Degradation of azo dyes in water by Electro-Fenton process

The degradation of the azo dyes azobenzene, p-methyl red and methyl orange in aqueous solution at room temperature has been studied by an advanced electrochemical oxidation process (AEOPs) under potential-controlled electrolysis conditions, using a Pt anode and a carbon felt cathode. The electrochemical production of Fenton's reagent (H₂O₂, Fe²⁺) allows a controlled in situ generation of hydroxyl radicals (^·OH) by simultaneous reduction of dioxygen and ferrous ions on the carbon felt electrode. In turn, hydroxyl radicals react with azo dyes, thus leading to their mineralization into CO₂ and H₂O. The chemical composition of the azo dyes and their degradation products during electrolysis were monitored by high performance liquid chromatography (HPLC). The following degradation products were identified: hydroquinone, 1,4-benzoquinone, pyrocatechol, 4-nitrocatechol, 1,3,5-trihydroxynitrobenzene and p-nitrophenol. Degradation of the initial azo dyes was assessed by the measurement of the chemical oxygen demand (COD). Kinetic analysis of these data showed a pseudo-first order degradation reaction for all azo dyes. A pathway of degradation of azo dyes is proposed. Specifically, the degradation of dyes and intermediates proceeds by oxidation of azo bonds and aromatic ring by hydroxyl radicals. The results display the efficiency of the Electro-Fenton process to degrade organic matter. Electronic Publication     

Physiological responses of Nodularia harveyana to osmotic stress

The effects of salinity stress on biomass yield, photosynthetic O₂ evolution and nitrogenase activity were investigated using axenic cultures of Nodularia harveyana (Thwaites) Thuret originally isolated from a salt marsh at Gibraltar Point, Lincolnshire, UK in 1971 and studied in this laboratory in 1983. Biomass yields, as chlorophyll a per culture, were highest in the 0 to 100% seawater (0 to 35 sea salt) range with negligible growth in 200% seawater; growth on NH ₄ ⁺ was greater than on N₂ and NO ₃ ^- , which did not differ significantly from each other. In short-term experiments, photosynthetic O₂ evolution remained high at salinities up to 150% seawater (52.5 sea salt); nitrogenase activity remained high at salinities up to 100% seawater (35 sea salt). The major internal low molecular weight carbohydrate which accumulated in response to increased salinity was sucrose, the levels of which fluctuated markedly and rapidly in response to salinity change.     

Degradation profile of azoxystrobin in Andisol soil: laboratory incubation

The fate of azoxystrobin in soil under the effect of different temperature is of interest because application directions specify soil-surface treatments for number of agricultural pests. Temperature is an important factor governing the rate of degradation in soil pore. The purpose of this investigation was to understand better the effect of temperature on the degradation of azoxystrobin in Japanese Andisol soil. This was done through laboratory incubation of soil at three different temperatures (5 °C, 20 °C, 35 °C). First-order kinetics could be used to describe degradation of azoxystrobin under controlled condition of temperature (r² ? 94). The results showed that, during the 120-day incubation period for azoxystrobin, 64%, 70%, and 78% of applied azoxystrobin were degraded at 5 °C, 20 °C, and 35 °C, respectively. By using the Arrhenius equation, the activation energy of degradation of azoxystrobin fungicide was calculated (7.48 ± 1.74 kJ mol^?1) in soils, which confirm that temperature had a significant influence on the degradation rate. Q₁₀ value of 1.11, for azoxystrobin, indicated that the response of fungicide dissipation to temperature was large. For azoxystrobin, there was a much larger difference in dissipation rates at 5 °C and 35 °C, indicating that biological and/or chemical degradation of azoxystrobin may have nearly reached its optimum at 35 °C.     

High reduction of 4-nitrophenol using reduced graphene oxide/Ag synthesized with tyrosine

There is a demand for the development of environmental friendly methods for the synthesis of graphene composites. Reduced graphene oxide/silver (RGO/Ag) nanocomposites are very good catalysts. Here, we propose a simple, green method for the synthesis of RGO/Ag nanocomposite using the amino acid tyrosine as bioreductant and stabilizing agent. RGO/Ag nanocomposite was characterized by using various analytical techniques and studied for its catalytic degradation of 4-nitrophenol. Results of attenuated total reflectance Fourier transform infrared spectroscopy and Zeta potential at ?55 mV reveal the surface capping of tyrosine onto the reduced graphene oxide nanosheets. RGO/Ag nanocomposites show excellent catalytic reduction of 4-nitrophenol with NaBH₄, when compared to actual individual silver nanoparticles.     

Effects of tidal fluctuations of salinity on pericardial fluid composition of the American oyster Crassostrea virginica

Crassostrea virginica Gmelin were subjected to simulated tidal fluctuations of salinity, and the subsequent effects on osmotic and ionic composition of the pericardial fluid, body water and valve movements were investigated. Ambient salinity fluctuation patterns of 20-10-20, 15-10-15 and 10-5-10 were simulated during 24.8-h periods. An additional 10-5-10 S experiment was performed using a dilution water approximating the ionic composition of Mississippi River water with regard to Mg⁺⁺, Ca⁺⁺ and SO ₄ ⁼ , instead of deionized water. Finally the effects of a 2-week diurnal fluctuation pattern between 20 and 10 S were investigated with respect to pericardial fluid composition. Pericardial fluid osmolality, concentrations of Cl^-, Na⁺, Mg⁺⁺, K⁺, Ca⁺⁺ and ninhydrin-positive substances (NPS) were analyzed periodically throughout all experiments. Pericardial fluid osmolality was slightly hyperosmotic as ambient water salinity decreased during a cycle, and then became slightly hyposmotic as ambient salinity increased. In the 2-week experiment, pericardial fluid osmolality tracked ambient seawater closely through Day 5, but became more intermediate between high and low seawater values as the experiment progressed. Similar patterns during fluctuations of salinity were observed for Na⁺, Cl^-, Mg⁺⁺ and Ca⁺⁺. Pericardial fluid K⁺ levels did not track ambient seawater as closely as did other ions. The ionic composition of dilution water had little effect on the osmotic or ionic response of the oyster's pericardial fluid. Pericardial fluid NPS level varied inversely with salinity during the 20-10-20 cycle. During the longterm fluctuation experiment, NPS values gradually decreased over the 2-week period compared to constant salinity control values. Percent body water also varied inversely with ambient salinity. Solute movement accounted for most of the change in pericardial fluid osmolality during the simulated cycles with water movement responsible for 1 to 11%. Water movement contributed more to the change of pericardial fluid osmolality during the decreasing salinity phase than the increasing phase of a given cycle. During 20-10-20 S cycles, oyster valves remained open 56% of the time (n=23). In contrast, when salinity was abruptly changed from 20 to 10 within 5 min, valve closure occurred in 4.8±0.3 min (n=20). Valves did not reopen for 19.3±1.2 h (n=15).     

Wet oxidation of recalcitrant lignin water solutions: experimental and reaction kinetics

The purpose of the research was to study the behavior of lignin degradation under different conditions (T 110–190°C, pO₂ 0.5–1.5 MPa, pH 5, 9 and 12) and to develop a predictive model. Temperature increase improved lignin removal from 75% at 110°C to 100% at 190°C (experimental). Increasing the pH enhanced the lignin removal efficiency from 30 to 97% (experimental). The developed model predicted the lignin degradation and changes in COD, BOD and TOC. The model agreed well with the experimental data (R ² = 0.93 at pH 5 and 12).     

The effect of pulsed versus gradual salinity reduction on the physiology and survival of Halophila johnsonii Eiseman

Plants of Halophila johnsonii Eiseman were exposed, in mesocosms, to either pulsed hyposalinity treatments of 30, 15, 10, and 8 or gradual salinity reductions of two every 2?days. When salinity was pulsed, survivorship (>80?%) and maximum quantum yields (>0.7) were high in the 30 and 15 salinity treatments, but both declined in the 10 and 8 salinity treatments. Leaf osmolality declined with respect to salinity treatment, but the difference between leaf and media osmolality remained relatively constant (675?±?177?mmol?kg^?1). In contrast, when salinity was gradually reduced, survivorship remained high from salinities of 30 to 4, and maximum quantum yields remained high from salinities of 30 to 6. Leaf osmolality declined linearly with respect to media osmolality and, similar to the pulsed treatments, the difference between leaf and media osmolality remained relatively constant from salinities of 30 to 2 (638?±?161?mmol?kg^?1). Trolox equivalent antioxidant capacity declined over time in both pulsed and gradual salinity reduction. The results indicate that H. johnsonii is more tolerant of hyposalinity than has previously been reported and that gradually reducing salinity extended its low-salinity tolerance threshold by approximately a salinity of 10.     

Utilization of a new bdelloid rotifer (Philodina acuticornis odiosa) assay to evaluate the effect of salinity on the toxicity of chlorothalonil

Acute (24 h) toxicity tests were conducted to determine the toxicity of the fungicide chlorothalonil towards the freshwater bdelloid rotifer (Philodina acuticornis odiosa). Since rotifers are the dominant zooplankton species in many inland freshwater lakes in Australia, the influence of salinity on chlorothalonil toxicty was also assessed. The rotifers used in this study appeared to be reasonably tolerant to changes in salinity, with little mortality observed at 3760 µS cm^?1, increasing thereafter at higher salinity. The bdelloid rotifers were, however, found to be highly sensitive to chlorothalonil (24 h LC50, 3.2 µg L^?1) with results also suggesting that as salinity increases, so does toxicity (e.g., 24 h LC50 at 5000 µS cm^?1, 0.5 µg L^?1).     

The effects of temperature and salinity on reproductive success of <Emphasis Type="Italic">Temora longicornis</Emphasis> in the Baltic Sea: a copepod coping with a tough situation

At specific locations within the Baltic Sea, thermoclines and haloclines can create rapid spatial and temporal changes in temperature (T) and salinity (S) exceeding 10°C and 9 psu with seasonal ranges in temperature exceeding 20°C. These wide ranges in abiotic factors affect the distribution and abundance of Baltic Sea copepods via species-specific, physiological-based impacts on vital rates. In this laboratory study, we characterized the influence of T and S on aspects of reproductive success and naupliar survival of a southwestern Baltic population of Temora longicornis (Copepoda: Calanoida). First, using ad libitum feeding conditions, we measured egg production (EP, no. of eggs female⁻¹ day⁻¹) at 12 different temperatures between 2.5 and 24°C, observing the highest mean EP at 16.9°C (12 eggs female⁻¹ day⁻¹). Next, the effect of S on EP and hatching success (HS, %) was quantified at 12°C for cohorts that had been acclimated to either 8, 14, 20 or 26 psu and tested at each of five salinities (8, 14, 20, 26 and 32 psu). The mean EP was highest for (and maximum EP similar among) 14, 20 and 26 psu cohorts when tested at their acclimation salinity whereas EP was lower at other salinities. For adults reared at 8 psu, a commonly encountered salinity in Baltic surface waters, EP was relatively low at all test salinities—a pattern indicative of osmotic stress. When incubated at 12°C and 15 different salinities between 0 and 34 psu, HS increased asymptotically with increasing S and was maximal (82.6–84.3%) between 24 and 26 psu. However, HS did depend upon the adult acclimation salinity. Finally, the 48-h survival of nauplii hatched and reared at 14 psu at one of six different temperatures (10, 12, 14, 16, 18 and 20°C) was measured after exposure to a novel salinity (either 7 or 20 psu). Upon exposure to 7 psu, 48-h naupliar mortality increased with increasing temperature, ranging from 26.7% at 10°C to 63.2% at 20°C. In contrast, after exposure to 20 psu, mortality was relatively low at all temperatures (1.7% at 10°C and ≤26.7% for all other temperatures). An intra-specific comparison of EP for three different T. longicornis populations revealed markedly different temperature optima and clearly demonstrated the negative impact of brackish (Baltic) salinities. Our results provide estimates of reproductive success and early survival of T. longicornis to the wide ranges of temperatures and salinities that will aid ongoing biophysical modeling examining climate impacts on this species within the Baltic Sea.     

Kinetic measurements of metal accumulation in two marine macroalgae

 We measured the uptake kinetics of four metals (Cd, Cr, Se and Zn) in two marine macroalgae (the green alga Ulva lactuca and the red alga Gracilaria blodgettii). Metal uptake generally displayed a linear pattern with increasing exposure time. With the exception of Cr, which exhibited comparable uptake rate constants at different concentrations, uptake rate constants of Cd, Se and Zn decreased with increasing metal concentration, indicating that the seaweeds had a higher relative uptake at lower metal concentration. Uptake of Cd and Zn was higher in U. lactuca than in G. blodgettii, whereas uptake of Cr and Se was comparable between the two species. Only Cd and Zn uptake in U. lactuca was significantly inhibited by dark exposure. A decrease in salinity from 28 to 10‰ enhanced the uptake of Cd, Cr, Se and Zn in U. lactuca 1.9-, 3.0-, 3.6-, and 1.9-fold, respectively. In G. blodgettii, Cd uptake increased twofold when salinity was decreased from 28 to 10‰, whereas uptake of Cr and Zn was not significantly affected by salinity change. The calculated depuration rate constants of metals in U. lactuca were 0.01 d⁻¹ for Cd, 0.05 to 0.08 d⁻¹ for Cr, 0.14 to 0.16 d⁻¹ for Se, and 0.12 to 0.15 d⁻¹ for Zn, and were relatively independent of the metal body burden in the algae. The predicted bioconcentration factor was 3 × 10⁴ for Cd, 2 × 10³ for Cr, 40 to 150 for Se, and 1 to 2 × 10⁴ for Zn in U. lactuca. Our kinetic study suggested that U. lactuca would be a good biomonitor of Cr and Zn contamination in coastal waters. Received: 14 September 1998 / Accepted: 29 May 1999     

Some observations on the influence of salinity on growth and photosynthesis inPorphyra umbilicalis

Notwithstanding the great importance of the salinity factor in the marine environment, the knowledge of influence of salinity on growth of marine benthic algae is very limited. Rate of growth (mg, cm²) and O₂ output of the intertidal red algaPorphyra umbilicalis from Helgoland, North Sea, were measured during a 3 week culture in 3 different salinities (1/2-, 1- and 2-concentrated artificial sea water; Table 1). Under hypertonic conditions (2-concentrated sea water) growth rate and photosynthesis rate were depressed, compared to values obtained in normal concentrated sea water. Under hypotonic conditions (1/2-concentrated sea water), growth expressed in mg was the same as in normal concentrated sea water, or higher when expressed in cm³. Rate of O₂ output was almost unaltered in one of the two experiments, lowered in the other. Cell size increased at higher salinity, while swelling of cell walls and intercellular substances as well as the intensity of colouring decreased with salinity. The discrepancies between growth and photosynthesis under hypotonic conditions cannot be completely explained by the observed influences of salinity on morphological structures (cell size, swelling of cell substances). Detailed studies on the time course of photosynthesis and respiration rates, and preparation of a metabolic balance for the algae are necessary.     

Isolation and characterisation of a carbofuran degrading Burkholderia sp. PCL3 from carbofuran-phytoremediated rhizosphere soil

A bacterial strain capable of degrading carbofuran as the sole carbon source was isolated from carbofuran-phytoremediated rhizosphere soil of rice. A 16S rRNA study identified the strain as Burkholderia sp. (isolate PCL3). Free cells of isolate PCL3 possessed inhibitory-type degradation kinetics with a q _max of 0.087 day^?1 and S _m of 248.76 mg·L^?1. Immobilised PCL3 on corncob and sugarcane bagasse possessed Monod-type degradation kinetics with a q _max of 0.124 and 0.098 day^?1, respectively. The optimal pH and temperature with the highest degradation rate coefficient of carbofuran were pH 7.5 and 35 °C, respectively.     

Effect of salinity fluctuation on the osmotic pressure and Na+, Ca2+ and Mg2+ ion concentrations in the hemolymph of bivalve molluscs

Specimens of Chlamys opercularis, Modiolus modiolus, Mytilus edulis, Crassostrea gigas, Scrobicularia plana and Mya arenaria were exposed to both gradual (sinusoidal) and abrupt (square-wave) salinity fluctuations and measurements made of osmotic, Na⁺, Mg²⁺ and Ca²⁺ concentrations in the hemolymph and where applicable in the mantle fluid. In both sinusoidal and square-wave regimes fluctuating between 100 and 50% seawater (100%=ca. 32 S), the hemolymph Na⁺, Mg²⁺, Ca²⁺ and osmotic concentrations followed the concentrations of the external medium in Chlamys opercularis. The hemolymph and mantle fluid osmotic Na⁺, Mg²⁺ and Ca²⁺ concentrations of Modiolus modiolus, Mytilus edulis, Crassostrea gigas and S. plana followed those of the external medium as long as the molluscs' shell valves remained open. There were no changes in the ionic or osmotic concentrations of the hemolymph or mantle fluid of any of these species during periods of shell-valve closure. The hemolymph osmotic, Na⁺ and Mg²⁺ concentrations of wedged-open Modiolus modiolus, Mytilus edulis, C. gigas and S. plana followed those of the external medium. Hemolymph Ca²⁺ concentrations showed a damped response in C. gigas and Mytilus edulis. The hemolymph osmotic, Na⁺, Ca²⁺ and Mg²⁺ concentrations of Mya arenaria fluctuated in a similar manner to the external medium, but were damped. Wedged-open Mytilus edulis exposed to fluctuating salinity and supplied with a constant supply of 10 mM Ca²⁺ showed greater changes in hemolymph ionic and osmotic concentrations than M. edulis exposed to the same salinity fluctuation without a constant Ca²⁺ supply. Chlamys opercularis and Modiolus modiolus survived in a 50% seawater minimum sinusoidal salinity fluctuation for 10 days; wedged-open M. modiolus survived only 3 days. Burrowing had no effect on the osmotic, Na⁺, Mg²⁺ or Ca²⁺ concentrations of the hemolymph of Mya arenaria or S. plana exposed to fluctuating salinities. All of the species studied were shown to be osmoconformers.     

Effects of salinity fluctuations on the respiration rate of the southern oyster drill Thais haemastoma and the blue crab Callinectes sapidus

Respiration rates of Thais haemastoma and Callinectes sapidus were determined as a function of salinity with a flow-through respirometer at 20°C. Respiration rates were measured at 10, 20 and 30 S for acclimated animals. The effects of 10-5-10, 20-10-20, 30-10-30 and 10-30-10 S semidiurnal cycles (12 h) of fluctuating salinity on the rate of respiration of the oyster drill were studied. During each cycle, salinity was changed from the acclimation salinity over a 4 h interval, held at that salinity for 2 h, returned to the acclimation salinity over 4 h and held at that salinity for 2 h. The effects of diurnal (24.8 h) salinity cycles on respiration in the oyster drill and blue crab were also studied. Salinity was changed from the acclimation salinity over a 10.4 h interval, held at that salinity for 2 h, then returned to the acclimation salinity over 10.4 h and held at that salinity for 2 h. The respiration rate of 30 S acclimated oyster drills (679 l O₂ g dry weight^–1 h^–1) was significantly higher than for individuals acclimated to 10 S (534 l O₂ g dry weight^–1 h^–1). Blue crab respiration was 170 l O₂ g dry weight^–1 h^–1 at 30 S, and was significantly higher at 10 and 20 S than at 30 S. With the exception of the 20-10-20 S semidiurnal cycle, the respiration rate of oyster drills declined as salinity fluctuated in either direction from the acclimation salinity and increased as ambient salinity returned to the acclimation salinity. Semidiurnal cycles (12 h) of fluctuating salinity produced greater changes in the respiration rate of snails than analogous diurnal cycles (24.8 h). A 10-30-10 S pattern of fluctuation caused a greater percentage reduction in the steady state respiration rate of oyster drills than the 30-10-30 S pattern. The respiration rate of blue crabs varied inversely with fluctuating salinity. Relatively minor changes occurred in blue crab respiration rate with fluctuating salinity. Blue crab respiration rate characteristically dropped during the initial phase of declining salinity at a rate directly proportional to the rate of salinity decrease, perhaps representing a metabolic adjustment period by the blue crabs. The respiratory response of T. haemastoma to salinity is consistent with its incomplete volume regulation, while the response of C. sapidus is compatible with its ability to regulate extracellular fluid osmotic and ionic composition.     

Respiration,pumping activity and heart rate in Ciona intestinalis exposed to fluctuating salinities

Specimens of Ciona intestinalis L. were exposed to both gradual (sinusoidal) and abrupt (square-wave) salinity fluctuations and the changes in pumping activity and oxygen sonsumption monitored. Heart rate was monitored under steady state conditions using a new in vivo method, and pumping activity was monitored as spontaneous squirting by use of a pressure transducer. Oxygen consumption was also monitored under steady state conditions and under conditions of declining oxygen tension. It was found that during periods of regular beating the mean heart rate for 5 ascidians was 13.2 beats min^-1 for the branchial pacemaker and 32.6 beats min^-1 for the visceral pacemaker. Regular periods of beating lasted for approximately 1 min, followed by periods of irregular activity prior to heart beat reversal. The heart beat became irregular and reversal occurred sporadically when the ascidians were exposed to dilute seawater. The ascidians showed a pumping rate of 14 squirts per hour in full-strength seawater. This rate declined during decreasing salinity and ceased entirely when the external seawater concentration reached approximately 60% seawater (100%=32% S). During periods of decreased salinity, the siphons were tightly closed and oxygen consumption was zero. The rate of oxygen consumption by C. intestinalis decreased during decreasing salinities and there was no evidence of an oxygen debt. Oxygen consumption under steady state conditions varied with body weight according to the following: oxygen consuption =0.515 W ^0.831 (where W is body weight). The rate of oxygen consumption was found to be dependent on the external oxygen tension.     

Effects of salinity on the uptake of lead and cadmium by two mangrove species Rhizophora apiculata Bl. and Avicennia alba Bl.

The uptake of lead (Pb) and cadmium (Cd) by Rhizophora apiculata and Avicennia alba under various salinity levels was examined using hydroponic cultivations. After 3 months of exposure at four levels of Pb (0, 0.03, 0.3 and 3 mg·L^?1) and four levels of Cd (0, 0.005; 0.05 and 0.5 mg·L^?1) at different salinities (0, 15 and 30), uptake of the metals was shown to be differently affected by salinity. For uptake of Pb by R. apiculata, the salinity effect was not significant for the leaves and was most significant in the stem, whereas for A. alba, the effect of salinity was significant only in the stem. Uptake of Pb in the roots and stems of both species was similar, but a higher concentration was recorded in the leaves of A. alba. Salinity was shown to affect the uptake of Cd by all tissues of R. apiculata, but most significantly roots. For A. alba, salinity significantly affects the total uptake of Cd, but this is most significant in the roots. The two mangrove species demonstrated different mechanisms of metal distribution into their organs which may be related to different adaptation mechanisms to saline conditions.     

Seasonal variations in distribution patterns of sympagic meiofauna in Arctic pack ice

During two expeditions of the R.V. Polarstern to the Arctic Ocean, pack ice and under-ice water samples were collected during two different seasons: late summer (September 2002) and late winter (March/April 2003). Physical and biological properties of the ice were investigated to explain seasonal differences in species composition, abundance and distribution patterns of sympagic meiofauna (in this case: heterotrophs >20 µm). In winter, the ice near the surface was characterized by extreme physical conditions (minimum ice temperature: –22°C, maximum brine salinity: 223, brine volume: 5%) and more moderate conditions in summer (minimum ice temperature: –5.6°C, maximum brine salinity: 94, most brine volumes: 5%). Conditions in the lowermost part of the ice did not differ to a high degree between summer and winter. Chlorophyll a concentrations (chl a) showed significant differences between summer and winter: during winter, concentrations were mostly <1.0 µg chl a l^–1, while chl a concentrations of up to 67.4 µmol l^–1 were measured during summer. The median of depth-integrated chl a concentration in summer was significantly higher than in winter. Integrated abundances of sympagic meiofauna were within the same range for both seasons and varied between 0.6 and 34.1×10³ organisms m^–2 in summer and between 3.7 and 24.8×10³ organisms m^–2 in winter. With regard to species composition, a comparison between the two seasons showed distinct differences: while copepods (42.7%) and rotifers (33.4%) were the most abundant sea-ice meiofaunal taxa during summer, copepod nauplii dominated the community, comprising 92.9% of the fauna, in winter. Low species abundances were found in the under-ice water, indicating that overwintering of the other sympagic organisms did not take place there, either. Therefore, their survival strategy over the polar winter remains unclear.Communicated by O. Kinne, Oldendorf/Luhe     

Exuviaella cordata red tide in Bulgarian coastal waters (May to June 1986)

The structure and some functional characteristics of the plankton community at the time of aExuviaella cordata red tide were investigated in Burgas Bay, Bulgaria, in May and June 1986. Characteristics of main plankton components (phyto-, bacterio-, nanoheterotrophic plankton, ciliates and mesoplankton) in the bloom area are presented. Development of theE. cordata bloom was determined by abiotic conditions among which eutrophication and salinity decrease caused the patchy character of its rapid development. Attainment of maximum red tide (ca. 1x10⁹ cells l^-1; 1x10³ g m^-3) from background (500 to 800x10³ cells l^-1; 600 mg m^-3) took 3 to 7d. Growth rate () during that period was 1.2 to 2.2 doublings per day. A sharp bloom decline (3 to 4d) was caused by parasitic flagellates destroying the alga's chloroplast. Diel biomass losses due to grazing remained below 5%. Metabolites and degradation products ofE. cordata revealed no pronounced toxic effects on the other components of the planktonic community. The rapid bloom degradation due to the effects of parasitic flagellates indicates the high potential of ecosystem self-regulation.     

Bacterivory of a mudflat nematode community under different environmental conditions

The fate of the benthic bacterial biomass is a topic of major importance in understanding how soft-bottom environments function. Because of their high abundance, production and nutritional value, benthic bacteria may constitute an important food resource for benthic fauna. The trophic role of bacteria for a nematode community on the Brouage mudflat (Marennes-Oléron-France), dominated by three species: Chromadora macrolaima (64% of the abundance), Daptonema oxycerca (15%) and Ptycholaimellus jacobi (8%), was determined in grazing experiments using ¹⁵N pre-enriched bacteria. On intertidal flats, seasonal, tidal and circadian cycles induce strong variations in environmental conditions. Grazing experiments were performed in order to measure the effects of abiotic (temperature, salinity and luminosity) and biotic (bacterial and algal abundances) factors on assimilation rates of bacteria by nematodes. In order to assess simultaneously bacteria and algal assimilation rates, algal abundances were modified adding ¹³C pre-enriched Navicula phyllepta. Assimilation rate was significantly lower at 5°C; moreover, general trend shows a prominent temperature effect with an optimum around 30°C. Assimilation at salinity 18 was not significantly different from the assimilation at salinity 31. Assimilation was higher under light conditions than in the dark. Above 10⁹ bacteria ml⁻¹, assimilation of bacteria remained unaffected by bacterial abundance. However, assimilation of algae increased with the algal concentration. Nematode kept feeding under conditions of stress, which are typical of the surficial sediment habitat and they appeared to be principally dependent on the algal resource.     

Metabolic response under different salinity and temperature conditions for glass eel Anguilla japonica

Diadromous fish often enter freshwater directly from seawater via fish ladders or channels built in estuarine dams. The oxygen consumption rates (OCR) of glass eel, Anguilla japonica, were determined using an automatic intermittent flow respirometer under various salinity and temperature regimes to physiologically explain this direct movement. The endogenous rhythm of the OCR in wild glass eels, freshly collected from estuaries, was nearly synchronous with the tidal pattern at the estuarine collection site. When the salinity was changed from 20 psu (12°C) at a constant temperature to that of freshwater, the OCR of the glass eels decreased by 21.6±7.0% (mean ± SD) (P<0.05), showing a dampened rhythm for about 48 h. After this period of impediment, the glass eels resumed normal metabolic activity. Direct migration from seawater to freshwater under constant temperature would result in a severe physiological stress for these glass eels for about two days. When the glass eels were exposed to a cyclic change in water temperature of 2°C 26 h⁻¹, as they encounter in estuaries, and then were introduced to freshwater abruptly, the OCR rhythm corresponded to the cyclic changes in water temperature after exposure to freshwater. Under these conditions, the mean OCR of the glass eels had a small difference before and after exposure to freshwater. These data explained how glass eels can directly move from sea water into the freshwater without any apparent metabolic stress in the estuaries showing cyclic change in water temperature (Δt=2°C).