Serge Y. Maestrini

Ammonium thresholds for simultaneous uptake of ammonium and nitrate by oyster-pond algae

Abstract Natural microalgal populations and axenic algal isolates from oyster ponds have been grown either in situ or in controlled conditions, in the presence of ammonium and nitrate as nitrogen sources. Both ions were added at various concentrations, up to 50 μg-at. N·l −1 ; other nutrients were in excess. In one experiment, urea was also added. Uptake of nitrate was followed by measuring disappearance of nitrate from the medium, and by incorporation of 15 NO 3 ; nitrate reductase (NR) activity and the intracellular nitrate pool were also measured. The uptake of nitrate was prevented by the presence of ammonium above a concentration which varied according to species. The ammonium threshold (in units of μg-at. N·l −1 ) was ≈ 30 for natural populations and the diatom Navicula ostrearia Bory, ≈ 21 for Nitzschia ovalis (sensu Hustedt), and ≈ 44 for Amphora coffeaeformis (sensu Hendey). Nitrate uptake started at a rate which was ≈ 39% of the eventual maximum rate observed for the natural populations, and from 11 to 17% for cultured strains. The initial low rate was maintained until the ambient ammonium concentration had decreased to ≈ 7.5 μ g-at. N·l −1 , except for A. coffeaeformis which shifted from slow to fast nitrate uptake at 23.5μg-at. N·l −1 . The nitrate uptake system then operated at a slightly higher rate than the one for ammonium (ammonium uptake/nitrate uptake = 0.86). Cultures with an initial ammonium concentration lower than the threshold values did not show an initial low rate or a lag phase for uptake of nitrate. NR activity was detectable even in the presence of ≈ 30 μ g-at. NH 4 -N·l −1 in the external medium. When urea and nitrate were presented simultaneously, urea was not taken up preferentially, as reported elsewhere; uptake was initially at a reduced rate until the external nitrate concentration decreased to 3.7 μg-at. N·l −1 . Then the rate of urea uptake increased to a maximum. It is suggested that because oyster-pond algae have evolved in an environment where concentrations of ammonium, nitrate, and organic nitrogen are continuously high, the threshold of inhibition by ammonium of uptake of these compounds is much higher than for similar pelagic and neritic species, so that they are able to assimilate other sources of nitrogen, such as nitrate and urea, simultaneously with ammonium.

Study of bacteria associated with marine algae in culture

Seventy seven organic compounds have been tested for receptivity to attack by bacteria strains isolated from marine algae cultures. Bacteria utilize amino and organic acids more frequently than sugars and derivatives, especially when growth substances are not included in the experimental medium.

Are some bacteria toxic for marine algae

It was observed in vitro that some bacteria from different origins, including the sea, are capable of inhibiting the growth of several marine algae. However, there is too much difference between in vitro experiments and in situ environmental conditions to assume that bacterial poisons may rule a great deal of algac-bacteria relationships in the sea as a whole. In the authors opinion the importance of bacterial poison is limited to special and rare instances.

Nitrogenous nutrition of sea-ice microalgae

SummaryThere are indications that the final biomass attained by sea-ice microalgae in southeastern Hudson Bay is nitrogen limited. The present study investigates the possibility that the rate at which the final yield is approached is also nitrogen limited. Nutrient data suggest that nitrogen was actively taken up by the microalgae, and periodically replenished by mixing processes related to fortnightly tides. High molar C:N ratios (>15), typical of nitrogen-deficient cells, have been observed at times of low dissolved inorganic nitrogen. Absolute transport rates of nitrogen were estimated from natural changes in dissolved inorganic and particulate organic nitrogen. Cell losses and nitrogen uptake rates were highest during periods of maximum current speed, suggesting that the rate of biological production at the ice-water interface could be limited by the accumulated biomass. These results suggest (1) that the sea-ice microalgae in southeastern Hudson Bay are nitrogen limited in their natural environment, and (2) that nutrient replenishment and perhaps losses of biomass governed by fortnightly tidal mixing periodically enhance the growth of microalgae at the ice-water interface.

The role of inorganic and organic nutrients on the development of phytoplankton along a transect from the Daugava River mouth to the Open Baltic, in spring and summer 1999

The importance of dissolved silicate (DSi), dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON), phosphate and dissolved organic phosphorus (DOP) on algal growth is analysed for the Gulf of Riga and the adjacent open Baltic Sea. The results of three cruises (May, June, and July, 1999) along a transect across the Gulf of Riga from the entrance to the Daugava River to the open Baltic are presented. Nutrient-limitation was identified on the basis of available nutrient concentrations and stoichiometric analysis. In spring, phosphate appeared to be the algal-growth-potential-limiting nutrient at the entrance of the Daugava River, DSi in the central Gulf, and DIN at the open Baltic station. There was no correlation between limiting nutrient and spring phytoplankton community structure. Both the DIN and phosphate pools of the upper mixed layer were exhausted by mid-May, except at the river mouth. In summer there was a good correlation between phytoplankton biomass and DOP along the transect. Contrary to the situation in the open Baltic, the lower layer DIN/phosphate ratio in the Gulf of Riga significantly exceeds the Redfield ratio, and upwelling likely does not favour nitrogen-fixing species. Therefore, the upper layer DOP pool should be regarded as potentially the main source of phosphorus for nitrogen-fixing cyanobacteria in the Gulf of Riga.

Nutrients limiting the algal growth potential (AGP) in the Po River plume and an adjacent area, northwest Adriatic Sea : Enrichment bioassays with the test algae Nitzschia closterium and Thalassiosira pseudonana

From April 1993 to March 1994, 135 samples were collected at two sites in the coastal Adriatic Sea, both near (14.5 km) and far (63 km) from the Po River delta. The nutrient(s) limiting algal growth potential (AGP) were estimated by bioassay usingNitzshia closterium (local isolate) andThalassiosira pseudonama (strain 3-H). Estimates were also made by comparing the nutrient molar ratios, ΣN:P and ΣN:Si (whereΣN=NO3−+NO2−+NH4++urea), to the Redfield Ratio (16∶1, 1∶1). According to the bioassay results, phosphorus was the sole nutrient limiting AGP in 2% of the samples and was the most limiting nutrient in 69% of the samples; nitrogen was sole limiting nutrient in 18% of the samples. In 11% of samples, nitrogen and phosphorus were equally co-limiting. Omission of phosphorus from spike enrichments allowed, on average, only a 1.6-fold increase in biomass over that in the unenriched controls. Similar omission of nitrogen allowed a 4-fold increase, while silicon, iron, and micronutrients resulted in 14-fold, 18-fold, and >20-fold increases, respectively. In most of the samples, ΣN:P was much greater than 16, indicating a marked phosphorus deficiency, while ΣN:Si values suggested that silicon was the third most limiting nutrient in 35% of samples. In water collected for from the Po delta, the yield ofN. closterium was not limited by any nutrients other than the three major ones: P, N and Si. In these same waters,T. pseudonana was also potentially limited by iron and, to a lesser extent, by vitamins. The role of iron varied. In samples collected near the Po delta, iron acted as the third most limiting nutrient forN. closterium in June and September; it appeared 29 times out of 78 on the list of potentially limiting nutrients forT. pseudonana, including 5 times as the most limiting. Altogether, comparison with published results suggests that the roles of iron and silicon in AGP limitation have increased during the past three decades, and could become even more important if eutrophication in the Adriatic Sea continues to increase.

Flow cytometry: instrumentation and application in phytoplankton research

In flow cytometry, light scattering and fluorescence of individual particles in suspension is measured at high speed. When applied to planktonic particles, the light scattering and (auto-)fluorescence properties of algal cells can be used for cell identification and counting. Analysis of the wide size spectrum of phytoplankton species, generally present in eutrophic inland and coastal waters, requires flow cytometers specially designed for this purpose. This paper compares the performance in phytoplankton research of a commercial flow cytometer to a purpose built instrument. It reports on the identification of phytoplankton and indicates an area where flow cytometry may supersede more conventional techniques: the analysis of morphological and physiological characteristics of subpopulations in phytoplankton samples.

Action de quelques antibiotiques sur le développement de cinq diatomées en culture

Abstract The action of twenty five antibiotics on the growth of five species of Bacillariophyceae has been tested. Some of them are strong inhibitors, e.g. acti-dion, thyrothricin and all the tetracyclin family. All the diatoms tolerate penicillin and streptomycin up to very high concentrations, but the results indicate that most of the antibiotic substances have specific actions. It was sometimes observed that low antibiotic concentrations give rise to enhanced growth of the diatoms.

In situ cell depletion of some marine algae enclosed in dialysis sacks and their use for the determination of nutrient-limiting growth in Ligurian coastal waters (Mediterranean sea)

Abstract During the late spring and early summer 1976, laboratory cultured cells of five marine algae were enclosed in dialysis sacks and grown in situ, in Ligurian coastal waters. Skeletonema costatum (Greville) Cleve did not grow at all. Hemiselmis virescens Droop stayed alive, but did not grow significantly. Platymonas suecica (Butcher) Manton & Parke grew on cell reserves. Only Phaeodactylum tricornutum Bohlin and Thalassiosira pseudonana Hasle & Heimdal took up nutrients from sea water when all reserves were exhausted. When division ended, all cells were capable of growing when sub-cultured, but physiologically were only slightly active. During immersion in oligotrophic waters, cell contents adapted quickly from nutrient-rich to nutrient-limited growth conditions. During adjustment to equilibrium with natural conditions, the three species became impoverished mainly in phosphorus (67–88% of initial values), ATP (54–92%), and chlorophyll a (59–89%); losses of nitrogen were lower (24–53%). To obtain algal material similar to that in the wild, the data suggest that the cells have to be kept in situ only until they divide five times, which usually requires no more than a week. Counting the cell density each day is probably the most convenient method of control, and each culture should be counted, because the difference of growth between aliquot dialysis cultures can be important (up to 28%). Data obtained for “wild-like” cells of Platymonas suecica, Phaeodactylum tricornutum, Thalassiosira pseudonana , and a wild contaminant population of Cylindrotheca closterium Rabenhorst with biochemical analysis used to run the Droops model and with enrichment bioassays demonstrate that, during the period studied, phosphorus was the limiting factor for the algal growth. Bioassays also demonstrate that there were some specific variations; some algae were permanently limited by phosphorus, while for a few others nitrogen and phosphorus could be equally limiting.

Nocturnal synthesis and diurnal degradation of phytoplankton biomass in surface waters

Natural populations of phytoplankton were collected near the Bay of Bourgneuf, France, in spring 1982, and were subjected to natural surface irradiance outdoors. They exhibited exponential growth on time scales of a week, but significant decreases in biomass indicators such as chlorophyll a and particulate nitrogen were observed during daytime. At night, these decreases were more than compensated by increases in the same biomass variables, which could double over 12 h of darkness. These features are characteristic of phytoplankton populations in surface waters which cannot escape high irradiances, and may be representative of situations in incubation bottles held at fixed depths near the surface. Under such conditions, a decrease in biomass during daytime should not necessarily be interpreted as irreversible damage unless growth measurements are carried out over the following night hours to check for possible recovery.