Physiological differences in the growth of <Emphasis Type="Italic">Sargassum horneri</Emphasis> between the germling and adult stages

The effects of temperature, irradiance, and daylength on Sargassum horneri growth were examined at the germling and adult stages to discern their physiological differences. Temperature–irradiance (10, 15, 20, 25, 30°C × 20, 40, 80 μmol photons m⁻²s⁻¹) and daylength (8, 12, 16, 24 h) experiments were carried out. The germlings and blades of S. horneri grew over a wide range of temperatures (10–25°C), irradiances (20–80 μmol photons m⁻²s⁻¹), and daylengths (8–24 h). At the optimal growth conditions, the relative growth rates (RGR) of the germlings were 21% day⁻¹ (25°C, 20 μmol photons m⁻²s⁻¹) and 13% day⁻¹ (8 h daylength). In contrast, the RGRs of the blade weights were 4% day⁻¹ (15°C, 20 μmol photons m⁻²s⁻¹) and 5% day⁻¹ (12 h daylength). Negative growth rates were found at 20 μmol photons m⁻²s⁻¹ of 20°C and 25°C treatments after 12 days. This phenomenon coincides with the necrosis of S. horneri blades in field populations. In conclusion, we found physiological differences between S. horneri germlings and adults with respect to daylength and temperature optima. The growth of S. horneri germlings could be enhanced at 25°C, 20 μmol photons m⁻²s⁻¹, and 8 h daylength for construction of Sargassum beds and restoration of barren areas.     

Effect of light and temperature on the cyanobacterium <Emphasis Type="Italic">Arthronema africanum</Emphasis> - a prospective phycobiliprotein-producing strain

The effect of light intensity (50–300 μmol photons m⁻² s⁻¹) and temperature (15–50°C) on chlorophyll a, carotenoid and phycobiliprotein content in Arthronema africanum biomass was studied. Maximum growth rate was measured at 300 μmol photons m⁻² s⁻¹ and 36°C after 96 h of cultivation. The chlorophyll a content increased along with the increase in light intensity and temperature and reached 2.4% of dry weight at 150 μmol photons m⁻² s⁻¹ and 36°C, but it decreased at higher temperatures. The level of carotenoids did not change significantly under temperature changes at illumination of 50 and 100 μmol photons m⁻² s⁻¹. Carotenoids were about 1% of the dry weight at higher light intensities: 150 and 300 μmol photons m⁻² s⁻¹. Arthronema africanum contained C-phycocyanin and allophycocyanin but no phycoerythrin. The total phycobiliprotein content was extremely high, more than 30% of the dry algal biomass, thus the cyanobacterium could be deemed an alternative producer of C-phycocyanin. A highest total of phycobiliproteins was reached at light intensity of 150 μmol photons m⁻² s⁻¹ and temperature of 36°C, C-phycocyanin and allophycocyanin amounting, respectively, to 23% and 12% of the dry algal biomass. Extremely low (<15°C) and high temperatures (>47°C) decreased phycobiliprotein content regardless of light intensity.     

Early development of germlings of <Emphasis Type="Italic">Sargassum thunbergii</Emphasis> (Fucales,Phaeophyta) under laboratory conditions

Morphology and culture studies on germlings of Sargassum thunbergii (Mertens et Roth) Kuntze were carried out under controlled laboratory conditions. Growth characteristics of these germlings grown under different temperatures (from 10 to 25°C), irradiances (from 9 to 88 μmol photons m⁻² s⁻¹), and under blue and white light conditions are described. The development of embryonic germlings follows the classic “8 nuclei 1 egg” type described for Sargassaceae. Fertilized eggs spent 5–6 h developing into multicellular germlings with abundant rhizoids after fertilization. Under conditions of 20°C, 44 μmol photons m⁻² s⁻¹ and photoperiod of 12 h, young germlings with one or two leaflets reached 2–3 mm in length after 8 weeks. Temperature variations (10, 15, 20, 25°C) under 88 μmol photons m⁻² s⁻¹ significantly influenced the growth rate within the first week, although this effect became less obvious after 8 weeks, especially at 15 and 20°C. Variation in germling growth was highly significant under different irradiances (9, 18, 44, 88 μmol photons m⁻² s⁻¹) at 25°C. Low temperature (10°C) reduced germling growth. Growth of germlings cultured under blue light was lower than in white light. Optimal growth of these germlings occurred at 25°C and 44 μmol photons m⁻² s⁻¹.     

Effects of Environmental Factors and Metal Ions on Growth of the Red Alga Gracilaria Chorda Holmes (Gracilariales, Rhodophyta)

Gracilaria is a potentially valuable source of marine biopolymers such as proteins and polysaccharides. In order to select suitable culture conditions, growth and tolerance of Gracilaria chorda Holmes from Shikoku Island in southwest Japan were investigated under variations of temperature (5–30 ^∘C), photon irradiance (20–120 μmol photons m⁻² s⁻¹), and photoperiod (12:12 h, 14:10 h light:dark regime) in a unialgal culture. Gracilaria chorda showed wide tolerances for all factors investigated, which is characteristic of eurythermal species. Maximum growth was observed at 18–24 ^∘C. The optimum photon irradiance for the algal growth was 60–120 μmol photons m⁻²s⁻¹. Instead of using ordinary sea salt (NaCl) to prepare artificial seawater, ultra pure salt was adopted. Gracilaria chorda grew faster in artificial seawater made with ultra-pure salt than that made with ordinary sea salt, probably because the former medium was clear, while the latter was milky. Effects of some metal ions on the growth were tested with artificial seawater. Iron ions affected algal growth, but cobalt ions did not. This study enables us to determine suitable culture conditions for G. chorda. A scaled-up 30 l culture of G. chorda under such conditions was successful.     

Temperature and irradiance impacts on the growth,pigmentation and photosystem II quantum yields of <Emphasis Type="Italic">Haematococcus pluvialis</Emphasis> (Chlorophyceae)

The microalga Haematococcus pluvialis Flotow has been the subject of a number of studies concerned with maximizing astaxanthin production for use in animal feeds and for human consumption. Several of these studies have specifically attempted to ascertain the optimal temperature and irradiance combination for growth of H. pluvialis, but there has been a great deal of disagreement between laboratories. “Ideal” levels of temperature and irradiance have been reported to range from 14 to 28°C and 30 to 200 μmol photons m⁻² s⁻¹. The objective of the present study was to simultaneously explore temperature and irradiance effects for a single strain of H. pluvialis (UTEX 2505) across an experimental region that encompassed the reported “optimal” combinations of these factors for multiple strains. To this end, a two-dimensional experimental design based on response surface methodology (RSM) was created. Maximum growth rates for UTEX 2505 were achieved at 27°C and 260 μmol photons m⁻² s⁻¹, while maximum quantum yield for stable charge separation at PSII (F_v/F_m) was achieved at 27°C and 80 μmol photons m⁻² s⁻¹. Maximum pigment concentrations correlated closely with maximum F_v/F_m. Numeric optimization of growth rate and F_v/F_m produced an optimal combination of 27°C and 250 μmol photons m⁻² s⁻¹. Polynomial models of the various response surfaces were validated with multiple points and were found to be very useful for predicting several H. pluvialis UTEX 2505 responses across the entire two-dimensional experimental design space.     

Combined effect of temperature and light intensity on growth and extracellular polymeric substance production by the cyanobacterium Arthrospira platensis

The effects of light intensity and temperature on Arthrospira platensis growth and production of extracellular polymeric substances (EPS) in batch culture were evaluated using a three-level, full-factorial design and response surface methodology. Three levels were tested for each parameter (temperature: 30, 35, 40°C; light intensity: 50, 115, 180 μmol photons m⁻² s⁻¹). Both growth and EPS production are influenced mainly by the temperature factor but the interaction term temperature*light intensity also had a significant effect. In addition, conditions optimising EPS production are different from those optimising growth. The highest growth rate (0.414 ± 0.003 day⁻¹) was found at the lowest temperature (30°C) and highest light intensity (180 μmol photons m⁻² s⁻¹) tested, no optima were detectable within the given test range. Obviously, optima for growth must be at a temperature lower than 30°C and a light intensity higher than 180 μmol photons m⁻² s⁻¹. For EPS production, light intensity had a positive linear effect (optimum obviously higher than 180 μmol photons m⁻² s⁻¹), but for the temperature parameter a maximum effect was detectable at 35°C.     

Carpospore early development and callus-like tissue induction of <Emphasis Type="Italic">Chrysymenia wrightii</Emphasis> (Rhodymeniaceae,Rhodophyta) under laboratory conditions

Morphological and culture studies of germlings derived from carpospores of Chrysymenia wrightii (Harvey) Yamada were carried out under various treatments combining temperature and irradiance. Basal, main, and tip branches were applied for inducing callus-like tissue. Focus was on how carpospores develop into germlings, how callus-like tissues are induced from explants, and how temperature and irradiance affect carpospore germination and discoid crust growth. Results show that carpospore development can be divided into three stages: division stage, discoid crust stage, and erect juvenile germling stage. Discoid crusts, even more than ten, might coalesce into a big discoid crust, and then developed into germlings. Filamentous fronds, formed on the rims of discoid crusts, exhibited in self-existence or co-existence form with germlings, could form spherical tufts if cultured separately. Filamentous callus-like tissues appeared on the tip branches after 13 days. PES is suitable for filament induction and culture, and filaments have potential use in germplasm preservation and vegetative propagation. Temperature (10, 15, 20, 25°C) and irradiance (8 and 36 μmol photons m⁻² s⁻¹) significantly influenced carpospore germination rate and discoid crust diameter. Carpospores germinated normally under 36 μmol photons m⁻² s⁻¹, 15~25°C, and maximum growth of discoid crusts was at 25°C, 36 μmol photons m⁻² s⁻¹; 10°C and 8 μmol photons m⁻² s⁻¹ did not favor carpospore germination or discoid crust growth.     

Photosynthetic acclimation to photon irradiance and its relation to chlorophyll fluorescence and carbon assimilation in the halotolerant green alga Dunaliella viridis

This work describes the long-term acclimation of the halotolerant microalga Dunaliella viridis to different photon irradiance, ranging from darkness to 1500 μmol m⁻² s⁻¹. In order to assess the effects of long-term photoinhibition, changes in oxygen production rate, pigment composition, xanthophyll cycle and in vivo chlorophyll fluorescence using the saturating pulse method were measured. Growth rate was maximal at intermediate irradiance (250 and 700 μmol m⁻² s⁻¹). The increase in growth irradiance from 700 to 1500 μmol m⁻² s⁻¹ did not lead to further significant changes in pigment composition or EPS, indicating saturation in the pigment response to high light. Changes in Photosystem II optimum quantum yield (F_v/F_m) evidenced photoinhibition at 700 and especially at 1500 μmol m⁻² s⁻¹. The relation between photosynthetic electron flow rate and photosyntetic O₂ evolution was linear for cultures in darkness shifting to curvilinear as growth irradiance increased, suggesting the interference of the energy dissipation processes in oxygen evolution. Carbon assimilation efficiencies were studied in relation to changes in growth rate, internal carbon and nitrogen composition, and organic carbon released to the external medium. All illuminated cultures showed a high capability to maintain a C:N ratio between 6 and 7. The percentage of organic carbon released to the external medium increased to its maximum under high irradiance (1500 μmol m⁻² s⁻¹). These results suggest that the release of organic carbon could act as a secondary dissipation process when the xanthophyll cycle is saturated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Complementary limiting factors of astaxanthin synthesis during photoautotrophic induction of <Emphasis Type="Italic">Haematococcus pluvialis</Emphasis>: C/N ratio and light intensity

We investigated the effect of carbon/nitrogen (C/N) ratio on astaxanthin synthesis in Haematococcus pluvialis during photoautotrophic induction by continuous input of both CO₂–air mixture and intense light. When H. pluvialis was induced by constant irradiance induction at 200 μmol photon m⁻² s⁻¹, there was a positive correlation with astaxanthin content and C/N ratio, which was similar to the case for heterotrophic induction. Lower C/N ratios did not retard Haematococcus encystment, but did increase culture biomass, resulting in a decrease in astaxanthin production because of light limitation. However, induction using variable irradiance showed that reduction of astaxanthin production at low C/N ratios was successfully overcome by simply increasing the light intensity from 200 to 300 μmol photon m⁻² s⁻¹ to overcome the light limitation. This resulted in a greatly enhanced astaxanthin synthesis in proportion to cell density in cultures with low C/N ratios. Our results indicate that light intensity is more critical than C/N ratio in astaxanthin production by H. pluvialis during photoautotrophic induction.     

Effects of daylength,irradiance and settlement density on the growth and reproduction of <Emphasis Type="Italic">Undaria pinnatifida</Emphasis> gametophytes

The effects of daylength, irradiance and spore settlement density on the growth, maturation and sporophyte production of Undaria pinnatifida (Harvey) Suringar gametophytes were examined using a factorial experimental design in culture. The growth of Undaria gametophytes increased with increasing daylength (8, 12 and 16 h), but the maximum fertility occurred at a daylength of 12 h followed by 8 and 16 h. Gametophytes grew better at the 16 h daylength under the same mean daily irradiance (MDI) of 20 μmol photons m⁻² s⁻¹. However, the fertility was higher at the short daylength (8 h), indicating that the maturation of U. pinnatifida gametophytes is influenced by daylength rather than by the MDI. Vegetative growth and sporophyte production of gametophytes were better at 60 μmol photons m⁻² s⁻¹ than at 30 μmol photons m⁻² s⁻¹ under a 8:16 h LD (Light: Dark) cycle, and their growth and maturation were density-dependant in 16 and 12 h daylength, respectively. These results suggest that the U. pinnatifida gametophytes require a certain amount of light for the growth and reproduction, and intraspecific competition occurred under the optimal growth and maturation conditions. However, the sporophyte recruits per unit has been enhanced with increasing spore settlement density at 8 and 12 h daylengths indicating that high settlement density gives a benefit for maintaining population, even though the sporophyte production of each female plant is inhibited. In conclusion, the vegetative growth, reproduction and sporophyte production of U. pinnatifida gametophytes are retarded at a low irradiance above growth saturation and a high settlement density, and are determined by daylength.     

Phenology of Chondrus ocellatus in Cheongsapo Near Busan, Korea

The reproductive phenology of Chondrus ocellatus and the effects of temperature and light on its growth were examined in Cheongsapo near Busan, Korea, from September 1994 to August 1995. The vegetative plants dominated over the year, with a peak occurrence in January. Gameto- and tetrasporophytes were most abundant in November and August. All vegetative and reproductive plants had a peak both in length and weight in October, when seawater temperature was highest (24°C). In laboratory culture, the maximum relative growth rate (RGR) of 2.94% day⁻¹ was obtained at 20°C and 100 μmol photons m⁻² s⁻¹, whereas the lowest value was recorded at 25°C and 100 μmol photons m⁻² s⁻¹ in a 12: 12 h LD photoperiod regime. Among the three photoperiod regimes (8:16 h, 12:12 h, 16:8 h LD) tested, there was evidence of a higher RGR in the 12:12 h LD cycle. This result suggests that the growth and reproduction of C. ocellatus are correlated with the seawater temperature based on laboratory culture and field observations.     

Life-cycle of <Emphasis Type="Italic">Scinaia interrupta</Emphasis> (Nemaliales,Rhodophyta)

The life-cycle of Scinaia interrupta (A.P. de Candolle) M. J. Wynne was investigated in vitro using four irradiance regimes: 4, 8, 12 and 16 μmol photons m⁻² s⁻¹. A triphasic heteromorphic life-cycle was observed. Carpospores released by cystocarps of gametophytes collected in the field developed into filamentous tetrasporophytes, which produced tetrahedral tetrasporangia. Tetrasporangial development was accelerated under higher irradiance levels. Tetraspores germinated into filamentous protonemal gametophytes, initially identical to the tetrasporophyte. Filamentous gametophytes developed apical utricles and gave rise directly to the fleshy gametophyte. Further development of the fleshy gametophyte was not observed at the lowest irradiance regime (4 μmol photons m⁻² s⁻¹). The present study reports for the first time the influence of the irradiance regime on the initial tetrasporangial development and in the development of the fleshy gametophyte, and reinforces the importance of light intensity on Scinaia life-cycle. Production of apical utricles by the filamentous gametophyte is newly reported for the genus.     

Growth responses and photosynthetic characteristics of wild and phycoerythrin-deficient strains of <Emphasis Type="Italic">Hypnea musciformis</Emphasis> (Rhodophyta)

The phycoerythrin-deficient strain (green phenotype) of Hypnea musciformis (Rhodophyta) originated from a green branch, which had arisen as a spontaneous mutation in a wild plant (brown phenotype) collected from the Brazilian coast. The present study describes the growth responses to irradiance, photoperiod and temperature variations, pigment contents, and photosynthetic characteristics of the brown and green strains of H. musciformis. The results showed that growth rates increased as a function of irradiance (up to 40 μmol photons m⁻² s⁻¹) but, with further increase in irradiance (from 40 to 120 μmol photons m⁻² s⁻¹), became light-saturated and remained almost unchanged. The highest growth rates of the brown and green strains were observed in temperatures of 20–25°C under long (14:10 h LD) and short (10:14 h LD) photoperiods. The brown strain had higher growth rates than the green strain in the short photoperiod, which could be related to the high concentrations of phycobiliproteins. Phycoerythrin was not detected in the green strain. The brown strain had higher concentrations of allophycocyanin and phycoerythrin in the short photoperiod while the green strain had higher concentrations of phycocyanin. The brown strain presented higher photosynthetic efficiency (α), and lower saturation parameter (I_k) and compensation irradiance (I_c) than the green strain. The brown strain exhibited the characteristics of shade-adapted plants, and its higher value of photosynthetic efficiency could be attributed to the higher phycoerythrin concentrations. Results of the present study indicate that both colour strains of H. musciformis could be selected for aquaculture, since growth rates were similar (although in different optimal light conditions), as the green strain seems to be adapted to higher light levels than the brown strain. Furthermore, these colour strains could be a useful experimental system to understand the regulation of biochemical processes of photosynthesis and metabolism of light-harvesting pigments in red algae.     

Assessment of optimal depth and photon irradiance for cultivation of the brown alga, <Emphasis Type="Italic">Sargassum fulvellum</Emphasis> (Turner) C. Agardh

This study was aimed at determining the optimal depth and photon irradiance for growth of Sargassum fulvellum. Sampling and measurement of underwater irradiance were carried out at farms cultivating S. fulvellum at Wando, southwestern coast of Korea, from May 2004 to April 2005. Growth of thalli, underwater irradiance and photosynthetic quantum yield were measured over a range of depths for three culture stages. During their nursery cultivation stage (Stage I), length increase was greatest at 1.5 m depth (2.5 ± 0.2 cm), where the average midday irradiance over 28 days was 488 ± 58 μmol photons m⁻² s⁻¹. During the pre-main cultivation stage (Stage II), the greatest length increase occurred at 1 m depth (10.9 ± 0.1 cm) with an average irradiance of 845 ± 169 μmol photons m⁻² s⁻¹. For the main cultivation stage (Stage III) of the alga, thalli showed maximal length growth in March and early April at depths of 1–2 m and 3 m. These results suggest that growth at each cultivation stage of S. fulvellum could be controlled by depth of cultivation rope. Presented at the 6th Meeting of the Asian Pacific Society of Applied Phycology, Manila, Philippines.     

Effects of temperature,photosynthetic photon flux density,photoperiod and O<Subscript>2</Subscript> and CO<Subscript>2</Subscript> concentrations on growth rates of the symbiotic dinoflagellate, <Emphasis Type="Italic">Amphidinium</Emphasis> sp.

Symbiotic dinoflagellates of the species Amphidinium are expected to be pharmaceutically useful microalgae because they produce antitumor macrolides. A microalgae production system with a large number of cells at a high density has been developed for the efficient production of macrolide compounds. In the present study, the effects of culture conditions on the cellular growth rate of dinoflagellates were investigated to determine the optimum culture conditions for obtaining high yields of microalgae. Amphidinium species was cultured under conditions with six temperature levels (21–35°C), six levels of photosynthetic photon flux density (15–70 μmol photons m⁻² s⁻¹), three levels of CO₂ concentration (0.02–0.1%), and three levels of O₂ concentration (0.2–21%). The number of cells cultured in a certain volume of solution was monitored microscopically and the cellular growth rate was expressed as the specific growth rate. The maximum specific growth rate was 0.022 h⁻¹ at a temperature of 26°C and O₂ concentration of 5%, and the specific growth rate was saturated at a CO₂ concentration of 0.05%, a photosynthetic photon flux density of 35 μmol photons m⁻² s⁻¹ and a photoperiod of 12 h day⁻¹ upon increasing each environmental parameter. The results demonstrate that Amphidinium species can multiply efficiently under conditions of relatively low light intensity and low O₂ concentration.     

Effects of light intensity and nitrogen starvation on growth, total fatty acids and arachidonic acid in the green microalga Parietochloris incisa

The effects of light and nitrogen deficiency on biomass, fatty acid content and composition were studied in Parietochloris incisa, the unicellular freshwater chlorophyte accumulating very high amounts of arachidonic-acid-rich triacylglycerols. P. incisa cultures grown on complete nutrient medium and under high light (400 μmol photons m^{− 2} s⁻¹) showed the highest rate of growth in comparison to medium (200 μmol photons m⁻² s⁻¹) and low (35 μmol photons m⁻² s⁻¹) light intensity. Cultures grown under high light (on complete BG-11 medium) attained higher volumetric contents of total fatty acids and arachidonic acid due to greater increase in biomass. Nitrogen starvation brought about a strong increase in the arachidonic acid proportion of total fatty acids. Thus, adjustments to cultivation conditions could serve as an efficient tool for manipulation of yield and relative content of arachidonic acid in P. incisa. The significance of the changes in lipid metabolism for adaptation of P. incisa to high-light stress and nitrogen deficiency is also discussed.     

A preliminary study of the bioremediation potential of Codium fragile applied to seaweed integrated multi-trophic aquaculture (IMTA) during the summer

In integrated multi-trophic aquaculture (IMTA), seaweeds have the capacity to reduce the environmental impact of nitrogen-rich effluents in coastal ecosystems. To establish such bioremediation systems, selection of suitable seaweed species is important. The distribution and productivity of seaweeds vary seasonally based on water temperature and photoperiod. In Korea, candidate genera such as Pophyra, Laminaria, and Undaria grow from autumn to spring. In contrast, Codium grows well at relatively high water temperatures in summer. Thus, aquaculture systems potentially could capitalize on Codium’s capacity for rapid growth in the warm temperatures of late summer and early fall. In this study, we investigated ammonium uptake and removal efficiency by Codium fragile. In laboratory experiments, we grew C. fragile under various water temperatures (10, 15, 20, and 25°C), irradiances (dark, 10, and 100 μmol photons m⁻² s⁻¹), and initial ammonium concentrations (150 and 300 μM); in all cases, C. fragile exhausted the ammonium supply for 6 h. At 150 μM of , ammonium removal efficiency was greatest (99.5 ± 2.6%) when C. fragile was incubated at 20°C under 100 μmol photons m⁻² s⁻¹. At 300 μM of , removal efficiency was greatest (86.3 ± 2.1%) at 25°C under 100 μmol photons m⁻² s⁻¹. Ammonium removal efficiency was significantly greater at 20 and 25°C under irradiance of 100 μmol photons m⁻² s⁻¹ than under other conditions tested.     

Cultivation of the brown alga Hizikia fusiformis (Harvey) Okamura: controlled fertilization and early development of seedlings in raceway tanks in ambient light and temperature

Commercial cultivation of the dioecious brown macroalga Hizikia fusiformis (Harvey) Okamura in East Asia depends on the supply of young seedlings from regenerated holdfasts or from wild population. Recent development of synchronized release of male and female gametes in tumble culture provides a possibility of mass production of young seedlings via sexual reproduction. In this paper, we demonstrate that controlled fertilization can be efficiently realized in ambient light and temperature in a specially designed raceway tank in which the sperm-containing water has been recirculated. The effective fertilization time of eggs by sperm was found to be within six hours. Fast growth and development of the young seedlings relied on the presence of water currents. Velocity tests demonstrated that young seedlings of 2–3 mm in length could withstand a water current of 190 cm s⁻¹ without detachment. Culture experiments at 24 h postfertilization showed that elongation of both the seedlings and their rhizoids were not hampered by high irradiance up to 600 μmol photons m⁻² s⁻¹. However, growth was slightly retarded if cultured at a temperature of 16 ^∘C compared to other culture temperatures of 22, 25 and 29 ^°C. No seedling detachment was observed after transfer of the young seedlings to raft cultivation in the sea after one and 1.5 months post-fertilization, indicating the feasibility of obtaining large quantity of seedlings in such a system.     

Morphometry and growth of three <Emphasis Type="Italic">Synechococcus</Emphasis>-like picoplanktic cyanobacteria at different culture conditions

Three phycocyanin-rich strains of Synechococcus-like picoplanktic cyanobacteria, isolated from the plankton of Czech oligotrophic to eutrophic freshwater reservoirs, were investigated in crossed gradients of light and temperature and in combination with two different culture media (BG-11 and WC). The strains exhibited similar growth and reproduction patterns and displayed overlapping ranges of cell size (1.5 × 0.8 μm) under standardized laboratory conditions (18 μmol m⁻² s⁻¹; 20°C). However, strains behavior differed in the crossed gradients. All strains preferred BG-11 medium, where also remarkable size changes could be observed. Length, width, cell abundance and growth rate of two strains were positively correlated with temperature and nutrients, whereas the impact of light intensity was insignificant. Maximum cell elongation (involution cells up to 19 μm) occurred in two strains only in BG-11 medium at highest temperature (28°C) and highest irradiance (53 μmol m⁻² s⁻¹). Cell dimensions in WC medium were constant under most conditions given. The third strain was influenced by all three factors, from which light and nutrients played pivotal role. The length of the lag-phase for all strains appeared to be temperature dependent (negative correlation). Despite the fact that the cell volume in all strains increased more than five times under the lowest light and low temperature (6 μmol m⁻² s⁻¹, <15°C) in both media, the length/width ratio remained unchanged. The strains differed in the degree of cell enlargement and cell division symmetry as well as in optimum temperature and light dependence. Based on this experimental work two strains could be identified as Synechococcus sp. and one as Cyanobium sp., which can be used as a support for the following genetical analyses.     

Effects of temperature and irradiance on photosynthesis and growth of a green-tide-forming species (<Emphasis Type="Italic">Ulva linza</Emphasis>) in the Yellow Sea

Samples of the massive drifting green alga, Ulva linza, were collected from the coastal waters of the Yellow Sea, southwest of Korea, in early July 2009, and cultured under laboratory conditions. The effects of various temperature (10–30°C) and irradiance levels (0–1,000 μmol photons m⁻² s⁻¹) on photosynthesis, growth, and tissue nutrient content of U. linza were investigated in laboratory for both individuals of the late-stage vegetation (LSV) and the early-stage vegetation (ESV). After 1 h acclimation to various irradiance and temperature conditions, maximum gross photosynthetic rate of ESV was significantly higher than those of LSV. In the long-term (7-d) acclimation experiments to various irradiance and temperature levels, gross photosynthetic rates of ESV individuals were also significantly higher than those of LSV individuals. High photosynthetic rate of ESV individuals induced increase in mass of about 60% over the growth saturation irradiance (136 μmol photons m⁻² s⁻¹) and about 20% under low temperature conditions (10–15°C) during 7-d. The gross photosynthesis of LSV individuals was low when examined under temperature and irradiance conditions that were optimum for ESV growth. Consequently, free-floating U. linza exhibits cellular senescence beginning in early July in the Yellow Sea, and green tides formed by this species cannot be maintained beyond this time in the open sea. However, we expect that U. linza can proliferate quickly after settlement on new coastal habitats of the Yellow Sea because of the high tissue nitrogen utilization for photosynthesis in ESV, which is formed by germination of reproductive cells.