Phytoplankton Flora Research Articles

Summer phytoplankton of Serranía de Cuenca (central Spain)

Since the number of studies on the phytoplankton of Serranía de Cuenca (central Spain) has been scarce, this is an attempt to increase our knowledge by describing the physico-chemistry, phytoplankton flora and biomass of seven stagnant environments in summer. They are located in a karstic depopulated area where abandonment of crops and livestock has resulted in decreasing human impacts. As a result, flagellate-rich taxa indicating clean waters are dominant, showing some rare species as well. Biomass is low and seemingly limited by phosphorus. These environments are worth of wider and detailed studies on its algal flora, which will probably result in the description of novel phytoplankton taxa and new records of rare species.

Floristic Composition of Plankton in Shitalakhsya River, Narayanganj, Dhaka

Information of phytoplankton flora of polluted river ecosystems of Bangladesh are scanty. The present study was undertaken to explore the phytoplankton flora at Dakshin Rupshi Station of the river Shitalakhsya, Narayanganj, Dhaka. The study was carried out from May 2017 to March 2018 by collecting pelagic plankton samples bimonthly. A total of 53 species under 36 genera were identified, of which 51 species have been illustrated through photomicrographic images and listing. Two species of phytoplankton namely, Pyrobotrys incurva Arnoldi and Phacus ranula Pochmann were identified from the river water but could not be produced here. The recorded algal divisions of phytoplankton are Cyanophyta (6), Chlorophyta (19), Euglenophyta (13), Chrysophyta (13) and Pyrrhophyta (2). The standing crops presented by each division are: 463.5, 428.33, 199.67, 664.33 and 26.25×103 ind/l by Cyanophyta, Chlorophyta, Euglenophyta, Chrysophyta and Pyrrhophyta, respectively. The trend in contributing the number of species is Chlorophyta > Euglenophyta and Chrysophyta > Cyanophyta > Pyrrhophyta. For standing crop, the trend is Chrysophyta > Cyanophyta > Chlorophyta > Euglenophyta > Pyrrhophyta. Pollutant loading from the urban sources actually cuts the penetration of light into the upper part of the river water and thus creating a shrinking environment for the survival of phytoplankton. The present floristic study of phytoplankton of the River Shitalakhsya adds knowledge to the species composition and their systematic position which would be helpful for any further floristic study of phytoplankton on the river ecosystems of Bangladesh. Dhaka Univ. J. Biol. Sci. 31(1): 45-57, 2022 (January)

Structure and spatial distribution of phytoplankton from the Bouake’s research station fishponds (Central, Côte D’ivoire

This study was carried out to evaluate phytoplankton structure from farmed environments at Bouaké’s Fisheries and Aquaculture Research Station (SRPAC). Measure of physical-chemical and phytoplankton flora sampling were realized from December, 2015 to March, 2016. Conductivity, water transparency and temperature were measured in situ. Phytoplankton was sampled in fishpond using a plankton net mesh-size 20 µm between 7 to 9 am. The results showed that conductivity varied from 19, 37 mS/cm ± 0, 21 to 23, 88 mS/cm ± 1, 20. Therefore, water transparency is relatively ranging from 16 cm ± 0,2 to 57 cm ± 0,5. The pond water temperature fluctuated between 28, 34 °C ± 0, 88 and 30, 20 °C ± 1, 27. Phytoplankton flora is spatially heterogeneous and is made up of 197 taxa divided into 7 branches. These are Chlorophyta (36,04%), Euglenophyta (24,87%), Bacillariophyta (14,72%), Cyanobacteria (13,71%), Charophyta (7,11%), Ochrophyta (2,54%) and Miozoa (1,02%).This phytoplankton study confirmed the existence of potential toxigenic microalgae identified in genus Anabaena, Anabaenopsis, Cylindrospermopsis, Lyngbya, Microcystis, Oscillatoria and Peridinium that could interfere with fish production. This study showed the main phytoplankton communities which dominate in the fish ponds of the Bouaké Research Station.

Checklist of phytoplankton of the foot hill belt of Arunachal Himalayas

Based on a yearlong random floristic survey on various locations, a checklist of the phytoplankton flora in the foot hill belt of Arunachal Himalayas was compiled. The current list contains 116 phytoplankton taxa representing 6 algal phyla, 35 families and 55 genera which were more than the results of all previous survey. With 34 taxa, Chlorophyta was the richest phylum followed by Charophyta (31), Bacillariophyta (27), Euglenozoa (14), Cyanobacteria (6) and Ochrophyta (4) respectively. Among the families, Desmidiaceae was the most species rich one with 19 species. Closterium and Cosmarium were the dominant genera with 11 species each. A total of 90 phytoplankton species were reported for the first time from foot hill belt of Arunachal Himalayas.

Study of phytoplankton flora and its use as a biomonitoring tool to determine the water quality of Krishnasayar Lake, Burdwan, West Bengal, India

AbstractThe present study focused on biomonitoring approaches involving the phytoplankton composition, density and diversity, and their relationships, with changes in environmental variables, and to determine the pollution status of Krishnasayar Lake in the Burdwan District of West Bengal, India. A total of 29 phytoplankton taxa belonging to Chlorophyceae (13), Cyanophyceae (9), Bacillariophyceae (5) and Euglenophyceae (2) were observed. The phytoplankton density exhibited a maximum value of 12,633 cells/litre in the post‐monsoon season and a minimum value of 7,266 cells/litre in the pre‐monsoon season. The results of two multivariate proficiencies (cluster analysis; CCA) indicated the distribution of phytoplankton groups are influenced by pH, electrical conductivity, and the nitrate, phosphate, potassium and dissolved oxygen concentrations. Various diversity indices, including the Shannon–Wiener Diversity Index, Gleason Species Richness Index, Pielou Evenness Index and Naughton Dominance Index, were explored to illustrate the seasonal phytoplankton fluctuations. The Shannon–Wiener Diversity Index values (2.524, 2.331 and 2.666, respectively, for the pre‐monsoon, monsoon and post‐monsoon seasons) indicate the moderation level of pollution status of the lake. The present study also highlights biomonitoring is a reasonable technique for establishing ecological conditions of lakes by considering the organisms within them, including planktonic algae, macrophytes, benthic macroinvertebrates, crustaceans and fishes on the basis of a single indicator species or a combination thereof. The present study used planktonic algae to determine changes in surrounding environmental conditions. As some of the studied phytoplankton species exhibit specific ecological preferences, their presence can indicate the health of that system. As examples, Coelastrum microporum, Pandorina morum and Euglena viridis indicate high levels of organic pollution. Krishnasayar Lake is integrated with the Krishnasayar ecological park, being affected by large levels of anthropogenic disturbance attributable mostly to uncontrolled and careless activities of some visitors, annual cultural activities, other programmes, etc., meaning relevant management activities are needed to protect the lake from further degradation.

Three decades of data on phytoplankton and phycotoxins on the French coast: Lessons from REPHY and REPHYTOX

In France, REPHY (Observation and Surveillance Network for Phytoplankton and Hydrology in coastal waters) and REPHYTOX (Monitoring Network for Phycotoxins in marine organisms) have been contributing to long-term time series on ocean health for more than 30 years. The aim of this paper is to describe these networks and to highlight their key results. Over the last 20 years, phytoplankton flora analysis on French coasts from the Channel to Mediterranean has shown that the five “emblematic” taxa are Chaetoceros, Skeletonema, Cryptophyceae, Leptocylindrus and Pseudo-nitzschia. The latter, together with the taxa of interest Dinophysis + Phalacroma, Alexandrium, and Karenia, have been consistently recorded along the entire French coastline. However, when taking into account frequency of occurrence some taxa exhibit more distinct geographical distributions. In particular, the occurrence of Phaeocystis appeared to be strongly specific to the northern coasts of the Channel. French coasts have been regularly affected since the 1980s by the presence of toxins in bivalve molluscs, leading to bans on fishing and sale of shellfish during periods of varying duration. Three categories of toxins were involved. PST and AST were absent from the French coasts, respectively before 1988 and 2000. DST (Diarrheic Shellfish Toxins) have affected many areas along the whole coast every year since 1987. For PST (Paralytic Shellfish Toxins), only a few areas have been affected, sometimes sporadically, since 1988 in the Channel, 1993 in the Atlantic, and 1998 in the Mediterranean. Many areas have been impacted since 2000 by AST (Amnesic Shellfish Toxins) episodes, mainly affecting scallops in the Channel and on Atlantic coasts. The patterns of change of shellfish toxicity episodes showed no real trend in any province over the entire period 1987–2018.

Seasonal and spatial variation of aquatic macrophytes and phytoplankton community at El-Quanater El-Khayria River Nile, Egypt

In this study, the phytoplankton biomass and species composition in El-Quanater El-Khayria (River Nile, Egypt) was analyzed at four sampling sites on a program of a seasonally sampling and supported by measurements of different water variables as well as biomass production of most common aquatic macrophytes. The major species of aquatic macrophytes were two submerged species (Ceratophyllum demersum and Ceratophyllum submersum), two emergent (Polygonum tomentosum and spontaneum), and one free floating aquatic macrophyte (Eichhornia crassipes). Considerable seasonal variations in water quality as well as macrophytes biomass were found in the studied areas, which result in a variation of phytoplankton flora. A total of 235 phytoplankton species belonging to 7 classes was recorded, with higher numbers in autumn and winter compared to spring and summer. The maximum number of phytoplankton (7238 × 104 L−1 cells) was recorded in winter, however, the lowest one (96 × 104 L−1 cells) recorded in spring. Chlorophyceae was the dominant group, forming 56.96% of the total phytoplankton biomass followed by Bacillariophyceae (34.82%), Cyanophyceae (7.99%), Cryptophyceae (0.10%), Dinophyceae (0.096%), Chrysophyceae (0.03%) and Euglenophyceae (0.02%). Chlorophyll a values ranged from 9.77 µg L−1 to 69.81 µg L−1, with a considerable seasonal and spatial variation. All phytoplankton classes as well as, chlorophyll a was negatively correlated with all aquatic macrophytes species except for C. submersum which correlated positively with chlorophyll a and Cyanophyceae. In addition, it was positively correlated with pH, conductivity and dissolved oxygen.

Method development for speciation analysis of nanoparticle and ionic forms of gold in biological samples by high performance liquid chromatography hyphenated to inductively coupled plasma mass spectrometry

A new method based on coupling high performance liquid chromatography (HPLC) to inductively coupled plasma mass spectrometry (ICP MS) has been developed for the speciation analysis of gold nanoparticles (AuNPs) and dissolved gold species (Au(III)) in biological samples. The column type, the composition and the flow rate of the mobile phase were carefully investigated in order to optimize the separation conditions. The usefulness of two polymeric reversed phase columns (PLRP-S with 100nm and 400nm pore size) to separate gold species were investigated for the first time. Under the optimal conditions (PLRP-S400 column, 10mmolL−1 SDS and 5% methanol as the mobile phase, 0.5mLmin−1 flow rate), detection limits of 2.2ngL−1 for Au(III), 2.8ngL−1 for 10nm AuNPs and 3.7ngL−1 for 40nm AuNPs were achieved. The accuracy of the method was proved by analysis of reference material RM 8011 (NIST) of gold nanoparticles of nominal diameter of 10nm. The HPLC-ICP MS method has been successfully applied to the detection and size characterization of gold species in lysates of green algae Acutodesmus obliquus, typical representative of phytoplankton flora, incubated with 10nm AuNPs or Au(III).

The taxonomic composition, distribution and abundance of the phytoplankton flora of the Obafemi Awolowo University Teaching and Research Farm Lake, Ile-Ife, Osun State, Nigeria

The study determined the abundance and distribution of phytoplankton flora of an impoundment in the Agricultural Teaching and Research Farm of ObafemiAwolowo University (O.A.U), Ile-Ife, Osun State, Nigeria. The study was carried out over an annual cycle from September 2006- August 2007, Phytoplankton and water samples were collected monthly from three sampling stations by filtering 50 litres of water through a phytoplankton net of 45μm mesh size to a concentrate volume of about 30ml preserved in 5% formalin solution. The phytoplankton were viewed under a compound light microscope at both scanning power (x40) and low power (x100), measured with an ocular micrometer drawn to scale, counted and later identified using various phytoplankton identification keys on Nigerian freshwaters.The results showed that one hundred and fifteen species of phytoplankton belonging to five divisions, seven classes, nineteen orders, forty seven families and eighty three genera were recorded. The predominant genera in terms of occurrence and abundance were members of the green algae (Division Chlorophyta) and included Tetradesmus, Ulotrix, Tetraspora, Protosiphon, Chlorella, Closteriopsis and Pediastrum. Phytoplankton occurrence and abundance were slightly higher in the rainy season (600±350) than in the dry season (533±186) (f= 0.918, p= 0.05). The highest values were recorded at the surface stations of the lake.It was concluded that the water body was comparatively rich in phytoplankton flora. Also the occurrence of some species in the water body such as scenedesmus, stauraastum, Tetradesmus, Ulotrix, Tetraspora and Pediastrum species suggested a high level of primary productivity and a non-polluted lake that was oligotrophic to moderately eutrophic.Keywords: Phytoplankton, composition, distribution, abundance

Spatial distribution characteristics of carbon, nitrogen and phosphorous and pollution status evaluation of sediments in the Haihe River Basin, China.

Studying the distribution of carbon, nitrogen and phosphorus of sediments on a whole-watershed scale is important to the research and management of water resources in the Haihe River Basin (HRB). In this study, total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) of 163 samples were investigated in the HRB. Based on these data, the pollution le-vels of sediments were assessed by using different quantitative indices. The results showed that the concentrations of TOC, TN, and TP in the HRB were heterogeneous at different locations. A decreasing trend of concentrations was found from downstream plains (e.g., the Beisihe River and the Heilonggang River) to mountain areas (e.g., the Yongdinghe River, the Beisanhe River, and the Luanhe River). In addition, the concentration of TOC in river sediments was higher than that of reservoir sediments. The statistical analyses showed that TN was significantly (P<0.01) correlated to TOC and TP, with a correlation coefficient of 0.704 and 0.250, respectively. The pollution level based on organic indices was classified as the clean level in the HRB. However, the areas with a relatively high pollution level were still found in some spots, such as the Beisihe River, and the Heilonggang River. Sediments of rivers and reservoirs were similar in the pollution intensity. The average C/N value of sediments in the HRB was 12.71, indicating that the TOC was derived from algae, phytoplankton flora and fauna, followed by higher plants. The C/N value of reservoir sediments was higher than that of river sediments, indicating that the contribution of terrigenous material inputs to TOC was larger in reservoirs than in rivers.

Using diatom assemblages and sulfur in sediments to uncover the effects of historical mining on Lake Arnoux (Quebec, Canada): a retrospective of economic benefits vs. environmental debt

Monitoring changes in environmental conditions is increasingly important as the Canadian economic infrastructure ramps up exploration and mining development in the more inaccessible northern regions of Canada. Governments are concurrently assessing effects from past mining activities and absorbing the economic cost to society with on-going remediation and monitoring initiatives. The abandoned Aldermac mine in northwestern Quebec, mined from 1932–1943, is an excellent case study for assessing the state of environmental and economic effects of past mining operations. A paleolimnological approach, using diatoms as environmental proxies, was used to evaluate the spatial and temporal impacts on aquatic receiving environments. Based on the inferences drawn from diatom assemblages in Lake Arnoux, prior to mining activity, lake water pH was similar to that of surrounding lakes (circumneutral to weakly acidic). After mining operations terminated, changes in pH and alkalinity in Lake Arnoux coincided with distinct increases in sediment sulphur content. Across a 30- to 40-year span (circa 1940 to 1970s) a significant decline in phytoplankton flora coincided with lake acidification and increased clarity of the water column. This resulted in an increase in the benthic diatom population (>90%), replacing the planktonic diatoms. Observed shifts in environmental proxies are concurrent with one, and possibly two, reported tailings pond breaches at the abandoned mine site. Adverse effects of the abandoned Aldermac mine on nearby ecosystems, combined with pressure from local citizens and environmental groups, forced responsible accountability for site restoration led by the Quebec government. Based on the historical period of economic growth, the financial benefits of the Aldermac mine were significant and justify the current pay-it-backward costs for environmental remediation. However, it has now been documented that the pay-it-backward model is not sustainable in the modern economy.

Phytoplankton communities in rock pools on the Åland Islands, SW Finland – environmental variables, functional groups and strategies

Studies of rock pools tend to focus on the surrounding emergent habitat. Moreover, research on phytoplankton in small, nutrient-rich water bodies is limited. Summer phytoplankton species, functional groups and life strategies, as well as physicochemical variables potentially influencing the phytoplankton, were surveyed in 34 brackish rock pools. Except from total nitrogen and total phosphorus, the pools were chemically quite similar. Phytoplankton abundance and biovolume consisted mainly of charophytes (Zygnematales), unidentified small flagellates, cyanobacteria, chlorophytes and dinoflagellates. Many of the phytoplankton functional groups were representative of shallow, nutrient-rich and light-abundant environments. The majority of the common and abundant species were classified as C-strategists (invasive opportunists). Total nitrogen, total phosphorus and phytoplankton biomass varied greatly between the rock pools, and were positively related. The rock pool depth and macrovegetation presence–absence played a central role in shaping the phytoplankton species distribution. Frequently occurring species, present in the majority of the rock pools, seldom dominated the phytoplankton. Species dominating the phytoplankton rock pool assemblages were not common components of the phytoplankton flora.

Changes of Phytoplankton and Water Quality under the Regulation of Filter‐Feeding Fishes and Submerged Aquatic Plants in a Large‐Scale Experiment

Biological regulation means to inhibit proliferation of harmful phytoplankton by adjusting the community structure of the lake ecosystem and to rebuild a stable and healthy one using the self‐regulating ability of the lake; but its effectiveness is still controversial. Two ways of biological control (i.e., a combination of filter‐feeding fishes plus submerged plants and submerged plants alone) were tested in a large‐scale in situ enclosure experiment, carried out at Gonghu Bay of Taihu Lake, China. Changes of both phytoplankton flora and water quality under two experimental conditions were dynamically monitored. The results showed that (1) filter‐feeding fishes decreased the phytoplankton density and promoted phytoplankton biodiversity, while submerged plants inhibited phytoplankton only in spring and showed no significant effect on phytoplankton biodiversity. (2) Submerged plants improved the water quality, however, filter‐feeding fishes had adverse impact on it. Thus, we tentatively concluded that filter‐feeding fishes is more effective than submerged plants in regulating phytoplankton flora, while submerged plants play an important role in improving water quality.

Impact of economic development on the dynamics of phytoplankton and physic-chemical quality of Dakhla Bay (South of Morocco)

A detailed monitoring of physic-chemical parameters and a complete inven-torization of phytoplankton species was conducted from May 2011 to May 2012 in Dakhla bay in south of Morocco. This study comes to bridge the gap of environmental data which has started since 2000 by Moroccan national institute of fisheries research (INRH) in this area. The results showed a differ-ence in the distribution of physic-chemical parameters (especially nutrient and dissolved oxygen). In addition, inventory of phytoplankton species has allowed identifying three different groups: diatoms (Rhizosolenia spp, Lepto-cylindrus spp, Thalassionema spp, Pseudo- nizschia spp.,...) represented 92% of the total phytoplankton flora, dinoflagellates (Scrippsiella sp, Prorocen-trum sp, Gymnodinium sp.,...) with 7%, while Silicoflagellates (Dictyocha sp) contributed with 1%. Seasonal fluctuation of these groups was governed, in first order, by the importance of upwelling in the region during the summer (intense phytoplankton activity). Yet this activity was much stronger in the PK25 site for tourism activity that suggested a remarkable anthropogenic input. An occurrence of Scrippsiella species (45% Hoja Iliamera growing area) and Prorocentrum sp (41% Duna Blanca aquaculture area), recognized as species of colored waters, was permanent at the study sites. Alexandrium sp represented 1% of the total dinoflagellates in Duna Blanca (&lt;1% in the other sites), whereas Dinophysis sp (&lt;1%) was observed in Lassarga (the entrance bay) and PK25 only. The latter two species are potentially the cause of PSP toxins's production (Paralytic Shellfish Poisoning) and DSP (Diarrheic Shellfish Poisoning) source of contamination of bivalves in the Bay during 2004 and 2006.

Spatial variation of phytoplankton assemblages and biomass in the New Zealand sector of the Southern Ocean during the late austral summer 2008

Up until now, only the floristic composition of large phytoplankton species has been studied in the Southern Ocean immediately south of New Zealand. To fill the gaps in our knowledge of the Antarctic phytoplankton flora and biomass, in relation to physical and chemical environments, New Zealand’s IPY project sampled water between New Zealand and Antarctica and into the Ross Sea in late summer. Near surface phytoplankton samples, collected between New Zealand and Antarctica, and vertical stations, between Scott Island and the Ross Sea ice shelf, allowed us to contrast the flora and biomass in the Ross Sea/Antarctic and Subantarctic waters. Spatially, diatoms were found to be more diverse in both shelf and offshore Antarctic than in Subantarctic waters. Over the Ross Sea shelf, the pennate diatom, Fragilariopsis kerguelensis, and a colonial prymnesiophyte, Phaeocystis antarctica, dominated both numerically and in biomass, contributing to greatest levels of chlorophyll a and cell carbon biomass over the shelf. In both shelf and Antarctic waters, heterotrophic taxa accounted for a greater proportion of total dinoflagellate cell carbon (avg. 95.4 and 91.9 %, respectively) than autotrophic, while in the Subantarctic waters, the reverse was true (avg. 48.6 %). A small number of potentially harmful dinoflagellates, Karenia and Karlodinium spp., were found for the first time in the New Zealand sector of the Southern Ocean. This study represents the first thorough description of the spatial variation of the floristic composition and biomass of phytoplankton in relation to physical and chemical properties, from New Zealand to Antarctica.

Limnological Notes on Ramsagar, Dinajpur, Bangladesh

Ramsagar, an artificial lake of Dinajpur district has been investigated limnologically. Mean alkalinity, DO, pH, TDS and conductivity of the lake were 0.50 meq/l, 7.99 mg/l, 6.73, 10.66 mg/l and 73.66 ?S/cm, respectively. The concentration of soluble reactive phosphorus and silicate was very low. Mean value of the former parameter was 3.16 ?g/l and the latter was 0.77 mg/l. Nitrate-nitrogen concentration was &lt; 0.1 mg/l. Phytoplankton biomass as chl a was 5.92 ?g/l and that of phaeopigment 3.65 ?g/l. Phytoplankton flora of the lake was found to be dominated by desmids. The dominant species were Staurastrum coarctatum var. subcurtum (59.35×104, ind/l); S. subgracillimum var. tortum (44.83×104 ind/l) and S. leptacanthum (29.06×104 ind/l). Among the blue-green algae, Anabaena utermöhlii was dominant. Chlorococcales was represented by seven species. The total density of phytoplankton was 163.53×104 ind/l. Considering the overall limnological characteristics, the lake could be characterized as acidic and nutrient poor.DOI: http://dx.doi.org/10.3329/bjb.v41i1.11091 Bangladesh J. Bot. 41(1): 119-121, 2012 (June)

Temporal distribution of phytoplankton in Lake Nyamusingiri in the Albertine Rift Valley, Uganda

AbstractA study aimed at investigating the temporal variation of phytoplankton assemblages in Lake Nyamusingiri was carried out during the period of December 1997–May 1998. Uganda’s freshwaters are ecologically diverse but a few are intensively studied. Research on phytoplankton has been restricted to large water bodies. There is little information on phytoplankton of the western Uganda crater lakes, which are important water and biodiversity resources. This study provided baseline data on phytoplankton, which will serve as a basis for monitoring the effects of human activities on the lake that might result in ecological transformations like loss of biodiversity because of overexploitation. A laboratory thermometer and Winker’s method were used to determine temperature and dissolved oxygen concentration, respectively. Lake transparency was measured by using the Secchi disc. A Van Dorn sampler was used to collect water samples. Nutrient and chlorophyll a concentrations were determined by using facilities at the Fisheries Resources Research Institute (FIRRI), Jinja. The Sedgwick‐Rafter counting chamber was used to analyse phytoplankton. Variation in temperature was small (25.4–26.2°C). Stable thermal stratification was not evident. The Secchi disc transparency was less than unity. The chlorophyll a value was high. Biomass was found to be light‐limited by nonalgal materials. Dissolved oxygen concentration was more than 100% in the surface waters but declined to &lt;20% at the bottom, which reflected the eutrophic nature of the lake. Diversity indices were low. Eighteen species and five classes of phytoplankton were revealed by this study. The phytoplankton flora was dominated by chlorococcal green algae characteristic of the large eutrophic East African lakes.

The oleaginous Botryococcus from the Triassic Yanchang Formation in Ordos Basin, Northwestern China: Morphology and its paleoenvironmental significance

High abundance but rather low diversity algal fossils were found in the hydrocarbon source rocks of the Ch 7-2–Ch 7-3 section, Triassic Yanchang Formation in the Xifeng area of southwest Ordos Basin, which are mainly composed of prolific Leiosphaeridia and Botryococcus. Botryococcus colonies are of various forms; the majority is nubbly, with some of cluster and cotton shape. The nubbly colonies appear globular, cordiform, ternate petal, obtuse triangle, chrysanthemum shape and so on. Most Botryococcus are saffron or brown and are frequently covered with clay under transmission microscope, and shows strong yellow and light brown under fluorescence microscope. Botryococcus could live in freshwater and brackish water. The Botryococcus colonies that lived in fresh water are small with small single cells arranged radially, with undulant or indented edges. The Botryococcus colonies that lived in brackish water are bigger, with larger single cells arranged irregularly, with slippery contours. The most of Botryococcus are discovered from the organic-rich argillaceous sediment with abundant pyrites in the semi- and deep-lake facies, and shows they were preserved in low-energy reducing environments. Taphonomic characteristics of various microfossils and the present of Pediastrum in the phytoplankton flora indicate that they are in situ or near burial. The lake area of the Ordos Basin was gradually expanding and reaching its most extensive flood surface in the Ch 7 of Yanchang Formation interval during the Middle and Late Triassic, with warm climate, plentiful rainfall, and luxuriant vegetation, as determined by the environmental analysis with Botryococcus in Xifeng area. The presence of two ecological types of Botryococcus indicates that the salinity of lake water was fluctuating in the Ch 7 interval. The occurrence of symbiotic acritarchs and geochemical salinity indices show that the Ordos Lake was a typical fresh-water lake, which was gradually desalted, and its salinity fluctuation was narrow during the Mid-Later Triassic. The ecological type of the palynological flora discovered from the Ch 7 to Ch 8 in Xifeng area is similar to that from the Fuxian Lake, with abundant Botryococcus in the Yungui Plateau of China. These findings imply that the Ordos Basin was in a lower-latitude area of temperate to subtropical climate during the Middle and Late Triassic.

Potential impact of some abiotic parameters on a phytoplankton community in a confined bay of the Eastern Mediterranean Sea: Eastern Harbour of Alexandria, Egypt

The Eastern Harbour (E.H.) is sheltered from the sea by a breakwater with two main entrances through which exchange with the netitic Mediterranean water takes place. Some physico-chemical parameters of the study area showed that dissolved oxygen ranged from 6.57 to 11.4 mg l-1 at the open sea station and 5.08 to 11.71 mg l-1 for the E.H. stations. Higher nutrient concentrations were recorded in the E.H. than that at the open sea station, except for ammonia and nitrate. The phytoplankton flora of the E. H. stations was much richer in species than the adjacent open sea station, attaining 96 and 74 species, respectively. As well as the average phytoplankton density, it was higher in the surface water than near the bottom water layer. With regard to the total phytoplankton community, Bacillariophyceae dominated at all sites, whereas Dinophyceae, Chlorophyceae, Cyanophyceae and Euglenophyceae were rarely recorded. The highest average density of phytoplankton abundance was recorded during March, both at the surface. Correlation coefficient of biological factors with some physico-chemical parameters and a series of stepwise multiple regression equations describing the dependence of phytoplankton density on the changes of most abiotic prevailing conditions are provided and discussed.

Tropical phytoplankton community development in mesocosms inoculated with different life stages

Many diatom species have the ability to form benthic resting stages, but the importance of these stages as a supply for planktonic blooms is uncertain. A mesocosm study was carried out in December 2005 to January 2006 in Mangalore, India. Mesocosms were inoculated with various com- binations of benthic and/or planktonic cells, sampled from the coastal SE Arabian Sea, and the devel- opment of the planktonic community was followed. Diatoms dominated the phytoplankton commu- nity in all mesocosms, irrespective of inoculum. The most significant differences among inoculum types were altered species composition, and the timings of the maximum cell abundances, which lagged behind in the sediment mesocosms. Populations of Thalassiosira were initiated by both plank- ton and benthic propagules. Taxa known from temperate coastal areas to seed bloom by benthic propagules, such as Chaetoceros and Skeletonema, were predominantly seeded by planktonic cells in this experiment; this implies differential seeding strategy within the same species at different latitudes. The species assemblage encountered in the plankton and sediment was similar, which indicates that the benthic resting stages seed an autochthonous phytoplankton flora in the area. High species diversity in all inoculated mesocosms was maintained throughout the experimental period, although the actual number of species was fewer at the end. The hydrographic conditions and timing of formation, survival, and germination of diatom resting stages in SE Arabian Sea are discussed.