In situ measurement of the urea decomposition rate and its turnover rate in the Pacific Ocean

The in situ decomposition rate of urea was measured using ¹⁴C-labelled urea at 3 areas in the North Pacific Ocean: Sagami Bay on the southern coast of central Japan, the northwestern Pacific central waters and the subarctic Pacific waters. The mean values of the decomposition rates of urea in surface waters of these areas were 44.5, 1.51 and 1.32 mol urea m^-3 d^-1, respectively. These rates decreased with depth. High rates of urea carbon incorporation into particulate matter and the CO₂ liberation from urea carbon into seawater were obtained in light bottles in the euphotic zone, while low rates were found in dark bottles. The turnover rates of urea in the 3 areas were calculated respectively as 12, 113 and 110 d at the surface, and the values increased with depth.     

Study of bacteria associated with marine algae in culture

Inhibitory action of some usual antibiotic, substances have been tested on 25 species of bacteria isolated from marine algae cultures. Penicillin, kanamycin, neomycin and streptomycin appear to be the most convenient antibiotics for eliminating or inhibiting polluting bacteria populations.     

Etude histologique,histochimique et biochimique des sécrétions ectodermiques des Cérianthes

Histological and histochemical observations were carried out concerning the different kinds of cells which make up the ectoderm layer of Cerianthi. The external tube secreted by some of the ectoderm cells has been analysed by biochemical methods. The results obtained were compared with those from some well known sedentary polychaete worms which also possess an external tube of similar texture.     

The Adsorption of Lead and Copper from Aqueous Solution on Modified Peat–Resin Particles

Raw peat was modified with sulfuric acid, then mixed modified with resin to prepare the modified peat–resin particles. Using the batch experimental systems, the removal of heavy metals (copper and lead) on the modified peat–resin particles was investigated. The data of the adsorption isotherm could be fitted by the Langmuir equation well. The adsorption rate of heavy metals on modified peat–resin particles was very swift. The removal processes of heavy metals on modified peat–resin particles could be well described by pseudo-second order model. The adsorption rate of lead was affected by the initial heavy metal concentration, initial pH, particle size, agitation speed and particle mass. In the adsorption of heavy metals (lead and copper) on the modified peat–resin particles, ion exchange was the major reaction mechanism. Desorption data showed that the lead adsorbed by modified peat–resin particle could be desorbed by 0.5 N or 1.0 N HNO₃. The desorption rate was swift. The experiments indicated that the modified peat–resin particles have great potential for the removal of heavy metals from wastewater.     

Gastrointestinal pH and development of the acid digestion in larvae and early juveniles of<Emphasis Type="Italic"> Sparus aurata</Emphasis> (Pisces: Teleostei)

Changes in digestive pH and protease activity have been determined throughout the transition from larvae to the juvenile stage in Sparus aurata in rearing conditions (from 0.04 to 100 g wet weight). Measurements of pH have been taken in the stomach and different segments along the length of the intestine using a pH microelectrode. In starved fish, the gastric pH ranged between 6.0 and 8.0 approximately, except in juveniles of intermediate size (between 1.0 and 7.0 g wet weight), which exhibited a wider pH range of 2.0–8.0. Fed fish with digestive content showed, in general, lower pH values in the stomach. A progressive decrease was observed from a pH range of 5.5–8.0 in the youngest animals (0.04 g) to a pH range of 2.0–6.2 when juveniles were approaching 1.0 g wet weight. Above this weight, the gastric pH remained constant (between 2.0 and 6.0 approximately). The pH values in the intestine ranged between 6.7 and 8.4. They were similar in the different segments and weight classes examined, and there were no significant differences between fed and starved animals. Specific acid protease activity (units per milligram soluble protein) in fed animals increased from small (0.04–1.0 g) to intermediate juveniles (1.0 and 7.0 g), but then remained similar in larger juveniles. On the contrary, specific alkaline protease activity in fed animals decreased from small to intermediate juveniles, and then remained at a similar level in larger juveniles. The results reflect a progressive transition during several months from alkaline digestion in larvae with undeveloped stomachs to the acid digestion in juveniles with fully developed stomachs. Full gastric capacity is developed in seabream juveniles of 1 g wet weight, which represents approximately 100 days post-hatching in cultured populations. Nevertheless, in the following 2.5 months, during which the intestine reaches the appropriate length, juveniles still show a transitional period in the regulatory mechanism of digestion, probably linked to the adaptation to a different feeding habit.Communicated by S.A. Poulet, RoscoffThis revised version was published in December 2003 with corrections to the legend of Fig. 3.     

Genetic heterogeneity among New Zealand species of hydrothermal vent mussels (Mytilidae: Bathymodiolus)

Molecular systematic studies provide evidence for three new species of Bathymodiolus-like hydrothermal vent mussels (Bivalvia: Mytilidae) from relatively shallow waters (depth less than 750 m) associated with the Kermadec Arc off northern New Zealand. Mitochondrial COI sequences from the three putative new species differed substantially from those of other known bathymodiolin species from the Pacific and Indian Oceans. Population genetic analysis of one of these species (Bathymodiolus new species NZ-1) revealed heterogeneity in allozyme gene frequencies between samples collected from two seamounts about 50 km apart. Factors that might contribute to genetic differentiation between neighbouring seamounts are discussed.Communicated by M.S. Johnson, Crawley     

Biochemical responses during starvation and subsequent recovery in postlarval Pacific white shrimp,Penaeus vannamei

Postlarval shrimp, Penaeus vannamei Boone, 1931, were held individually in cages and exposed to two feeding regimes. One group was starved for 12 d and then fed during the following 12 d. A second group was fed throughout the 24 d study. Four individuals were sampled from each of the two groups on Days 0, 1, 2, 4, 8, 12, 13, 14, 16, 20, and 24. Molting and growth among the starved-fed postlarvae stopped after 2 d starvation, while fed postlarvae increased significantly in size throughout the 24 d study. Among the starved-fed postlarvae, water content increased rapidly in response to starvation. DNA and sterol concentrations increased significantly during starvation due to selective catabolism of cellular components. After 12 d, RNA concentration was not significantly different between the fed and starved-fed postlarvae, but became significantly higher in the starved-fed postlarvae 48 h after feeding resumed. Triacylglycerol reserves were severely depleted during the first day of starvation, while protein concentrations began to decrease after the second day of starvation. RNA, protein, and the polyamines spermidine and spermine, when expressed as a ratio to DNA, decreased in response to starvation. Concentrations of all measured parameters in the starved-fed postlarvae returned to levels similar to those in the fed group 8 to 12 d after feeding resumed. Results of this study suggest that triacylglycerol provides energy during short periods of starvation, while protein is utilized during prolonged starvation. The ratios of RNA:DNA, protein:DNA, spermidine:DNA, spermine:DNA, two unidentified amine compounds, and percent water content are all useful indicators of prolonged nutritional stress in postlarval P. vannamei.     

UV induces reactive oxygen species,damages sperm,and impairs fertilisation in the sea urchin <Emphasis Type="Italic">Anthocidaris crassispina</Emphasis>

We demonstrated that environmentally relevant levels of UVA and UVB can reduce sperm motility (UVA: by 38–58%; UVB: by 42–85%; P < 0.05) and subsequently fertilisation success (UVA: by 38–72%; UVB: by 91–98%; P < 0.05) of urchins (Anthocidaris crassispina) in a dose-dependent manner, implicating that recruitment of urchin populations might be reduced by UVR (ultraviolet radiation) prevailing in their natural habitats. Concomitantly, reactive oxygen species (ROS) production was enhanced by UVA and UVB in a dose-dependent manner (UVA: by 1.3-fold; UVB: by 6.6–7.3-fold; P < 0.05), and the increase in ROS resulted in an increase in lipid peroxidation (LPO) in urchin sperm (UVA: by 4.2–7.2-fold; UVB: by 2.3–2.7-fold; P < 0.05). This study demonstrated that ROS production and oxidative damages enhanced by UVR may account for the observed declines in sperm motility and fertilisation, and suggests that levels of UVR prevailing in the environment may pose a significant threat to the reproductive success of natural populations of urchins spawning in shallow waters.     

Rapid assessment of metabolic activity in marine microalgae: application in ecotoxicological tests and evaluation of water quality

A new method for the assessment of the effects of several contaminants on marine microalgae,Tetraselmis suecica (Kyling) Butcher,Skeletonema costatum (Grev.) Cleve, andProrocentrum lima (Ehrenberg) Dodge was developed in 1990. The method is based on the measurement of cell esterase activity using a fluorimetric stain, fluorescein diacetate (FDA), selected from amongst three stains (FDA, Neutral Red, thiazolyl tetrazolium bromure) for its higher sensitivity. Biochemical (K _m,V _max) and physiological (growth, specific activity) aspects of the enzymatic activity as revealed by the FDA method are discussed. Different categories of compounds (weed-killers, insecticides, metals) and some water samples from Seine Bay were tested for their toxic effects on microalgae. Experiments were performed on microplates using a fluorimetric microplate reader. The various steps of the experiments and data-processing were controlled by software. Applications of the system to rapid ecotoxicological tests (determination of the IC₅₀, i.e., the concentration at which 50% inhibition of growth occurs) and to the assessment of environment quality by studying the toxic effect of water samples on microalgae are proposed.     

Thermochemical studies of the toxic actions of heavy metal ions on Rhizopus nigricans

By using a LKB2277 BioActivity Monitor (heat conduction microcalorimeter), stopped-flow method, the thermogenetic curves of Rhizopus nigricans growth at 25 degrees C inhibited by four kinds of heavy metal ions are determined, parameters such as growth rate constants k, inhibitory ratio I, half inhibitory concentration IC50 et al. are obtained. The experimental results show that heavy metal ions can inhibit Rhizopus nigricans growth obviously, low concentration of Cu2+ has promoting action. The inhibitory sequence is Cd2+ > Hg2+ > Pb2+ > Cu2+, half inhibitory concentration of them are Cd+ 0.8 micro g x ml(-1), Hg2+ 1.7 micro g x ml(-1), Pb2+ 48.0 micro g x ml(-1), Cu2+ 110 micro g x ml(-1). This microclorimetric bioassay for acute cellular toxicity is based on metabolic heat evolution from cultured cells. The assay is quantitative, inexpensive, and versatile; moreover, toxicological information can be obtained with cell from other species of interest.