Chroomonas Salina Research Articles

Effect of nitrogen to phosphorus ratios on cell proliferation in marine micro algae

The ratio of nitrogen/phosphorus (N/P) is known to affect cell proliferation of some marine micro algae. We evaluated the effect of N/P ratios on the proliferation and succession of phytoplankton using five marine micro algae species. We used two sources of nitrogen, NH4Cl (N1) and urea (N2), and a single source of phosphorous, NaH2PO4(P). The optimal N/P ratio that differed among the five species was affected by the source of nitrogen, being as follows (N1/P, N2/P in order): Thalassiosira sp. (30/1, 20/1), Heterosigma akashiwo (30/1, 30/1), Chroomonas salina (20/1, 30/1), Chaetoceros gracilis (40/1, 60/1), and Alexandrium sp. (10/1, 30/1). Thus, the source of nitrogen must be considered when analyzing the N/P ratio. Our results provide insight for predicting phytoplankton succession in coastal waters and may be used to forecast the potential risk of harmful algal blooms.

광합성 측정기를 이용한 미세조류의 광합성 효율 측정

In this study, the PHYTO-PAM-fluorometric method was used to evaluate the ETR<TEX>$_{max}$</TEX> in terms of sensitivity to DIN/DIP against 14 microalgae: Prorocentrum micans, Heterocapsa triquetra, Gymnodinium impudicum, Cymnodinium catenatum, Amphidinium caterae, Chlorella vulgaris, Chroococcus minutus, Microcystis aeruginosa, Chlorella ellipsoidea, Nannochloris oculata, Oocystis lacustris, Chroomonas salina, Gloeocystis gigas, and Prymnessium parvum. We found that P. micans, H. triquetra, and A. caterae exposed to the maximum level of DIN/DIP were significantly smaller in the ETR<TEX>$_{max}$</TEX> than that of the minimum and moderate mixture. Unlikely the ETR<TEX>$_{max}$</TEX>, the initial slope alpha was not significantly different at the level of 60 DIN/DIP. In G. catenatum, the moderate levels of 15 and 20 in DIN/DIP were found to be significantly different from the ETR<TEX>$_{max}$</TEX> at Chl-Ch4. Gymnodinium impudicum had a higher value than that of the ETR<TEX>$_{max}$</TEX> than that of dinoflagellates used in this study, ranging from 306.1 (Ch4, DIN/DIP: 10) to 520.1 (Ch4, DIN/DIP: 30). The ETR<TEX>$_{max}$</TEX> value obtained from other microalgae was similar to C. impudicum at any of the ratios of DIN/DIP and channels. Consequently, the influence of offshore water current assures us of the suppression of photosynthesis and electron transport rate in dinoflagellates. Gymnodinium impudicum has not been researched in the area of red tides in Korea, but it will be enough to creat the massive algal blooms in the future because of higher potential photochemical availability.

Food type and concentration affect chlorophyll and carotenoid destruction during copepod feeding

To evaluate the use of pigments as tracers for determining copepod grazing rates and selectivity, we examined the stability of several biomarker pigments during copepod feeding incubations. During these incubations, we measured changes in phytoplankton‐derived chlorophylls and carotenoids in the particulate and dissolved pools. Budgets were calculated to determine changes in pigment concentrations in the food, copepod fecal pellets, copepod guts, and dissolved/colloidal fraction. For each of six algal diets, adult female Acartia tonsa copepods were fed limiting and saturating food concentrations, approximately 100 and 500 µg C L−1 , respectively. Thalassiosira weissflogii, Rhodomonas lens, Chroomonas salina, Dunaliella tertiolecta, and two Tetraselmis strains were used in the feeding experiments to investigate the fate of fucoxanthin, alloxanthin, lutein, chlorophyll (Chl) b, and Chl a. In all experiments using saturating food concentrations, the dissolved/colloidal pool contained no more than 3% (usually less than 1%) of any pigment, whereas in experiments using limiting food conditions, pigments were undetectable in the dissolved/colloidal pool. Pheopigments were present in fecal pellets and copepod guts in most of the experiments. Chl a destruction (conversion to colorless products) was variable among the different experiments, depending on algal species and food concentration and, in most cases, Chl a was destroyed to a greater extent than the carotenoids. In all cases, pigment destruction was higher when copepods were fed limiting rather than saturating food concentrations. These data attribute the variability in pigment destruction to algal species and concentration, and suggest caution when pigments are used as tracers of herbivory. In such studies, assumptions about conservative behavior, even for the carotenoids, would need to be verified for each set of experimental conditions and grazers.

Gas chromatographic-mass spectrometric identification of betaine lipids in Chroomonas salina

The betaine lipids diacylglycerylhydroxymethyltrimethyl-β-alanine (DGTA) and diacylglyceryltrimethylhomoserine (DGTS) can be identified by derivatization of their polar groups. Demethylation, deacylation and silylation of DGTS yields demethyl-deacyl-DGTS-TMSi; dihydro-deamino-deacyl-DGTA-TMSi is produced by deamination, hydrogenation, deacylation and silylation of DGTA. The characterization of the derivatives by GC-MS was used as a diagnostic method for the identification of DGTA in Chroomonas salina, where this lipid accounts for 20% of the total polar lipids. Major fatty acids of DGTA (%) are 22:6 n−3 (22), 20:5 n−3 (14), 18:1 n−7 (12), 18:4 n−3 (11), 16:0 (8), and 14:0 (8), indicating that this lipid contains a broad variety of different molecular species in this alga.

Temperature and nutrition as factors in conditioning broodstock of the commercial scallop Pecten fumatus Reeve

Difficulty in obtaining ripe broodstock of the commercial scallop Pecten fumatus from wild populations in New South Wales prompted the development of hatchery conditioning protocols. Microalgal diets, feeding rates and holding temperatures conducive to rapid gonadal growth and development were identified. Results of microalgal clearance rate experiments indicated that the species Pavlova lutheri, Tahitian Isochrysis aff. galbana, Chroomonas salina and Chaetoceros gracilis are ingested by adult scallops at similar rates at 14, 18 and 21 °C, but more slowly at 11 °C. Maximum (satiation) ingestion rate using mixed diets containing approximately equal numbers of cells of these four species, was estimated as about 6 × 10 9 cells per day for broodstock in the range 55 to 75 mm shell height. Large numbers of cells of the microalga Tetraselmis suecica passed through the digestive tract of scallops undigested. Egg production rate, gonad size and condition factors were all highest when broodstock were held at 15 °C, lowest for scallops maintained at 21 °C and of intermediate values at temperatures of 12 and 18 °C. Gonad condition and egg production increased as feeding rates were raised from 12.5 to 100% of satiation at all test temperatures in the range 12 to 21 °C. Frequent spawning triggered by routine handling of broodstock during these experiments emphasised the need for conditioning equipment and protocols that minimise handling and other disturbance factors. No unplanned spawning occurred at feeding rates of 25% or 12.5% of satiation at 12 °C. The use of low temperature and low feeding rate might therefore enable short term stockpiling of broodstock once they attain prime breeding condition. Findings of these experiments were successfully applied to a subsequent large scale conditioning and induced spawning trial.

Reduction in omega-3 fatty acids by UV-B irradiation in microalgae

UV-B irradiation reduced the levels of omega-3 fatty acid, eicosapentaenoic acid (EPA, 20:5ω3) and docosahexaenoic acid (DHA, 22:6ω3), in microalgae; the degree of reduction varied with species.Chaetoceros calcitrans andSkeletonema costatum were high UV-B tolerant species, followed byPhaeodactylum tricornutum, Chroomonas salina, Pavlova lutheri, andThalassiosira pseudonana.Isochrysis galbana (T.ISO) andProrocentrum micans were UV- B sensitive. Cells in logarithmic phase were most sensitive to UV- B irradiation. Nitrate-, phosphate-, or sulphate-starved cells were more UV-B sensitive than non-starved cells grown in a complete basal medium. A relatively short exposure to high UV-B was more damaging than a longer exposure to lower irradiance. Visible light intensity levels had a profound impact on the sensitivity of microalgal cultures to UV-B, with high levels decreasing UV-B dependent damage. Addition of polyamines (putrescine, spermidine or spermine) or an amino acid (cysteine) to the culture medium minimized the reduction of omega-3 fatty acid content in microalgae caused by UV-B irradiation.

Influence of composition of Brachionus plicatilis and Artemia on growth of larval sablefish ( Anoplopoma fimbria Pallas)

Larval sablefish, Anoplopoma fimbria, were fed rotifers, Brachionus plicatilis, and later brine shrimp, Artemia, reared on the microalgae, Nannochloropsis oculata, Isochrysis galbana (T-Iso) and Chroomonas salina. Diet composition significantly influenced growth and time to 50% mortality of larvae. Survival was greatest for the group fed zooplankton reared on N. oculata and least in the group reared on C. salina. Protein content was significantly higher in rotifers reared on I. galbana (T-Iso) than on the other algae, but was not correlated with larval growth or survival. Lipid content of rotifers was independent of algal species used in production. Carbohydrate was highest in rotifers fed N. oculata and may have influenced the survival of sablefish larvae. Contents of protein, lipids and carbohydrate in Artemia reared on different algae were not significantly different, minimizing any influence on growth and development of the larvae. Contents of constituent fatty acids in rotifers, but not Artemia, were the major differences in these dietary plankton fed to fish larvae. B. plicatilis contained 15% 20:5 n−3 (EPA) and 0.3% 22:6 n−3 (DHA) when reared on N. oculata, 3.3% EPA and 5.2% DHA when reared on I. galbana (T-Iso) and 5.6% EPA and 3.0% DHA when reared on C. salina. The failure to rear the larvae beyond day 60 from first feeding and the observed 50% n−3 HUFA in lipid of sablefish eggs and pelagic zooplankton, suggests that the dietary HUFA levels used to feed larvae in this study were too low to meet the apparent HUFA requirement.

The ascorbic acid content of eleven species of microalgae used in mariculture

The ascorbic acid (vitamin C) concentrations in 11 species of microalgae commonly used in mariculture were determined. The species examined were 4 diatoms (Chaetoceros calcitrans (Paulsen) Takano,Chaetoceros gracilis Schutt,Skeletonema costatum (Greville) Cleve,Thalassiosira pseudonana (Hustedt, clone 3H) Hasle and Heimdal); 2 prymnesiophytes (Isochrysis sp. (clone T.ISO) Parke,Pavlova lutheri (Droop) Green); 1 prasinophyte (Tetraselmis suecica (Kylin) Butcher); 2 chlorophytes (Dunaliella tertiolecta Butcher,Nannochloris atomus Butcher); 1 eustigmatophyte (Nannochloropsis oculata (Droop) Green); and 1 cryptophyte (Chroomonas salina (Wislouch) Butcher). Duplicate cultures of each species were grown under defined conditions and analysed during both logarithmic and stationary phase of growth. Average values for ascorbic acid ranged from 9.4 fg cell−1 (N. oculata, stationary phase) to 700 fg cell−1 (S. costatum, stationary phase). This value was generally related to cell size. Levels of ascorbic acid cell−1 increased during the stationary growth phase forS. costatum andD. tertiolecta and decreased forC. gracilis, T. pseudonana, C. salina andN. oculata. Levels did not change significantly for the remaining species. Average values for per cent ascorbic acid ranged from 0.11% (T. pseudonana, stationary phase) to 1.62% of dry weight (C. gracilis, logarithmic phase). The per cent ascorbic acid was not related to algal class. Also, the percentage between logarithmic and stationary phase cultures differed for many of the species, but differences were unrelated to algal class.Chaetoceros gracilis, T. pseudonana, N. oculata andIsochrysis sp. (T.ISO) had higher per cent ascorbic acid during the logarithmic phase, whereasD. tertiolecta andN. atomus contained more per cent ascorbic acid during the stationary phase. Despite the differences in the composition of the different microalgae (0.11–1.62% ascorbic acid), all species would provide a rich source of ascorbic acid for maricultured animals, which can require 0.003–0.02% of the vitamin in their diet.

The amino-acid and sugar composition of 16 species of microalgae used in mariculture

The biochemical compositions of 16 species of microalgae commonly used in mariculture were determined. The species examined were six diatoms [ Chaetoceros calcitrans (Paulsen) Takano, Chaetoceros gracilis Schutt, Nitzchia closterium (Ehrenb.) W. Smith, Phaeodactylum tricornutum Bohlin, Skeletonema costatum (Greville) Cleve, Thalassiosira pseudonana (Hustedt, clone 3H) Hasle and Heimdal], four prymnesiophytes [ Isochrysis galbana Parke, Isochrysis aff. galbana Parke (T-iso), Pavlova lutheri (Droop) Green, Pavlova salina (N. Carter) Green], two prasinophytes [ Tetraselmis chui Butcher, Tetraselmis suecica (Kylin) Butcher], two chlorophytes [ Dunaliella tertiolecta Butcher, Nannochloris atomus Butcher], one eustigmatophyte [ Nannochloropsis oculata (Droop) Green] and one cryptophyte [ Chroomonas salina (Wislouch) Butcher]. The microalgae were grown under defined conditions and harvested during the log phase of growth. Levels of protein, lipid and carbohydrate were quite variable between species. In particular, N. atomus contained almost twice the proportion of carbohydrate compared to all other species. The amino-acid compositions of the microalgae were quite similar, although T. chui and T. suecica were richer in arginine, while N. atomus had high levels of proline. The amino-acid compositions were compared with those of oyster Crassostrea gigas Thunberg larvae to assess the protein quality of the microalgae. The levels of the essential amino-acids in the microalgae were either similar to or greater than the levels of the same amino acids in oyster larvae, thus indicating a high protein quality for all microalgal species. Therefore, in relation to differences in the nutritional value of the microalgae, the amino-acid composition may not be critical. The sugar composition of the polysaccharides from microalgae did however show major differences between species and between classes. Glucose was the principal sugar, while rhamnose, fucose, ribose, arabinose, xylose, mannose, and galactose were detected in varying proportions. The variations in the sugar composition could contribute to differences in the nutritional value of some species, since animals digest polysaccharides of different composition at different rates.

Filtration rate of blue mussels as a function of flow velocity: preliminary experiments

The filtration rate of adult blue mussel Mytilus edulis L. was measured in flume flows ranging from 6–38 cm · s −1 at a constant seston concentration. At > 25 cm · s −1, blue mussel filtration rates were low, <10% of 10 4 cells · ml −1 of Chroomonas salina filtered · h −1 vs. up to 41% at 6.8 cm· s −1. The mechanism of flow-induced inhibition of filtration rate in the blue mussel could not be determined by the experimental approach used. Two previously described mussel pump characteristics initiated in response to increases in ambient flow pressure — pump shutdown or gill bypass shunting — are possible explanations for feeding inhibition.

Differential Effects of the Substituted Pyridazinone Herbicide Sandoz 9785 on Lipid Composition and Biosynthesis in Photosynthetic and Non-Photosynthetic Marine Microalgae

The effect of the substituted pyridazinone, 4-chloro-5-(dimethylamino)-2-phenyl-3(2H)-pyridazinone (Sandoz 9785), on fatty acid synthesis in two photosynthetic species (Chroomonas salina and Nannochloropsis oculata) and one non-photosynthetic species (Crypthecodiniun cohnii) of marine microalgae were examined. Effects were more obvious in C. salina than in C. cohnii or N. oculata. In C. cohnii the relative distribution amongst polyunsaturated fatty acids (PUFA) of radioactivity incorporated from 14C-acetate was not influenced by the herbicide to any great extent and no major changes in the fatty acid composition of lipid fractions were observed. In C. salina, Sandoz 9785 reduced the proportions of radioactivity recovered in 20: 5 (n−3) and 22: 6 (n−3) of the phospholipid fraction. The distribution pattern of radioactivity in the fatty acids of monogalactosyldiacylglycerol (MGDG) in this species was not greatly affected by the herbicide whereas its presence significantly reduced the proportions recovered in 18: 4 and 20: 1 in digalactosyldiacylglycerol (DGDG). The level of 20: 5 (n−3) in DGDG of C. salina was increased from 4.0 to 19.8% by growing the algae in the presence of Sandoz 9785. The only notable effect of the herbicide on the synthesis of PUFA in N. oculata was a reduction from 18.3% to 11.3% of the proportion of radioactivity recovered in 20: 5 in phospholipids. The herbicide had no effect on the distribution of radioactivity in PUFA of galactolipids or on the fatty acid composition of lipid fractions. The results are discussed in relation to the potential role of galactolipids and phospholipids as substrates for desaturations involved in the formation of long chain PUFA in marine microalgae.

Fatty acid and lipid composition of 10 species of microalgae used in mariculture

Total fatty-acid composition, lipid classes, Chl a contents and cell volumes of 10 species of microalgae commonly used in mariculture were examined. The microalgae were grown under defined conditions and harvested during log phase. Significant concentrations of the polyunsaturated fatty acid 20:5(n-3) (eicosapentaenoic acid) were present in each of the four diatoms Chaetoceros calcitrans, Chaetocerosgracilis, Skeletonema costatum and Thalassiosira pseudonana (4.6–11.1% of the total fatty acids), the cryptomonad Chroomonas salina (10.9, 11.9%) and the prymnesiophyte Pavlova lutheri (19.7%). Very small amounts were found in another prymnesiophyte, Isochrysis sp., and the green algae Nannochloris atomus and Tetraselmis suecica but none was detected in the green alga Dunaliella tertiolecta. In contrast, high concentrations of 22:6(n-3) (docosahexaenoic acid) were present only in the two prymnesiophyte algae and Chroomonas salina. Chl a and total fatty-acid contents were not related to cell volume. Fatty acids were four to six times more abundant than Chl a in most species. Relative concentrations of intact lipids were determined for each species using latroscan thin-layer chromatography-fiame-ionisation detection. Polar lipids predominated in all species but triacyglycerols were abundant only in Chaetoceros gracilis, Isochrysis sp. and Chroomonas sp. Free fatty acids were particularly abundant in the two Chaetoceros species. The importance of these data for determining the nutritional value of the microalgae as food for animals in mariculture is discussed.

Lipid composition and biosynthesis in ageing cultures of the marine cryptomonad, Chroomonas salina

Changes in the lipid composition of cultures of the marine cryptomonad Chroomonas salina allowed to age at 20 and 7° were examined. At both temperatures the proportion of wax esters present in lipid increased with culture age. After 14 weeks, 31% and 25% of the lipids from cultures maintained at 20 and 7° respectively were wax esters. The fatty acids of wax esters and triacylglycerols were predominantly saturated at both temperatures. The fatty alcohols of the wax esters were almost exclusively saturated and contained high proportions of 13:0 and 15:0. Polyunsaturated fatty acids (PUFA), particularly 18:4(n-3), 20:5(n-3) and 22:6(n-3), accounted for a higher proportion of the fatty acids in total polar lipid from cultures aged at 7° than at 20°. Cultures of the alga maintained under the same light intensity at 20 and 10° incorporated 11.8 and 22.9% respectively of total radioactivity assimilated from 14CO2 into lipid. The amount of radioactivity from 14C-labelled CO2, acetate and 18:1(n-9) incorporated into triacylglycerols and wax esters increased with the age of cultures. The proportions of radioactivity from all three substrates recovered in trienoic and polyunsaturated fatty acids of total lipid were higher in cultures maintained at 10° than at 20°.

Effect of temperature on lipid composition of the marine cryptomonad Chroomonas salina

The lipid compositions of the marine cryptomonad Chroomonas salina cultured at 20 and 8° were compared. Algae cultured at 8° had a higher lipid content than those maintained at 20°. Triacylglycerols (TAG) were the major lipid class at both temperatures. The proportion of sterols in total lipid exhibited the most significant change in relation to temperature. Saturated fatty acids always predominated in TAG although their proportion was decreased, and that of monoenes increased, by culturing the alga at 8°. Monogalactosyldiacylglycerol and digalactosyldiacylglycerol, particularly the latter, were characterised by high levels of C 18 polyunsaturated fatty acids (PUFA). Culturing algae at 8° resulted in significant increases in the proportion of 18:4( n-3) with corresponding decreases in those of 18:2( n-6) and 18:3( n-6), in both these galactolipids. PUFA also predominated in phospholipids but the levels of 20:5( n-3) and 22:6( n-3) were higher than in galactolipids. The magnitude of changes in fatty acid composition in relation to temperature was smaller in phospholipids than in galactolipids.

The use of 0.2-μm membrane-filtered seawater for improved control of bacterial levels in microalgal cultures fed to larval Pacific oysters ( Crassostrea gigas)

Microalgae ( Isochrysis galbana, Chaetoceros calcitrans, Chroomonas salina, Dunaliella tertiolecta, Thalassiosira pseudonana, Tetraselmis suecica, Pavlova lutheri) cultured in 500-l bags and harvested semi-continuously, were studied in a commercial hatchery. Treatment of seawater used in the microalgal growth medium by 0.2-μm membrane filtration compared to pasteurization, resulted in much lower bacterial counts (expressed in log 10 units). The 0.2-μm filtered seawater contained 1.50 bacteria 100 ml −1 and microalgal cultures at harvest contained 5.87 bacteria ml −1. In contrast, significantly higher counts of bacteria were obtained in pasteurized seawater, 4.08 ml −1, and in cultures at harvest, 6.38 ml −1. Larval oyster production was limited by the incidence of fatal bacterial infections transmitted via microalgal cultures with >6.3 bacteria ml −1. The use of 0.2-μm filtered seawater resulted in the % of cultures with >6.3 bacteria ml −1 decreasing from 55.6% to 20.6% to 10.9% in successive production seasons, associated with the yield of ready-to-set larvae increasing from 1.3% to 3.2% to 4.6% of fertilized eggs. In cultures of all microalgal spp. fed, mixed rather than single bacterial biotypes were responsible for disease but these very rarely included Vibrio or Flavobacterium/Cytophaga spp., and never red-pigmented Pseudomonas spp. Bacteria colonized the surface of microalgae in 30–36% of speciemens examined by scanning electron microscopy.

Food and growth relations of the marine microzooplankter, Synchaeta cecilia (Rotifera)

The trophic interactions of the marine rotifer Synchaeta cecilia were investigated by determining its feeding and growth rates on a wide variety of marine phytoplankton and by determining its susceptibility to predation by the calanoid copepod, Acartia tonsa. Reproduction of S. cecilia was sustained in four-day feeding trails by 13 of 37 algal species tested. Growth-supporting species included species of Cryptophyceae, Dinophyceae, Chlorophyceae and Haptophyceae in sizes from 4 to 47 μm. Within these taxa, other species in the acceptable size range failed to support growth. No species of Cyanophyceae, Bacillariophyceae, or Chrysophyceae supported growth of the rotifer. S. cecilia can be maintained on unialgal cultures of Cryptophyceae but growth is enhanced by a combination of two or three species; a mixture of Chroomonas salina (Cryptophyceae), Heterocapsa pygmaea (Dinophyceae), and Isochrysis galbana (Haptophyceae) has sustained laboratory stocks of S. cecilia for over four years. The expected response of S. cecilia to food quantity was observed: as food concentration was increased from 58 to 1154 μg C 1−1, the population growth constant increased from 0.17 to 0.60 d−1 at 20°C. This is equivalent to population doubling times of 4.0 and 1.1 days at H. pygmaea densities of 500 and 104 cells ml−1, respectively. The susceptibility of S. cecilia to predation was investigated by determining its rate of capture by the omnivorous marine copepod Acartia tonsa. At prey densities of 5 to 35 μg C 1−1 (0.3 to 1.9 individuals 1−1), A. tonsa readily ingested S. cecilia at rates up to 3 μg C copepod−1 day−1.

Interactive effect of diet and temperature on the growth of juvenile clams

Small juveniles (0.3–3 mg live weight) of three clam species, Tapes semidecussata Reeve, T. decussata L., and Mercenaria mercenaria L., were fed eight single-species algal diets at a range of temperatures. Nutritional value of the algae tested was in the order: Isochrysis aff galbana (T. ISO) = Skeletonema costatum > Chaetoceros calcitrans = Chroomonas salina = Thalassiosira pseudonana > Tetraselmis suecica > Phaeodactylum tricornutum > Chlamydomonas coccoides, when the same weight of these species was given in the diet to each clam species. Reasons for differences in nutritional value are discussed with reference to the biochemical content of the algae and the relative growth efficiency of the animals. Respiration rate, food cell clearance rate, and growth (as increase in organic weight) of M. mercenaria and T. semidecussata increased with temperature from 10 to 25 °C. Growth rates decreased at > 25 °C. T. decussata showed only a slightly increased growth response at > 15 °C.

EXCITATION ENERGY TRANSFER IN THE CRYPTOPHYTES. FLUORESCENCE EXCITATION SPECTRA AND PICOSECOND TIME‐RESOLVED EMISSION SPECTRA OF INTACT ALGAE AT 77 K

AbstractExcitation spectra of chlorophyll‐a (Chl‐a) fluorescence in intact cells of Cryptomonas ovata, Chroomonas pauciplastida and Chroomonas salina were determined at 77 K. For all species the excitation spectra for emission from Chl‐a associated with photosystem II (PSII) showed increased contributions by a carotenoid (493 nm) and phycobiliproteins, and decreased contributions by carotenoid (417 nm, 505 nm) and Chl‐a (445 nm) as compared to excitation spectra for emission from Chl‐a associated with photosystem I (PSI). Excitation spectra of C. salina and C. ovata showed an increased contribution by Chl‐c2 to PSII Chl‐a fluorescence emission. In all three species the absorbance band positions of Chl‐a, as determined from the excitation spectra, were similar to those previously described in green plants. green algae and phycobilisome‐containing organisms. Time‐resolved 77 K fluorescence emission spectra of C. ovata and C. salina showed successive emission from both phycoerythrin and Chl‐c2, PSII Chl‐a, and PSI Chl‐a. C. pauciplastida showed successive emission from phycocyanin, PSII Chl‐a, and PSI Chl‐a. Spectral red‐shifts with time were observed for the phycobiliprotein peaks in all three species. The fluorescence decay of phycoerythrin in C. ovata and C. salina was faster than that of phycocyanin in C. pauciplastida. The results are discussed in relation to the organization of the antenna pigments of PSII and PSI in the cryptophyte algae.

Relative growth and growth efficiency of Ostrea edulis L. spat fed various algal diets

Recently settled spat of Ostrea edulis L. were grown in upwelling tubes in 50-l recirculation systems. Five different marine microalgae species were fed singly and in various mixtures. Greatest growth was with Chaetoceros calcitrans as a single-species diet. Nutritional value of the other single-species diets was in the order Chroomonas salina > Isochrysis galbana > Skeletonema costatum > Tetraselmis suecica. Of the mixtures tested 30% C. calcitrans 70% T. suecica , 50% C. calcitrans 50% S. costatum and 50% T. suecica 50% S. costatum supported growth equivalent to the C. calcitrans-fed control. Percentage composition of the mixtures was based on the organic weight of the cells. Possible reasons for the different nutritional values of the algae investigated are discussed. The size (live weight)-specific total organic content was higher and food cell clearance lower for spat given diets which promoted greater growth rates. Decreased food cell clearance was associated with lower metabolic energy expenditure. Net and gross growth efficiency were greater with higher food value diets. Growth potential of the spat was dependent on the amount of lipid reserves in the larvae at the time of settlement as well as on post-larval diet. Faster growing spat accumulated greater lipid reserves, which were, in turn, associated with relatively higher growth rates when spat were transferred to the sea.

Particle selection, ingestion, and absorption in filter-feeding bivalves

Measurements were made of the clearance rate of six bivalve species each in the presence of mixed cell suspensions of the dinoflagellate Prorocentrum minimum (Pavillard) Schiller (clone Exuv), the diatom Phaeodactylum tricornutum Bohlin (clone Phaeo), and the cryptomonad flagellate Chroomonas salina (Wislouch) Butcher (clone 3C). Use of flow cytometry allowed estimation not only of the clearance rate of individual cell types, but also of their proportional occurrence in the pseudofaeces and faeces. It has been recognized that at least three mechanisms of selecting suspended particles may be present in isolation or in combination. These are: (a) preferential clearance on the ctenidia: Ostrea edulis L., for example, preferentially clears the dinoflagellate Exuv compared with similar sized cells of the diatom Phaeo and the cryptomonad flagellate 3C; (b) preingestive selection on the labial palps: the diatom Phaeo was consistently and preferentially rejected in the pseudofaeces of Ensis directus Conrad, Placopecten magellanicus (Gmelin) and Arctica islandica (L.), (c) differential absorption in the gut i.e., post-ingestive selection: of the mixed diet which was ingested, there is clear evidence of a preferential absorption of the cryptomonad flagellate 3C in the majority of the bivalves from which we obtained faecal material. The possibility of selective removal of particular components of the available food resource, especially in the case of our experiments with the cryptomonad flagellate 3C, suggests that such organisms may be quantitatively more important in the diet of bivalves than their relative abundance under natural conditions might lead us to suppose. The ability of the oyster Ostrea edulis to selectively clear the dinoflagellate Exuv from mixed cell suspensions also may have important implications in our understanding of how toxic dinoflagellates may be concentrated on the ctenidia of commercially significant bivalves.