Growth and competition of the marine diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana. II. Light limitation

The marine diatoms Phaeodactylum tricornutum (Bohlin) and Thalassiosira pseudonana (Hasle and Heimdal) were grown under both continous illumination and a 14 h light: 10 h dark cycle at light intensities ranging from 1.53×10^-4 to 2.95×10^-1 ly min^-1. Under both photoperiods, T. pseudonana exhibited higher division rates than P. tricornutum at high light intensities, but the reverse was true at all light intensities <3×10^-3 ly min^-1. Comparison of these results with available data on light-limited growth of other planktonic algae suggests that P. tricornutum may be unusually efficient at maintaining its cell division rate at low light intensity. This efficiency may contribute substantially to its success in turbid, nutrient-enriched mass algal culture systems, the only environments in which it is known to attain great numbers.Contribution No. 4086 from the Woods Hole Oceanographic Institution.     

Evaluation of the copepod Tigriopus californicus as a bioassay organism for the detection of chemical feeding deterrents produced by marine phytoplankton

Marine phytoplankton have been shown to use chemical feeding deterrents to reduce or inhibit zooplankton grazing. In order to screen phytoplankton species for feeding deterrent production and to isolate and identify feeding deterrent compounds, a new, rapid, and reliable laboratory bioassay was developed. This bioassay used the laboratory-reared harpacticoid copepod Tigriopus californicus and measured inhibition of feeding by measuring the fecal pellet production rate. The bioassay was capable of detecting deterrent compounds: (1) adsorbed onto ground fish food (a normally palatable food); (2) dissolved in a mixture of seawater and live Thalassiosira pseudonana cells (a species of diatom which had no feeding deterrent activity); and (3) present in live cell cultures. Method (2) was recommended for use in bioassay-guided fractionation (isolation of chemical compounds), as it was reliable, rapid, accurate, and easy to perform with large numbers of samples. The total bioassay time was < 48 h, and data collection required only a microscope. Methanolic cell extracts of several phytoplankton species were screened for feeding deterrent activity. Extracts from the diatom Phaeodactylum tricornutum and the dinoflagellate Gonyaulax grindleyi gave feeding deterrent responses, while extracts from the diatom Thalassiosira pseudonana gave no feeding deterrent responses. Live P. tricornutum cells deterred feeding at densities of 6x10⁵ cells ml^-1. This bioassay should provide a valuable tool in screening phytoplankton for feeding deterrent compounds and determining the chemical nature of these compounds.     

Feeding deterrence properties of apo-fucoxanthinoids from marine diatoms. II. Physiology of production of apo-fucoxanthinoids by the marine diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana,and their feeding deterrent effects on the copepod Tigriopus californicus

The marine diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana have been shown to produce apo-fucoxanthinoid compounds which act as feeding deterrents against the harpacticoid copepod Tigriopus californicus. The amounts and types of apo-fucoxanthinoids produced were species specific. Th. pseudonana produced small quantities of apo-12-fucoxanthinal and apo-13-fucoxanthinone only during senescence, while P. tricornutum produced much greater quantities of these two compounds during both log and senescence phases, in addition to producing a third compound, apo-10-fucoxanthinal, only during senescence. For both species, production of apo-fucoxanthinoids increased as the cells entered senescence phase due to phosphate limitation. The amounts of apo-fucoxanthinoids necessary to reduce feeding in T. californicus by 50% ranged from 2.22 to 20.2 ppm. This range was approximately 1000 times lower than the total apo-fucoxanthinoid concentration in P. tricornutum. The amounts of apo-fucoxanthinoids necessary to cause a 50% mortality in a population of T. californicus ranged from 36.8 to 76.7 ppm. Thus, these compounds are present in concentrations which may have ecological significance in the control of bloom formation and grazing. The production of apo-fucoxanthinoids may be a phenomenon common to many diatoms, particularly as they enter senescence due to nutrient limitation.     

Polychlorinated biphenyl (PCB) effects on marine phytoplankton photosynthesis and cell division

Inhibition of photosynthesis and cell division by polychlorinated biphenyls (PCBs) was studied using 7 marine phytoplankton species representing 4 algal classes. PCB concentrations as low as 1.0 g l^-1 reduced cell division of Thalassiosira pseudonana 3H and Isochrysis galbana. Both photosynthesis and cell division of T. pseudonana 3H, Chaetoceros socialis, Skeletonema costatum, T. pseudonana 13-1, Monochrysis, lutheri and I. galbana were inhibited at a PCB concentration of 10.0 g l^-1. The effects on photosynthesis were immediate and probably resulted in reduced rates of cell division. Interspecific differences in susceptibility were observed. These differences have significance with respect to primary production and the species composition of phytoplankton communities. The initial slopes of photosynthesis-irradiance (P-I) curves for the diatoms S. costatum and T. pseudonana 3H were reduced in the presence of PCBs. These results suggest that PCBs affect the photosynthetic light reactions.     

Bioseston production by Mytilus edulis and its effect in experimental systems

Mytilus edulis L. (Bivalvia: Mollusca) can produce appreciable quantities of 3.4 to 5.4 m diameter bioseston, when previously fed on Phaeodactylum tricornutum and Tetraselmis suecica. Bioseston production, observed in flowing filtered sea water, is shown to originate from resuspension of faeces and can cause filtration-rate underestimates of up to 35% under certain experimental conditions. Feeding with Thalassiosira pseudonana below a concentration of 4x10⁷ particles l^-1 caused no significant bioseston production and this alga would, therefore, be suitable for use in quantitative estimates of filtration rate.     

Energy budgest,growth and filtration rates in Mytilus edulis at different algal concentrations

Growth of Mytilus edulis L. was measured in aquaria with through-flowing sea water at different levels of constant algal concentrations. The amount of food and oxygen consumed by the mussels were measured over given periods as well as the changes in dry organic weight during the same periods. From these parameters it was possible to make simple energy budgets and to compare the estimated growth with actual growth, and, further, to determine growth efficiences at different food levels. Energy budgets were made for mussels grown at algal concentrations of 0, 1.6×10³, 3.0×10³ and 26.0×10³ Phaeodactylum tricornutum cells x ml^-1. The estimated growth was found to be close to actual growth at algal concentrations above maintenance level and the net growth efficiency was found to be between 18% (3.0×10³ cells x ml^-1) and 61% (26×10³ cells x ml^-1). It has been shown that the filtration rate is independent of algal concentrations between about 1.5×10³ to 30×10³ P. tricornutum cells x ml^-1. Outside this range a decrease in filtration rate was noticed.     

溢油污染物在栉孔扇贝不同组织的富集特异性及生物放大效应的初步研究

本文采用半静态暴露实验法,研究了栉孔扇贝(Chlamys farreri)的不同组织对船舶常用燃料油0#柴油分散液和乳化液的富集及其在食物链传递过程中的生物放大效应。结果表明:(1)在不同浓度柴油分散液和柴油乳化液中,扇贝暴露8 d后不同软组织对柴油的生物富集系数BCF均表现为鳃(889.40～127.92 mL·g~(-1)、830.80～123.43 mL·g~(-1))内脏团(293.80～58.46 mL·g~(-1)、184.00～130.53 mL·g~(-1))肌肉(147.60～39.68 mL·g~(-1)、149.80～62.40 mL·g~(-1)),腮和内脏对石油的富集能力强于肌肉,各组织对柴油分散液的富集能力强于柴油乳化液;(2)用石油烃(TPH)浓度分别为1.74×10~(-10)mg·cell~(-1)、4.44×10~(-10)mg·cell~(-1)的三角褐指藻(Phaeodactylum tricornutum Bohlin)喂养扇贝后,扇贝体内石油烃(TPH)浓度随时间的延长和藻体浓度的上升都表现出增加的趋势,到第8天实验结束时扇贝体内TPH浓度达到7.79 mg·kg~(-1)和9.61 mg·kg~(-1),表明TPH通过浮游植物的摄食在扇贝体内造成累积,通过食物链进行了传递。     

Silicon and the ecology of marine plankton diatoms. II. Silicate-uptake kinetics in five diatom species

The variation of the rate of silicate uptake with varying silicate concentration in the medium was investigated in short-term experiments with the following marine diatom species:Skeletonema costatum, Thalassiosira pseudonana, T. decipiens, Ditylum brightwellii, andLicmophora sp. The uptake conformed to Michaelis-Menten kinetics only after a correction had been made for reactive silicate that apparently could not be utilized by the diatoms. The magnitude of this correction was in the range of 0.3 to 1.3 g-at Si/l. Mean values of the half-saturation constant of silicate uptake were calculated for the different species. The lowest value was found inS. costatum (0.80 g-at Si/l) and the highest inT. decipiens (3.37 g-at Si/l). Growth limitation by low silicate concentrations could be a cause of species succession in marine plankton-diatom blooms.     

Growth response of Chaetoceros calcitrans (Bacillariophyceae) in batch culture to a range of initial silica concentrations

Batch cultures of the marine unicellular centric diatom Chaetoceros calcitrans (Paulsen) Takano were maintained by serial subculturing every 4 d into nutrient-enriched natural sea-water medium supplemented with 350, 950 and 1 400 g-at Si l^-1. The diatom cultures removed initial silica concentrations of 350 and 950 g-at l^-1 from the medium within 2 and 3 d, respectively. About 30 g-at l^-1 of the highest initial concentration remained in the medium after 4 d. The mean final cell density with an enrichment of 350 g-at Si l^-1 was 3.43±0.26×10⁴ cells l^-1 (median cell volume = 77.5±5.0 m³); with 950 g-at Si l^-1, 8.55±0.55×10⁴ cells l^-1 (50.0±4.5 m³); and with 1 400 g-at Si l^-1, 9.72±0.48×10⁴ cells l^-1 (37.3±5.0 m³). There was no significant difference in the final total organic weight of cells produced, which was in the range of 170 to 190 mg per 250 ml culture. This consisted of proportionately more lipid and carbohydrate and less protein from the treatment with 350 g-at Si l^-1 than from the 1 400 g-at Si l^-1 treatment.     

HPLC analysis of nonprotein thiols in planktonic diatoms: pool size,redox state and response to copper and cadmium exposure

A sensitive method was developed to analyze low molecular weight thiols involved in metal homeostasis and detoxification in phytoplankton. The aims of this study were to (1) separate and measure all relevant thiols in a single HPLC run, (2) measure redox states of the thiols and (3) identify specific responses of thiols (pools, redox) to heavy metals by testing diatoms with different metal tolerances (Ditylum brightwellii, Phaeodactylum tricornutum, Skeletonema costatum andThalassiosira pseudonana). Copper or cadmium were dosed at a maximum tolerable, species-dependent level, to exponential phase cells growing in artificial medium (14 salinity). Loss of cell viability was monitored by the decrease of fluorescein fluorescence after a 24-h metal exposure. Thiols in extracts of exposed cells and controls were labeled with monobromobimane. Picomoles of cysteine, glutathione, -glutamylcysteine and phytochelatins (PCs) were detected and separated by reversed-phase high performance liquid chromatography. Cysteine increased in all species after metal exposure. The species with the largest glutathione pools in the control (P. tricornutum) synthesized the largest PC pools upon metal exposure, however, at a 40% loss of glutathione. A considerable increase of glutathione was observed inD. brightwellii upon metal exposure. However, it produced little PC (and only with Cu). In controls ( 3 pM Cu²⁺), PC₂ was detectable inS. costatum, P. tricornutum andT. pseudonana. Oxidized thiol fractions were recovered by the reductants DTT and TCEP, both performing identically. Compared to the other thiols, cysteine had low redox ratios. InD. brightwellii glutathione and PC redox ratios were lower than inP. tricornutum, S. costatum andT. pseudonana. It was expected that Cu-induced oxidative stress would decrease the thiol redox ratios, however, this was not observed.This is Communication No. 2172 of NIOO.     

The ammonium/methylammonium uptake system of Symbiodinium microadriaticum

The substrate analogue [¹⁴C]-methylammonium was used to study ammonium/methylammonium uptake by Symbiodinium microadriaticum (zooxanthellae). The value of the Michaelis constant (K _m) for the uptake system was approximately 35 M with methylammonium as substrate; ammonium was a competitive inhibitor of methylammonium uptake, and the K _m for ammonium uptake (determined as the inhibition constant, K _i, for methylammonium) was 6.6 M. Methylammonium uptake by zooxanthellae was light-dependent. Methylammonium uptake rates of zooxanthellae which had been freshly isolated from the hermatypic coral Acropora formosa (0.85±0.05x10^-10 mol min^-1 cell^-1) were lower than those of axenic cultures of the zooxanthellae from Montipora verrucosa (Acroporidae) grown under various nitrogen regimes (1.6 to 12x10^-10 mol min^-1 cell^-1). Maximum uptake rates were found for ammonium-starved cultured M. verrucosa zooxanthellae (10.2 to 12x10^-10 mol min^-1 cell^-1); M. verrucosa zooxanthellae growing with ammonium as nitrogen source and zooxanthellae which had been freshly isolated from A. formosa gave similar and considerably lower uptake rates (0.85 to 1.6x10^-1 mol min^-1 cell^-1). These results suggest that either coral tissue contains sufficient ammonium to repress synthesis of the uptake system of the algal symbionts or, alternatively, there are additional barriers to ammonium transport for zooxanthellae in vivo.     

Light-shade adaptation by the oceanic dinoflagellates Pyrocystis noctiluca and P. fusiformis

Species-specific rates of photosynthetic carbon uptake (P), chlorophyll a content and P versus irradiance (P-I), have been measured for cells of Pyrocystis noctiluca and P. fusiformis isolated from natural populations collected in the euphotic zone within and below the surface mixed layer in the Sargasso Sea. These same measurements and the assay for ribulose bis-phosphate carboxylase (RuBP-Case), have been made for cultures of P. noctiluca in a 12 h L: 12 h D photoperiod at 9 different constant or at changing light intensities. In nature chl a cell^-1 was constant throughout the euphotic zone. The photosynthetic capacity (P_max), of cells captured below the surface mixed layer was lower by a factor of 10 compared with cells collected from the surface mixed layer. The P_max for P. noctiluca collected and incubated within the surface mixed layer was the same as for cell cultures grown under high light, non nutrient-limiting conditions, suggesting that photosynthesis in the natural system was not nutrient limited. In laboratory cultures under constant low light intensities, chl a cell^-1 increased by a factor of 5 while both P_max and RuBPCase activity decreased by a factor of ca 4 compared with high light intensities. In changing light intensities both P_max and RuBPCase activities were decreased by factors of 4 during low light intervals while chl a cell^-1 approached a constant intermediate value. The change in chl a cell^-1 in response to prolonged exposure to constant low light intensities was first order with a rate constant of 0.33 d^-1. For all irradiance conditions in culture, the P-I dependence could be described by the simple Michaelis-Menten formula. The ratio of P_max to K_I, (the light intensity where P=P_max/2) was a constant with a Coefficient of Variation of 12%: The constancy of this ratio, the parallel changes in RuBPCase activity with P_max and the constant chl a cell^-1 in the Sargasso Sea imply that for P. noctiluca and presumably P. fusiformis in nature, a dark enzymatic step rather than changes in photosynthetic pigment concentrations may regulate the photosynthetic capacity in the changing photic environment.Contribution no. 1141 from McCollum-Pratt Institute and Department of Biology, The Johns Hopkins University. Supported by DOE contract no. EY 76S20 3278, NSF no. OCE 76-02571 and ONR no. N300014-81-C-0062     

Development of rapid ammonium uptake during starvation of batch and chemostat cultures of the marine diatom Thalassiosira pseudonana

Cell nitrogen quotas and uptake rates following ammonium additions were measured during ammonium-limited growth transients obtained by starving batch and chemostat cultures of Thalassiosira pseudonana (Clone 3 H). During starvation, cell quotas decreased by more than 50% in batch cultures. In chemostat cultures, the drop in cell quota during starvation decreased with dilution rate, from more than 50% at 1.45 d^-1, to less than 10% at 0.22 d^-1. Minimal levels of 3 to 4×10^-2 pg-at. N cell^-1 were reached after 24 h starvation in both batch and chemostat cultures. Uptake rates over the first minute of perturbation experiments were 3 times the long-term (10 to 30 min) rates. In batch cultures, specific uptake rates increased from 4 d^-1 to 20 d^-1 after 24 h starvation. Uptake rates per cell were independent of starvation time and dilution rate in chemostat cultures, but lower in non-starved batch cultures. The implications of these data for models of phytoplankton growth are discussed: the data support models which predict a depression in average growth rates when diatoms encounter microscale patches in oligotrophic environments.     

The influence of suspension density and temperature on the filtration rate of Hiatella arctica

The rate of filtering Phaeodactylum tricornutum and Isochrysis galbana was measured in Hiatella arctica (L.) by the indirect suspension depletion method monitored by optical density measurement. The filtration rate of H. arctica was found to be 1.412×10^–2 l/h/g wet weight at a temperature of 15°C when fed with P. tricornutum, at average cell concentrations up to 3.5×10⁶ cells/ml. The filtration rate dropped almost to zero when the concentration of P. tricornutum reached 11×10⁶ cells/ml. The filtration rate of I. galbana diminished at a much lower cell concentration of 1×10⁶ cells/ml, and almost ceased at 3 to 4×10⁶ cells/ml. In mixed cultures of I. galbana and P. tricornutum, the filtration rate ratio was 0.37 to 1.00, and this was believed to be due to a proportion of the smaller former cells passing through the ostia. However, when resuspended in sea water, I. galbana cells were taken at a rate slightly less than P. tricornutum. The medium in which the I. galbana cells had been grown was inhibitory to the filtering activity of H. arctica, since, when cells of either alga were resuspended in the medium, the filtration rate was considerably reduced. No inhibitory factor existed in either of the original nutrient media. Hence, the importance of using low cell concentrations and of eliminating any inhibitory metabolic products when measuring filtration rates of bivalves is stressed. H. arctica shows a typical activity temperature eurve for a boreo-arctic species, with a steady rise from 0°C to a maximum between 15° and 17°C, and a sharp fall in activity to about zero at 25°C. The rates of filtration of various species at temperatures approaching the optimum were compared after allowance was made for fall in filtration rate with increasing body weight. The results suggested that the Mytilacea had the highest filtration rates and that H. arctica possesses one of the lowest filtration rates recorded.     

Regulation of the Si and C uptake and of the soluble free-silicon pool in a synchronised culture of<Emphasis Type="Italic"> Cylindrotheca fusiformis</Emphasis> (Bacillariophyceae): effects on the Si/C ratio

Silicon and carbon uptake rates were studied over a 24 h light/dark cycle in a synchronised culture of the marine diatom Cylindrotheca fusiformis (Reimann et Lewin) using ³²Si and ¹⁴C. The silicic acid uptake rate per cell (^cSi) varied between 1.2 and 20.0 fmol Si cell^–1 h^–1 and was closely correlated to the G2+M phase of the cell cycle. A linear and significant relationship was determined between the percentage of cells present in G2+M and ^cSi. Evolution of the soluble free-silicon pool was studied simultaneously. The concentration of the total soluble free pool of silicon (Q^PSi) varied from 1% to 7% of the total silicon content. A significant difference of 1.5 fmol Si cell^–1 between Q^PSi and the labelled free pool (Q^npSi) was measured, indicating the presence of an unlabelled fraction of the pool. The concentration of Q^npSi was around 1.0 fmol Si cell^–1 prior to cell division and did not change as a function of ^cSi, which indicated a feedback mechanism coupling uptake into the free pool and incorporation into the frustule. In parallel, ¹⁴C uptake variation (^cC) was measured during the division of the population. The value of ^cC varied between 0.44 and 0.78 pmol C cell^–1 h^–1 and appeared to be maximal when cells were in the G1 phase. This variation of ^cC marginally affected the total carbon content of the cells (Q^TC) in comparison with the light/dark cycle. The variations in the Si/C ratio, from 0.021 to 0.046, demonstrated the different control mechanisms of Si and C metabolisms during the course of the cell- and photocycle.Communicated by S.A. Poulet, Roscoff     

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.     

Effects of ethyl 2-methyl acetoacetate (EMA) on the growth of Phaeodactylum tricornutum and Skeletonema costatum

We investigated the effects of ethyl 2-methyl acetoacetate (EMA) on growth of the marine diatom algae Phaeodactylum tricornutum (P. tricornutum) and Skeletonema costatum (S. costatum). Growth of P. tricornutum was significantly inhibited by the minimum concentration (3.5 mmol·L ^?1) of EMA at lower initial algal densities (IADs) (3.6×10⁴ and 3.3×10⁵ cells·mL ^?1). However, at the highest IAD, significant growth inhibition was found at above 7 mmol·L ^?1 of EMA exposure. In S. costatum, EMA concentrations of 10.5 mmol·L ^?1 or more significantly inhibited growth at lower IAD (3×10⁴ and 1.8×10⁵ cells·mL ^?1); at the highest IAD, only EMA concentrations above 14 mmol·L ^?1 obviously inhibited the growth of S. costatum. Changes in specific growth rates and pigment were consistent with algal growth, but only at higher EMA concentrations or lower IAD values was the ratio of chlorophyll a (Chla) to carotenoid significantly lower than the control. Medium effective concentration (EC ₅₀) values were in the order 4.07, 8.03 and 12.27 mmol·L ^?1 for P. tricornutum and 7.48, 11.92 and 17.22 mmol·L ^?1 for S. costatum. All these results show that the effect of EMA on the growth of algae was species specific and mainly depended on IAD, which might be an important factor to influence algal growth.     

Effect of suspended bottom material on growth and energetics in Mytilus edulis

The influence of suspended, natural silt (0 to 20 mg l^-1) in addition to unicellular algal cells (Phaeodactylum tricornutum) (o to 20.000 cells ml^-1) on clearance, growth and energetics in Mytilus edulis has been studied. Clearance increased by 32 to 43% by the addition of 5 mg silt l^-1 as compared to clearance in a pure algal suspension. Ingestion and growth rate increased with algal concentration, and growth rate was further increased by 30 to 70% by the addition of 5 mg silt l^-1. A growth rate comparable to maximum natural growth rates was reached only at the highest algal concentration in the presence of 5 mg siltl^-1. Assimilation efficiency of P. tricornutum decreased from 77% at 5,000 cells ml^-1 to 52% at 20,000 cells ml^-1. In the experiments with silt added, some 20 to 30% of the assimilated organic matter originated from the suspended bottom material. Net growth efficiency increased with growth rate at a decelerating rate, approaching a maximum of about 70%. It is concluded that suspended bottom material, which is always present in M. edulis' natural habitats, serves as an additional food source, and that M. edulis depends on suspended bottom material to exploit fully its clearance potential, and to reach the maximum growth rates observed in nature.     

Use of high-performance liquid chromatography to investigate the production of paralytic shellfish toxins by Protogonyaulax spp. in culture

Procedures have been developed for the extraction and high-performance liquid chromatography (HPLC) analysis of paralytic shellfish poisoning (PSP) toxins from Protogonyaulax spp. grown in batch culture. Using these procedures, the toxin content of two isolates of P. tamarensis (NEPCC 183 and 255) and one isolate of P. catenella (NEPCC 355) were examined. Total toxin and individual toxin concentrations were measured for each isolate during the exponential and stationary phases of growth in batch culture. The total toxicity of each isolate as measured by HPLC analysis was found to agree with toxicity as determined by the standard mouse bioassay. Two of the isolates (255 and 355) were found to be toxic and the third (183) was non-toxic. The toxic isolates (255 and 355) both showed higher average total PSP toxin content during the exponential phase (35 and 23 fmol toxin cell^-1, respectively) than during the stationary phase (21 and 8 fmol toxin cell^-1, respectively). These cultures differed dramatically in their toxin composition. P. tamarensis (255) contained a large proportion of the N(21) sulfo toxins (B₁, B₂, C₁, C₂) while P. catenella (355) contained primarily Gonyautoxins 1 through 4. The percent composition of individual toxins was found to be constant throughout the growth cycle for both toxic isolates, even though the total toxin concentration varied. Our results suggest that PSP toxin profiles might be useful as chemotaxonomic indicators.     

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.