Different Species Of Phytoplankton Research Articles

Latitudinal Dynamics of Vibrio along the Eastern Coastline of Australia

The marine genus of bacteria, Vibrio, includes several significant human and animal pathogens, highlighting the importance of defining the factors that govern their occurrence in the environment. To determine what controls large-scale spatial patterns among this genus, we examined the abundance and diversity of Vibrio communities along a 4000 km latitudinal gradient spanning the Australian coast. We used a Vibrio-specific amplicon sequencing assay to define Vibrio community diversity, as well as quantitative PCR and digital droplet PCR to identify patterns in the abundances of the human pathogens V. cholera, V. parahaemolyticus and V. vulnificus. The hsp60 amplicon sequencing analysis revealed significant differences in the composition of tropical and temperate Vibrio communities. Over 50% of Vibrio species detected, including the human pathogens V. parahaemolyticus and V. vulnificus, displayed significant correlations with either temperature, salinity, or both, as well as different species of phytoplankton. High levels of V. parahaemolyticus and V. vulnificus were detected in the tropical site at Darwin and the subtropical Gold Coast site, along with high levels of V. parahaemolyticus at the subtropical Sydney site. This study has revealed the key ecological determinants and latitudinal patterns in the abundance and diversity of coastal Vibrio communities, including insights into the distribution of human pathogens, within a region experiencing significant ecological shifts due to climate change.

Spatial and temporal variations of phytoplankton composition and biomass in Lake Bunyonyi, South-Western Uganda.

The purpose of this study was to examine the spatial and temporal variations of phytoplankton species composition and biomass in Lake Bunyonyi, South-Western Uganda. Samples were collected monthly from nine fixed stations in the lake from October 2019 to September 2020. Based on the morphological characterization, 52 different species of phytoplankton were recorded. These were dominated by cyanobacteria (21 species) and chlorophytes (15 species) followed by diatoms (10 species), euglenophytes (4 species), dinoflagellates (2 species), and cryptophytes (1 species). The biomass (Chl-a concentration) ranged from 0.019 ± 0.009mg/L at Heissesero station to 0.045 ± 0.013mg/L obtained at Nyombe station. On a temporal basis, the highest mean Chl-a concentration of 0.044 ± 0.03mg/L was recorded in March 2020while the least concentration of 0.015 ± 0.011mg/L was obtained in September 2020. Significant differences existed in the Chl-a concentration values between stations and across sampling months. Chl-a concentration was significantly positively correlated with dissolved oxygen (DO), turbidity but negatively correlated with temperature. The Shannon-Wiener index and evenness put it clear that the distribution of phytoplankton species in the lake is inequitable. Besides, 94.2% of the phytoplankton species revealed had never been reported by the previous studies in the study area. The dominance of species cyanobacteria (such as Microcystis spp., Cylindrospermopsis raciborskii, Anabaenopsis sp., and Anabaena sp.) presents potential future challenges to water quality management. Therefore, the establishment of a strong and committed committee dubbed "Lake Bunyonyi Water Management Committee" to oversee the activities and avert potential water quality challenges is strongly recommended. The existence of some toxic phytoplankton species calls for regular monitoring and careful use of the lake and its food products.

Impact of salinity variation and silicate distribution on phytoplankton community composition in Pearl River estuary, China

Monitoring the primary producer diversity is crucial in understanding ecosystems balance, as imbalanced nutrients richness and diversity may induce red tide situations. The present study deals with evaluating the impact of hydrological factors regulating the dynamics of phytoplankton communities and the influence of chemical parameters on phytoplankton growth in Pearl River Estuary (PRE). During wet season (April), around 50 different species of phytoplankton were identified at 14 different sampling sites including 24 diatoms, 9 dinoflagellates, 10 green algae and 6 cyanobacterial species respectively. The diatom Melosira granulate was the dominant species at most of the sampling sites. Phytoplankton surveys during the dry season (November) showed Bellerochea malleus and Skeletonema costatum species as dominant at most of the sampling locations. Silicate (SiO3) distribution was one of the reason for the abundance of diatoms in west shoal sites. The concentration of nutrients and hydrological factors like water depth and salinity strongly supported phytoplankton growth. In addition, PRE west and middle shoal sites showed evidence of rich phytoplankton diversity when compared to east shoal and channel sites. The Non-metric Multidimensional Scaling (NMDS) analysis and cluster grouping analysis demonstrated the uniqueness of plankton species diversity at PRE west and east shoal sites. The results of Canonical Correspondence Analysis (CCA) suggested that diversity of phytoplankton communities was significantly influenced by environmental factors such as salinity, depth and SiO3 concentration. From these results, one may conclude that salinity with SiO3 distribution plays a crucial role in PRE phytoplankton community composition assisting in maintaining healthy intertidal ecosystem.

Biodiversity in the occurrence of different species of phytoplankton along the Chennai coast

Phytoplankton is the major food of zooplankton and small pelagic occurring along the Chennai coast. The distribution of phytoplankton vary from place to place and the occurrence of different species decides the biodiversity of the ecosystem. This paper describes the occurrence and the characteristics of most common phyto organisms along the Chennai coast using primer 6.0 software. The phytoplankton distribution consists of dissolved volume, Ceratium species, Navicula, Bidulphia, Nitzschia, Gyrosigma and Chlorella during the year’2011. The occurrence of the phytoplankton, Chaetoceros, 38.01%, followed by Thalasirrothrix is 11.95%, Nitzschia is 8.94%, Navicula, 8.19%, Gyrosigma is 7.22%, Bidulphia is 6.57%, Coscinodiscus, 5.85%, Pleurosigma, 5.81%, Ceratium species, 4.58%, Chlorella is 2.74% and dissolved volume is 0.03% of the total phytoplankton distribution. The primer graphs for eclidean distance of different months for different species of phytoplankton were drawn. From the bray Curtis similarity graph it is evidenced that the distribution of phytoplankton component. Chaetocerus is far from the other species since its occurrence is more during the month of Jan’11. From the similarity graph, it is found that Chaetoceros and Coscinodiscus are closely related, Ceratium species and Pleurosigma are closely related, Navicula and Bidulphia are closely related. The occurrence of Chlorella is not closely related to any species. Bubble plots displays the individuals species abundances in relation to the overall community pattern. Funnel graphs are drawn for the number of phytoplankton. As the temperature increases during the summer month the phytoplankton decreases. The environmental variables, temperature, pH, salinity, TSS, TDS, dissolved oxygen, chlorophyll a, b and c, primary productivity, gross and net, nutrients, phosphate and ammonia vary significantly with the phytoplankton occurrence. The correlation coefficient of occurrence of Ceratium-Nitzschia (0.78), Ceratium- Thalassirothrix-(0.98), Ceratium- Pleurosigma (0.90), Navicula-Bidulphia (0.57), Navi cula-Nitzscia (0.10), Navicula -Gyrosigma (0.95), Navicula- Chaetoceros (0.93), Navicula- Coscinodiscus (0.57), Navicula-Pleurosigma (0.19), Bidulphia-Nitzschia (0.50), Bidulphia - Gyrosigma (0.31), Bidulphia- Chaetoceros (0.25), Bidulphia- Coscinodiscus (0.94), Nitzschia-Thalassirothrix (0.82), Nitzschia-Coscinodiscus (0.34), Nitzschia-Pleuro -sigma (0.64), Gyrosigma-Chaetoceros (0.99), Gyrosigma- Coscinodiscus (0.33), Gyro sigma-Pleurosigma (0.26), Chaetoceros-Coscinodiscus (0.26), Chaetoceros –Pleurosigma (0.30), Gyrosigma-Chlorella (0.09), Chaetoceros-Chlorella (0.05). The species richness, d varies from 0-2.40, Pielous’s index of evenness (J') varies from 0-0.97, Shannon–Wiener’s diversity index (H'), 0-2.32, simpson’s dominance index, , 0-0.9. The species richness, species evenness, species diversity and dominance index are all significant at p  0.05. The correlation between the environmental variables and the phytoplankton species distribution were worked out.

Fractional Fourier-Radial Transform for Digital Image Recognition

This paper presents a new system for pattern recognition in digital images, called Fractional Fourier-Radial Transform, invariant to translation, scale and rotation (TSR invariant) taking advantage of the well-known properties of some integral transform as Fourier Transform, Mellin Transform and the Radial Hilbert Transform. The main contribution of this work is the use of the Fractional Fourier Transform to avoid, or reduce the overlap between results due to the optimal order selection for each reference image, assuming α = β for computing optimization, which helps to get a higher difference between the reference images spectrum. This system was tested using different species of phytoplankton obtaining a level of confidence of at least 92.68% invariant to position, size, and rotation, supporting scale variations of ±20%. The mean of the highest confidence values for the scale variation correlations is 98.47%, for rotation variation correlations is 100%, and for the rotation and scale variation correlations is 98.15%. The testing dataset images are selected due to their morphology complexity; they have a real pattern to be recognized instead of using a test-book data set.

Allelopathic effects of Margalefidinium polykrikoides and Gymnodinium impudicum in the growth of Gymnodinium catenatum

Harmful algae blooms (HABs) are characterized for the coexistence of phytoplankton species with dynamic and complex biotic interactions (e.g., competition, symbiosis, predation, parasitism, allelopathy), that occur at fine temporal and spatial scales, and are relevant to understand the role that different species of phytoplankton play in the regulation of HABs. In this work the allelopathic effects of Margalefidinium polykrikoides (=Cochlodinium polykrikoides) and Gymnodinium impudicum on Gymnodinium catenatum were evaluated. The allelopathic abilities of M. polykrikoides and G. impudicum were investigated in bi-algal culture experiments and in trials in which target species were co-cultured, separated by a 10 μm membrane to prevent a direct cell-to-cell contact; and also by the addition of different volumes of culture media without cells. For all trials, cells of each species were harvested during exponential phase and cultured together by triplicate at three relative abundances: 1:1 (200 Cells mL–1 of each species, G. catenatum and M. polykrikoides or G. impudicum), 2:1 (400 Cells mL–1 of G. catenatum and 200 Cells mL–1 of M. polykrikoides or G. impudicum), and 1:2 (200 cells mL–1 of G. catenatum and 400 Cells mL–1 of M. polykrikoides or G. impudicum). All bioassays were carried out by triplicate in 250 mL Erlenmeyer flasks with 150 mL of modified GSe medium with an initial inoculum of 200 or 400 Cells mL−1. During experiments G. catenatum abundances were enumerated daily. In bi-algal culture experiments mortalities of G. catenatum were from 50% to 100% after 48 h of cell contact with M. polykrikoides or G. impudicum. In the case of culture media without cells, only M. polykrikoides caused a decrease in the cell abundance and growth rate of G. catenatum. Morphological changes occurred in G. catenatum when in contact with M. polykrikoides and G. impudicum, such as membrane shedding, prominent nucleus, loss of flagella, cell lysis, as well as the separation of long chains into individual cells. These results suggest that in the natural environment M. polykrikoides and G. impudicum have allelopathic interactions in G. catenatum, which could negatively affect its growth and survival, indicating that these species could displace blooms of G. catenatum.

Co-occurrence patterns between phytoplankton and bacterioplankton across the pelagic zone of Lake Baikal during spring.

Phytoplankton and bacterioplankton play a key role in carbon cycling of aquatic ecosystems. In this study, we found that co-occurrence patterns between different types of phytoplankton, bacterioplankton, and environmental parameters in Lake Baikal during spring were different over the course of three consecutive years. The composition of phytoplankton and bacterial communities was investigated using microscopy and 16S rRNA gene pyrosequencing, respectively. Non-metric multidimensional scaling (NMDS) revealed a relationship between the structure of phytoplankton and bacterial communities and temperature, location, and sampling year. Associations of bacteria with diatoms, green microalgae, chrysophyte, and cryptophyte were identified using microscopy. Cluster analysis revealed similar correlation patterns between phytoplankton abundance, number of attached bacteria, ratio of bacteria per phytoplankton cell and environmental parameters. Positive and negative correlations between different species of phytoplankton, heterotrophic bacteria and environmental parameters may indicate mutualistic or competitive relationships between microorganisms and their preferences to the environment.

Measuring the in situ carbon isotopic composition of distinct marine plankton populations sorted by flow cytometry

AbstractThe carbon isotope ratio (δ13C value) of marine particulates is a potentially useful tracer for elucidating pathways of carbon flow in the marine environment. Different species of phytoplankton vary in fractionation vs. CO2 by up to 24‰ in laboratory cultures under varying nutrient and growth conditions, a signal that should propagate through the microbial food web. However, such contrasts have been difficult to confirm in field measurements due to analytical limitations. Here, we combine fluorescence‐activated cell sorting (FACS) with a specialized micro‐combustion interface and isotope‐ratio mass spectrometry (SWiM‐IRMS) to provide some of the first direct measurements of whole‐cell δ13C values for specific phytoplankton populations in the wild. For three samples collected off Scripps Pier in 2010–2011, Synechococcus averages δ13C values of −25.7 ± 2.0‰, Prochlorococcus averages −23.0 ± 1.3, and diatoms average −20.8 ± 1.7‰. Diatoms were ∼3‰ enriched in 13C when measured during a bloom (March 2011) as compared with mid‐summer (July 2010). Sorted particles thought to represent living heterotrophic bacteria averaged −25.4 ± 2.5‰, whereas total filterable particles averaged −19.6 ± 1.0‰, indicating a strong similarity to diatom biomass. These variations demonstrate that in situ differences in δ13C among different populations of particles can be exploited to follow carbon flow through successive trophic levels, and throughout organic matter remineralization, sinking, and preservation.

Life strategists and morpho-functional groups applied to the phytoplankton of a Pampean shallow lake

Phytoplankton and environmental variables were studied during a year in a shallow eutrophic lake and its inflow in the ‘depressed Pampa’ of Argentina. The taxa were classified according to the competitors, stress tolerators, ruderals and intermediate categories (CSR) model and were allocated to morpho-functional groups (MFG). As was expected according to the trophic state, scarce transparency and mixing condition, the R-strategists (several cyanobacteria and pennate diatoms) dominated almost all of the study period. C-strategists were more scarce and favoured by short periods of transparency, whereas only three species were attributed to the S-strategist category. Each MFG was represented by a single species at a time, resulting in a high functional miscellany in this shallow lake. Thus, we can assume that the CSR approach is a useful tool to explain the success of the different species of phytoplankton in this shallow lake.

Evaluation of the antibacterial activity of different species of phytoplankton

The antibiotic activity of organic extracts from cultures of six species of phytoplankton, Synechococcus elongatus, Synechocystis sp., Amphiprora paludosa, Porphyridium cruentum, Chaetoceros muelleri and Dunaliella tertiolecta was examined. The bacteria used were Gram(-) strains, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae, and the Gram(+) strains were Bacillus subtilis, Staphylococcus aureus, and Microccocus luteus. All extracts inhibited the growth of B. subtilis and effected the generation of inhibition halos, ranging in diameter from 7.06 to 15.23 mm, for several bacteria species. Wide-spectrum antibacterial activity was observed in extracts from S. elongatus, Synechocystis sp., A. paludosa, P. cruentum, and C. muelleri. Thus, this five phytoplankton species can be used to control bacteria.

Digestive enzymes and in-vitro digestibility of different species of phytoplankton for culture of the freshwater pearl mussel, Hyriopsis (Hyriopsis) bialatus

Hyriopsis (Hyriopsis) bialatus has been cultured during the mussel life cycle from glochidia to the adult stage with a low total survival of 6% up to 130-day-old juveniles. The main digestive enzymes (amylase and proteinases) were not detectable in one-day-old juveniles, and increased during development. The stomach, including diges- tive glands, was the major digestive organ for both carbohydrate and protein. The optimum conditions for amylase activity were 40C and pH 7; for acidic proteinases they were 60C and pH 5. Two main alkaline proteinases were found in the intestine, with optimum conditions of 30C and pH 8 and 60C and pH 8. To improve mussel survival by finding suitable phytoplankton species and age as food for juveniles and adults, an in-vitro digestibility test was performed on ten algal species three and seven days old using amylase and proteinases in crude enzyme extracts from different mussel life stages. Among the phytoplankton selected, the three most efficiently digested by juveniles were seven- day-old Chlorella sp.2, seven-day-old Chlorococcum sp. and seven-day-old Kirchneriella incurvata, in the ratio 1:1:3 for 30-day-old juveniles and 3:1:1 for 130-day-old juveniles. For the adult mussel, three-day-old Chlorella sp.2, seven-day-old Coccomyxa sp., and seven-day-old Monoraphidium sp., in the ratio 3:1:1, were the most digestible phyto- plankton. Levels of in-vitro digestibility were related to the quality (not the concentrations) of carbohydrate and protein in the phytoplankton mixtures, and protein digestibility seemed to be the key factor determining food quality for the mussel.

Bioaccumulation and transfer of benzo(a)pyrene in a simplified marine food chain

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 312:101-111 (2006) - doi:10.3354/meps312101 Bioaccumulation and transfer of benzo(a)pyrene in a simplified marine food chain Xinhong Wang, Wen-Xiong Wang* Department of Biology, The Hong Kong University of Science and Technology (HKUST), Clear Water Bay, Hong Kong, SAR *Corresponding author. Email: wwang@ust.hk ABSTRACT: We examined the toxicokinetics of benzo(a)pyrene (BaP) and the trophic transfer in a marine planktonic food chain comprising phytoplankton, copepods, and fish. Kinetic parameters including the uptake rate from the dissolved phase, the assimilation efficiency (AE) from the ingested food, and the elimination rate were quantified. Influences of food quality and quantity and different routes of exposure (aqueous and food) on the biokinetics were also examined. The uptake rate constants were 390 to 1090 ml mg–1 h–1 in different species of phytoplankton, 1.2 ml mg–1 h–1 in the copepods, and 0.157 ml mg–1 h–1 in the fish, respectively. The assimilation efficiencies were 2 to 24% in the copepods and 32 to 51% in the fish ingesting different prey types. Increasing food concentration significantly reduced the AEs, whereas the AEs varied little among the different food diets tested at the same biomass. The elimination rate constants by the copepods were 0.8 to 1.7 d–1, and comparable following uptake from the aqueous phase and the dietary phase. A kinetic modeling calculation suggests that more BaP accumulated in the copepods originates from the dietary intake than the aqueous intake. For fish, both trophic transfer and aqueous uptake are important in BaP bioaccumulation. Feeding rates contribute to the differences in the relative proportion of accumulated BaP in the fish. KEY WORDS: PAHs · Bioaccumulation · Kinetic modeling · Food chain Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 312. Online publication date: April 24, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Development of digestive enzymes and in vitro digestibility of different species of phytoplankton for culture of early juveniles of the freshwater pearl mussel, Hyriopsis (Hyriopsis) bialatus Simpson, 1900

Summary In vitro culture of the glochidia of the freshwater pearl mussel, Hyriopsis (Hyriopsis) bialatus Simpson, 1900, in M199 medium supplemented with common carp plasma resulted in 95 ± 2% survival, of which 97 ± 2% were transformed to juveniles. Transformation occurred within 10 days. After transformation, early juvenile mussels were reared and fed for 15 days with a mixture of four species of phytoplankton (Chlorella sp.2, Kirchneriella incurvata, Navicula sp. and Coccomyxa sp.). Digestive enzyme activities, not detected in glochidia, were induced after feeding in transformed juveniles. Analysis of juvenile crude enzyme extracts after 15 days of feeding revealed the presence of amylase, proteinases, lipase and cellulase with specific activities 7.29 ± 0.12 U mg protein−1, 0.003 ± 0.0001 U mg protein−1, 1.85 ± 0.24 U mg protein−1 and 0.03 ± 0.01 U mg protein−1, respectively, which corresponded to 39%, 25%, 42% and 6%, respectively, of those found in the gastrointestinal tract of adult mussels. In vitro digestibility of the four species of phytoplankton using juvenile crude enzyme extract resulted in digestion of carbohydrate, protein and lipid content of Chlorella sp.2, K. incurvata, Navicula sp. and Coccomyxa sp., respectively, at the following levels: carbohydrate, 414 ± 46, 234 ± 38, 98 ± 19 and 188 ± 31 μg of reducing sugar per mg phytoplankton; protein, 75 ± 13, 164 ± 19, 63 ± 7 and 120 ± 11 μg of cleaved peptides per mg phytoplankton; lipid, 369 ± 24, 18 ± 3, 56 ± 7 and 80 ± 11 μg of fatty acid per mg phytoplankton. Among different nutrient digestibilities, that of protein is apparently the key factor determining food quality, followed by carbohydrate as the secondary factor in herbivorous species like mussels. The data indicate that a combination of Chlorella sp.2 and K. incurvata is a suitable food formula for juvenile culture.

Benzo[a]pyrene absorption and exposure pathways in the green mussel Perna viridis

The absorption efficiency (AE) of benzo[a]pyrene (BaP), a representative polycyclic aromatic hydrocarbon compound, in the green mussel Perna viridis was measured under different biological and food conditions (body size, food quantity, and food species). Uptake of BaP from the aqueous phase by different species of phytoplankton and green mussels was also experimentally quantified. A bioenergetic-based kinetic model was then used to separate the exposure pathways of BaP accumulation in the green mussels. Our results demonstrated that the AE of BaP in the green mussels ranged between 17 and 47%. Body size did not significantly affect the AE of BaP in the mussels. The AEs increased with a decrease in food availability, largely as a result of lengthening the gut passage of chemicals. The AEs differed by up to 2.3 times (17-39%) among the different food diets tested (four phytoplankton diets and one sediment diet). The BaP associated with the sediment was assimilated least efficiently. The difference in gut passage also appeared to account partially for the difference in AEs observed among different food types. No correlation between the AE and the distribution of BaP in the cytoplasm of phytoplankton cells was found. The concentration factor of BaP measured in four different marine phytoplankton species was in the range of 10(4)-5 x 10(4) (L/kg). The calculated uptake rate constant of BaP in the green mussels was 6.37 L/g/d, and the efficiency of absorption of BaP from the aqueous phase was 6.6 to 8.8%. The model calculation indicated that under most circumstances, >56% of BaP in mussels can indeed be derived from the uptake from the aqueous phase. However, the relative importance of aqueous and dietary exposure can be affected by the variation of AE, mussel's ingestion rate, and concentration of BaP in ingested food particles.

The effect of light and temperature on DOC excretion by phytoplankton

The separate effects of light intensity (0–3,000 µmol quanta m−2 s−1) and temperature (5°–45°C) on excretion of dissolved organic carbon (DOC) by three phytoplankton species were examined under controlled laboratory conditions in axenic cultures. Ours is the first comparative study of the effects of a wide temperature and irradiance range on DOC excretion by different species of phytoplankton under identical conditions. Tight coupling was found between the rates of carbon fixation and of absolute DOC excretion over a wide range of irradiances (0–1,500 µmol quanta m−2 s−1) in all three species with excretion ranging from 1 to 55% of production. Chlorella vulgaris and Synechococcus sp. showed parallel temperature‐dependent changes in photosynthesis and of absolute DOC excretion (5°–45°C); in Isochrysis galbana absolute excretion was temperature‐independent, but photosynthesis was temperature‐dependent. In all cases, increased excretion percentages were found under extreme irradiances and temperatures that depressed photosynthesis. In general, we suggest that high fluxes of DOC toward bacterial food chains may be expected only under conditions favorable for photosynthesis, although the percentage of DOC excretion is then low.

Discrimination of phytoplankton via light‐scattering properties

Measurements of multiangle light scattering were made on individual phytoplankter cells in vitro by means of a commercial light#x2010;scattering photometer and in situ with a new instrument capable of measurements in an unconfined environment. Both instruments contain collimated detectors that measure light scattered from a small, defined#x2010;volume element of a detector#x2010;circumscribed, plane#x2010;polarized laser beam. As a single phytoplankter enters this volume, a scattering signal detected at a selected angle triggers repeated electronic scans of the particle as it moves through the volume. Data collected at up to 16 distinct angles are recorded 100 times during a period of a few hundred milliseconds. A subsequent analysis of data from 1,265 individual phytoplankters covering 12 distinct species confirms (for this group) the hypothesis that different species of phytoplankton produce distinctive scattering signals.

CELL DIVISION RATES OF EUCARYOTIC ALGAE MEASURED BY TRITIATED THYMIDINE INCORPORATION INTO DNA: COINCIDENT MEASUREMENTS OF PHOTOSYNTHESIS AND CELL DIVISION OF INDIVIDUAL SPECIES OF PHYTOPLANKTON ISOLATED FROM NATURAL POPULATIONS

The cell cycle marker event of DNA replication in eucaryotic algae was identified using 3H-Thymidine (3H-TdR) incorporation. The frequency of cells (F) within a population undergoing DNA replication was estimated and the cell division rate (μF) calculated. In laboratory cultures the rates of cell division calculated from changes in cell numbers (μN) and μF were similar. Dual labelling with 3H-TdR and NaH14CO3 enabled rates of cell division and photosynthesis to be coincidently measured for individual species of algae. Using these single species radioisotope techniques, several distinct photosynthesis irradiance and cell division irradiance relationships were found for: (1) different species of phytoplankton isolated from the same sample, and (2) the same species isolated from different environments. These techniques allow the coupling between photosynthesis and cell division to be examined with high resolution for algae in situ.

Metal uptake by different species of phytoplankton in culture

Cadmium and copper uptake by cultures of Prasinocladus marinus, Amphidinium carterae, Chaetoceros curvisetum and Chaetoceros protuberans was considered as a function of exposure time (from 0.5 to 72 h) and of metal concentrations added to the culture medium (from 5 to 20 µg l−1). For cadmium uptake, A. carterae exhibited a particular behaviour: the accumulation was not dependent on exposure time or on metal concentration. An adsorption process appeared to govern both Cadmium uptake by phytoplankton species (except A. carterae) and that of copper. In addition to adsorption, another active process might be involved in the Cadmium uptake of P. marinus, C. curvisetum and C. protuberans.

The effect of Brachionus plicatilis grown on three different species of phytoplankton on the ultrastructure of the hepatocytes of Chanos chanos (Forskål) fry

The effect of the rotifer, Brachionus plicatilis, grown on unialgal cultures of Isochrysis galbana, Tetraselmis sp. and Chlorella sp. on the hepatocytes of milkfish fry was evaluated by electron microscopy. Rotifers grown on the three different species of phytoplankton brought about different ultrastructural features in milkfish fry hepatocytes. Best results were obtained from fry reared on Isochrysis-fed rotifers. The use of marine Chlorella-fed rotifers as feed for fry resulted in the poorest hepatocyte ultrastructure, indicating that this was nutritionally the least adequate cultured food. None of the three diets, however, produced an optimal hepatocyte ultrastructure similar to that obtained by feeding the fry with a mixture of artificial feed and newly hatched Artemia nauplii.

Comparison of rates of feeding and biodeposition of the American oyster, Grassostrea virginica Gmelin, fed different species of phytoplankton

The feeding and biodeposition rates of small (2.4 cm) and large (5.2 cm) Crassostrea virginica were differently affected in experiments using flowing systems by moderate (292 μ C/1 sea water) and high (487 μ C/1 sea water) concentrations of the following phytoplankton: the diatoms, Thalassiosira pseudonana (Hasle & Heindal) ( Cyclotella nana), Skeletonema costatum (Greville) Cleve, Nitzschia closterium (Ehrenberg) Wm. Smith, and the green alga, Dunaliella tertiolecta Butcher. The average feeding rate of the oysters on the different phytoplankton was: Dunaliella < Nitzschia < Skeletonema < Thalassiosira. In contrast, oysters fed on Thalassiosira had the lowest rate of biodeposition (1.626 × 10 −3 g ash-free dry wt/g dry flesh wt per day) but oysters cultured on Nitzschia showed the highest rate of biodeposition (2.952 × 10 −3 units). The response of the feeding rate of the two sizes of oysters to food concentration differed according to the algal food source. Oysters fed on Thalassiosira and Skeletonema exhibited a higher feeding rate at a higher food level: in contrast, oysters fed on Nitzschia showed no significant differences and those cultured on Dunaliella a depressed feeding rate at the higher food concentration. We observed no differences in feeding rate between small and large oysters fed on Skeletonema and Dunaliella, but small oysters had a higher feeding rate than large oysters when cultured on Thalassiosira and a lower feeding rate when fed on Niitzschia. The smaller size of Thalassiosira and larger size of Nitzschia might account for these differences in the feeding efficiency of small oysters. The biodeposition rates of both sizes of oysters were also affected by food concentration of the different algae. At the high food concentration with Skeletonema, Nitzschia, and Dunaliella, all oysters showed a marked increase in the rate of biodeposition, but oysters fed on Thalassiosira exhibited no great change. On all species of phytoplankton, the larger oysters produced greater biodeposition than the smaller oysters. These differences in response of feeding and biodeposition rates are important to our knowledge of food chain dynamics and may be used to optimize aquaculture systems.