Association of picophytoplankton distribution with ENSO events in the equatorial Pacific between 145°E and 160°W

Climatological variability of picophytoplankton populations that consisted of >64% of total chlorophyll a concentrations was investigated in the equatorial Pacific. Flow cytometric analysis was conducted along the equator between 145°E and 160°W during three cruises in November–December 1999, January 2001, and January–February 2002. Those cruises were covering the La Niña (1999, 2001) and the pre-El Niño (2002) periods. According to the sea surface temperature (SST) and nitrate concentrations in the surface water, three regions were distinguished spatially, viz., the warm-water region with >28 °C SST and nitrate depletion (<0.1 μmol kg⁻¹), the upwelling region with <28 °C SST and high nitrate (>4 μmol kg⁻¹) water, and the in-between frontal zone with low nitrate (0.1–4 μmol kg⁻¹). Picophytoplankton identified as the groups of Prochlorococcus, Synechococcus and picoeukaryotes showed a distinct spatial heterogeneity in abundance corresponding to the watermass distribution. Prochlorococcus was most abundant in the warm-water region, especially in the nitrate-depleted water with >150×10³ cells ml⁻¹, Synechococcus in the frontal zone with >15×10³ cells ml⁻¹, and picoeukaryotes in the upwelling region with >8×10³ cells ml⁻¹. The warm-water region extended eastward with eastward shift of the frontal zone and the upwelling region during the pre-El Niño period. On the contrary, these regions distributed westward during the La Niña period. These climatological fluctuations of the watermass significantly influenced the distribution of picophytoplankton populations. The most abundant area of Prochlorococcus and Synechococcus extended eastward and picoeukaryotes developed westward during the pre-El Niño period. The spatial heterogeneity of each picophytoplankton group is discussed here in association with spatial variations in nitrate supply, ambient ammonium concentration, and light field.     

Polycyclic aromatic hydrocarbons in surface seawater and in indigenous mussels (Mytilus galloprovincialis) from coastal areas of the Saronikos Gulf (Greece)

Polycyclic aromatic hydrocarbons (PAHs) were identified and measured in surface seawater and in the tissues (gills and mantle) of indigenous black mussels, Mytilus galloprovincialis, collected from three coastal sites of Saronikos Gulf (Greece), a gulf that exhibits high levels of pollution. The total PAHs measured by spectrofluorometry in the surface seawater were found in the range of 425–459 ng L⁻¹ at the most polluted sites 1 and 2 (Elefsis Bay–Salamis Island) and in the range of 103–124 ng L⁻¹ at site 3 (Aegina Island). PAHs' sources in seawater were identified by application of specific PAH ratios, such as phenanthrene/anthracene and fluoranthene/pyrene. Levels of PAHs in soft tissues (gills and mantle) of indigenous mussels were much higher than those reported for seawater. Total PAH concentrations in mantle tissues were in the range of 1300–1800 ng g⁻¹ dry weight (dw) tissue at sites 1 and 2 and approximately 380 ng g⁻¹ dw at site 3. In gill tissues total PAH concentrations were in the range of 1480–2400 ng g⁻¹ dw at sites 1 and 2 and approximately 430 ng g⁻¹ dw at site 3. PAHs composition was dominated by two-, three- and four-ring compounds in seawater, where 17 different PAH compounds were identified and measured in mussel tissues. Mussels can be used as sentinel organisms to monitoring PAHs' contamination, since they concentrate PAHs from the surrounding water media and therefore making the chemical analysis simpler and less prone to error than that for water. In surface seawater possible weathering and photodegradation due to hot climates contribute to reduced PAHs concentrations.     

Short-term under-ice variability of prokaryotic plankton communities in coastal Antarctic waters (Cape Hallett, Ross Sea)

During the 2006 Italian Antarctic expedition a diel sampling was performed close to Cape Hallett (Ross Sea) during the Austral summer. Under-ice seawater samples (4 m) were collected every 2 h for 28 h in order to estimate prokaryotic processes' variability and community structure dynamics. Prokaryotic and viral abundances, exoenzymatic activities (β-glucosidase, chitinase, lipase, alkaline phosphatase and leucine aminopeptidase), prokaryotic carbon production (³H-leucine incorporation) and community structure (Denaturing Gradient Gel Electrophoresis – DGGE fingerprints) were analysed. Results showed that the diel variability of the prokaryotic activity followed a variation in salinity, probably as a consequence of the periodical thawing of sea ice (driven by solar radiation and air temperature cycles), while negligible variation in viral and prokaryotic abundances occurred. The Bacterial and Archaeal community structures underwent an Operational Taxonomic Units (OTUs) temporal shift from the beginning to the end of the sampling, while Flavobacteria-specific primers highlighted high variations in this group possibly related to sea ice melting and substrate release.     

Current status and historical trends of organochlorine pesticides in the ecosystem of Deep Bay, South China

To characterize the current status and historical trends in organochlorine pesticides (OCPs) contamination in Deep Bay, an important water body between Hong Kong and mainland China with a Ramsar mangrove wetland (Maipo), samples from seawater, suspended particulate matter (SPM), surface sediment, sediment core and fish were collected to determine the OCPs concentrations. Sediment core dating was accomplished using the ²¹⁰Pb method. The average concentrations of DDTs, HCHs and chlordanes in water were 1.96, 0.71, 0.81 ng l⁻¹, while in SPM were 36.5, 2.5, 35.7 ng g⁻¹ dry weight, in surface sediment were 20.2, 0.50, 2.4 ng g⁻¹ dry weight, and in fish were 125.4, 0.43, 13.1 ng g⁻¹ wet weight, respectively. DDTs concentrations in various matrices of Deep Bay were intermediate compared with those in other areas. Temporal trends of the targeted OCPs levels in sediment core generally increased from 1948 to 2004, with the highest levels in top or sub-surface sediment. Both DDT composition and historical trends indicated an ongoing fresh DDT input. A positive relationship between the bioconcentration factor (BCF) of target chemicals and the corresponding octanol–water partition coefficient (K_ow), and between the biota-sediment accumulation factors (BSAF) and the K_ow were observed in the Bay. The risk assessment indicated that there were potential ecological and human health risks for the target OCPs in Deep Bay.     

Vertical Migrations and Feeding Rhythms of Acartia clausi and Pseudodiaptomus hessei (Copepoda: Calanoida) in a Tropical Lagoon (Ebrié, Côte d'Ivoire)

Diel changes in vertical distribution and gut pigment contents of Acartia clausi andPseudodiaptomus hessei were studied during several 24-h time series performed between 1993 and 1997 in four sites of the Ebrié Lagoon (Côte d'Ivoire). The sites differed by their morphology and their hydrological structure and by the vertical distribution of chlorophyll biomass. Both species showed classical diel vertical migrations (DVM). Copepodites and adult stages of P. hessei were almost benthic during the day and evenly distributed through the water column at night. The amplitude of DVM of A. clausi increased from copepodites I–III to adults. Copepodites and adults of A. clausi increased significantly their gut fluorescence at night, whereas those of P. hessei showed no clear diel feeding rhythm (DFR). These results suggest that A. clausi feed mostly at night on phytoplanktonic particles and P. hessei feed mostly on benthic algal particles during the day and on sestonic particles at night. No relationship was observed between DFR and DVM because both patterns occurred when food was either vertically homogeneous or vertically stratified. The daily average gut fluorescence of A. clausi increased with ambient chlorophyll concentration until around 12–15 μg l⁻¹, whereas no relationship was found for P. hessei. The implication of these patterns on the adaptation capacities and the behaviour of the two species are discussed. The DVM of P. hessei should explain its rarity in the estuarine area. The comparison of our results with previous ones suggests an evolution of A. clausi DFR between 1981–1982 and 1996–1997, in relation to an intensification of eutrophication.     

Improving estuarine net flux estimates for dissolved cadmium export at the annual timescale: Application to the Gironde Estuary

Dissolved Cd (Cd_D) concentrations along the salinity gradient were measured in surface water of the Gironde Estuary during 15 cruises (2001–2007), covering a wide range of contrasting situations in terms of hydrology, turbidity and season. During all situations dissolved Cd concentrations displayed maximum values in the mid-salinity range, reflecting Cd addition by chloride-induced desorption and complexation. The daily net Cd_D fluxes from the Gironde Estuary to the coastal ocean were estimated using Boyle's method. Extrapolating Cd_D concentrations in the high salinity range to the freshwater end member using a theoretical dilution line produced 15 theoretical Cd concentrations (Cd_D⁰), each representative of one distinct situation. The obtained Cd_D⁰ concentrations were relatively similar (201 ± 28 ng L⁻¹) when freshwater discharge Q was >500 m³ s⁻¹ (508 ≤ Q ≤ 2600 m³ s⁻¹), but were highly variable (340 ± 80 ng L⁻¹; 247–490 ng L⁻¹) for low discharge situations (169 ≤ Q ≤ 368 m³ s⁻¹). The respective daily Cd_D net fluxes were 5–39 kg day⁻¹, mainly depending on freshwater discharge. As this observation invalidates the existing method of estimating annual Cd_D net fluxes, we proposed an empirical model, using representative Cd_D⁰ values and daily freshwater discharges for the 2001–2007 period. Subsequent integration produced reliable Cd_D net flux estimates for the Gironde Estuary at the annual timescale that ranged between 3.8–5.0 t a⁻¹ in 2005 and 6.0–7.2 t a⁻¹ in 2004, depending on freshwater discharge. Comparing Cd_D net fluxes with the incoming Cd_D fluxes suggested that the annual net Cd_D addition in the Gironde Estuary ranged from 3.5 to 6.7 t a⁻¹, without any clear temporal trend during the past seven years. The annual Cd_D net fluxes did not show a clearly decreasing trend in spite of an overall decrease by a factor 6 in Cd gross fluxes during the past decade. Furthermore, in six years out of seven (except 2003), the annual Cd_D net fluxes even exceeded river borne total (dissolved + particulate) gross Cd fluxes into the estuary. These observations were attributed to progressive Cd desorption from both suspended particles and bottom sediment during various sedimentation–resuspension cycles induced by tidal currents and/or continuous dredging (navigation channel) and diverse intra-estuarine sources (wet deposition, urban sources, and agriculture). Provided that gross fluxes remain stable over time, dissolved Cd exportation from the Gironde Estuary to the coastal ocean may remain at the present level for the coming decade and the estuarine sedimentary Cd stock is forecast to decrease slowly.     

Uptake and metabolism of arsenate by anexic cultures of the microalgae Dunaliella tertiolecta and Phaeodactylum tricornutum

Axenic cultures of the microalgae species, Dunaliella tertiolecta and Phaeodactylum tricornutum were grown at arsenic (As) concentrations typically found in uncontaminated marine environments ( 2 µg L^− 1) under different phosphorus concentrations. D. tertiolecta accumulated higher arsenic concentrations (mean: 13.7 ± 0.7 µg g^− 1 dry mass) than P. tricornutum (mean: 1.9 ± 0.2 µg g−1 dry mass). Media phosphorus concentrations (0.6–3 mg/L) had little influence on microalgae growth rates or arsenic accumulation. Arsenic was present as lipid bound (29–38%; 4.2–9.5%), water-soluble (20–29%; 26–34%) and residue bound (41–45%; 57–69%) arsenic species in D. tertiolecta and P. tricornutum respectively. Hydrolysed lipids contained mostly glycerol arsenoribose (OH- ribose), dimethylarsinate (DMA) and inorganic arsenic (As(V)) moieties. Water-soluble species of microalgae were very different. D. tertiolecta contained inorganic arsenic (54–86%) with variable amounts of DMA (7.4–20%), arsenoriboses (5–25%) and traces of methylarsonate (MA) ( 1%). P. tricornutum contained mostly DMA (32–56%) and phosphate arsenoribose (PO₄-ribose, 23–49%) and small amounts of OH-ribose (3.8–6.5%) and As(V) (9–16%). Both microalgae contained an unknown cationic arsenic species. The residue fractions of both microalgae contained predominately inorganic arsenic (99–100%). These results show that at natural seawater arsenic concentrations, both algae take up substantial amounts of inorganic arsenic that is complexed with structural elements or sequestered in vacuoles as stable complexes. A significant portion is also incorporated into lipids. Arsenic is metabolised to simple methylated species and arsenoriboses.     

The barnacle Balanus amphitrite as a biomonitor for Cd: Radiolabelled experiments

Radiolabelled experiments were carried out to measure necessary parameters in the development of a biodynamic ecotoxicological simulation model of Cd accumulation in the barnacle biomonitor Balanus amphitrite. The Cd uptake rate constant from the dissolved phase, the Cd assimilation efficiency (AE) from suspended particulate matter (SPM) and the efflux rate constant were obtained using ¹⁰⁹Cd. A Cd uptake rate constant from the dissolved phase (k_u) of 0.0072 L g⁻¹ h⁻¹ was determined for the barnacle under environmentally realistic dissolved Cd concentrations (maximum of 400 ng L⁻¹). Cd AE from SPM was determined from the barnacle feeding on SPM with low and high chl a concentrations, resulting in AEs of 39.0% and 48.7%, respectively, and an efflux rate of 0.0072 d⁻¹. The difference between the AEs resulted from differences in chl a:SPM ratios suggesting a general tendency of higher AE when SPM is enriched with chl a. These results reinforce that the accuracy of ecotoxicological models for metal accumulation in organisms depends on how representative the selected food items are of the organism’s natural diet.     

Comparison of β-dimethylsulfoniopropionate (DMSP) levels in two mediterranean ecosystems with different trophic levels

β-dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) concentrations were recorded from September 1999 to September 2000 in two geographically close ecosystems, differently affected by eutrophication: the Little Bay of Toulon and the Niel Bay (N.W. Mediterranean Sea, France). Little Bay had higher nutrient levels ([NO₃⁻]_max. = 30.3 μM; [PO₄³⁻]_max. = 0.46 μM) and higher chlorophyll a concentrations ([chl a]_mean = 2.4 μg/L) compared to Niel Bay ([NO₃⁻]_max. = 19.7 μM; [PO₄³⁻]_max. = 0.17 μM; [chl a]_mean = 0.4 μg/L). In the two sites, we measured dissolved (DMSP_d < 0.2 μm) and particulate DMSP (DMSP_p > 0.2 μm) concentrations. The DMSP_p was particularly analysed in the 0.2–5, 5–90 and > 90 μm fractions. In the eutrophicated Little Bay, DMSP_d concentrations showed a clear seasonality with high values from January to March (124–148 nM). The temporal profile of the DMSP_p concentrations was similar, peaking in February–March (38–59 nM). In the less eutrophic Niel Bay, DMSP_p concentrations were much lower (6–9 nM in March–April), whereas DMSP_d concentrations were relatively high (110–92 nM in February–March). DMS concentrations were elevated from the end of the winter to the spring in Little Bay, ranging from 3 nM in October to 134 nM in March. In the less eutrophic Niel Bay, lower DMS levels were observed, generally not exceeding 20 nM. Each particulate fraction (0.2–5; 5–90; > 90 μm) contained less DMSP in Niel Bay than in Little Bay. At both sites, the 5–90 μm fraction made up most of the DMSP_p. This 5–90 μm fraction consisted of microphytoplankton, principally Dinophyceae and Bacillariophyceae. The 5–90 μm biomass calculated from cell biovolumes, was more abundant in Little Bay where the bloom at the end of the winter (165 μg/L in March) occurred at the same time as the DMSP peaks. The estimated DMSP_p to biomass ratio for the 5–90 μm fraction was always higher in Little Bay than in Niel Bay. This suggests that the high DMSP levels recorded in Little Bay were not only due to a large Dinophyceae presence in this ecosystem. Indeed, the peak of DMSP_p to biomass ratio obtained from cell biovolumes (0.23 nmol/μg in March) was consistent with the proliferation of Alexandrium minutum. This Dinophyceae species may account for between 50% (2894 cells/L) and 63% (4914 cells/L) of the total phytoplankton abundance in the Little Bay of Toulon.     

Seasonal variability of leaf litter removal by crabs in a Kandelia candel mangrove forest in Jiulongjiang Estuary, China

The seasonal variability of leaf litter removal by crabs was observed from May 2006 to April 2007 in a Kandelia candel mangrove forest in Jiulongjiang Estuary, China. Daily average quantities of leaf fall ranged 0.85–3.86 gDW m⁻² d⁻¹, with high values in May, August, October and November. The whole-year's leaf fall was 6.48 t ha⁻¹ yr⁻¹ (1.81 gDW m⁻² d⁻¹). The standing stock of leaf litter on the forest floor was 7.78 gDW m⁻² averaged from the whole year's data, with the lowest value in December (1.23 gDW m⁻²) and the highest in April (16.18 gDW m⁻²). Annually averaged removal (consumption on mangrove floor + burial in burrows) rate of leaf litter by crabs was 0.59 gDW m⁻² d⁻¹. High seasonal variability was observed in the removal rates of leaf litter by crabs. Removal rates in the winter months (December, January and February) were 0.07–0.09 gDW m⁻² d⁻¹, much lower than those in other months with values of 0.59–1.18 gDW m⁻² d⁻¹. Annually averaged percentage of leaf fall removed by crabs was 33%, with the highest values in September (reached 76%) and the lowest values in winter months. Of leaf litter removed by crabs, a large proportion was buried by crabs, and only 12% was consumed by crabs on the forest floor. Leaf litter removal rate, consumption rate on the forest floor, percentages of leaf fall and standing stock removed on the forest floor were significantly positively correlated with air temperature, indicating that leaf removal ability by crabs was higher in warm months than in cold months.     

Butyltin in ballast water of merchant ships

The time series of analyzed values indicated that concentration of butyltin (BT) compounds in ballast water varied widely depending on the tanks, depths, and dates of sampling, ranging 4–93 ng l⁻¹ during 7-day voyage. Variations in concentrations of BT in the two ballast tanks corresponded well with the level of BT contamination in different pumping sites of ballast waters. Concentrations of BT species detected in ballast water were rather consistent with those found in port waters and sediment of Taiwan and Japan. This study suggested that the problems concerning BT contamination were neither static nor localized.     

Distribution of nitrogenous nutrients and denitrifiers strains in estuarine sediment profiles of the Tanshui River, northern Taiwan

Chemical profiles of both oxidized (nitrate and sulfate) and reduced (ammonium, sulfide, acid-volatile sulfide [AVS], and pyrite) materials and the corresponding distribution of denitrifier microbial communities were measured at low tide in sediments at Guandu in the estuary of the Tanshui River, northern Taiwan in August 2002. Denitrifier strains were isolated for physiological and phylogenic analyses. Based on the distribution of nitrogenous compounds and denitrifier abundances, the vertical profile of Guandu sediments could be separated into four layers: a mixed layer (the top 1 cm of depth, respectively containing 0.82–2.37 and 535.9–475.0 μM of nitrate and ammonium), a nitrate-concentrated layer (1–5 cm in depth, 2.37–0.53 and 475.0–1192.1 μM, respectively), a denitrifier-aggregation layer (5–7 cm in depth, 0.53–0.72 and 1192.1–1430.1 μM, respectively), and an ammonium-enriched layer (7–12 cm in depth, 0.72–0.78 and 1430.1–2196.6 μM, respectively). Denitrifier strains were detected in all layers except for the mixed layer. A variety of metabolic processes by these strains may occur in different layers. Bacillus jeotgali-, Bacillus sphaericus-, and Bacillus firmus-related strains isolated from the nitrate-concentrated layer may be involved in the nitrification-denitrification coupling process due to the relatively low nitrate concentrations (maximum = 2.37 μM), and may contribute to denitrification not nitrification. Bacillus bataviensis- and B. jeotgali-related strains isolated from the denitrifier-aggregation layer comprised the predominant denitrifier population (3.64 × 10⁴ cells/g of denitrifier abundance). They possess the ability of dissimilatory nitrate reduction to ammonium (DNRA). Bacillus jeotgali-related strains and two newly identified strains of GD0705 and GD0706 isolated from the ammonium-enriched layer possibly use fermentative processes as the main metabolic pathway instead of denitrification when nitrate is scarce, and this further supports the high ammonium concentrations (up to 2.20 mM) found in the Guandu sediments. In addition, spore formation also enhances the chance of survival of these strains in the face with such a nitrate-deficient environment.     

Seasonal and daily variation of mercury evasion at coastal and off shore sites from the Mediterranean Sea

Dissolved gaseous mercury (DGM) was measured continuously using two newly developed techniques and a manual technique. The continuous techniques were based on the equilibrium between the aqueous and gaseous phase (DGM = Hg_extr / H', Hg_extr is the measured mercury concentration in the gas phase, H' is the Henry's Law coefficient at the desired temperature). In order to calculate the annual mercury evasion from the Mediterranean Sea, diurnal and seasonal measurements of DGM, total gaseous mercury in air (TGM), water temperature and wind speed were performed. During August 2003, March–April 2004 and October–November 2004 measurements of these parameters were conducted on board the RV Urania. The continuous measurements of DGM showed a diurnal variation in concentration, at both coastal and off shore sites, with higher concentrations during daytime than nighttime. The concentration difference could be as large as 130 fM between day and night. The degree of saturation was calculated directly from the measurements, S = Hg_extr / TGM and was found to vary between the different seasons. The highest average degree of saturation (850%) and the largest variation in saturation (600–1150%) was observed during the summer. The spring showed the lowest variation (260–360%) and the lowest average degree of saturation (320%). The autumn also showed a large variation in saturation (500–1070%) but a lower average (740%) compared to the summer cruise. This might be explained by the temperature difference between the different seasons, since that parameter varied the most. The flux from the sea surface was calculated using the gas exchange model developed by Nightingale et al. [Nightingale, P.D., Malin, G., Law, C.S., Watson, A.J., Liss, P.S., Liddicoat, M.I., Boutin, J., Upstill-Goddard, R. C., 2000. In situ evaluation of air–sea gas exchange parameterization using novel conservative and volatile tracers. Global Biogeochemical Cycles, 14(1):373–387]. The evasion varied between the different seasons with the highest evasion during the autumn, 24.6 pmol m^− 2 h^− 1. The summer value was estimated to 22.3 pmol m^− 2 h^− 1 and the spring to 7.6 pmol m^− 2 h^− 1. Using this data the yearly evasion from the Mediterranean Sea surface was estimated to 77 tons.     

Heterotrophic bacterial production in the Cretan Sea (NE Mediterranean)

In March and September 1995, bacterial production was measured by the ³H-leucine method in the oligotrophic Cretan Sea (Aegean Sea, Eastern Mediterranean) in the framework of the CINCS/MTP program. Samples were obtained from four stations (a coastal, a continental shelf and 2 open-sea stations) for the construction of vertical profiles of bacterial abundance and production. Bacterial production ranged from 0.1 μg C m⁻³ h⁻¹ at 1500 m depth, to 82 μg C m⁻³ h⁻¹ in March at 50 m at the coastal station. Higher bacterial integrated production was observed in March at the coastal station (131 mg C m⁻² d⁻¹ for the 0–100 m layer). Bacterial production, integrated through the water-column, was similar in March and September for the open-sea stations (60–70 mg C m⁻² d⁻¹). Relative to production, bacterial concentrations varied little between stations and seasons ranging from 9×10⁵ ml⁻¹ to 3×10⁵ ml⁻¹. Relationships between bacterial biomass and bacterial production indicated seasonal differences, likely reflecting resource limitation of bacterial biomass in March (bloom situation), and predator limitation of bacterial biomass in September (post-bloom situation).     

Seasonal appearance ofProchlorococcus in Suruga Bay,Japan in 1992–1993

Seasonal appearance ofProchlorococcus was studied by flow cytometry in Suruga Bay, Japan in 1992–1993.Prochlorococcus cells were in high concentrations (>1×10⁴ cells ml^–1) from July to October 1992 and September 1993, when the water temperature was over 20°C. The 16S rRNA of the isolated cells showed 98.5% sequence homology with that ofP. marinus (Sargasso strain), indicating that they are the same species. The former has a high divinyl-chlorophyll (DV-Chl.)a/b ratio similar to the Mediterranean strain and different from the Sargasso strain. Maximum concentration ofProchlorococcus at the surface water was 2.5×10⁴ cells ml^–1 in August 1992 and their DV-Chl.a accounted for 4.0% of the total chlorophylla. A decrease in cell density to less than 5×10³ cells ml^–1 was observed from December to May with an exceptional rise in January 1993. WhileProchlorococcus showed a maximum concentration of 3.6×10⁴ cells ml^–1 at 10 m depth in September 1992, phycoerythrin (PE)-richSynechococcus spp. were dominant with their maximum concentration of 2.2×10⁵ cells ml^–1 in the same water body. On the other hand, phycocyanin (PC)-richSynechococcus spp. and the larger phytoplankters showed maximum concentrations in the surface waters in May and June. BothProchlorococcus and PE-richSynechococcus showed their lowest concentrations in April. A significant positive correlation was obtained between cell concentrations of the PE-richSynechococcus andProchlorococcus.     

Distribution of heterotrophic nanoflagellates and their importance as the bacterial consumer in a eutrophic coastal seawater

Seasonal and vertical changes in abundances of bacteria and heterotrophic nanoflagellates (HNF), and HNF grazing on bacteria were investigated in a small eutrophic inlet of Uranouchi-Wan throughout the years. Bacterial densities in the surface water ranged from 1.2 to 11 (average 4.3)×10⁶ cells ml^–1 with a couple of maxima following the algal blooming. Densities of HNF ranged from 0.54 to 73 (average 16.4)×10³ cells ml^–1 in the surface, and showed almost similar fluctuation pattern to that of bacteria with a time lag of about 1 to 2 weeks. Grazing rates of HNF on bacteria obtained by FLB method were 4.78 to 16.9 (average 10.3±SD 4.8) cells HNF^–1h^–1 in the surface layer in summer, and consequent total bacterial consumption rates by HNF fluctuated from 4 to 99×10⁴ cells ml^–1h^–1. In deeper layers, however, as HNF densities and grazing rates on bacteria were low, the grazing pressure of HNF on bacteria was small. Turnover times of bacteria by HNF grazing in the surface layer were calculated as relatively constant values of 40 to 60 h, however, it decreased to as low as 6 to 7 h when the HNF activity was highest. These results indicate that bacteria grew so actively by consuming organic matter in seawater as to compensate high HNF grazing pressure, and that bacteria and HNF in the microbial loop play important roles on the turnover of substrates in coastal ecosystems.     

Modelling trace metal concentration distributions in estuarine waters

The concentration of dissolved organic carbon (DOC) was measured every few months from September 2000 through October 2001 at a coastal location in the center of Suruga Bay, Japan (34°51′N, 138°38′E). Water samples were collected three times per day (midday, night and predawn). DOC concentrations ranged from 91.3 to 45.2 μM C on the surface to 100 m depth. Diel variation in DOC concentrations, among the three sampling times, was greater in the upper 20 m, with a maximum difference of 21.7 μM C in July 2001, and reflected in diel DOC inventory variations from the surface to 50 m. Diel variations were controlled by both physical and biological factors. DOC concentrations were significantly correlated with potential density in the deeper layers (100–1000 m), indicating that the distribution of DOC concentrations in the deeper layer was mainly due to mixing. Most DOC concentrations in the upper layer (0–50 m) did not display the same relationship as in the deeper layer. Using the relationship with potential density at 100–1000 m, the DOC concentration in the upper layer, due simply to mixing, was calculated. The difference between the calculated and observed DOC was used to estimate biological contribution. The biological contributions to the DOC inventory in the upper layer (0–50 m) were found greatly in November 2000 and April 2001. This indicates that excess DOC accumulated, by biological processes, in the upper layer during these periods. In November 2000, the excess DOC in the inventory was constant throughout the sampling days (0.36–0.37 mol C m⁻²), whereas diel variations of DOC in the vertical profile were large and contrary to the variation between 10 and 20 m. This suggests that the excess DOC was contributed biologically during daytime in the uppermost layer and reached to the 50 m depth by deeper mixing. As a result, the inventory appeared to be stable over a day because of the compensating effects of DOC production and consumption throughout 50 m. In contrast, in spring and summer, there was a distinct diel inventory decrease in the nighttime, with apparent rates ranging from −0.61 to −0.35 μM C h⁻¹. It is probable that the DOC, which accumulated during the daytime, was mostly labile, with a turnover time of a few hours. The results indicate that the dynamics of diel DOC variations varied seasonally, and suggest that these variations need to be considered when estimating seasonal DOC pools in the coastal ocean.     

Downward carbon transport by diel vertical migration of the copepods Metridia pacifica and Metridia okhotensis in the Oyashio region of the western subarctic Pacific Ocean

Seasonal change in the downward carbon transport due to respiration and mortality through diel vertical migration (DVM) of the calanoid copepods Metridia pacifica and Metridia okhotensis was estimated in the Oyashio region, western subarctic Pacific during six cruises from June 2001 to June 2002. M. pacifica (C4, C5 and adult females) was an active migratory species throughout the year though its DVM amplitude varied among seasons and stages. The mean distribution depths of adult females during the daytime were positively related with the illumination level in the water column, being shallowest in April and deepest in January. M. okhotensis generally showed less-extensive migrations than M. pacifica. Therefore, together with their lower abundance, this species is considered to be a less-important mechanism of downward transport of carbon except for April when their DVM was more active and descended deeper than M. pacifica, which remained in the upper 150 m even during the daytime. The mean migrating biomass of the two Metridia species was 558 mg C m⁻² d⁻¹ and was high during summer to winter (263–1676 mg C m⁻² d⁻¹) and low during spring (59–63 mg C m⁻² d⁻¹). Total downward flux through DVM fluctuated between 1.0 and 20.0 mg C m⁻² d⁻¹ with an annual mean of 8.0 mg C m⁻² d⁻¹. Contribution of the respiratory flux was greater than the mortality flux and accounted for 64–98% of total migratory flux throughout the year except for January when contribution of both fluxes was equal. Overall the annual carbon transport by DVM of Metridia spp. was estimated as 3.0 g C m⁻² year⁻¹, corresponding to 15% of the annual total POC flux at 150 m at the study site, suggesting that DVM is a significant process for carbon export in the subarctic region as well as that in tropical and subtropical oceanic regions. Since DVM in M. pacifica is more active during the non-bloom season when the gravitational flux of particulate matter is low, this species plays an important role in driving the biological pump in the subarctic Pacific during summer to winter.     

Trichodesmium erythraeum (Ehrenberg) bloom along the southwest coast of India (Arabian Sea) and its impact on trace metal concentrations in seawater

The incidence of a large scale Trichodesmium erythraeum bloom along the southwest coast of India (Arabian Sea) observed in May 2005 is reported. Around 4802 filaments of T. erythraeum ml⁻¹ seawater was observed and a colony consisted of 3.6 × 10⁵ cells. The bloom was predominant off Suratkal (12° 59′N and 74° 31′E) with a depth of about 47 m, covering an area of 7 km in length and 2 km width. The concentrations of Zinc, Cadmium, Lead, Copper, Nickel and Cobalt were determined in samples collected from the bloom and non-bloom sites using stripping voltammetry. The observed hydrographical and meteorological parameters were found to be favorable for the bloom. The concentrations of Zinc, Cadmium and Nickel were found to be higher at bloom stations, while the concentrations of Lead, Copper and Cobalt were found to be very low at bloom stations. Elevated concentrations of Cadmium and Cobalt were observed at Valappad mainly due to the decomposition of detrital material produced in the bloom. Statistically significant differences (P > 0.01) in metal concentrations between the bloom and non-bloom stations were not observed except for Copper. Metals such as Lead, Copper and Cobalt were removed from the seawater at all places where bloom was observed. Cadmium was found to be slowly released during the decaying process of the bloom.     

Sorption model for dissolved and particulate aluminium in the Conway estuary, UK

Dissolved Al carried in river water apparently undergoes a fractional removal at the early stages of mixing in the Conway estuary. On the other hand, dissolved Al behaves almost conservatively in high salinity (>13) estuarine waters. In order to understand the geochemistry of Al in these estuarine waters, simple empirical sorption models have been used. Partitioning of Al occurs between solid and solution phases with a distribution coefficient, K_d, which varies from 0.67 × 10⁵ to 3.38 × 10⁶ ml g⁻¹ for suspended particle concentrations of 2–64 mg l⁻¹. The K_d values in general decrease with increasing suspended particulate matter and this tendency termed the “particle concentration effect” is quite pronounced in these waters. The sorption model derived by previous workers for predicting concentrations of dissolved Al with changing suspended sediment loads has been applied to these data. Reasonable fits are obtained for K_d values of 10⁵, 10⁶ and 10⁷ ml g⁻¹ with various values of α. Further, a sorption model is proposed for particulate Al concentrations in these waters that fits the data extremely well defined by a zone with K_d value 10⁷ ml g⁻¹ and C₀ values 16 × 10⁻⁶ mg ml⁻¹ and 92 × 10⁻⁶ mg ml⁻¹. These observations provide strong evidence of sorption processes as key mechanisms influencing the distribution of dissolved and particulate Al in the Conway estuary and present new insight into Al geochemistry in estuaries.