Analyse des paramètres hydrobiologiques dans la remontée de Cabo Frio (Brésil)

South Atlantic Central Waters (SACW) upwell close to Cabo Frio (Brazil, Rio de Janeiro) shore. The resultant typical hydrobiological conditions were studied at an anchorage station over an annual cycle from February 1973–February 1974. Multivariate analyses of hydrological and planktonic data revealed the structure of the ecosystem and the factorial relations governing its dynamics. Alternation, superposition or mixing of the water masses of different origin (Brazil current, coastal, SACW) constitute the most important factors responsible for the great hydrobiological variability observed in the study area. Spasmodic changes in wind direction and force are superimposed on a seasonal trend of more frequent upwelling in summer than during the rest of the year. The deep water is characterized by temperatures of <18°C, nitrate contents of 10 g-at l^-1 and by organic matter mainly composed of detritic elements from the shelf. Temperature variations together with nutrient contents (NO₃ or PO₄) reflect variations in primary biomass at the surface but not at 50 m depth, where detrital matter precluded valid measurements. Water of the Brazilian Current (salinity 36.0) frequently mixes with deep water of the thermal front, or with coastal water (<35.0) which invades the area when south-west winds prevail. This lower-salinity water is rich in seston particles. During the study period, primary biomass was relatively low due to eutrophication. We observed less than 3 g l^-1 chlorophyll and 10⁶ phytoplankton cells per litre: the phytoplankton populations were highly diversified, indicating an advanced degree of complexity and evolution of this ecosystem. The observed formation of a thermocline constitutes an important inducing factor for an algal bloom. Simultaneous phyto- and zooplankton maxima would induce an increased grazing rate by herbivorous zooplankton which would also partly explain the relatively low level of primary biomass. Zooplankton is as abundant here as in other great upwelling regions: 100 organisms l^-1 and 200 mg organic matter m^-3.     

Spatial and temporal variability of phytoplankton biomass,primary production and community structure in the Pontevedra Ria (NW Iberian Peninsula): oceanographic periods and possible response to environmental changes

The spatial distribution of phytoplankton assemblages, chlorophyll, primary production and physical and chemical parameters were studied in the Pontevedra Ria in Galicia (NW Iberian Peninsula) from October 1997 to October 1998. In addition to the usual oceanographic periods described for the Galician Coast, two other periods were observed: a Prebloom or winter bloom, occurring during calm, sunny days in winter and a Continental period, related to the allochthonous intrusion of low salinity water from the Miño River in late spring. The phytoplankton biomass and production in both periods reached values of up to 145 mgChl-a m^?2 and 3.6 gC m^?2 day^?1, respectively, which were similar to those found in summer upwelling blooms. Throughout the year, the phytoplankton biomass and primary production gradients along the ria’s axis were highly dependent on the balance between upwelling and runoff. When the latter prevailed, increased values were measured toward the inner ria, while the opposite pattern was observed during summer upwelling blooms. According to projections derived from climate models and the analysis of wind patterns, temperature and precipitation trends in the area, a drop in the productivity of the ria would be expected as a result of reduced upwelling intensity in summer and decreasing rainfall in spring. In any case the estuarine part of the ria would be the most seriously affected.     

Primary production and environmental factors in an oligotrophic biome in the Aegean Sea

The rate of the primary production of the phytoplankton community in the Petalion Gulf, Aegean Sea, was studied from January 1970 to May 1971, at a station situated at approximately Latitude 37°54N; Longitude 24°11E. A variety of physical and chemical parameters such as chlorophyll, primary nutrients (N,P,Si), temperature, salinity, oxygen and light penetration were also studied simultaneously. The rate of the gross primary production varied from 40 to 200 mg C m^-2 day^-1, with a mean value of 90 mg C m^-2 day^-1. The annual gross primary production was calculated to be 33 g C m^-2, which is the minimum known value in the Aegean and Mediterranean Seas. Maximum production was found at the depth of 20 m on the average, mainly due to high light intensities. Petalion Gulf supports a small photosynthetic biomass, as indicated by the low seasonal values of chlorophyll a (0.01 to 0.18 mg m^-2), the highest values being found in the summer. The low production rate noted may have been due to the low nutrient concentrations found: N, 0.04 to 0.32 g-at/1; P, 0.00 to 0.15 g-at/1; Si, 0.45 to 2.25 g-at/1. It is suggested that inorganic phosphorus and nitrogen may alternate in limiting primary production rates in these oligotrophic waters. The temperate waters of the Petalion Gulf are stratified in summer (15.5° to 24.7°C) and well-mixed in winter (12.9° to 15.0°C); they are oxygen-saturated throughout the year, and of high transparency, with 86 m depth for the euphotic zone on the average yearly. The Petalion Gulf is therefore characterized as a typical oligotrophic biome in the Aegean and Eastern Mediterranean Seas.     

Autecology and clonal variability of the marine centric diatom Thalassiosira rotula (Bacillariophyceae) in response to light,temperature and salinity

The influence of 49 combinations of salinity (10–40 S, at 5 S intervals) and temperature (0°–30°C, at 5C° intervals) on the maximum daily division rate (K) and 18 combinations of light intensity (six levels) and temperature (5°, 15°, and 25°C) on photosynthesis, cell division, and chlorophyll a was examined using two clones of Thalassiosira rotula Meunier isolated from the upwelling area of Baja California (clone C8) and from Narragansett Bay, Rhode Islands (clone A8). Physiological differences appear to characterize these to clones with regard to their temperature tolerance (C8 5°–30°C, A8 0°–25°C), maximum growth rate (C8 K=2.9, A8 K=2.4), chlorophyll a content, and in the rates of growth and photosynthesis in response to light intensity and temperature. Optimum salinity for both clones (25–30 S) was generally independent of temperature, while chlorophyll a content decreased with temperature. T. rotula is a cosmopolitan paractic species; experimental studies indicate that it is eurythermal and moderately euryhaline. Comparison of five additional Narragansett Bay isolates of T. rotula reveal minimal spacial or temporal variability in genetically determined physiological characteristics within this local population.     

Carbon and nitrogen dynamics during growth and degradation of phytoplankton under natural surface irradiance

Under conditions of natural irradiance, the development and decline of a flagellate-dominated phytoplankton population was followed in a coastal North Atlantic pond over a 3 d period in summer 1986. Irradiance negatively affected phytoplankton biomass estimated as chlorophyll a, which decreased during the day at photosynthetically available radiation (PAR) levels above 600 to 1000 mol m^-2s^-1; chlorophyll a increased at PAR values below this threshold. In addition, an inverse relationship was found between changes in chlorophyll a and changes in dissolved inorganic nitrogen, indicating synthesis of nitrogenous biomass mainly at night and degradation mainly during the day, with intense exchanges of material between the particulate and dissolved nitrogen fractions. The natural abundance of ¹³C in particulate matter increased initially, and then remained constant, and was controlled mainly by the ratio -carboxylases activity: ribulose biphosphate carboxylase activity. The hypothesis that the latter enzyme is broken down under high irradiance and is partly responsible for increases in external dissolved nitrogen was rejected.     

Reproductive strategy of<Emphasis Type="Italic"> Calanoides carinatus</Emphasis> and<Emphasis Type="Italic"> Calanus helgolandicus</Emphasis> during a summer upwelling event off NW Spain

Reproductive activity and production of the calanoid copepods Calanus helgolandicus and Calanoides carinatus were measured during a summer upwelling event off the coast of NW Spain. The upwelling pattern affected the distribution and fecundity of both species in the study area. The demographic composition of both populations and the stage of gonad maturation (e.g. the high abundance of fertilised females with mature ova) indicated active reproduction. C. carinatus, a highly fecund species associated with the African upwelling zones and considered as an upwelling specialist, showed low production rates (overall means of 15 eggs female^–1 day^–1 and 3% body C day^–1), despite the fact that the food conditions (high phytoplankton biomass dominated by diatoms) seemed to be optimal for this species. By contrast, C. helgolandicus, a temperate species that shows a strong link between spring phytoplankton blooms and reproduction time, seems to be flexible enough to take full advantage of shorter-term, enhanced feeding conditions associated with the pulsed nature of the summer coastal upwelling. Both the egg and carbon-specific production rates attained by this species (overall means of 26 eggs female^–1 day^–1 and 12% body C day^–1) were similar to values reported for a spring bloom situation. This high production would imply a long spring–summer recruitment event of C. helgolandicus in these waters. For both species the stage of gonad maturation was significantly correlated with their egg production rates and likely influenced by the food conditions; a species-specific nutritional requirement for final oogenesis is suggested. The carbon condition factor (carbon weight/prosome volume) of C. carinatus females was higher than that of C. helgolandicus, suggesting differential use of the carbon ingested; C. helgolandicus seems to use all ingested carbon to produce eggs at a high rates, whereas C. carinatus seems to store part of the ingested carbon as lipid reserves to ensure female survival and to support production during subsequent unfavourable food conditions.Communicated by S.A. Poulet, Roscoff     

Nutrient regeneration by zooplankton during a red tide off Peru,with notes on biomass and species composition of zooplankton

During March and April 1976, a red tide, dominated by the dinoflagellate Gymnodinium splendens Lebour, developed in the vicinity of 15°06'S and 75°31'W off Peru. At the height of the bloom, the euphotic zone was 6 m deep and the chlorophyll a at the surface was 48 g l^-1. A daily collection of zooplankton at 09.00 hrs showed large fluctuations of biomass, from 0.2 to 3.84 g dry weight m^-2 in a water column of 120m. Copepodids and nauplii dominated the collections. During a period of reduced wind, the adult copepods were a mixture of the species characteristic of the coastal upwelling system and the neritic species associated with more northerly, tropical waters. Nitrogen regeneration by the zooplankton varied with the development of the bloom, the type of zooplankton dominating the experiment, and biomass fluctuations, but never accounted for more than 25% of the nitrogen uptake by phytoplankton.     

The composition and biosynthesis of lipids in Thysanoessa raschi from the Clyde Estuary,Scotland

The lipid composition and biosynthesising activity of Thysanoessa raschi collected from the Clyde Estuary, Scotland, in May 1981 were examined. Triacylglycerols were the major lipid class present, although 16.7% of the total lipid were wax esters in which phytol was the dominant fatty alcohol. The thoracic contents (hepatopancreas) of the krill were capable of biosynthesising lipids in vitro from various labelled substrates. Radioactivity from [1-¹⁴C] palmitic acid was incorporated into lipids in the order phospholipids>triacylglycerols>wax esters; the bulk of the radioactivity was present in all cases in the fatty acyl moieties of the lipids. [U-¹⁴C] glucose labelled lipids in the order phospholipids>triacylglycerols>free fatty acids> was esters; in the first two lipids the radioactivity was mainly in the glycerol moieties, whereas in was esters it was solely in the fatty acyl moieties. The extent of labelling of these lipids from [U-¹⁴C] alanine was less than that from [U-¹⁴C] glucose, but the pattern of labelling was generally similar. More than 90% of the radioactivity incorporated into total lipid from ³H₂O was present in free fatty acids from which it was calculated that the hepatopancreas of T. raschi can synthesise 2.5 g of fatty acid per hour at 15°C. This value is approximately three times lower than that previously determined for T. inermis from Balsfjorden, northern Norway. The results are discussed in terms of the sources of the dietary lipids of krill and the role of endogenous biosynthesis in contributing to its lipid reserves.     

Zooplankton of tikehau atoll (Tuamotu archipelago) and its relationship to particulate matter

The standing stock and taxonomic composition of zooplankton (>200 m) were monitored in the lagoon of Tikehau atoll from April 1985 to April 1986. These data were supplemented by two 10 d studies on the variability, structure and functioning of the pelagic ecosystem. The biomass of animals >200 m comprised 50% of the total biomass of all organisms from 35 to >2000 m. The zooplankton populations were characterized by successive blooms of copepods, larvaceans, pteropods and salps, probably arising from the periodic input of detritus from the reef during windy periods. As a result, the ecosystem was not in a steady state and the data for the fluxes of organic matter are presented separately for April 1985 and April 1986. Using the C:N:P ratio method, net growth efficiencies, K ₂, were calculated for total mesozooplankton, mixed copepods, and two planktonic species, Undinula vulgaris and Thalia democratica. Combined with nitrogen and phosphorus excretion rates, these K ₂ values enabled the assessment of production rates. On a 24 h basis, P:B ratios (%) were close to 100 for the total zooplankton and 54, 34 and 800 for mixed copepods, U. vulgaris and T. democratica, respectively. These ratios are 5.7 times lower than that recorded for phytoplankton. High productivity may be ascribable to the high density of seston, the high temperature (29.5°C), and the kind of organisms present. Zooplankton production equalled 38 and 30% of ¹⁴C uptake during April 1985 and April 1986, respectively. Ingestion of animals >35m was calculated by means of assimilation efficiencies and amounted to 17 and 7% of particulate organic carbon, 100 and 38% of living carbon, and 64 and 140% of primary production during the two periods, respectively. Finally, inorganic exduring was 32 and 18% of phytoplankton nitrogen and phosphorus requirements. A model based on the dimensional structure of the pelagic food-web, has been drawn to illustrate the biomass and carbon, nitrogen and phosphorus fluxes in the study area. The lagoon appears to export part of its planktonic biomass, which is 4.2 times lower one sea mile outside the main pass connecting the lagoon to the open ocean.     

Environmental information stored in otoliths: insights from stable isotopes

The present study compares the stable oxygen-and carbon-isotope ratios (¹⁸0:¹⁶O;¹³C:¹²C) in the otoliths of Atlantic cod,Gadus morhua, with those expected at equilibrium with seawater. Otoliths from juveniles reared for a 3 mo period under controlled conditions indicate that otoliths are formed in isotopic disequilibrium with seawater. This is probably due to positive metabolic fractionating of the heavier isotopes. This vital effect remains constant over the temperature range studied here (9 to 16°C) but may differ among other species. Our data indicate that the concentration of¹⁸O in calcium carbonate is inversely related to temperature and is described as ¹⁸O_a – _w – 3.79 – 0.200(T°C). The¹³C:¹²C ratios of otoliths and body tissues are related to the carbon ratio in the food source, although we found that the¹³C concentration is considerably higher in the otoliths relative te, the body tissues and the diet.     

Temporal variability in zooplankton prey capture rate of the passive suspension feeder<Emphasis Type="Italic"> Leptogorgia sarmentosa</Emphasis> (Cnidaria: Octocorallia), a case study

There is increasing evidence that suspension feeders play a significant role in plankton–benthos coupling. However, to date, active suspension feeders have been the main focus of research, while passive suspension feeders have received less attention. To increase our understanding of energy fluxes in temperate marine ecosystems, we have examined the temporal variability in zooplankton prey capture of the ubiquitous Mediterranean gorgonian Leptogorgia sarmentosa. Prey capture was assessed on the basis of gut content from colonies collected every 2 weeks over a year. The digestion time of zooplankton prey was examined over the temperature range of the species at the study site. The main prey items captured were small (80–200 µm), low-motile zooplankton (i.e. eggs and invertebrate larvae). The digestion time of zooplankton prey increased when temperature decreased (about 150% from 21°C to 13°C; 15 h at 13°C, 9 h at 17°C, and 6 h at 21°C), a pattern which has not previously been documented in anthozoans. Zooplankton capture rate (prey polyp^–1 h^–1) varied among seasons, with the greatest rates observed in spring (0.16±0.02 prey polyp^–1 h^–1). Ingestion rate in terms of biomass (g C polyp^–1 h^–1) showed a similar trend, but the differences among the seasons were attenuated by seasonal differences in prey size. Therefore, ingestion rate did not significantly vary over the annual cycle and averaged 0.019±0.002 g C polyp^–1 h^–1. At the estimated ingestion rates, the population of L. sarmentosa removed between 2.3 and 16.8 mg C m^–2 day^–1 from the adjacent water column. This observation indicates that predation by macroinvertebrates on seston should be considered in energy transfer processes in littoral areas, since even species with a low abundance may have a detectable impact.Communicated by S.A. Poulet, Roscoff     

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.     

Untersuchungen über die heterotrophe Aktivität in der zentralen Ostsee

The distribution of some microbial parameters was studied at 3 stations in the Central Baltic Sea (Bornholm Basin, BB; Danzig Deep, DD; and Gotland Deep, GD) during May 1976. The following analyses were performed: total bacterial numbers and biomass, viable counts and maximum uptake velocity (V _max) of glucose. The values found for thesurface, samples were, total bacterial counts: 0.6x10⁶ (BB); 1.7x10⁶ (DD); 0.4x10⁶ (GD) cells/ml; bacterial biomass: 1.9 g C/l (BB); 6.9 g C/l (DD); 1.6 g C/l (GD); viable counts: 0.37x10³ (BB); 17x10³ (DD); 0.4x10³ (GD) counts/ml; V _max: 0.01 g glucose-C/l (BB), 0.06 g glucose-C/l (DD); 0.01 g glucose-C/l (GD). The relatively high microbial numbers and activities of the Danzig Deep may be associated with the fertilization of the area by the River Vistula. The vertical distribution of the microbial parameters in the Bornholm Basin and Danzig Deep showed high values both in the top layer (0 to 20 m) and in the deep layer (>40 m). In the intermediate layer, however, the values decreased significantly. It is suggested that the high values of the microbial parameters at depth are caused by at least two major processes during the inflow of North Sea water into the deep layers of the Baltic Sea: (1) the North Sea water may already have contained high numbers of bacteria; (2) during the inflow, the high concentrations of bacteria normally located at the sediment-water interface are distributed throughout the whole deep layer by mixing.

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Beitrag Nr. 143 aus dem Sonderforschungsbereich 95 Wechselwirkung Meer-Meeresboden, Universität Kiel.     

Seasonal composition of meroplankton and holoplankton in the Bristol Channel

A decreasing gradation in the plankton standing stock of the Bristol Channel was observed from the seaward section to the inner, less saline, reaches. Two sub-regions of our survey, the North Outer Channel (NOC) and the Inner Channel (IC), represented the extremes of this gradient and were selected for detailed comparison. The integrated zooplankton biomass, over the 307 d sampling period (4 November 1973 to 6 September 1974), was 2 475 mg C m^-3 (266 mg C m^-2 d^-1) in the NOC and 335 mg C m^-3 (20 mg C m^-2 d^-1) in the IC. The omnivorous plankton accounted for 76% of the standing stock in the NOC and 89% in the IC, of which 58 and 23% were meroplankton and 39 and 71% were holoplankton, respectively; the remainder was unassigned. The majority of the meroplankton in both subregions was decapod larvae and adults, whereas the holoplankton biomass was dominated in the NOC by copepods (89%) and in the IC by mysids (57%), mainly Schistomyzis spiritus. Centropages hamatus was the most abundant copepod species in the NOC and accounted for 32% of the total holoplankton omnivore standing stock. In the NOC and IC, the carnivorous plankton accounted for 24 and 11% of the total plankton biomass, respectively. In the two sub-regions, 20 and 21% of the carnivores were meroplanktonic (primarily larvae of sprats and pilchards), while the holoplankton carnivores contributed 75 and 74% to the NOC and IC, respectively (Sagitta elegans, Pleurobrachia pileus). S. elegans dominated the holoplankton carnivore biomass for the majority of the year and accounted for 96% in the NOC and 60% in the IC. The integrated total particulate carbon over the 307 d period was 200 g C m^-3 (6 600 g C m^-2) in the NOC and 838 g C m^-3 (15 084 g C m^-2) in the IC. The annual primary production ranged from 164.9 g C m^-2 yr^-1 in the Outer Channel (North and South) to 6.8 g C m^-2 yr^-1 in the IC. The zooplankton biomass reached a maximum in July. The total particulate carbon (TPC) in July was 400 mg C m^-3 in the NOC of which ca. 78 mg C m^-3 were phytoplankton and ca. 21 mg C m^-3 were zooplankton; these values compare favourably with those found in the adjoining Celtic Sea. In the IC, the TPC was 2 800 mg C m^-3, of which ca. 107 mg C m^-3 were phytoplankton and 2.8 mg C m^-3 were zooplankton. From the low primary production estimates for the IC it can be concluded that the majority of the chlorophyll, like the TPC, was allochthonous in origin. Furthermore it is suggested that zooplankton plays a minor role in this estuarine ecosystem and is not the main consumer of the suspended particulate carbon; the benthic filter-feeding communities are presumed to fulfill this role in the Bristol Channel.     

Light and temperature requirements for growth and reproduction in gametophytes of Ecklonia maxima (Alariaceae: Laminariales)

The morphological and reproductive development of gametophytes of Ecklonia maxima (Osbeck) Papenf. has been studied in vitro under a wide range of light and temperature conditions, and the results related to the natural environment over the range of the distribution of the species. Initial vegetative growth was light saturated at 20 E m^-2 s^-1, and maximal at 17.5° and 20°C. Most rapid egg production corresponded to low cell number of female gametophytes, and this process was light saturated at 60 E m^-2 s^-1, and optimised at 15° and 17.5°C. Cell number was also low at lower temperatures, with reduced fertility rates. Sub-saturating irradiances and supraoptimal temperatures caused females to become filamentous, producing many more cells, and reducing reproductive rates. The final egg production per female was, however, greater in these sub-optimal conditions, and this phenomenon is interpreted as an ecological adaptation which improves survival prospects in conditions prevailing at the fringes of the depth and geographical distribution of the species. The optimal, and maximum (22.5°C) temperatures for reproduction are far higher than those of northern hemisphere Laminarians. E. maxima is very much a warm temperate organism, and this could have implications for marine phytogeographical studies on the west coast of southern Africa.     

Seasonal changes of benthic bacteria in a seagrass bed (Posidonia oceanica) of the Ligurian Sea in relation to origin,composition and fate of the sediment organic matter

Variations in number and biomass of benthic bacteria were examined in the surface sediments of a Mediterranean seagrass bed [Posidonia oceanica (L.) Delile] in the Gulf of Marconi (northwestern Mediterranean Sea) from 1990 to 1991. The annual dynamics of benthic bacterial density and biomass were compared to changes in elemental (organic C and total N) and biochemical (lipids, proteins, carbohydrates) composition of sediment organic matter, as well as to microphytobenthic biomass, dissolved inorganic nutrients and ATP. Bacterial densities exhibited marked seasonal variations (5.12 to 322.7x10⁸ cells g^-1 sediment dry wt) with highest values in late spring. Bacterial standing stocks (15.8 to 882.33 g C g^-1 of sediment dry wt) were high. Bacterial biomass did not correlate with organic C, total N or to specific biochemical components, but correlated significantly with chlorophyll a, ATP and porewater phosphate concentrations. There is evidence that benthic bacteria were responding to variations of algal biomass. Bacterial biomass accounted, on average, for 30% of total living carbon (calculated on the basis of the ATP concentrations) and 8.4% of total organic carbon.     

Spatial mesoscale patterns of West Pacific picophytoplankton as analyzed by flow cytometry: their contribution to subsurface chlorophyll maxima

Vertical distributions of picophytoplankton (ppp) (<2 m) were studied by ship-board flow cytometry during two cruises in Western Pacific waters to Palau and to Australia in 1990. Weak red-fluorescing small ppp, supposed to be free-living prochlorophytes (Chisholm et al. 1988), were abundant in the area surveyed. These ppp, designated the prochlorophytes, were abundant in the surface waters (>10⁴ cells ml^-1) at the northern region (27°03N; 7°11N) in November, whereas in December at the southern tropical stations (0°23.54S; 9°20.30S; 13°50.6S), they formed subsurface maximum layers (>10⁵ cells ml^-1) on a nitracline at a depth of 3.5 to 5.4% surface irradiation. Their fluorescence intensity increased with depth below 10% surface irradiation. The prochlorophytes at a depth of 1% surface irradiation had ten times higher fluorescence than those at the surface layer. The total fluorescence intensity of the prochlorophytes accounted for 32 to 63% of the sum of the total fluorescence intensity of all fluorescing phytoplankton detected at subsurface chlorophyll maxima in the tropical area. These results suggest that distribution of the prochlorophytes is greatly affected by nitracline and by light intensity and that their chlorophyll is a major contributor to the subsurface chlorophyll maximum in the pelagic West Pacific Ocean.     

Grazing rates of the copepods Calanus glacialis and C. finmarchicus in arctic waters of the Barents Sea

Natural feeding rates of Copepodite Stages IV and V, and adult female Calanus glacialis (Jaschnov) and Copepodite Stage V and adult female C. finmarchicus (Gunnerus) were estimated using fluorescence analysis of gut contents. Measurements were made on copepods sampled from arctic waters east of Svalbard (Barents Sea) during the spring phytoplankton increase, in the period from 27 May to 13 June, 1983. Observations on Copepodite Stages IV and V and adult female C. glacialis suggest that the gastric evacuation rate is independent of developmental stage, whereas C. finmarchicus Copepodite Stage V showed a lower gastric evacuation rate than adult females. Gut fullness displayed a low correlation with the ambient chlorophyll concentrations. Ingestion rates calculated for C. glacialis were 0.3, 2.3, and 11.0 g C h^-1 for Copepodite Stages IV and V and adult females, respectively. Copepodite Stage V and adult female C. finmarchicus ingested 0.9 and 1.1 g C h^-1 at a temperature of ca.-1.0°C. The maximum ingestion rate in terms of percent body carbon d^-1 was higher for adult female C. glacialis and C. finmarchicus than for the respective Copepodite Stage V's. The results are discussed both in relation to the physiological state of the species and to the environmental conditions.     

Mechanisms of production and fate of organic phosphorus in the northern Adriatic Sea

In the period from 1980 to 1984 organic phosphorus, nutrients, primary production rates (¹⁴C), chlorophyll a (chl a) standing crops, and basic oceanographic parameters were measured during 23 cruises at six stations in the open waters of the northern Adriatic Sea. These waters are significantly influenced by polluted Po River discharge. Organic phosphorus was correlated with several parameters which characterize phytoplankton activity and organic matter decomposition processes. In the late winter-spring period, organic phosphorus is produced during phytoplankton blooms. It is hypothesized that microzooplankton grazing is the main factor increasing the organic phosphorus concentrations in summer (up to 1.1 mol 1^-1). Fall and winter had much lower values (below 0.3 mol 1^-1) due to remineralization processes and an increased water mass exchange between the northern and central Adriatic regions. The direct contribution of organic phosphorus by freshwater discharge was not found to be significant. The higher organic phosphorus concentrations that can occur in low salinity waters are most likely due to their increased capability to support primary production.     

A survey of environmental features in a section of the Vellar-Coleroon estuarine system,south India

A survey was conducted on 15th November, 1970, in mangrove forests and backwater regions of a section of the Vellar-Coleroon estuarine complex; a total of 19 stations were occupied. Detailed investigations on nutrients, pigments, and plankton were carried out. The following ranges in values were recorded: salinity, 10.40 to 30.50; pH, 7.50 to 8.30; temperature, 29.50° to 30.50°C; total phosphorus, 0.72 to 3.34 g at/l; inorganic phosphate, 0.19 to 1.59 g at/l; ammonia, 0.34 to 0.36 g at/l; nitrite, 0.11 to 0.25 g at/l; nitrate, 2.85 to 6.94 g at/l; silicate, 18.49 to 134.92 g at/l. Dissolved oxygen content ranged from a minimum of 3.69 ml to a maximum of 5.44 ml/l. Chlorophyll a ranged from an undetectable amount to 1.01 mg/m³, chlorophyll b from 0.02 to 0.85 mg/m³, chlorophyll c from 0 to 0.41 mg/m³ and carotenoids from 0 to 0.74 MSPU/m³. The plankton displacement volume ranged from a negligible amount to 3.60 cm³/m³; seston varied between 0.29 and 0.91 g/l. Phytoplankton was abundant at 3 stations; at other stations zooplankton was abundant. Coscinodiscus, Asterionella and Ditylum were the dominant forms among the phytoplankton; Oithona, Acrocaanus, Euterpina, Centropages, Corycaeus, Lucifer and Oikocreura were dominant among the zooplankton. Phytoplankton and zooplankton populations, as percentage of the total plankton, varied between 3.70 and 89.00% and between 11 and 96.30%, respectively. Average gross production values in the mangrove and back-water stations were 7.56 and 3.33 g C/m³/day, and the net production values 6.29 and 2.67 g C/m³/day, respectively.