Deep chlorophyll maximum distribution in the central Tyrrhenian Sea described by a towed undulating vehicle

The towed undulating vehicle (TUV), named SARAGO, was used for two fine-scale surveys between the Italian and the Sardinian coasts during the Astraea 2 cruise (6-7 and 26-27 September 1995), studying the deep chlorophyll maximum distribution. SARAGO sections identify a sub-surface doming with higher chlorophyll a and primary production concentrations in the upwelling area of a cyclonic gyre region, detected by sea-surface temperature images. In the first section, the cyclone presents a double doming, in density and salinity, with shallower and concentrated patches of chlorophyll a for about 2 miles. Twenty days later, the second section shows that the gyre changes shape and extension, showing a single doming with higher primary production and chlorophyll a concentrations, distributed over a large area of about 40 nautical miles. SARAGO allows analysis of this high-variability phenomenon (cyclonic gyre) and allows concentrated patches (2 nm) to be identified, thus proving the importance of TUVs in the study of mesoscale processes.     

Relationships between nucleic acid concentrations and primary production in the Catalan Sea (Northwestern Mediterranean)

We explored the relationships between classical estimators of autotrophic biomass and primary production, such as chlorophyll a concentration and ¹⁴C-fixation rates, and biochemical indices based on DNA and RNA determinations, which have been proposed as indicators of physiological state in natural plankton populations. The measurements were made during two cruises across the Catalan Front, carried out in May 1989 and February 1990, corresponding respectively, to periods of stratification and moderate mixing. DNA and RNA concentrations (measured by a double-staining fluorimetric technique) were significantly correlated with chlorophyll a in February 1990, but not in May 1989, when a marked deep chlorophyll maximum was present. Significant positive correlations between RNA concentration and primary production and between RNA: DNA and primary production were found during both surveys, probably reflecting both higher RNA concentrations per cell and enhanced bacterial and microheterotrophic growth in high primary production situations. The results support the potential usefulness, in biological oceanography, of biochemical indicators based on DNA and RNA concentrations.     

The distribution of primary production relative to a cyclonic gyre in Baie des Chaleurs

Primary production within the Baie des Chaleurs, Canada, is dominated by a cyclonic gyre system. The pattern of production fits the theoretical expectation of increased productivity associated with colder, nutrient-rich water being brought closer to the surface within the gyre. Upper reaches of the bay, west of the gyre, follow a normal esturine form of circulation with lower rates of production. East of the gyre, in the Gulf of St. Lawrence, primary production is less.Travaux sur les Pêcheries du Québec, no. 30, Direction des Pêcheries, Ministère de l'Industrie et du Commerce du Québec.     

Profiles of photosynthetic pigments in the ocean using thin-layer chromatography

Phytoplankton pigments at a coastal station off Sydney, Australia, were studied by cellulose thinlayer chromatography. The chromatographic procedure distinguished chlorophylls a, b and c, chlorophyllide a, pheophytin a and pheophorbide a, and the major carotenoids carotene, astaxanthin, fucoxanthin, peridinin, diadinoxanthin and neoxanthin. Chlorophyllide a and pheophorbide a were the most significant chlorophyll-a degradation products in the water column, chlorophyllide a coming from chlorophyllase activity of senescent diatoms, and pheophorbide a from faecal pellets of copepods. Chlorophyll c occurred in every sample, even where there was no trace of chlorophyll a. Because of the greater chemical and biological stability of chlorophyll c compared to chlorophyll a, high chlorophyll c:a ratios result from a large proportion of senescent or detrital material in the samples. Determining the position of patches of copepods, diatoms, green algae and dinoflagellates in the water column was easily done by noting the presence of definitive pigments on the chromatograms.     

Aspects of water column primary productivity in the Chukchi Sea during summer

Measurements of primary productivity, chlorophyll a, incident solar radiation, phosphate-P, silicate-Si, nitrate-N, nitrite-N, ammonium-N, temperature and salinity were made in the Marginal Ice Zone of the Chukchi Sea in summer 1974. Low to moderate levels of primary productivity (0.07 to 0.97 g C m^-2 half-day^-1) were observed; primary productivity exceeded 3 g C m^-2 half-day^-1 at two stations. Surface primary productivity was nitrogen-limited at most stations. Mean chlorophyll a concentration in the photic zone varied from 0.4 to 17.8 mg m^-3. Higher concentrations and significant subsurface accumulation of chlorophyll a, reaching 40 mg m^-3, were observed in July at stations near the ice-edge than those in open water. No chlorophyll maximum was noted in September, when values ranged from 0.4 to 2.2 mg m^-3. It is postulated that the contribution of sea-ice algae to the total chlorophyll content can be substantial, but that the stay of these cells in the water column may not be long. Non-linear regression estimates from solar radiation and chlorophyll-specific primary productivity data showed a maximal photosynthetic rate of 18 mg C mg chlorophyll a ^-1 half-day^-1, an optimal light intensity of 54 langleys half-day^-1, and markedly reduced primary productivity at moderately higher light intensities. These features indicate that phytoplankton was shade-adapted.     

The effects of ammonium and phosphate enrichments on clorophyll a,pigment ratio and species composition of phytoplankton of Vineyard Sound

Seawater containing natural phytoplankton populations from Vineyard Sound, USA was enriched in the laboratory with three levels each of ammonium and phosphate and with a combination of ammonium and phosphate which provided three different N:P ratios. The addition of ammonium produced more cells and chlorophyll a than the control or the phosphate enrichments. However, enrichment with ammonium and phosphate, regardless of the N:P ratio, yielded the most cells and chlorophyll a. Thus, nitrogen seems to be the primary limiting nutrient, with phosphate showing secondary limiting effects. The ratios of photosynthetic pigments decreased with the increased chlorophyll a production in the enriched cultures. There were no significant changes in the species composition within the cultures, so that the observed changes in pigment ratio and chlorophyll a content were due to physiological responses.     

Biomass and production in polar planktonic and sea ice microbial communities: a comparative study

Algal and bacterial biomass and production were measured in the plankton, platelet ice and congelation ice communities at one station in McMurdo Sound, Antarctica during September and October 1986. Bacterial abundances and particulate organic carbon and nitrogen were 10 to 100 times greater in the plankton than in the sea ice, whereas the chlorophyll a concentrations in the plankton and sea ice microbial communities (SIMCO) were similar Rates of both light-limited and light-saturated photosynthesis and daily primary production were 2 to 6 times greater in the plankton than in the SIMCO. Bacterial growth rates ranges from 0.7 to 1.5 d^-1 in all three communities; however, because of the greater bacterial biomass in the plankton, bacterial production was 15 to 20 times higher there than in the SIMCO. These results suggest that during the early austral spring, planktonic production contributes significantly to total production in ice-covered environments.     

UV absorption by mycosporine-like amino acids in Phaeocystis antarctica Karsten induced by photosynthetically available radiation

Mycosporine-like amino acids (MAAs), which occur in diverse taxonomic groups, exhibit in vivo absorption maxima between 310 nm and 360 nm and may play a photoprotective role against ultraviolet (UV) exposure. Using cultures of colonial Phaeocystis antarctica, we examined the relationship between MAA concentration, in vivo UV absorption, photoprotective (carotenoid) and photosynthetic pigments, and photosynthetically available radiation (PAR, 350–700 nm). UV absorption was high; chlorophyll-specific absorption, a ^* _ph, at 330 nm ranged from 0.06 to 0.41 m²/mg chlorophyll a. Values of a ^* _ph (330) were 4–13 times greater than a ^* _ph (676). Mycosporine-glycine, shinorine, and mycosporine-glycine valine are responsible for the strong in vivo UV absorption. The sum of all MAAs increased with irradiance when normalized to chlorophyll a or carbon concentrations, whereas individual MAAs varied independently from each other. Mycosporine-glycine concentrations showed no statistically significant change over the range of light intensities, whereas mycosporine-glycine and shinorine concentrations increased at higher irradiances. The relative fluorescence yield for chlorophyll a was low in the UV region compared to the visible region, implying that absorbed UV radiation (<375 nm) is transferred inefficiently to chlorophyll a in the reaction center. Quantitative estimates of UV screening by MAAs are attributed to elevated MAA concentrations and increased diameter at high light. Received: 31 March 1999 / Accepted: 13 July 2000     

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.     

Phytoplankton photosynthetic activity and growth rates in the NW Adriatic Sea

Taxonomic composition, biomass, primary production and growth rates of the phytoplankton community were studied in two stations in the NW Adriatic Sea on a seasonal basis, in areas characterized by differing hydrological and trophic conditions. The main differences between the two stations were quantitative rather than qualitative, most phytoplankton species being common to both stations. The effects of differing nutrient concentrations and plume spreading were evident. Biomass and primary production rates were significantly higher in the coastal station (S1), and the phytoplankton distribution in the water column was markedly stratified in S1 and more even in the offshore station (S3). However, chlorophyll a specific production, potential growth rate and production efficiencies were very similar in both stations, even when phosphorus concentrations were limiting. A discrepancy between potential and actual growth rate was observed: as a feature common to both stations, comparisons between potential and actual growth rates revealed that little carbon produced by phytoplankton accumulated as algal biomass; therefore, very high loss rates were estimated.     

Sea-water seasonal changes at a heavy tourism investment site on the Jordanian northern coast of the Gulf of Aqaba,Red Sea

The Gulf of Aqaba exhibits a strong seasonality due to convective mixing during winter and stratification during summer. The present study provides a detailed appraisal of summer and winter sea-water characteristics at the northern coast of the Gulf of Aqaba, that is witnessing rapid development and increasing changes in its geomorphological characteristics. Sea-water temperature, salinity, nutrients, and chlorophyll a concentrations were measured biweekly at five coastal and four cross-sectional stations during the periods February to April and July to September 2004. Meteorological conditions were continuously recorded at the Marine Science Station. The coastal study sites included four open coastal stations and a marina with one-way exchange with the open water. The effect of convective mixing was clearly apparent on the sea-water characteristics. Natural seasonal characteristics of higher nutrients and chlorophyll a concentrations were recorded during winter at most of the open coastal stations. In the cross-sectional stations, the concentrations of nutrients and chlorophyll a were not different between the surface and the bottom during winter, but the bottom waters had generally higher concentrations during summer. Some deviations from the natural seasonal cycle were recorded at the marina and other coastal stations. Here, higher nutrient and chlorophyll a concentrations were recorded in summer than in winter. These deviations that are most likely due to anthropogenic effects are discussed.     

Plankton community dynamics of the central Great Barrier Reef Lagoon: Analysis of data from Ikeda et al.

Plankton data collected by Ikeda et al. (1980) from the central region of the Great Barrier Reef, and spanning two years (1976 through 1978) of zooplankton records, have been analyzed extensively for spatial and temporal patterns. Estimates of net zooplankton (including chaetognaths, copepods, and larvaceans) and microzooplankton (juvenile copepods, encompassing nauplii and copepodites, and ciliates) were assessed at three stations across the 60 km lagoon. Temperature, salinity, and chlorophyll a were also measured. A cross-lagoonal gradient was identified in the plankton, concurring with results of related surveys of benthic taxa, such as scleractinian corals, soft corals, macro-algae, fish, sponges, crinoids, etc. Two associations of net zooplankton were identified. The first was associated primarily with the inner lagoon; the second with the outer lagoon. The inshore association was characterized by higher abundances of almost all net zooplankton taxa, particularly chaetognaths, copepods, polychaetes, decapods, and meroplanktonic larvae as well as higher concentrations of chlorophyll a. This inshore association wove back and forth across the lagoon through time, dominating the lagoon entirely during periods of high river discharge, reaching the mid-shelf platform reefs in this region, and sometimes being entirely absent during dry periods. Both seasonal and annual peaks in plankton abundance were generally linked with degree of runoff. Summer/autumn peaks of abundance were evident in chaetognaths, copepods, and larvaceans while annual variation was detected in the former two as well as in chlorophyll a concentrations. Depth stratification was noted in juvenile copepods and chlorophyll a concentrations at the center of the lagoon, with higher abundances recorded in deeper waters. The central Great Barrier Reef lagoon was found to be typical of other tropical coastal waters where plankton community dynamics are controlled primarily by physical factors. We suggest that any substantial changes in river discharge in this area will affect plankton production.A.I.M.S. Contribution No. 242     

Seasonal variations in microzooplankton grazing in the region of the Subtropical Convergence

Microzooplankton grazing and community structure were investigated in the region of the Subtropical Convergence (STC) during three cruises of the South African Antarctic Marine Ecosystem Study (SAAMES) in austral summer (January/February 1993; December 1994/January 1995) and winter (June/July 1993). Chlorophyll a concentrations were consistently dominated by the <20 m size fraction during all three cruises, while the contribution of the microphytoplankton (>20 m) to total chlorophyll a concentrations varied considerably between cruises. Microzooplankton communities were numerically dominated by protozoans comprising ciliates (aloricates and tintinnids) and dinoflagellates. Instantaneous growth coefficients of phytoplankton in the vicinity of the STC showed no seasonal trends. However, marked seasonal differences were observed in the size structure of the phytoplankton. The grazing impact of microzooplankton was highest when the <20 m chlorophyll fraction contributed >95% of the total. Under these conditions, the instantaneous grazing rates ranged between 0.15 and 0.66 d^-1. These correspond to daily losses of 14 to 48% of the inntial standing stock and between 45 and 81% of the potential primary production. At stations where microphytoplankton contributed significantly (-20%) to total chlorophyll concentrations, the grazing coefficients were lower, ranging between 0 and 0.53 d^-1. This corresponds to a loss of <41% of the initial standing stock, or between 0 and 56% of the potential production. Our data suggest that microzooplankton represent the main grazing sink for production when the <20 m chlorophyll size-class dominates total chlorophyll. These facts suggest that the efficiency of the biological pump may vary over time.     

Primary production of sands in the lagoon of an atoll and the role of foraminiferan symbionts

Chlorophyll content and in situ oxygen production of sands were measured in the lagoon of Takapoto Atoll, Tuamotu Islands (French Polynesia). Stations were spaced from a depth of 17 m to the water limit on the beach. Photosynthetic pigments and net primary production for the top 3 cm of sediment ranged from 56 to 907 mg chlorophyll a m^-2 and from 115 to 354 mg O₂ m^-2 h^-1, respectively. Responsible organisms were mostly Foraminifera, among which Amphistegina lessoni, containing unicellular symbionts, dominated. The sands are thus significant contributors to the lagoon's primary production, while the role of phytoplankton is comparatively negligible.     

The trophic role of glycolic acid in coastal seawater. II. Seasonal changes in concentration and heterotrophic use in Ipswich Bay,Massachusetts, USA

Glycolic acid is a known algal excretory product which is found in marine waters and is readily metabolized by marine bacteria. The following parameters were measured over the course of a year in Ipswich Bay: chlorophyll a, temperature, viable bacteria, heterotrophic uptake of glycolate, and glycolate concentrations. The latter two were combined to give estimates of the flux of glycolate for a station 3 km out in the bay and for an inshore station. Pronounced seasonal changes were found for all parameters. Statistically significant correlations between heterotrophic V _max and glycolic acid concentrations and temperature were found, but not between planktonic chlorophyll a and any of the other parameters. Measurements of glycolic acid flux yielded an annual flux of 2.84 g m^-2 for the bay station, which is about 0.5% of the bay phytoplankton production. Glycolic acid turns over roughly 12 times per year in the bay. It contributes perhaps as much to bacterial metabolism as any other single substrate, but is apparently not of dominating importance.     

Microphytobenthos of the Dogger Bank: a comparison between shallow and deep areas using phytopigment composition of the sediment

The surface sediment characteristics related to benthic microalgae primary production were studied at the Dogger Bank, North Sea, in order to evaluate the potential role of microphytobenthos as a food source for the macrobenthic fauna. Twenty-one stations were sampled in July 2001 and May 2002, with water depth ranging from 16.3 to 68.5 m. High-performance liquid chromatography pigment analyses revealed that concentrations of chlorophyll a, chlorophyll c and fucoxanthin are mainly associated with benthic diatom flora at most parts of the Dogger Bank. High percentage of phytopigments (>50%) was firmly attached to sand grains at the stations shallower than 40 m water depth. The deeper stations were characterized by a phytopigment composition originating from pelagic phytoplankton settled on the sea floor. Qualitative microscopy showed that the benthic microflora on top of the Bank mainly consists of small diatoms (5–10 μm), such as e.g., Diploneis spp., living attached to the sand grains. The results are discussed concerning possible implications for ecology and biogeochemistry of the Dogger Bank area.     

Effects of melatonin on cadmium accumulation in the accumulator plant Perilla frutescens

To enhance the phytoremediation ability of the heavy metal accumulator Perilla frutescens, melatonin (MT) was applied at different concentrations (0, 25, 50, 100, 150, and 200?μmol/L) to P. frutescens growing in cadmium (Cd) contaminated soil (10?mg/kg). The MT treatments increased the root and shoot biomasses of P. frutescens, with the maximum increase in the 150?μmol/L MT treatment (79.51% and 36.18% higher, respectively, than those of the control). The MT treatments also enhanced superoxide dismutase activity, peroxidase activity, and the soluble protein concentration of P. frutescens, and 100–200?μmol/L MT increased the chlorophyll a, chlorophyll b, and total chlorophyll concentrations in P. frutescens. The MT treatments increased the Cd concentrations in roots and shoots of P. frutescens in a dose-dependent manner. Different MT concentrations increased the Cd accumulation amounts of roots and shoots of P. frutescens, with the maxima accumulation amounts in the 150?μmol/L MT treatment (226.98% and 85.89% higher, respectively, than those of the control). These results show that MT can promote the growth and phytoremediation ability of P. frutescens growing in Cd-contaminated soil, and the optimum MT dose is 150?μmol/L.     

Diel changes in phytoplankton photosynthetic efficiency in Brackish waters

From 18 to 23 September 1974, investigations on the diel changes in phytoplankton were carried out in the Baltic Sea. Every 4 h, water samples were collected from 2 and 15 m, and PO₄, chlorophyll a, temperature, salinity, pH, phytoplankton composition and phytoplankton light photosynthesis relationship were determined. Continuous measurements of surface irradiance and some estimations of zooplankton were also made. P ^B (photosynthesis per unit chlorophyll a at low light levels of 2·10^-2 cal cm^-2 min^-1) revealed only random variation during the sampling period, i.e., 1.0 to 1.6 mg C (mg chlorophyll a)^-1 h^-1. P _m ^B (Light-saturated photosynthesis per unit of chlorophyll a) displayed pronounced diel fluctuations with the highest value of about 6 mg C (mg chlorophyll a)^-1 h^-1 around noon, and the lowest value of about 2.5 mg C (mg chlorophyll a)^-1 h^-1 during the night, during which latter period the value of P _m ^B was more or less constant. Reasons for the diel fluctuations are discussed, and an equation which describes these fluctuations is proposed. Using this equation, the daily phytoplankton production estimated in incubators by a previously described method can be corrected for the time of day at which samples are collected.     

Phytoplankton dynamics and species diversity in a shallow eutrophic,natural mid-altitude lake in Himachal Pradesh (India): role of physicochemical factors

Rewalsar Lake, a mid-altitude, shallow and recreational water body located in the north-western Himalayas, Himachal Pradesh (India) was studied through monthly surveys in two consecutive years (March 2008 to February 2010). Forty-seven species belonging to seven groups of phytoplankton were identified from the lake. Microcystis aeruginosa and Synedra ulna exhibited a perennial habit. Ankistrodesmus falcatus, Chlorella vulgaris, Scenedesmus bijugatus, Chlamydomonas reinhardi, Eudorina elegans, Navicula cuspidate, Synedra ulna, Euglena acus, Euglena oxyuris, Spirulina gomontii, Oscillatoria princeps and Arthrospira khannae were abundant, and Oscillatoria limosa and Microcystis aeruginosa were highly abundant. Twenty-one important criteria were studied, for example, temperature, free carbon dioxide, biochemical oxygen demand, total alkalinity, nitrate, silicate and phosphate, which provide an idea of the portability of water for irrigation and drinking purposes as per the permissible limits given in World Health Organization, Indian Council of Medical Research and Indian Standards Institute standards. Pearson's correlation revealed a significant relationship between physicochemical parameters and different algal groups. Both plankton and chlorophyll a showed a bimodal pattern of fluctuation. High annual mean concentrations of chlorophyll a (mg L^?1) were recorded as 11.44 in 2008–09, and 11.04 in 2009–10. As per the Palmer pollution index, 13 pollution-tolerant algal species with a pollution score of 37 were observed. The Central Pollution Control Board categorised the water at Rewalsar Lake as ‘D–E’.     

Differences in productivities between the Great Australian Bight and the Gulf of Carpentaria,Australia, in summer

Phytoplankton standing crop (chlorophyll a) and primary productivity were recorded, and zooplankton biomass was estimated in the two large bays of Australia, the Great Australian Bight on the south coast (December, 1965) and the Gulf of Carpentaria on the north coast (December, 1968). In the Gulf of Carpentaria, the phytoplankton standing crop (average, 27.3 mg chlorophyll a m^-2) and primary productivity (average, 133.1 mg C m^-2 h^-1), as well as zooplankton biomass (average, 305.3 mg wet weight m^-3) are much higher than in the Great Australian Bight (12.1 mg chlorophyll a m^-2, 18.2 mg C m^-2 h^-1, 7.1 mg wet weight m^-3, respectively). The unexpectedly low productivity values in the Great Australian Bight are attributable to environmental conditions of this bay, which obtains neither replenishment of nutrients from the land nor receives upwelling of deep water.