Lead and cadmium in urban allotment and garden soils and vegetables in the United Kingdom

In order to assess the intake of lead and cadmium by consumers of home grown vegetables in urban areas, replicated experimental plots of uniform size, comprising summer and winter crops, were established in 94 gardens and allotments in nine towns and cities in England.The geometric mean lead and cadmium concentrations for the soils (n = 94) were 217 g g^–1 (ranging from 27 to 1,676 g g^–1) and 0.53 g g^–1 (<0.2–5.9 g g^–1), respectively. Compared with agricultural soils, the garden and allotment soils contained elevated levels of lead but not cadmium.Lead concentrations in the vegetables ranged from <0.25 g g^–1 to 16.7 g g^–1 dry weight and cadmium concentrations ranged from <0.025 g g^–1 to 10.4 g g^–1 dry weight. Lead concentrations were higher than reported background levels, although <1% exceeded the statutory limit for saleable food in the UK (1 g g^–1 fresh weight). Cadmium concentrations were generally similar to background levels.     

Primary productivity and sizes of pools of organic carbon in the mixed layer of the ocean

We estimated primary productivity and distributions of carbon in the phytoplankton, micro-zooplankton, and suspended and dissolved matter in various areas of the World Ocean to increase our information about the organic carbon cycle in the surface layer of the sea. Primary productivity ranged from about 0.1 gC m^–2 day^–1 in the Gulf of Mexico to 9 gC m^–2 day^–1 in nutrient-rich water off Peru. Phytoplankton carbon ranged from less than 10 g/l in the former to 750 g/l in the latter and in nutrient-rich water off southwest Africa. Micro-zooplankton carbon usually was less than 50 g/l in all waters, and was dominated by ciliates, copepodids, and copepod nauplii in all areas. Concentrations of particulate carbon ranged from 12 g/l off the east coast of South America to 850 g/l off southwest Africa. Concentrations of dissolved organic carbon varied between 0.5 and 1.5 mg/l in all areas except off Peru, where maximum values of 4.5 mg/l were observed. Turnover rates of carbon by small standing crops of micro-flagellates (1 to 5 longest dimension) and dinoflagellates in nutrient-poor waters were lower than those by large standing crops of diatoms and micro-flagellates in nutrient-rich waters. Concentrations of phytoplankton usually accounted for 20 to 55% and micro-zooplankton for 2 to 30% of the particulate carbon in the surface layer of the sea. Concentrations of dissolved organic carbon were not related to concentrations of particulate carbon in most waters except off Peru, where they appear to be directly related.     

Background levels of soil beryllium in several countries

Beryllium and aluminium contents in uncontaminated soils from six countries are reported. The means and ranges of beryllium in the surface soils were as follows: 1.43(0.20–5.50)g g^–1 in Thailand (n=28), 0.7 (0.31–1.03) g g^–1 in Indonesia (n=12), 0.99(0.82–1.32) g g^–1 in New Zealand (n=3), 0.58(0.08-1.68)g g^–1 in Brazil (n=16), 3.52(2.49–4.97)g g^–1 in the former Yugoslavia (n=10), and 1.56(1.01–2.73) g g^–1 in the former USSR (n=8). The mean and range of beryllium contents of the surface soils in Japan (1.17(0.27–1.95)g g^–1 n=27) are situated within the values of the soils from these countries except for the Yugoslav soils derived from limestones. The mean of the mean beryllium contents of the surface soils in all these countries is 1.42 g g^–1 which will be used as a tentative average content of beryllium in uncontaminated surface soils, except for the soils derived from parent materials high in beryllium content. The beryllium contents of the subsoils were higher than those of the surface soils in New Zealand and Yugoslavia as is the case with Japan. The correlation coefficient between the contents of beryllium and aluminium in all the soil samples (n=113) including surface soils and subsoils was 0.505 (p < 0.001).     

Uptake of dissolved organic matter by larval stage of the crown-of-thorns starfish Acanthaster planci

The life-history of the crown-of thorns starfish (Acanthaster planci) includes a planktotrophic larva that is capable of feeding on particulate food. It has been proposed, however, that particulate food (e.g. microalgae) is scarce in tropical water columns relative to the nutritional requirements of the larvae of A. planci, and that periodic shortages of food play an important role in the biology of this species. It has also been proposed that non-particulate sources of nutrition (e.g. dissolved organic matter, DOM) may fuel part of the nutritional requirements of the larval development of A. planci as well. The present study addresses the ability of A. planci larvae to take up several DOM species and compares rates of DOM uptake to the energy requirements of the larvae. Substrates transported in this study have been previously reported to be transported by larval asteroids from temperate and antarctic waters. Transport rates (per larval A. planci) increased steadily during larval development and some substrates had among the highest mass-specific transport rates ever reported for invertebrate larvae. Maximum transport rates (J _max ⁱⁿ) for alanine increased from 15.5 pmol larva^–1 h^–1 (13.2 pmol g^–1 h^–1) for gastrulas (J _max ⁱⁿ=38.7 pmol larva^–1 h^–1 or 47.4 pmol g^–1 h^–1) to 35.0 pmol larva^–1 h^–1 (13.1 pmol g^–1 h^–1) for early brachiolaria (J _max ⁱⁿ just prior to settlement=350.0 pmol larva^–1 h^–1 or 161.1 pmol g^–1 h^–1) at 1 M substrate concentrations. The instantaneous metabolic demand for substrates by gastrula, bipinnaria and brachiolaria stage larvae could be completely satisfied by alanine concentrations of 11, 1.6 and 0.8 M, respectively. Similar rates were measured in this study for the essential amino acid leucine, with rates increasing from 11.0 pmol larva^–1 h^–1 (or 9.4 pmol g^–1 h^–1) for gastrulas (J _max ⁱⁿ=110.5 pmol larva^–1 h^–1 or 94.4 pmol g^–1 h^–1) to 34.0 pmol larva^–1 h^–1 (or 13.0 pmol g^–1 h^–1) for late brachiolaria (J _max ⁱⁿ=288.9 pmol larva^–1 h^–1 or 110.3 pmol g^–1 h^–1) at 1 M substrate concentrations. The essential amino acid histidine was transported at lower rates (1.6 pmol g^–1 h^–1 at 1 M for late brachiolaria). Calculation of the energy contribution of the transported species revealed that larvae of A. planci can potentially satisfy 0.6, 18.7, 29.9 and 3.3% of their total energy requirements (instantaneous energy demand plus energy added to larvae as biomass) during embryonic and larval development from external concentrations of 1 M of glucose, alanine, leucine and histidine, respectively. These data demonstrate that a relatively minor component of the DOM pool in seawater (dissolved free amino acids, DFAA) can potentially provide significant amounts of energy for the growth and development of A. planci during larval development.     

Effect of heavy metals (Zn,Hg, Cu,Cd, Pb,Ni) on the length growth of Mytilus edulis

The shortterm (10–22 d) effect of Zn, Hg, Cu, Cd, Pb, and Ni on the length growth of Mytilus edulis is studied. Significant reductions of growth rate was found at 0.3 g Hgl^-1, 3 g Cul^-1, 10 g Znl^-1, and 10 g Cdl^-1 added to the local sea water, while concentrations of up to 200 gl^-1 of Pb and Ni had no effect on the growth. With exposure to Cu and Zn, there was a linear reduction in growth rate with increasing metal concentration up to about 6 g Cul^-1 and 100 g Znl^-1. Above these levels, growth stopped with Cu, while with Zn it was stabilized at about 20% of control growth. When Hg and Cd were added, a curvilinear relationship between growth and metal concentration is indicated. With Hg, growth rate is nearly zero above 3–4 g Hgl^-1, while the growth rate was 50% of control after 10 d of exposure to 100 g Cdl^-1. At 2 g Cdl^-1 there was a significant stimulation of length increase. Observed EC₅₀-values for growth were 0.3–0.4 g Hgl^-1, 3–4 g Cul^-1, 60 g Znl^-1, and 100 g Cdl^-1.     

Grazing of Acartia hudsonica (A. clausi) on Skeletonema costatum in Narragansett Bay (USA): Influence of food concentration and temperature

Grazing experiments were performed with temperatureacclimated Acartia hudsonica fed the diatom Skeletonema costatum in concentrations ranging from 50 to 3×10⁴ cell ml^-1 at 5°, 10° and 15°C. The ingestion data were best fit by an Ivlev equation. Feeding threshold values of 39 and 59 cells ml^-1 were not significantly different from zero; however, filtration rates were depressed at low food concentrations. Maximum filtration rates increased exponentially with temperature, reaching a maximum with copepods collected at 14°–15°C, and then declining. Both the increase in ingestion rate with increasing food concentration and the maximum ingestion rate were significantly greater as experimental temperature was increased. Maximum ingestion rates were reached at concentrations greater than 6×10³ cells ml^-1. Percent of body carbon ingested per day at 5 g C L^-1 increased from 1.5% at 5°C to 6.7% at 15°C. At 500 g C L^-1, the ingestion increased from 84% (5°C) to 660% (15°C). Percent of body nitrogen at 0.5 g N L^-1 increased from 0.6% per day at 5°C to 2.5% per day at 15°C. At 50 g N L^-1, the ingestion was 42% body nitrogen at 5°C and 250% at 15°C. The influence of grazing by A. hudsonica on phytoplankton in Narragansett Bay, USA was estimated for 1972–1977. The percent of standing stock removed by grazing rarely exceeded 5% per day except during the late spring when S. costatum growth becomes nutrient limited and higher temperatures favor the rapid population growth of A. hudsonica.     

Effects of cadmium and low magnesium on cell division and calcification in the marine coccolithophorid Cricosphaera (Hymenomonas) carterae

Cadmium (Cd) added to normal media and to magnesium (Mg)-deficient media produced inhibitory effects on cell division and cell calcification in the marine coccolithophorid alga Cricosphaera (Hymenomonas) carterae. Compared with controls in normal media (with 25 mM Mg), cell growth decreased progressively with Cd at concentrations of 5–20 M. In Mg-deficient media (with 6 mM and 0.08 mM Mg) the inhibitory effects were more pronounced with complete arrest of cell division at 20 M Cd. The greatest Cd inhibition occurred in media with the lowest Mg concentration (0.08 mM). Cadmium (5–40 M) also decreased recalcification (coccolith formation) in cells previoasly decalcified with CO₂ with complete inhibition at 40 M Cd. Inhibition of recalcification in various Cd concentrations (5–40 M) was more pronounced in low-Mg medium (with 6 mM and 0.08 mM Mg) compared with normal medium (25 mM Mg). Partial or complete reversal of the inhibitory effects of Cd and low Mg media on cell division and calcification occurred following a wash and resuspension of the cells in normal control medium (25 mM Mg).     

Diurnal gut pigment rhythm and metabolic rate of<Emphasis Type="Italic"> Calanus euxinus</Emphasis> in the Black Sea

The vertical distribution, diel gut pigment content and oxygen consumption of Calanus euxinus were studied in April and September 1995 in the Black Sea. Gut pigment content of C. euxinus females was associated with diel vertical migration of the individuals, and it varied with depth and time. Highest gut pigment content was observed during the nighttime, when females were in the chlorophyll a (chl a) rich surface waters, but significant feeding also occurred in the deep layer. Gut pigment content throughout the water column varied from 0.8 to 22.0 ng pigment female^–1 in April and from 0.2 to 21 ng pigment female^–1 in September 1995. From the diel vertical migration pattern, it was estimated that female C. euxinus spend 7.5 h day^–1 in April and 10.5 h day^–1 in September in the chl a rich surface waters. Daily consumption by female C. euxinus in chl a rich surface waters was estimated by taking into account the feeding duration and gut pigment concentrations. Daily carbon rations of female C. euxinus, derived from herbivorous feeding in the euphotic zone, ranged from 6% to 11% of their body carbon weight in April and from 15% to 35% in September. Oxygen consumption rates of female and copepodite stage V (CV) C. euxinus were measured at different temperatures and at different oxygen concentrations. Oxygen consumption rates at oxygen-saturated concentration ranged from an average of 0.67 g O₂ mg^–1 dry weight (DW) h^–1 at 5°C to 2.1 g O₂ mg^–1 DW h^–1 at 23°C for females, and ranged from 0.48 g O₂ mg^–1 DW h^–1 at 5°C to 1.5 g O₂ mg^–1 DW h^–1 at 23°C for CVs. The rate of oxygen consumption at 16°C varied from 0.62 g O₂ mg^–1 DW h^–1 at 0.65 mg O₂ l^–1 to 1.57 g O₂ mg^–1 DW h^–1 at 4.35 mg O₂ l^–1 for CVs, and from 0.74 g O₂ mg^–1 DW h^–1 at 0.57 mg O₂ l^–1 to 2.24 g O₂ mg^–1 DW h^–1 at 4.37 mg O₂ l^–1 for females. From the oxygen consumption rates, daily requirements for the routine metabolism of females were estimated, and our results indicate that the herbivorous daily ration was sufficient to meet the routine metabolic requirements of female C. euxinus in April and September in the Black Sea.Communicated by O. Kinne, Oldendorf/Luhe     

Modification of the feeding behavior of marine copepods by sub-lethal concentrations of water-accommodated fuel oil

The feeding behaviors of Acartia clausi and A. tonsa were measured in samples of water containing low levels of a water-accommodated fraction of No. 2 fuel oil. The copepods fed normally at a hydrocarbon concentration of 70 g l^-1, but their feeding behavior was altered both quantitatively and qualitatively at a concentration of 250 g l^-1. Three types of response to the higher oil level were found. The first was total suppression of feeding. Both other types involved suppression of feeding on particles between 7 and 15 m diameter, but one showed no change in the ingestion of larger particles, whereas the other displayed increased feeding on particles larger than 15 m diameter. These results suggest that the species of Acartia studied use three different modes of feeding, each on a different size range of particulate material. Low-level hydrocarbon pollution affects each feeding mode differently.Contribution No. 973, Center for Environmental and Estuarine Studies of the University of Maryland     

Heavy metals in the Sea-Skater Halobates robustus from the Galápagos Islands: Concentrations in nature and uptake experiments,with special reference to cadmium

Samples of Halobates robustus Barber (Heteroptera: Gerridae) from the Galápagos Islands were analysed by optical emission spectrometry. The levels (in g g^-1 dry weight) of Zn (134), Cu (155), Pb (< 1), Cd (7), and Cr (3) were not significantly different among insects of different sexes or developmental stages. The low natural levels of Cd in H. robustus from the relatively unpolluted environment of the Galápagos Islands are compared to the high concentrations of Cd in Halobates spp. from relatively polluted regions. Since the measured levels of Cd in their natural zooplankton food rarely exceed 10 g g^-1, and very little of the Cd is found in the soft tissues, the high Cd concentrations (100 to 200 g g^–1) in some seaskater species have evidently been derived by drinking from the surface microlayer of the seawater.     

Seasonal variation of total dissolved arsenic and arsenic speciation in a polluted surface waterway

Seasonal differences in the dissolved arsenic concentration and speciation in a contaminated urban waterway in northwest England have been determined using a coupled ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS) technique. Waters sampled in the vicinity of an industrial works during relatively dry conditions in April 2000 were found to contain total arsenic concentrations (As) of up to 132 g L^–1, more than an order magnitude greater than the 4 g L^–1 maximum found in December 2000. The difference in As between the April and December sampling periods is speculated to be largely due to the irregular anthropogenic supply of arsenic to the watercourse. For both sampling periods, the dissolved arsenic was exclusively inorganic in nature and had an As(V)/As ratio of between 0.6 and 0.8. Analysis of samples taken downstream of the industrial site, after the confluence with a relatively As-poor stream, revealed that As(III), As(V) and As concentrations were lower than would be expected from conservative mixing. The As(V)/As ratio was also observed to decrease markedly. The loss of arsenic from solution is thought to be due to adsorption on the iron oxyhydroxide-rich sediment observed to coat the riverbed downstream of the confluence. The reduction in the As(V)/As ratio is believed to be due to the more rapid adsorption of As(V) compared to that of As(III). Deviations from conservative behaviour were more marked during the relatively dry April 2000 sampling period and suggest the increased importance of adsorption processes controlling arsenic availability during this time.     

A role forAmanita muscaria L. in the circulation of cadmium and vanadium in a non-polluted woodland

The sporophore of the fungusAmanita muscaria L. contains greatiy elevated levels of cadmium (29.9 g g^–1 dwt) and vanadium (344.9 g g^–1 dwt) in comparison with the soil in a birch woodland (total (HNO₃-extractabie Cd 0.4 g g^–1 dwt, V 11.7 g g^–1 dwt). The significance of this remarkable concentration of normally rare and dispersed elements in terms of their circulation in the woodland has been investigated. Both elements are released from sporophore tissue in a form which can be taken up by a test plant (lettuce), cultivated in the woodland soil amended with different quantities of sporophore tissue, Cadmium levels in all plant tissues were elevated in comparison to the non-amended controls; only root vanadium levels responded to the amendment of the soil. The results are discussed in terms of their significance for the natural cycling of both elements. It is calculated that an abundant population of sporophores could circulate 1.4% of the total cadmium and 0.65% of the total vanadium pool found in the litter layer and 0–5 cm soil horizon in the sampled woodland over a period of 14 days (mean life span of a sporophore).     

Temporal variation and distribution of trace metals in freshwater and fish from Calabar River, S.E. Nigeria

An investigation on the abundance and distribution of trace metals (Fe, Cu, Zn, Mn, Cr, Cd and Pb) in water, and nine species of fish samples from Calabar river was carried out in 1992. The concentrations of iron (6000–7240gl^–1), zinc (4910–7230gl^–1), and cadmium (3–7gl^–1) showed moderate pollution while those of copper (420–630gl^–1), manganese (23–48gl^–1), chromium (<10–20gl^–1) and lead (<1–10gl^–1) in water were well below WHO permissible levels. Significant seasonal changes (0.001p0.25) were obtained for iron, copper, zinc, manganese and cadmium in water. Furthermore, iron, zinc and cadmium showed statistically significant spatial changes (0.005p0.10). Of the nine fish species studied, no statistically significant relationship between body weight and the concentrations of the metals was observed. The concentrations of the metals per mean total body weight apparently decreases in the order Fe>Zn>Cu>Mn>Pb>Cd=Cr and were within the limits that were safe for consumption.     

Growth of plankton algae as a function of N-concentration,measured by means of batch technique

Employing a special batch technique which involves extremely low concentrations of the alga Selenastrum capricornutum, it is shown that a growth rate of ca. 75% of optimum growth occurs at a concentration of 0.02 g-at N(NH₄ ⁺) l^-1. The low concentrations of this N-source in the oligotrophic parts of the oceans (ca. 0.06 g-at l^-1) thus give rise to a borderline deficiency. As the half-saturation constant (K _S) for growth was recorded at 0.05 g-at N(NO₃ ^-), this ion can hardly be of much importance at the low concentrations present in these parts of the oceans. It is wrong to assert that N is the primary limiting nutrient. Phosphate also is found at concentrations giving rise to a borderline deficiency.     

Environmental impact of heavy metals (Fe, Ni, Cr, Co) in soils waters and plants of triada in euboea from ultrabasic rocks and nickeliferous mineralisation

Soil, water and vegetation samples were collected from the Triada area of Central Euboea and analysed for heavy metals in order to evaluate their environmental impact. The geology of the area studied includes ultrabasic rocks that are overlaid by Upper Cretaceous limestones whereas Fe–Ni mineralisation is intercalated between either the ultrabasic parent rocks or the karstified Jurassic/Triassic carbonates and the transgessive Upper Cretaceous limestones. All the samples were analysed for heavy metals by using atomic absorption spectroscopy. The heavy metal ranges (in g g^–1) for soils samples are: Ni 480–4000, Cr 240–2720, Co 40–208, Fe 24,000–380,000, Mn 46–1680, Pb 16–56, Zn 40–144, Cu 2–82. The values of soil samples of the Triada area are much higher than the values found for Ni, Cr, Co and Fe, in normal soils of the world. The heavy metal ranges (in g L^–1) for water samples are: Ni 19–24, Cr 19–476, Co <5, Fe <100, Mn <100, Mg 5.7–220.5, As 30–69, Cd <2, Pd <10, Zn 5–11, Cu 2–7. The water samples of the Triada area have Cr and Mg concentrations higher than the permittable values. The heavy metal ranges (in g g^–1) for vegetation samples are: Ni 1–135, Cr 0–24, Co 1–21.5, Fe 20–680, Mn 10–206, Cd 0–10, Pb 0–14, Zn 14–70, Cu 0–10.5. The vegetation samples of the Triada area have so high values of Ni, Cr and Co that are considered toxic. The intercorrelated elements Fe, Ni, Cr, Co of the Triada soils, waters and vegetation reflect their association with the ultrabasic rocks and with the Fe–Ni mineralisation.     

Effects of light intensity on nitrate and nitrite uptake and excretion by Chaetoceros curvisetus

Michaelis-Menten uptake kinetics were observed at all light intensities. With constant illumination, the V_max and K₁ in nitrate uptake over the natural light intensity range of 0 to 2000 E were 0.343 g-at NO₃–N(g)^-1 at protein-N h^-1 and 26 E, respectively. Nitrate uptake was inhibited at higher light intensities. The K_s for nitrate uptake did not vary as a function of light intensity remaining relatively constant at 0.62 g-at NO₃–N 1^-1. With intermittent illumination, the V_mzx for light intensity in nitrate uptake over a light intensity range of 0 to 5000 E was 0.341 g-at NO₃–N(g)^-1-at protein-N h^-1. No inhibition of nitrate uptake was observed at higher than natural light intensities. Chaetoceros curvisetus will probably never experience light inhibition of nitrate uptake under natural conditions.     

Lead exposure in Saudi Arabia from the use of traditional cosmetics and medical remedies

Twenty Henna samples were collected and analysed for lead by electrothermal atomic absorption spectrophotometry after a microwave acid digestion procedure. The mean lead concentration was 5.50 g g^–1, with a range from 1.29 g g^–1 to 16.48 g g^–1. The data did not show a high concentration of lead in these samples. However, if we take into account the popular use of henna, the cumulative effects of prolonged exposure to low lead especially in children cannot be ruled out.     

Eulerian sampling of zooplankton from Marseilles' Vieux Port over a 24 h period

A 24 h continuous study of hydrological parameters and zooplanktonic populations was carried out in Marseilles' Vieux-Port, a semi-closed area supposed to be a fairly homogeneous body of water. Sampling was performed in spring 1980 with a pump system. Samples were taken every 30 min over a period of 24 h, during which time only slight temperature variations were recorded (min.=14.5°C, max.=15.1°C); salinities were high and fairly stable (min.=37.49, max.=37.63%.). It can thus be assumed that the water was homogeneous. Concentrations of suspended particulate matter were high and fairly stable (x = 11.8 mg 1^-1). In most samples, nitrate levels were fairly low (x = 0.84 g-at 1^-1); conversely, phosphate contents fluctuated greatly (min.=0.24 g-at 1^-1, max.=2.24 g-at 1^-1). As a result of these fluctuating nutrient-salt values, the N:P ratios were often unbalanced (between 0.5 and 2.0). Detergent values were low (often less than 0.2 ppm). Zooplanktonic populations were made up of a few eurybiotic species, the most thriving of which were the cladoceran Podon polyphemoides and the copepod Acartia clausi. These two species perform nychthemeral migrations towards the surface: P. polyphemoides during the day and A. clausi at night. As a result of these opposite patterns of migrations, the planktonic biomass remained fairly stable near the surface. There were also some meroplanktonic species (especially cirripede larvae) and a small number of other copepods present. This study revealed a regular hydrological and faunal cycle with a return to initial conditions at the end of the 24 h period.     

Sexual reproduction of the solitary sunset cup coral<Emphasis Type="Italic"> Leptopsammia pruvoti</Emphasis> (Scleractinia: Dendrophylliidae) in the Mediterranean. 1. Morphological aspects of gametogenesis and ontogenesis

Information on the reproduction in scleractinian solitary corals and in those living in temperate zones is notably scant. Leptopsammia pruvoti is a solitary coral living in the Mediterranean Sea and along Atlantic coasts from Portugal to southern England. This coral lives in shaded habitats, from the surface to 70 m in depth, reaching population densities of >17,000 individuals m^–2. In this paper, we discuss the morphological aspects of sexual reproduction in this species. In a separate paper, we report the quantitative data on the annual reproductive cycle and make an interspecific comparison of reproductive traits among Dendrophylliidae aimed at defining different reproductive strategies. The present study on L. pruvoti is the first in-depth investigation of the reproductive biology of a species of this genus. As expected for a member of the family Dendrophylliidae, L. pruvoti is a gonochoric and brooding coral. The gastrodermal tissue of the gametogenetic mesenteries we examined was swollen and granular, which led us to hypothesize that interstitial cells could have a trophic function favoring gametogenesis. Undifferentiated germ cells arose in the gastrodermis and subsequently migrated to the mesoglea, where they completed gametogenesis. During spermary development, spermary diameter increased from a minimum of 14 m during the immature stages to a maximum of 410 m during the mature stages. As oogenesis progressed, we observed a gradual reduction in the nucleus to cytoplasm ratio due to the steady synthesis of yolk. During the final stages of oogenesis, after having migrated to the extreme periphery of the oocyte and having firmly adhered to the oolemma, the nucleus became indented, assuming a sickle or dome shape. We can hypothesize that the nucleus migration and change of shape may have to do with facilitating fertilization and determining the future embryonic axis. During oogenesis, oocyte diameter increased from a minimum of 20 m during the immature stage to a maximum of 680 m when mature. Embryogenesis took place in the coelenteron. We did not see any evidence that even hinted at the formation of a blastocoel; embryonic development proceeded via stereoblastulae with superficial cleavage. Gastrulation took place by delamination. Early and late embryos had diameters of 204–724 m and 290–736 m, respectively. When released, the larvae had completed ontogenesis and swam by a ciliary movement with the aboral pole at the anterior, their shape varied from spherical to cylindrical (in the latter the oral–aboral axis measured 695–1,595 m and the transversal one measured 267–633 m).Communicated by R. Cattaneo-Vietti, Genova     

Hydrobiological parameters during an annual cycle in the Arcachon Basin

Temperature, salinity, nutrients and phytoplankton biomass were monitored on a weekly to bimonthly frequency at six stations in the Bay of Arcachon from July 1984 to July 1985. This particular period appears to have differed from the last ten years in displaying higher amplitudes of both temperature and salinity (1.5° to 24.5°C and 20 to 34.5) at high tide. However, although in spring both temperature and salinity were normal (14°C, 28), an important phytoplankton spring bloom occurred, with maximum chlorophyll levels reaching 15 g l^-1 in April. Utilization of nutrients was high, particularly for nitrate and silicate, the concentrations of which decreased, respectively, from 10–15 to 0.1–2 M and 10–20 to 0.25–3 M from February to May. Exhaustion of nitrate was observed in May, except in areas subjected to river input. In contrast, silicate increased throughout the study area from May to July.