin County has high nitrate concentrations and discharge is most likely to occur adjacent to Little Lagoon. Blooms of Pseudo-nitzschia spp. at Little Lagoon Pass in spring were highly correlated with discharge from the Styx River, a proxy for groundwater discharge. Little Lagoon Pass may therefore be a hot-spot for blooms of Pseudo-nitzschia spp., because local maxima in discharge result in nutrient availability without significant reductions in salinity.     

Characterization of a toxic Pseudo-nitzschia spp. bloom in the Northern Gulf of Mexico associated with domoic acid accumulation in fish

A toxic bloom of Pseudo-nitzschia spp. was observed in the Alabama coastal waters of the northern Gulf of Mexico (NGOM) in June 2009 that resulted in the accumulation of domoic acid (DA) in fish. The bloom initiated following a large storm event that likely caused increased groundwater discharge 16–20 days prior to peak densities. Eleven sites, located in littoral shoreline waters and inshore embayments spanning the entire Alabama NGOM coastline, were sampled during peak densities to assess Pseudo-nitzschia species composition and toxicity, and associated water-quality parameters. Small fish (0.27–11.9 g body weight) were collected at six of these sites for analysis of DA content. High Pseudo-nitzschia spp. densities (8.27 × 10⁴–5.05 × 10⁶ cell l⁻¹) were detected at eight sites located in the littoral shoreline and particulate DA was detected at six of these littoral sites (48.0–540 pg ml⁻¹). The bloom consisted primarily (>90%) of Pseudo-nitzschia subfraudulenta, a species previously characterized as forming only a minor component of Pseudo-nitzschia assemblages and not known to produce DA. Pseudo-nitzschia spp. were at low densities or not detected at the inshore sites and DA was detected at these sites. Pseudo-nitzschia spp. density varied along an estuarine gradient, with greater densities occurring in the most saline, clear, and nutrient-poor waters. Cell density was strongly and negatively correlated with silicate (Si) concentrations and the ratios of silicate to dissolved inorganic nitrogen and phosphate (Si:DIN and Si:PO₄). Cell toxin quota was negatively correlated with phosphate, and strongly and positively correlated with the ratio of total nitrogen to total phosphorus (TN:TP). These relationships are consistent with previous observations that indicate Pseudo-nitzschia spp. density and toxicity are likely to be greater in high salinity, high irradiance, and nutrient-poor waters. DA was detected in 128 of 131 (98%) of the fish collected, which included seven primary and secondary consumer species. This is the first demonstration of trophic transfer of DA in this region of the NGOM, indicating that toxic blooms of Pseudo-nitzschia spp. in Alabama coastal waters have the potential to transfer DA to recreationally and commercially important fish species.     

The relationship between Pseudo-nitzschia (Peragallo) and domoic acid in Scottish shellfish

The diatom genus Pseudo-nitzschia (Peragallo) associated with the production of domoic acid (DA), the toxin reposnsible for amnesic shellfish poisoning, is abundant in Scottish waters. A two year study examined the relationship between Pseudo-nitzschia cells in the water column and DA concentration in blue mussels (Mytilus edulis) at two sites, and king scallops (Pecten maximus) at one site. The rate of DA uptake and depuration differed greatly between the two species with M. edulis whole tissue accumulating and depurating 7 μg g⁻¹ (now expressed as mg kg⁻¹) per week. In contrast, it took 12 weeks for DA to depurate from P. maximus gonad tissue from a concentration of 68 μg g⁻¹ (now mg kg⁻¹) to <20 μg g⁻¹ (now mg kg^‐1). The DA depuration rate from P. maximus whole tissue was <5% per week during both years of the study. Correlations between the Pseudo-nitzschia cell densities and toxin concentrations were weak to moderate for M. edulis and weak for P. maximus. Seasonal diversity on a species level was observed within the Pseudo-nitzschia genus at both sites with more DA toxicity associated with summer/autumn Pseudo-nitzschia blooms when P. australis was observed in phytoplankton samples. This study reveals the marked difference in DA uptake and depuration in two shellfish species of commercial importance in Scotland. The use of these shellfish species to act as a proxy for DA in the environment still requires investigation.     

Stimulating denitrification in a stream mesocosm with elemental sulfur as an electron donor

The heavy use of fertilizers in agricultural lands can result in significant nitrate (NO₃⁻) loadings to the aquatic environment. We hypothesized that biological denitrification in agricultural ditches and streams could be enhanced by adding elemental sulfur (S^o) to the sediment layer, where it could act as a biofilm support and electron donor. Using a bench-scale stream mesocosm with a bed of S^o granules, we explored NO₃⁻ removal fluxes as a function of the effluent NO₃⁻ concentrations. With effluent NO₃⁻ ranging from 0.5 mg N L⁻¹ to 4.1 mg N L⁻¹, NO₃⁻ removal fluxes ranged from 228 mg N m⁻² d⁻¹ to 708 mg N m⁻² d⁻¹. This is as much as 100 times higher than for agricultural drainage streams. Sulfate (SO₄²⁻) production was high due to aerobic sulfur oxidation. Molecular studies demonstrated that the S^o amendment selected for Thiobacillus species, and that no special inoculum was required for establishing a S^o-based autotrophic denitrifying community. Modeling studies suggested that denitrification was diffusion limited, and advective flow through the bed would greatly enhance NO₃⁻ removal fluxes. Our results indicate that amendment with S^o is an effective means to stimulate denitrification in a stream environment. To minimize SO₄²⁻ production, it may be better to place S^o deeper in the sediment layer.     

Are most of the domoic acid-producing species of the diatom genus Pseudo-nitzschia cosmopolites?

Records from all oceans, most of them published during 1990–2000, and personal unpublished observations of nine Pseudo-nitzschia taxa known as potential domoic acid (DA) producers have been used to outline their geographical distribution. Pseudo-nitzschia seriata f. seriata as the only taxon was found in the North Atlantic Ocean exclusively. The records of P. multistriata were too few and the identification of P. turgidula from the North Atlantic too unreliable to provide an idea about their distribution. Pseudo-nitzschia pungens and the less frequently recorded P. fraudulenta, P. multiseries and P. australis appeared to be cosmopolites. The wide distribution of the apparently most efficient DA producers, P. australis and P. multiseries, is especially noteworthy. The records of P. delicatissima and P. pseudodelicatissima also indicate a cosmopolitan distribution although with the qualification of certain taxonomic and identification ambiguities. Hence, the question of whether most DA-producing Pseudo-nitzschia species are cosmopolites may be answered with a tentative “yes”.     

Seasonal variations in foraminiferal flux in the Southern Ocean, Campbell Plateau, New Zealand

Time-incremental sediment trap moorings were deployed at two sites across Campbell Plateau, New Zealand; one in the relatively quiet waters of the plateau interior (Pukaki Rise) and the other at the Antarctic Circumpolar Current-swept margin (eastern Campbell flank). A continuous record of particle flux over 416 days identifies marked differences in faunal composition and seasonal occurrence in response to these two dynamically different Southern Ocean settings. In the shallow and thermally isolated interior of the Pukaki Rise site, the flux of foraminifera was closely linked to the austral spring pulse of primary production, at which time 97% of the total foraminiferal production for the year occurred. This seasonal flux of foraminifera at Pukaki Rise was dominated by the species Globorotalia inflata and Globigerina bulloides. The collapse of phytoplankton production at the end of spring was most likely a result of a co-limitation of iron and silicic acid. Over the deep and dynamic eastern flank of Campbell Plateau there were four seasonal pulses of foraminiferal flux, the largest in spring when almost half of the foraminiferal production occurred. Most of the spring flux at this site consisted of Globorotalia inflata and Globigerinita glutinata. Summer at eastern Campbell flank, exhibited the lowest flux of foraminifera, but the highest species diversity, while autumn and winter fluxes were dominated by the deep-dwelling Globorotalia truncatulinoides. Although there was only a single pulse of foraminiferal flux at Pukaki Rise, its mass (g m^{− 2}d^{− 1}) was still greater than that which occurred over the flank, summed across all four seasons. However, the overall standing stock (tests m^{− 2}d^{− 1}) on the flank was more than twice that which occurred at the Pukaki Rise site.An examination of core-top material taken from gravity cores collected in the vicinity of the sediment trap locations, revealed typical Southern Ocean foraminiferal assemblages that were markedly dissimilar in proportion to those observed in the sediment traps.     

Phosphorus dynamics and bioavailability in sediments of the Penzé Estuary (NW France): in relation to annual P-fluxes and occurrences of Alexandrium Minutum

The macrotidal estuary of Penzé (Brittany, Western part of the Channel, France) has been subjected to recurrent annual toxic blooms of Alexandrium minutum since 1988. This study aims to specify the phosphorus dynamics and bioavailability in sediments in order to improve our understanding of Alexandrium occurrences. Sediment-P pools and diffusive phosphate fluxes were studied under similar hydrodynamic conditions, in the intermediate estuary in May, June and July 2003 and along the salinity gradient from August 2004 to June 2005. The results highlight a decrease in bioavailable phosphorus (iron and organic bound) from the inner part of the estuary seaward. The ratio of iron-bound phosphorus to iron-oxyhydroxides is lower in the inner and intermediate estuaries (5–8) than in the outer site (15), suggesting a saturation of sorption sites and greater phosphorus bioavailability in this area. Pools of bioavailable phosphorus in surficial sediments are about eight times higher than the annual net-export of P (7 ton year⁻¹). Phosphate releases from sediments are always lower than 5 μmol m⁻² d⁻¹ in March. The highest supplies occur in June and August in the intermediate area (up to 400 μmol m⁻² d⁻¹) where they represent up to 50% of river loadings. These results further suggest that phosphate pulses coincide with occurrences of Alexandrium reported in June.     

我国沿海拟菱形藻属的2新记录种及其产毒特征分析

为澄清我国沿海拟菱形藻属(Pseudo-nitzschia)的物种多样性,并确认中国海域拟菱形藻属是否具有产生多莫酸(Domoicacid)的能力,采用毛细管显微操作技术从我国沿海水体中分离、纯化拟菱形藻细胞,建立了单克隆培养株系,并基于核糖体转录间隔区ITS1-5.8S-ITS2 序列构建了分子系统树。结果表明,结合在光学显微镜和透射电镜下观察的形态学特征和分子系统发育分析数据,鉴定到我国拟菱形藻属的2新记录种:银河拟菱形藻(P. galaxiae Lundholm & Moestrup)和微孔拟菱形藻(P. micropora Priisholm, Moestrup & Lundholm),对其形态学特征进行了详细描述,并与相似种类进行了比较研究。利用高效液相色谱(HPLC)技术对多莫酸特征进行了检测,结果表明培养株系并不产生多莫酸。这些为我国拟菱形藻属物种多样性和产毒特征研究提供了基础数据。