Growth inhibition of phytoplankton populations cultured in disphotic zone water by insufficient amounts of dissolved organic carbon

Phytoplankton cultures occurring in disphotic zone water were conducted to examine dissolved organic carbon (DOC) for possible controlling agent of the initial lag period and growth rate. Culture media of various concentrations of DOC were prepared by mixing low DOC disphotic zone water with high DOC surface water. Natural phytoplankton populations showed strong correlations in their lag period with DOC concentrations in the range from 0.75 mgC·I^–1 to 1.2 mgC·I^–1 in the water (r=–0.833,n=8) and in their population growth rate () (r=0.899,n=8). Similar tendencies were confirmed with a marine diatom (Skeletonema costatum) dominating in the present disphotic zone water by culture experiments. By reducing DOC concentrations in seawater samples by pretreatments of ultraviolet radiation, charcoal adsorption and Amberlite XAD-2 resin adsorption, lag periods ofS. costatum increased in every case, but their population growth rates were almost identical. These results obviously show that prolonged lag period at least occurs in low DOC water, which can explain the observations by Barber and Ryther (1969) that low photosynthetic carbon uptake rate occurs in newly upwelled low DOC water. It is found that the essential substance to shorten lag periods of phytoplankton cultured in disphotic zone water is a portion of dissolved organic matter, which is poor in disphotic zone water and rich in surface water, and the effect of the substance analogous to Na₂EDTA strongly suggests that the substances are organic ligands.     

Toxic chemistry of heavy metals on Isochrysis galbana (parke)in inshore water

Effects of heavy metals on Isochrysis galbana (Parke) were studied in our laboratory. The research focused on toxic effects of metals on algal cells, effects of water-soluble and lipid-soluble organic ligands on metal toxicity and processes of metal uptake by cells. Interactions between two metals and the mechanisms involved were also studied in detail. Finally, some relationships between toxicity and chemical property of metals were revealed.     

Bioaccumulation des métaux chez le mytilidae hydrothermal Bathymodiolus sp. de la ride médio-atlantique

The hydrothermal environment is characterised, among other things, by a high metal concentration, related to the convective sea-water circulation inside the oceanic crust and its interaction with basaltic rocks. The biological communities associated with the hydrothermal system can survive in this toxic environment owing to their ability to regulate their intracellular metal levels by excretion or accumulation of metal ions in non-toxic forms. Various detoxification processes have been previously studied within an hydrothermal organism: immobilisation and precipitation of the metal in lysosomal systems, or binding to specific and soluble ligands such as metallothioneins. The later are heat stable and characterised by a high content of cysteine. The quantification of Fe, Zn, Cu, Mn, Cd, Ag, Ba and Sr in the tissues of the vent mussel Bathymodiolus sp. indicates a high accumulation of these metals in two target organs, the gill and the digestive gland. This accumulation is in relation with high concentrations of metallothioneins, but the subcellular distribution of metals indicates a higher contribution of the insoluble compartment for detoxification processes. These results are compared with the literature data about metal bioaccumlation in Bathymodiolus thermophilus collected at the Galapagos Rift.     

The effects of glutathione depletion on reproductive success in oysters, Crassostrea virginica.

Glutathione (GSH) is a ubiquitous tripeptide that functions as a very important modulator of cellular homeostasis, including detoxification of metals and oxyradicals. Therefore, depletion of GSH may predispose organisms to pollutant stress. Reproductively active oysters (Crassostrea virginica) were exposed to buthionine sulfoximine in the laboratory to deplete gonadal GSH. The effects of metal exposures (Cd and Cu) on fertilization and developmental assays were evaluated using gametes from control and GSH-depleted adults. Fertilization success was not affected by GSH status, i.e. the fertilization rates of gametes derived from GSH-depleted adults were the same or slightly higher. However, GSH depletion did increase the susceptibility of developing embryos to metal toxicity, i.e. adverse effects on embryonic development were observed at lower metal concentrations with gametes derived from GSH-depleted adults. These effects may be related to diminished removal of free radicals or increased availability of metals. Whereas sperm penetration of embryonic membranes and fertilization success may be facilitated by free radicals, the persistence of free radicals during subsequent developmental periods may adversely affect differentiation and normal development. GSH probably also plays an important role in scavenging toxic metals and reducing metal interactions with essential developmental processes. These results suggest that parental depletion of GSH may increase the susceptibility of embryos to metal toxicity.     

Uptake of Zn and Mn into body tissues and renal concretions by the Southern Quahog, Mercenaria campechiensis (Gmelin): Effects of elevated phosphate and metal concentrations

The seawater chemistry of potentially toxic metals can affect their availability to marine organisms. Investigation of the relationship between metal chemistry and metal bioavailability has progressed slowly due to difficulties in controlling and measuring metal speciation in uptake media. Recent work with strong metal chelators such as NTA and EDTA has allowed a closer examination of how metal chemistry relates to biological accumulation and toxicity.^1–3 However, the presence of a strong chelator at membrane transport sites and the possible alteration of microenvironments by strong chelators could create unnatural uptake behavior. This study presents another method for stabilizing metal chemistry in accumulation experiments. A cation exchange resin was used to study Mn⁵⁴ accumulation by a small bivalve Donax variabilus. The resin proved an effective method for buffering manganese chemistry in seawater and could provide a useful tool to look for subtle effects present in other metal buffered seawater systems.     

Iron regeneration and organic iron(III)-binding ligand production during in situ zooplankton grazing experiment

To elucidate iron regeneration and organic iron(III)-binding ligand formation during microzooplankton and copepod grazing on phytoplankton, incubation experiments were conducted in the western subarctic Pacific. During 8 days of dark incubation of ambient water and that amended with plankton concentrate, dissolved iron and organic iron(III)-binding ligands accumulated, approximately proportionally to the decrease in chlorophyll a. The observed increases in dissolved iron concentration were much greater than those expected from the consumption of phytoplankton biomass and previously reported Fe:C value of cultured algal cells, suggesting resolution from colloidal or particulate iron adsorbed onto the algal cell surface. When copepods were added to the ambient water, organic iron(III)-binding ligands accumulated more rapidly than in the control receiving no copepod addition, although consumed phytoplankton biomass was comparable between the two treatments. Bioassay experiment using filtrates collected from the incubation experiment showed that organic ligands formed during microzooplankton grazing reduced the iron bioavailability to phytoplankton and suppressed their growth. Moreover, picoplankton Synechococcus sp. and Micromonas pusilla were more suppressed by the organic ligands than the diatom Thalassiosira weissflogii. In conclusion, through microzooplankton and copepod grazing on phytoplankton, organic iron(III)-binding ligands as well as regenerated iron are released into the ambient seawater. Because the ligands lower iron bioavailability to phytoplankton through complexation and the degree of availability reduction varies among phytoplankton species, grazing by zooplankton can shift phytoplankton community structure in iron-limited waters.     

A comparison of iron limitation of phytoplankton in natural oceanic waters and laboratory media conditioned with EDTA

The solubility of iron in oxic waters is so low that iron can be a limiting nutrient for phytoplankton growth in the open ocean. In order to mimic low iron concentrations in algal cultures, Ethylenediaminetetraacetate (EDTA) is commonly used. The presence of EDTA enables culture experiments to be performed at a low free metal concentration, while the total metal concentrations are high. Using EDTA provides for a more reproducible medium. In this study Fe speciation, as defined by EDTA in culture media, is compared with complexation by natural organic complexes in ocean water where Fe is thought to be limited. To grow oceanic species into iron limitation, a concentration of at least 10⁻⁴ M EDTA is necessary. Only then does the calculated [Fe³⁺] concentrations resemble those found in natural sea water, where the speciation is governed by natural dissolved organic ligands at nanomolar concentrations. Moreover, EDTA influences the redox speciation of iron, and thus frustrates research on the preferred source of Fe-uptake, Fe(III) or Fe(II), by algae. Nowadays, one can measure the extent of natural organic complexation in sea water, as well as the dissolved Fe(II) state, and can use ultra clean techniques in order to prevent contamination. Therefore, it is advisable to work with more natural conditions and not use EDTA to create iron limitation. This is especially important when the biological availability of the different chemical fractions of iron are the subject of research. Typically, many oceanic algae in the smallest size classes can still grow at very low ambient Fe and are not easily cultivated into limitation under ambient sea water conditions. However, the important class of large oceanic algae responsible for the major blooms and the large scale cycling of carbon, silicon and other elements, commonly has a high Fe requirement and can be grown into Fe limitation in ambient seawater.     

Analysis of temporal and spatial variability of phytoplankton by physical-biological models

I reviewed my research on analysis of temporal and spatial variability of phytoplankton by physical-biological models. This paper was prepared for a lecture of the member awarded the Okada Prize for 1991 from the Oceanographical Society of Japan.Temporal change of phytoplankton in a local upwelling was studied by simulated upwelling experiments conducted with natural phytoplankton communities under natural surface light conditions. Results of the culture experiments was explained by a simple model. This model allows to predict the chlorophyll and nutrient concentration changes in a given upwelled water mass.Above model was verified by a local upwelling observed off Izu, Japan, on May, 1982. Phytoplankton growth and nutrient decrease in surface water of the local upwelling were observed within two days followed by decrease of phytoplankton concentration under depleted nutrient environment. The phytoplankton growth and nutrient decrease could explained by the model with phytoplankton removal rate of about half of the growth rate. Centric diatom was the dominant phytoplankton group and pennate diatom showed less abundance in the upwelled water. Pennate diatom showed fast growth rate when nutrient was abundant and fast decreasing rate after nutrient depleted. On the other hand, flagellate and monads showed relatively slow change of biomass under the change of nutrient concentrations. Furthermore, resting spore formation of centric diatom,Leptocylindrus danicus, was observed in a response to nutrient depletion.Temporal and spatial variability of phytoplankton in the southeastern U.S. continental shelf ecosystem was studied by physical-biological models. First, differences of the biological responses to frontal eddy upwelling during spring and to intrusion during summer was considered by Lagrangian particle tracing experiments with optimally-interpolated flow fields. In spring, particles showed residence time of a few days; however, particles in summer intrusion stayed on the shelf nearly 30 days. It was concluded that difference of particle residence time of upwelled water make the difference of plankton communities. Similar flow fields and particle tracing experiments were used to trace the features in chlorophyll distributions during spring of 1980 derived by Coastal Zone Color Scanner (CZCS). Phytoplankton patchness were created and deformed by frontal eddy events. Eularian physical-biological model was constructed to understand the CZCS-chlorophyll distributions. Statistical comparisons with series of numerical experiments indicate that horizontal advection is an important process for the chlorophyll distributions and that upwelling and associated phytoplankton growth are responsible for the across-shelf gradients and maintenance of concentrations. Furthermore, the CZCS data were assimilated to the model to improve the phytoplankton concentrations, and phytoplankton carbon flux across shelf was estimated. Processes causing the time changes of chlorophyll concentrations were estimated with the model and satellite data further indicated that the both physical and biological forcing is important for the time chages. Several other studies conducted presently were mentioned.     

Effects of heavy metal ions on larval Penaeus chinensis and comparative study on their elimination methods

In order to establish a new method to eliminate toxicities of heavy metal ions to larval penaeid shrimp, the effects of copper, zinc, lead and cadmium ions on larval metamorphosis of Penaeus chinensis at each stage were determined in detail, and two methods eliminating toxicities were compared. The results indicate that sensitivity of larvae to heavy metal ions decreases in the order of nauplii, protozoea, mysis and postlarvae. The phytoplankton food can reduce, by chetating, the toxicities of heavy metal ions. Both EDTA chelation and PHMA absorption can be used to eliminate the toxicities effectively and there is no significant difference between the two methods. EDTA is harmful to larval P. chinensis at high concentration but affects neither survival nor metamorphosis at below 10 mg/dm3. It is preliminarily observed that copper and zinc ions at low concentration are beneficial to the development of larvae after protozoea stage. It is suggested that it is unnecessary to e-liminate the effects of heavy     

重金属锌对海洋微藻藻源氨基酸产出的影响

锌是海洋微藻生长必需的金属元素,低浓度时可促进微藻的生长,而在高浓度时则表现为抑制其生长。受人类活动的影响,海洋中锌有富集增加的趋势,从而会对海洋微藻的生长产生影响。本论文探究了锌离子以及纳米氧化锌对硅藻中肋骨条藻(Skeletonemacostatum)和新月菱形藻(Nitzschia closterium)生长的影响,特别是对藻源氨基酸产生的影响,结果发现:纳米金属颗粒会通过释放离子的形式抑制海洋浮游植物的生长,中肋骨条藻比新月菱形藻对锌的响应更敏感。锌离子和纳米氧化锌可通过抑制浮游植物的生长来减少氨基酸的释放量和改变藻源氨基酸的种类,从而可能会对海洋氮循环过程产生影响。     

海水磷限制条件下汞对角毛藻的污染效应

本实验选择了实验室最佳磷限制条件,并采用连续及一次培养方式研究了海水在磷限制条件下汞对角毛藻的污染效应。实验结果表明;不论连续培养还是一次培养,低磷营养盐浓度受汞毒害更敏感,延缓期延长,指数生长阶段拖后。测得浮游植物对汞的浓集具有高富集倍数,富集因子达10~5数量级,与围隔生态系中所测浮游植物对汞的浓集因子一致。     

Cellular responses of molluscan tissues to environmental metals

The use of marine organisms as monitors of pollution assumes that the processes involved in sequestration provide a response which is proportional to the concentration of the pollutant in the environment. This assumption is considered in relation to the known cellular properties of the systems involved. Studies on the kinetics of uptake of certain metals in estuarine conditions have included the possibility that they can occur in non-polar, lipid-soluble forms which may penetrate cell membranes very rapidly. It is concluded that the uptake of these metals is governed by firstorder kinetics and that many of the assumptions undertaken during biological monitoring programmes are, in fact, valid as a first approximation.Many heavy metals of interest to environmentalists are retained within the tissues by reactive ligands. These may be inducible, metabolized and excreted, and it is the ‘turnover’ and availability of these ligands which may ultimately determine the final concentration of the metal in the animal. Models and experimental studies of these activities indicate that the ligands are either non-specific in nature and capable of binding a wide variety of metals or are very specific for particular metals. The former ligands may contribute to a general system of detoxification whilst the latter appear to be integrated into precise metabolic pathways.     

Response of a benthic suspension feeder (Crassostrea virginica Gmelin) to three centuries of anthropogenic eutrophication in Chesapeake Bay

Biogenic reefs built by oysters and other suspension feeders are vital components of estuarine ecosystems. By consuming phytoplankton, suspension feeders act to suppress accumulation of organic matter in the water column. Nutrient loading increases the rate of primary production, thereby causing eutrophication. As suspension feeders consume more organic matter from increasing abundance of phytoplankton, their rate of growth should also increase if they are food limited. We show here that the eastern oyster, Crassostrea virginica (Gmelin), from St. Mary's and Patuxent rivers, Chesapeake Bay, grew faster during anthropogenic eutrophication relative to C. virginica before eutrophication. Growth of shell height, shell thickness and adductor muscle increased after eutrophication began in the late 18th century. After 1860, growth decreased, perhaps reflecting the negative effects of hypoxia, harmful algal blooms, disease and fishing on oyster growth. These results are consistent with the view that an increasing supply of phytoplankton resulting from eutrophication enhanced growth of C. virginica between 1760 and 1860, before oyster reefs were degraded by destructive fishing practices between 1870 and 1930. Alternative factors, such as changes in water temperature, salinity, and fishing are less likely to be responsible for this pattern. These results have implications for restoration of oyster reefs in order to mitigate the effects of eutrophication in estuaries, as well as the paleoecological relationship between suspension feeders and paleoproductivity.     

Thermal Stratification in Saldanha Bay (South Africa) and Subtidal, Density-driven Exchange with the Coastal Waters of the Benguela Upwelling System

A study was conducted to understand the mechanisms driving observed subtidal variability in the stratification of Saldanha Bay, located in the southern Benguela system. It was found that the 6–8 day period variability in bay stratification was caused by the inflow and outflow of cold upwelled water driven by changing baroclinic pressure gradients between the coastal and bay domains. The direction and magnitude of the pressure gradients were governed by coastal upwelling activity and a lag in the response of the bay to changes in density structure in the coastal ocean. When the pressure gradients were bayward and cold water was being driven into the bay the cycle was termed to be in an ‘ active phase ’ and the reverse was termed the ‘ relaxation phase ’. The upwelling-favourable equatorward wind stress impacted the bay stratification in two ways: on the regional scale, wind drives upwelling and governs the inflow–outflow of cold upwelled bottom water, which strengthens stratification; conversely, on the local bay scale, wind drives vertical mixing, which weakens stratification. A four-phase model is used to describe the observed variability in stratification in the bay. The associated density-driven exchange flows are capable of flushing the bay in 6–8 days, about one-third of the time for tidal exchange alone (c. 25 days). These inflows of cold bottom water are ecologically critical as they supply nutrients to the bay and thus impose a control on new production within the bay environment. Further ecological implications of this bay–ocean exchange include export of phytoplankton new production to the coast, limitation of the risk of harmful algal blooms (HABs) and the division of the system into two distinct ecosystems (bay and lagoon).     

Growth stimulation and inhibition of natural phytoplankton communities by model organic ligands in the western subarctic Pacific

The influence of organic ligands on natural phytoplankton growth was investigated in high-nitrate low-chlorophyll (HNLC) waters and during a phytoplankton bloom induced by a mesoscale iron enrichment experiment (SEEDS II) in the western subarctic Pacific. The growth responses of the phytoplankton in the treatments with iron complexed with model ligand were compared with those with inorganic iron or a control. Desferrioxamine B and protoporphyrin IX were used as models for hydroxamate-type siderophore and tetrapyrrole-type cell breakdown ligand, respectively. In the HNLC water, iron associated with protoporphyrin IX especially stimulated smaller phytoplankton (<10 μm) growth, 1.5-fold more than did inorganic iron. Surprisingly, only the addition of protoporphyrin IX stimulated small phytoplankton growth, suggesting that these cell breakdown ligands might be more bioavailable for them. The protoporphyrin IX’s stimulatory effect on small phytoplankton was not observed during bloom decline phase. The growth of phytoplankton was inhibited in the treatment with desferrioxamine B-complexed iron, suggesting its low bioavailability for the natural phytoplankton community. Its inhibitory effects were particularly pronounced in pico-eukaryotic phytoplankton. During the iron-induced bloom, the phytoplankton’s iron-stress response gradually increased with the desferrioxamine B concentration, suggesting that the competition for iron complexation between natural ligands and desferrioxamine B affected phytoplankton growth. However, the pico-eukaryotes did seem better able to utilize the desferrioxamine B-complexed iron during the bloom-developing phase. These results indicate that the iron bioavailability for phytoplankton differs between bloom-developing and bloom-decline phases.     

Bacterial growth rate and the relative abundance of bacteria to heterotrophic nanoflagellates in the euphotic and disphotic layers in temperate coastal waters of Sagami Bay,Japan

This study aimed to clarify the vertical differences in bacterial growth and grazing pressure on bacteria by heterotrophic nanoflagellates (HNF) and to identify the controlling factors of bacterial growth in temperate coastal waters of Sagami Bay, Japan. In addition to environmental factors, the annual monthly variations in bacterial growth rate (BGR) and the relative abundance of bacteria to HNF (BA/HNFA) were investigated in the euphotic and disphotic layers between May 2012 and May 2013. Significant vertical differences in BGR and BA/HNFA were evident between the two layers during the thermal stratification times of May to October 2012 and April to May 2013. BGR indicated significantly stronger limitation of bacterial growth in the euphotic layer compared to the disphotic layer. In contrast, significantly lower BA/HNFA was observed in the euphotic layer, suggesting significantly higher grazing pressure on bacteria by HNF. However, significant differences in BGR and BA/HNFA were not observed between the two layers from November 2012 to Match 2013, when the water column was well-mixed vertically due to the cooling and wind-induced mixing of surface water. This study indicates that bacteria in the euphotic layer grow less actively and are more vulnerable to predatory grazing by HNF relative to the disphotic layer during the stratification period. Further, multiple regression analyses indicate that bacterial growth was most controlled by the concentrations of chlorophyll a and dissolved organic carbon in the euphotic and disphotic layers, respectively.     

Role of metal-organic complexes in the marine environment: A comparison of the copper and ligand titration methods

The differences in quality of the conditional stability constants deduced from ligand titration and metal titration methods are theoretically examined. The ecological role of the metal-organic complexes in seawater was considered on the basis of the concept of the metal buffering capacity index which is calculated from the conditional stability constant and the organic ligand concentration. The results of theoretical examination of the effect of metal contamination on the uptake of metals by phytoplankton indicate that the ecological significance of metal-organic complexes is essentially in the metal-buffering action. This means that the activities of free metal ions are maintained at a native constant level against relatively small perturbations by the addition or uptake of metals in the marine environment.     

Strong CO2 outgassing from high nutrient low chlorophyll coastal waters off central Chile (30°S): The role of dissolved iron

Carbonate system parameters (pH and alkalinity) were used to estimate the coastal water CO₂ fluxes off central Chile (30°S) during September 2007. Coastal waters rich in nitrate and silicate were strongly CO₂ supersaturated and normally poor in chlorophyll a. MODIS satellite chlorophyll a data suggest that phytoplankton biomass remained particularly low during September 2007 although coastal waters were highly fertilized with nitrate and silicate. The phytoplankton gross primary productivity in macronutrient-rich waters was very low with the exception of shallow waters (e.g. within or near bays). Several iron-enrichment bottle experiments show that fCO₂ rapidly decreases during iron-enrichment treatments compared to controls. This suggests that iron limitation of phytoplankton growth (mainly diatoms) plays a role in maintaining high-CO₂ outgassing by preventing rapid interception of upwelled CO₂.     

Relating the reproductive toxicity of five ingested metals in calanoid copepods with sulfur affinity

The sublethal toxicity of dietary Ag, Cd, Hg, Mn, and Zn to marine copepods, measured as depressed egg production, was evaluated as a function of ambient metal concentrations and metal concentrations in copepod tissues. All metals were toxic following 4-h feedings on metal-contaminated phytoplankton food, but there was a four order of magnitude difference between the inhibitory concentration in copepod tissues of the most toxic (2.4 nmol g(-1) dry wt. for Hg) and least toxic (13.4 micromol g(-1) dry wt. for Mn) metals. Metal concentrations in copepods that elicited a toxic response were about 3 times higher than background concentrations for Ag and 9 times higher for Hg, about 2 times higher for Cd, two orders of magnitude higher for Mn, and only 5% higher for Zn. Copepods exposed to lower concentrations of Zn for longer periods (1 week), resulting in tissue Zn concentrations similar to those in the short-term exposures, were not affected, suggesting that copepods were capable of adjusting to slowly increasing Zn by sequestration of this metal. Toxic metal concentrations in copepod tissues were directly proportional (r2 = 0.85) to the affinity of the metals for sulfur, as indicated by the solubility products of the metal sulfides. This relationship, together with protein analysis of eggs, published recently, suggests that metals affect egg production by binding to enzymes involved with vitellogenesis.     

重金属、螯合剂以及铁、锰离子对叉边金藻生长的影响及其混合效应

采用微藻一次培养实验,研究了铜、锌、镉离子,微藻渗出物,螯合剂EDTA对叉边金藻生长的影响。铜、镉,对叉边金藻的毒性较强,锌较弱。螯合剂EDTA对叉边金藻的生长有促进作用。混合实验表明,铁、锰离子,EDTA都能有效地降低铜的毒性;藻渗出物也能在一定程度上缓解铜的毒性;镉、锌对铜的毒性有拮抗效应。此外,通过测定介质和细胞铜的含量,研究了铜在细胞表面的吸附行为,并在铜致毒机理以及其他化学因子的去毒机理方面作了探讨。