EFFECT OF LIGHT AND TEMPERATURE INTERACTIONS ON GROWTH OF CRYPTOMONAS EROSA (CRYPTOPHYCEAE)1

Cryptomonas erosa Skuja, a planktonic alga, was grown in batch culture at different combinations of light intensity and temperature, under nutrient saturation. Growth was maximal (1.2 divisions · day^?1) at 23.5 C and 0.043 ly · min^?1, declining sharply with temperature (0.025 divisions-day^?1 at 1 C). With decreasing temperature, the cells showed both light saturation and inhibition at much reduced light intensities. At the same time the compensation light intensity for growth declined towards a minimum of slightly above 0.4 × 10^?4 ly · min^?1 (~1 ft-c) at 1 C or <0.1 ly · day^?1 (PAR). Cell division was more adversely affected by low temperature than carbon uptake, and the resulting excess production of photosynthate was both stored and excreted. Extreme storage of carbohydrates resulted in cell volumes and carbon content ca. 22 and 30 × greater, respectively, than the maxima observed for cells incubated in the dark, whereas, at growth inhibitory light levels, as much as 57% of the total assimilated carbon was excreted. A marked increase in cell pigment was observed at the lowest light levels (<10^?3 ly · min^?1), at high temperature. The growth response of C. erosa in culture provides insight into the abundance and distribution of cryptomonads and other small algal flagellates in nature.     

THE EFFECT OF PHOTON IRRADIANCE ON THE BEHAVIORAL ECOLOGY AND POTENTIAL NICHE SEPARATION OF FRESHWATER PHYTOPLANKTONIC FLAGELLATES1

Photoresponsive behavior in phytoplanktonic flagellates potentially controls depth regulation, vertical migration, and the accumulation of cells in preferred conditions and hence has major implications for photosynthesis, growth, and species competition. This study used microscale laboratory chambers with cell track analysis and mesoscale lake studies to investigate the responses of five phylogenetically contrasting freshwater flagellates to gradients of light. Laboratory results demonstrated that these species differed in their light preferences despite being grown at the same photon irradiance. Preferred photon irradiances were 20–120, 20, 65–120, 4–20, and>200 μmol photons·m^?2·s^?1, respectively, for Ceratium furcoides (Levander) Langhans, Chlamydomonas moewusii Gerloff, Dinobryon sertularia Ehrenberg, Euglena gracilis Klebs, and Plagioselmis nannoplanctica (Skuja) Novarino. Analysis of the response of individual cells showed that in all species, photoresponsive preference was the result of positive and negative phototaxis combined with step‐up and step‐down photophobic reactions. There was no evidence for photokinesis or cell memory. Only in C. furcoides did the preferred photon irradiance alter with growth conditions. In C. furcoides, D. sertularia, and P. nannoplanctica, irradiance preference matched the optimal irradiance for growth, whereas in the two remaining species a lower than optimal irradiance was preferred, suggesting that light may be used as an indicator of other ecological conditions. Mesoscale experiments in a lake demonstrated that the laboratory microscale measurements provide information relevant to understanding ecological distributions. Behavioral responses to light contribute to the delineation of vertical niche separation and provide a method for predicting the spatial and temporal distribution of flagellates.     

Growth model for raceway pond cultivation of Desmodesmus sp. MCC34 isolated from a local water body

Biofuel production by microalgae has the advantage of higher biomass productivity over land crops. The selection of potential microalgae depends on the growth in outdoor mass cultivation during different seasons, which can be predicted by a mathematical model. Here, freshwater green algae were isolated from a local water body in Pilani, Rajasthan, India (geographical coordinates: 28°22′N 75°36′E) and characterized by microscopy and ribosomal RNA analysis. The strain was submitted to the Indian Agricultural Research Institute's microbial culture collection (IARI, India) and identified as Desmodesmus sp. MCC34. This strain, along with a fresh water green algae (Chlorella minutissima), two marine green algae species (Dunaliella salina and Dunaliella tertiolecta) and two nitrogen fixing cyanobacteria (Nostoc muscorum and Anabaena doliolum), were screened for lipid productivity and growth kinetics under culture room and raceway pond conditions. Desmodesmus sp. MCC34 showed the highest specific growth rate (0.26 day^?1), biomass production (1.9 g L^?1) and lipid productivity (103 mg L^?1 day^?1). The optimal temperature and saturating light intensity for maximal growth of Desmodesmus sp. MCC34 were 35 °C and 75 μmol m^?2 s^?1 with molar extinction coefficient of 0.22 m² g^?1, respectively. Desmodesmus sp. MCC34 was then subjected to outdoor cultivation in a 20‐m long raceway pond for 18 days during March and November 2013. The areal biomass productivity and volumetric biomass productivity were 13946.23 kg ha^?1 year^?1 and 56.94 mg L^? 1day^?1 during the month of March, decreasing to 6262.28 kg ha^?1 year^?1 and 25.57 mg L^? 1day^?1 during the month of November. A mathematical model was constructed to explain the relationship between biomass production and growth parameters such as temperature, light intensity and nutrient concentration. The productivity values predicted with the proposed model correspond well with the experimental data, suggesting the validity of the model.     

The influence of irradiance,photoperiod and temperature on the growth kinetics of three planktonic diatoms

The influence of irradiance, photoperiod and temperature was determined for the growth kinetics of the diatoms Aulacoseira subarctica, Stephanodiscus astraea and Stephanodiscus hantzschii and the results compared with those of cyanobacteria. Irradiance and photoperiod relationships were qualitatively similar to those for cyanobacteria in that: (1) growth rate (K) was proportionally greater under short photoperiods, with ratios of K under continuous light to K under 3:21 light:dark (LD) cycles of 1·50, 1·80 and 2·96 for A. subarctica, S. astraea and S. hantzschii respectively; (2) at subsaturating irradiances, K was proportional to irradiance and independent of temperature with a negligible predicted maintenance growth rate requirement. Apparent growth efficiencies (GE) at subsaturating irradiances were 0·26±0·03, 0·42±0·03 and 0·50±0·03 divisions mol^-1m² for A. subarctica, S. astraea and S. hantzschii with the values for Stephanodiscus species comparable to values for Oscillatoria species. Under a 3:21 LD cycle at 4 °C, light-saturated growth rates were 0·066±0·004, 0·197±0·033 and 0·285±0·018 divisions day^-1 for A. subarctica, S. astraea and S. hantzschii. S. hantzschii growth rate at 4 °C exceeded maximum Oscillatoria growth rates at 23 °C and the S. astraea growth rate at 4 °C was equivalent to O. agardhii growth rate at 20 °C. Temperature increases above 4 °C gave Q₁₀ values between 4 °C and 12 °C of 3·68, 2·39 and 1·92 for A. subarctica, S. astraea and S. hantzschii, but higher temperatures resulted in minor increases in K. S. astraea growth rate peaked at 16 °C, declining sharply at higher temperatures. February to March in situ growth rates in Lough Neagh, mean temperature 4·3 °C, showed that the A. subarctica in situ K of 0·058 divisions day^-1 was close to the laboratory K at 4 °C, but that S. astraea in situ K of 0·101 divisions day^-1 was lower than the laboratory K at 4 °C.     

Encarsia formosa parasitizing the Poinsettia-strain of the cotton whitefly,Bemisia tabaci, on Poinsettia: bionomics in relation to temperature

Adult longevity, developmental time and juvenile mortality ofEncarsia formosa Gahan (Hymenoptera:Aphelinidae) parasitizing the Poinsettia-strain ofBemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) on Poinsettia (Euphorbia pulcherrima Willd.) were investigated in laboratory experiments at three temperatures: 16 °C, 22 °C and 28 °C. Furthermore, the parasitoid's preference for different larval stages of the whitefly was determined at 24.5 °C. The lifespan ofE. formosa decreased with temperature from one month at 16 °C to nine days at 28 °C. A lower temperature threshold of 11 °C for adult development was found. The development of juvenile parasitoids inB. tabaci lasted more than two months at the lowest temperature, but was only 14 days when temperature was 28 °C. The lower temperature threshold for immature development was 13.3 °C, yielding an average of 207 day-degrees for the completion of development into adults. Juvenile mortality was high, varying from about 50% at 16 °C to about 30% at 22 °C and 28 °C.E. formosa preferred to oviposit in the 4th instar and prepupal stages ofB. tabaci followed by the 2nd and 3rd instars. The preference for the pupal stage was low. The parasitoid used all instars of the whitefly for hostfeeding, with no apparent differences between the stages. The average duration of the oviposition posture was four minutes. Demographic parameters were calculated from life tables constructed from the data. The intrinsic rate of increase (r _m) and the net reproductive rate (R ₀) increased with temperature from 0.0279 day⁻¹ at 16 °C to 0.2388 day⁻¹ at 28 °C and from about 12 at 16 °C to about 66 at 28 °C, respectively.     

Thermal acclimation and photoacclimation of photosynthesis in the brown alga Laminaria saccharina

Thermal acclimation and photoacclimation of photosynthesis were compared in Laminaria saccharina sporophytes grown at temperatures of 5 and 17 °C and irradiances of 15 and 150μmol photons m^?2 s^?1. When measured at a standard temperature (17°C), rates of light-saturated photosynthesis (P_max) were higher in 5 °C-grown algae (c. 3.0 μmol O₂ m^?2 s^?1) than in 17 °C-grown algae (c. 0.9 μmol O₂ m_-2 s_-1). Concentrations of Rubisco were also 3-fold higher (per unit protein) in 5 °C-grown algae than in algae grown at 17 °C. Light-limited photosynthesis responded similarly to high temperature and low light Photon yields (α) were higher in algae grown at high temperature (regardless of light), and at 5 °C in low light, than in algae grown at 5 °C in high light Differences in a were correlated with light absorption; both groups of 17 °C algae and 5 °C low-light algae absorbed c. 75% of incident light, whereas 5 °C high-light algae absorbed c. 55%. Increased absorption was correlated with increases in pigment content PSII reaction centre densities and the fucoxanthin-Chl ale protein complex (FCP). Changes in a were also attributed, in part, to changes in the maximum photon yield of photosynthesis (0_max). PSI reaction centre densities were unaffected by growth temperature, but the areal concentration of PSI in low-light-grown algae was twice that of high-light-grown algae (c. 160.0 versus 80.0 nmol m^?2). We suggest that complex metabolic regulation allows L, saccharina to optimize photosynthesis over the wide range of temperatures and light levels encountered in nature.     

Effects of temperature,salinity and their interaction on growth of the benthic dinoflagellate Ostreopsis cf. ovata (Dinophyceae) from Japanese coastal waters

Benthic dinoflagellates of the genus Ostreopsis produce palytoxin (PTX)‐like compounds. The worldwide distributed Ostreopsis ovata/O. cf. ovata is potentially responsible for outbreaks of human health problems around the coasts of tropical, subtropical, and temperate regions. The present study examined growth responses of an O. cf. ovata strain s0662 collected from coastal waters of Japan with 35 different combinations of temperature (15–35°C) and salinity (20–40) and discusses the bloom dynamics of the organism in Japanese coastal environments. The O. cf. ovata strain s0662 tolerated a wide range of temperature (17.5–35°C) and salinity (25–40). Results of a two‐way ANOVA showed significant effects of temperature‐salinity interaction on growth rates and biomass yields of the O. cf. ovata strain (F(24,70) > 127, P < 0.001). The strain showed a maximal growth rate (1.03 divisions day^?1) and biomass yield (240 relative fluorescence) at temperature 25°C and salinity 30. The high growth rates of over 1.0 division day^?1 were obtained in conditions of temperature 25–30°C and salinity 30–35, which indicates that strain s0662 prefers high temperature and salinity conditions. The growth rates of O. cf. ovata under the optimal conditions were higher than those of other benthic toxic‐dinoflagellates, Coolia monotis, Gambierdiscus toxicus, and Prorocentrum lima (Dinophyceae) previously reported. Taken together, we suggest that O. cf. ovata is able to grow faster than the other benthic dinoflagellates in waters of high temperature and salinity. The physiological feature probably confers an ecological advantage on O. cf. ovata in the bloom development during warmer seasons in Japan and may be responsible for outbreaks of PTX‐like poisoning in the region especially during the warmer seasons.     

TEMPERATURE AND IRRADIANCE EFFECTS ON GROWTH OF PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) AND SPIROGYRA SP. (CHAROPHYCEAE)1

Growth responses of Pithophora oedogonia (Mont.) Wittr. and Spirogyra sp. to nine combinations of temperature (15°, 25°, and 35°C) and photon flux rate (50, 100, and 500 μmol·m^?2·s^?1) were determined using a three-factorial design. Maximum growth rates were measured at 35°C and 500 pmol·m^?2·s^?1 for P. oedogonia (0.247 d^?1) and 25°C and 500 μmol·m^?2·s^?1 for Spirogyra sp. (0.224 d^?1). Growth rates of P. oedogonia were strongly inhibited at 15°C (average decrease= 89%of maximum rate), indicating that this species is warm stenothermal. Growth rates of Spirogyra sp. were only moderately inhibited at 15° and 35°C (average decrease = 36 and 30%, respectively), suggesting that this species is eurythermal over the temperature range employed. Photon flux rate had a greater influence on growth of Spirogyra sp. (31% reduction at 50 pmol·m^?2·s^?1 and 25°C) than it did on growth of P. oedogonia (16% reduction at 50 μmol·m^?2·s^?1 and 35°C). Spirogyra sp. also exhibited much greater adjustments to its content of chlorophyll a (0.22–3.34 μg·mg fwt^?1) than did P. oedogonia (1.35–3.08 μg·mg fwt^?1). The chlorophyll a content of Spirogyra sp. increased in response to both reductions in photon flux rate and high temperatures (35°C). Observed species differences are discussed with respect to in situ patterns of seasonal abundance in Surrey Lake, Indiana, the effect of algal mat anatomy on the internal light environment, and the process of acclimation to changes in temperature and irradiance conditions.     

Effect of temperature on cell growth and production of transparent exopolymer particles by the diatom Coscinodiscus granii isolated from marine mucilage

In the autumn of 2007, marine mucilage caused by the diatom Coscinodiscus granii occurred in the central area of Ariake Sound, Japan, and resulted in damage to fishery. To elucidate the mechanism underlying the outbreak of marine mucilage, we examined the effect of temperature on cell growth and production of transparent exopolymer particles (TEPs) in a culture of this species. Growth and TEP production of C. granii are influenced by temperature. The maximum growth rate (1.63 divisions day⁻¹) and cell yield (1,280 cells mL⁻¹) at all temperatures were obtained at 30°C. Optimal growth rates (>1.15 divisions day⁻¹: ca. 70% of maximum) and cell yield (>900 cells mL⁻¹: ca. 70% of maximum) were observed at temperatures of 25–30°C. TEP production by C. granii depended on whether volume- or cell-related values were considered. The maximum volume-normalized increase rates and concentrations of TEP at all temperatures were observed at 25°C. However, when production rates and concentrations of TEP were normalized to cell numbers, optimal values were measured at 10–15°C. In Ariake Sound, when marine mucilage caused by C. granii occurred, the temperature ranged from 25.0 to 25.4°C. This suggests that growth conditions of C. granii are important factors for production of marine mucilage.     

OLISTHODISCUS LUTEUS (CHRYSOPHYCEAE) I. EFFECTS OF SALINITY AND TEMPERATURE ON GROWTH. MOTILITY AND SURVIVALS1, 2

The effect of salinity and temperature on Olisthodiscus luteus Carter has been examined to across the relative importance of these factory on dynamics of natural population. A salinity range 2–50% was observed with increased tolerance to low salinity (<5%.) at higher temperature (20–30°C). Slinities at 4–5%. Had densities of 10³ cells/ml^?1, and growth >0.5 division day^?1 at temperature of 15–30°C higher salinities (5–50%.) variable but distinct optima for density, growth and motility were observed 5, 10 and 30°C. Density and motility showed no clear optima from 10–10%.15–25°C where maximum growth rates >1.0 division/day^?1 were common. Temperature increased from (0.5–1.9 division. Day^?1) and increases of three orders of magnitude (10^2?10³) for maximum densities. Temperature optima 20°C for growth 5–35%. And 25°C for >40%. were observed. The implications of these findings to natural populations of O. luleus are discussed.     

Temperature-induced changes in the life cycle of Leuctra nigra(Plecoptera: Leuctridae) from a Lake District stream

1. The life cycle of Leuctra nigra (Olivier) took 2 years in a small stream in the English Lake District and the exponential growth of the larvae was scarcely affected by variations in water temperature (range 4.2-14.0°C). Mean growth rates for three year-classes were 0.43±0.01, 0.42±0.01, 0.39±0.05% body length day^?1. There were thirteen or fourteen larval instars for males and fourteen or fifteen for females. The ratio between successive instars was a constant 1.20 (conformed with Dyar's rule). 2. Larval growth and mortality were exponential at six constant temperatures (5.9, 8.2, 12.1, 15.8, 18.2, 19.8°C) in the laboratory. Mean growth rates (% body length day^?1) increased directly with temperature from 0.37 (5.9°C) to 0.55 (19.8°C). Mean mortality rates (% day^?1) increased directly with temperature from 0.20 (5.9°C) to 0.26 (12.1°C) and then markedly increased to 0.54-0.58 at the three higher temperatures. Only 7-10% of animals completed their life cycle at the three higher temperatures compared with 23–27% at the three lower temperatures. Egg production also decreased considerably at the higher temperatures. 3. As growth rates in the stream and laboratory were similar at similar temperatures (<14°C), the optimum conditions for growth in the laboratory were probably similar to those in the stream; therefore resources such as food and space were not restricting growth in the stream. 4. The implications of the temperature-induced changes in growth and mortality are discussed and it is concluded that although the life cycle can change from semivoltine to univoltine with increasing temperature, the costs of a univoltine life cycle are high in terms of survival and egg production, both of which decreased markedly between 12.1 and 15.8°C. Therefore the optimum habitat for this species appears to be a summer cool stream (maximum temperature <14°C) and the optimal life cycle appears to be about 2 years from egg to adult.     

The effect of temperature on growth characteristics and competitions of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> and <Emphasis Type="Italic">Oscillatoria mougeotii</Emphasis> in a shallow,eutrophic lake simulator system

Blue-green algal blooms formed by Microcystis and Oscillatoria often occur in shallow eutrophic lakes, such as Lake Taihu (China) and Lake Kasumigaura (Japan). Growth characteristics and competitions between Microcystis aeruginosa and Oscillatoria mougeotii were investigated using lake simulator systems (microcosms) at various temperatures. Oscillatoria was the superior competitor, which suppressed Microcystis, when temperature was <20°C, whereas the opposite phenomenon occurred at 30°C. Oscillatoria had a long exponential phase (20 day) and a low growth rate of 0.22 day⁻¹ and 0.20 day⁻¹ at 15°C and 20°C, respectively, whereas Microcystis had a shorter exponential phase (2–3 days) at 30°C and a higher growth rate (0.86 day⁻¹). Interactions between the algae were stronger and more complex in the lake simulator system than flask systems. Algal growth in the lake simulator system was susceptible to light attenuation and pH change, and algae biomasses were lower than those in flasks. The outcome of competition between Microcystis and Oscillatoria at different temperatures agrees with field observations of algal communities in Lake Taihu, indicating that temperature is a significant factor affecting competition between Microcystis and Oscillatoria in shallow, eutrophic lakes.     

Cold shocks of Anammox biofilm stimulate nitrogen removal at low temperatures

The adaptation of Anammox (ANaerobic AMMonium OXidation) to low temperatures (10–15°C) is crucial for sustaining energy‐efficient nitrogen removal from the mainstream of municipal wastewater. But, current adaptation methods take months or even years. To speed up the adaption of Anammox to low temperatures, this study describes a new approach: exposing Anammox microorganisms to an abrupt temporary reduction of temperature, i.e., cold shock. Anammox biomass in a moving bed biofilm reactor was subjected to three consecutive cold shocks (reduction from 24 ± 2 to 5.0 ± 0.2°C), each taking eight hours. Before the cold shocks, Anammox activity determined in ex situ tests using the temperature range of 12.5–19.5°C was 0.005–0.015 kg‐N kg‐VSS^?1 day^?1. Cold shocks increased the activity of Anammox at 10°C to 0.054 kg‐N kg‐VSS^?1 day^?1 after the third shock, which is similar to the highest activities obtained for cold‐enriched or adapted Anammox reported in the literature (0.080 kg‐N kg‐VSS^?1 day^?1). Fluorescence in situ hybridization analysis showed that Ca. Brocadia fulgida was the dominant species. Thus, cold shocks are an intriguing new strategy for the adaptation of Anammox to low temperature. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:277–281, 2018     

Temperature × light interaction and tolerance of high water temperature in the planktonic freshwater flagellates Cryptomonas (Cryptophyceae) and Dinobryon (Chrysophyceae)

Using microcosm experiments, we investigated the interactive effects of temperature and light on specific growth rates of three species each of the phytoplanktonic genera Cryptomonas and Dinobryon. Several species of these genera play important roles in the food web of lakes and seem to be sensitive to high water temperature. We measured growth rates at three to four photon flux densities ranging from 10 to 240 μmol photon · m^?2 · s^?1 and at 4–5 temperatures ranging from 10°C to 28°C. The temperature × light interaction was generally strong, species specific, and also genus specific. Five of the six species studied tolerated 25°C when light availability was high; however, low light reduced tolerance of high temperatures. Growth rates of all six species were unaffected by temperature in the 10°C–15°C range at light levels ≤50 μmol photon · m^?2 · s^?1. At high light, growth rates of Cryptomonas spp. increased with temperature until the temperature optimum was reached and then declined. The Dinobryon species were less sensitive than Cryptomonas spp. to photon flux densities of 40 μmol photon · m^?2 · s^?1 and 200 μmol photon · m^?2 · s^?1 over the entire temperature range but did not grow under a combination of very low light (10 μmol photon · m^?2 · s^?1) and high temperature (≥20°C). Among the three Cryptomonas species, cell volume declined with temperature and the maximum temperature tolerated was negatively related to cell size. Since Cryptomonas is important food for microzooplankton, these trends may affect the pelagic carbon flow if lake warming continues.     

Development,Reproduction and Growth Pattern of two Coexisting,Pond Dwelling Cladocerans

Laboratory investigations on life history parameters of 2 coexisting cladocerans (Daphnia obtusa. Moina brachiata) from a nearly temporary pond in South Germany revealed that the species have different temperature tolerances and temperature optima. D. obtusa experienced the highest reproductive success at 15 and 20 °C and was able to survive and to reproduce at 2 °C but died at 30 °C. The reproductive success of M. brachiata was highest at 25 and 30 °C and the species could not withstand temperatures <15 °C and ≥35 °C. At temperatures between approximately 20 and 25 °C, where both cladocerans coexisted in nature, M. brachiata showed a faster population growth due to its approximately twofold higher egg production rates (10–12 eggs female⁻¹ day⁻¹ compared to approximately 5 eggs female⁻¹ day⁻¹ in D. obtusa) and its shorter juvenile development (3.3 and 2.4 days compared to 6.3 and 5.3 days in D. obtusa); M. brachiata needs generally only 3 molts to reach maturity while D. obtusa requires 5–6 molts.     

Ecophysiological adaptations of two Mediterranean red algae in relation to distribution

Effects of irradiance and temperature on the Mediterranean red algae Eupogodon spinellus and Eupogodon planus were tested. Growth of both species was saturated at an irradiance of 10–20?μmol?m^?2?s^?1, which is in accordance with their sublittoral habitat. Eupogodon spinellus and E. planus survived permanently at temperatures between 8 and 30?°C. The temperature optimum for growth was 25?°C with suboptimal growth occurring at (10?)15 and 30?°C in both species. At their collection locality (Corsica), potential monthly growth yields would be highest in summer and in winter would be only about 20% of the maximum. Reproductive requirements could be determined only in E. planus. Gametophytes reproduced both in long and in short days but only at 20?°C. Tetrasporophytes reproduced at 15–20?°C but only in short days. Geographic distribution boundaries are not set by growth or survival limits. However, the reproductive requirements of E. planus did account for its restricted distribution in the Mediterranean and on the Canary Islands.     

Effects of temperature and salinity on the growth of the red tide flagellates Heterocapsa circularisquama (Dinophyceae) and Chattonella verruculosa (Raphidophyceae)

Growth responses of the red tide flagellates, Heterocapsa circularisquama(Dinophyceae) and Chattonella verruculosa (Raphidophyceae),were examined with 36 different combinations of temperature(5–30°C) and salinity (10–35 PSU). Heterocapsacircularisquama did not grow at or below a temperature of 10°C.The maximum growth rate of H.circularisquama (1.3 divisionsday^–1) was obtained with a combination of 30°C and30 PSU. In contrast, C. verruculosa did not grow at 10 PSU andat temperatures of 25°C or more. The maximum growth rateof C. verruculosa (1.74 divisions day^–1) was obtainedwith a combination of 15°C and 25 PSU. A significant temperature-salinityinteraction on growth was found by factorial analysis. Basedon the physiological characteristics obtained in the presentstudy, these novel flagellates have a potential for future outbreaksof red tides in pre viously unaffected waters.     

The effect of temperature on growth and lipid and fatty acid composition on marine microalgae used for biodiesel production

Cultivation temperature is one of the major factors affecting the growth and lipid accumulation of microalgae. In this study, the effects of temperature on the growth, lipid content, fatty acid composition and biodiesel properties of the marine microalgae Chaetoceros sp. FIKU035, Tetraselmis suecica FIKU032 and Nannochloropsis sp. FIKU036 were investigated. These species were cultured at different temperatures (25, 30, 35 and 40 °C). The results showed that the specific growth rate, biomass and lipid content of all microalgae decreased with increasing temperature. With regards to fatty acids, the presence of saturated fatty acids (SFAs) in T. suecica FIKU032 and Nannochloropsis sp. FIKU036 decreased with increasing temperature, in contrast with polyunsaturated fatty acids (PUFAs). Moreover, Chaetoceros sp. FIKU035 was the only species that could grow at 40 °C. The highest lipid productivity was observed in Chaetoceros sp. FIKU035 when cultivated at 25 °C (66.73 ± 1.34 mg L^?1 day^?1) and 30 °C (61.35 ± 2.89 mg L^?1 day^?1). Moreover, the biodiesel properties (cetane number, cold filter plugging point, kinematic viscosity and density) of the lipids obtained from this species were in accordance with biodiesel standards. This study indicated that Chaetoceros sp. FIKU035 can be considered as a suitable species for biodiesel production in outdoor cultivation.     

TEMPERATURE EFFECTS ON SILICON- AND PHOSPHORUS-LIMITED GROWTH AND COMPETITIVE INTERACTIONS AMONG THREE DIATOMS1

Three diatom species, Stephanodiscus hantzschii (Ehr.) Grun., Asterionella formosa Hass. and Fragilaria crotonensis Kitt. Hass. were isolated from Lake Maarsseveen where they are dominant and show a successional sequence. The physiological responses of each species to temperature and limitation by silicon and phosphorus were determined over the temperature range of 5° to 20° C using short-term batch culture methods. Stephanodiscus hantzschii had higher maximum growth rates than the other two species at all temperatures, and the maximum growth rates of all species increased with increasing temperature. Temperature affected not only maximum growth rates but also half-saturation constants (K_s) and the minimum cell quotas. S. hantzschii had low silicon requirements for growth under Si-limiting conditions, and A. formosa and F. crotonensis had higher and nearly identical silicon requirements. The K_s values for silicon for S. hantzschii were essentially constant from 5° to 20° C but varied greatly for the other two species. A. formosa had the lowest requirements for growth under phosphorus limitation, F. crotonensis was intermediate and S. hantzschii had the highest growth requirements for phosphorus. The K₁ values for phosphorus were constant over the temperature range for both A. formosa and F. crotonensis and were much higher and variable for S. hantzschii. Nutrient competition experiments were performed in continuous cultures at four temperatures and various Si:P ratios. The results generally, but not always, confirmed the predictions based on the Monod relationships for each species. Results not in agreement with predictions were usually because of similar physiological properties of A. formosa and F. crotonensis or because of decreased loss rates for F. crotonensis due to wall growth. In cultures with all three species phosphorus-limited (Si:P > 75), A. formosa often dominated as predicted, although F. crotonensis was sometimes the most abundant species. As predicted, S. hantzschii never dominated at high Si:P ratios. At intermediate Si:P ratios when A. formosa and F. crotonensis were both Si-limited and S. hantzschii P-limited, all three species coexisted because A. formosa and F. crotonensis have almost identical silicon requirements, although sometimes F. crotonensis was more abundant than predicted. At 10°C the results agreed best with the predictions; A. formosa dominated at high Si:P ratios and S. hantzschii dominated as predicted at low Si:P ratios when all three species were Si-limited.     

Bioremediation potential of Chondrus crispus (Basin Head) and Palmaria palmata: effect of temperature and high nitrate on nutrient removal

To evaluate the nutrient removal capabilities of two red macroalgae, apical blades were cultured in the lab for 4?weeks at either 6, 10, or 17°C and nitrate at either 30 or 300?μM, typical of the seasonal range of conditions at a land-based Atlantic halibut farm. Stocking density was 2.0?g?L^?1, irradiance 125?μmol?photons?m^?2?s^?1, photoperiod 16:8 (L:D), and nitrogen to phosphorus ratio 10:1. For both species, the highest growth rate was at 300?μM NO ₃ ^? with Palmaria palmata growing fastest at 6°C, 5.8%?day^?1, and Chondrus crispus growing best at 17°C, 5.5%?day^?1. Nitrogen and carbon removal by P. palmata was inversely related to temperature, the highest rate at 6°C and 300?μM NO ₃ ^? of 0.47?mg N and 6.3?mg C per gram dry weight per day. In contrast, C. crispus removal of N was independent of temperature, with mean removal of 0.49?mgN?gDW^?1?day^?1 at 300?μM NO ₃ ^? . The highest carbon removal by C. crispus was 4.4?mgC?gDW^?1?day^?1 at 10°C and 300?μM nitrate, though not significantly different from either 6 or 17°C and 300?μM nitrate. Tissue carbon:nitrogen ratios were >20 in both species at 30?μM nitrate, and all temperatures indicating nitrogen limitation in these treatments. Phycoerythrin content of P. palmata was independent of temperature, with means of 23.6?mg?gFW^?1 at 300?μM nitrate. In C. crispus, phycoerythrin was different only between 6°C and 17°C at 300?μM nitrate, with the highest phycoerythrin content of 12.6?mg?gFW^?1 at 17°C. Morphological changes were observed in P. palmata at high NO ₃ ^? concentration as curling of the fronds, whilst C. crispus exhibited the formation of bladelets as an effect of high temperature.