Genera Of Phytoplankton Research Articles

Climate influence on Dinophysis spp. spatial and temporal distributions in Greek coastal water

Presence of Dinophysis spp., the main phytoplankton genus responsible for the occurrence of lipophilic biotoxins of the okadaic acid group (Diarrhetic Shellfish Poisoning; DSP) in Greek mussels, was recorded in the pe- riod 2003-2008 in five major mussel culture areas of Greece. Dinophysis spp. abundances were simultaneously stud- ied with climatological parameters (air temperature, rainfall, wind direction and velocity) and the occurrence of DSP toxic episodes in mussels. Dinophysis spp. blooms occurred with a seasonal periodicity. Highest cell abundances of the bloom appeared steadily between late winter and spring, whereas occurrence of DSP toxicity in mussels followed a similar time pattern, with mouse bioassay-positive samples ranging between 10.2-28.1% of the total samples anal- ysed. Maximum mean Dinophysis spp. counts coincided with air temperatures in the range of 10-20°C; abundances higher than 1,000 cells L -1 were more frequently recorded at air temperatures in the range of 4-20°C in combination with low rainfall and low velocity winds (<Beaufort scale 4), blowing from the north (NW, N and NE) and south (SE and S). To our knowledge, this is the first report to correlate the occurrences and abundances of potentially toxic Dinophysis spp. and climatological data for the majority of the shellfish production areas studied. Such observations may contribute to the clarification of the occurrence patterns of DSP toxic episodes, hence bettering the economical management of mussel production.

Diversity and abundance of rotifers during an annual cycle in the reservoir Valerio Trujano (Tepecoacuilco, Guerrero, Mexico)

We analyzed the diversity and density of monogonont rotifers collected from 10 sites, 5 in the littoral zone and 5 in the pelagic zone, during a 1-year period from March 2010 to April 2011 in the reservoir Valerio Trujano, altitude 820 m a.s.l. (Tepecoacuilco de Trujano, State of Guerrero, Mexico). We also measured physicochemical variables such as temperature, pH, hardness, nitrates, and phosphates. The rotifers were identified to species level and quantified using a Sedgwick-Rafter chamber. We found 62 species belonging to 28 genera and 19 families, representing 22% of total species reported for Mexico. The most abundant species were Brachionus caudatus, B. falcatus, Horaëlla thomassoni, Filinia longiseta, Conochilus dossuarius, and Keratella cochlearis. The highest rotifer densities were those of B. caudatus (around 300 ind. L−1) in June and July. The common phytoplankton genera were Pediastrum, Cosmarium, Closterium, Nitzschia, Suriella, Microcystis, Oscillatoria, and Merismopedia. The species diversity of Rotifera in the reservoir ranged from 1.3 to 3.2 in both the littoral and the pelagic regions. The saprobic index varied from 1.2 to 2 in the pelagic and 1.4 to 2.1 in the littoral region of the reservoir. Nutrient levels and indicator species (Brachionus and Trichocerca) showed that the reservoir, which was nitrogen rather than phosphorus limited, is eutrophic and moderately polluted by organic matter.

查干湖湿地浮游植物与环境因子关系的多元分析

This study investigated the biodiversity and community structures of phytoplankton and their relations with environmental factors in Chagan Lake during the intermediate( May) and rainy season( September) in 2012. Combining field investigations with cluster analysis,multi-dimensional scaling( MDS) analysis and redundancy analysis( RDA),and applying Shannon,Pielou and Margalef indices,the study identified a total of 127 phytoplankton species( belonging to 53genera and 5 phyla). Among these species,52 were members of Bacillariophyta,46 Chlorophyta,and 25 Cyanophyta,accounting for 40.94%,36.22%,and 19.69% of the total phytoplankton species,respectively. In terms of algal populationdistribution,in the intermediate season Cyanophyta was the most abundant phylum of planktonic algae( accounting for 39.85% of algal population),followed by Bacillariophyta( 36. 193%) and Chlorophyta( 21. 33%),whereas in the rainy season Chlorophyta( 70. 84%) was the dominant phylum. Consisting of two connected parts( the main lake body and Xinmiao wetland),Chagan lake was found to sustain significant temporal-spatial variations of phytoplankton populations.The abundance of phytoplankton in the intermediate season( averaging 658.0 × 104cells /L) was considerably higher than that in the rainy season( averaging 459. 3 × 104cells /L). In both seasons,phytoplankton abundance was found to be positively correlated with water salinity( i. e. greater salinity coinciding with higher phytoplankton populations),and negatively affected by pH and phosphate( PO3-4) concentration in the intermediate season. In either season,the abundance of phytoplankton in the main lake was 8-10 times of that in Xinmiao wetland. In the intermediate season,such discrepancy was caused by different salinity and nutrients in these two water bodies; salinity in the main lake( 52.0 mg /L) was 3.3times of that in Xinmiao wetland( 16. 0 mg /L),whilst PO3-4in the main lake( 0. 045 mg /L) was 3. 8 times of its concentration in Xinmiao wetland. In the rainy season,there was no significant difference in nutrient levels in the whole lake,so water salinity was the main factors affecting the distribution of phytoplankton. In addition to field investigation results,cluster and MDS analyses based on Bray-Curtis measures of similarity also illustrated significant discrepancy between the main lake and Xinmiao wetland in terms of phytoplankton abundance. RDA results indicated that in the intermediate season the key environmental factors influencing the phytoplankton assemblages were pH,total nitrogen( TN)and phosphate( PO3-4),whereas salinity,phosphate( PO3-4) and 5-day biological oxygen demand( BOD5) were the key factors in the rainy season. In the intermediate season,dominant phytoplankton genera were those favoring low alkalinity,low phosphorus and high nitrogen levels. Rainy season benefitted genera that were more tolerant alkalinity,salinity,phosphorus and BOD5. Most dominant genera indentified in this study were micro-phytoplankton,common in temperate climate and capable of rapid multiplying and fast growing through nutrient assimilation,could form a higher abundance in rich nutrients. When phytoplankton was used as a bio-indicator in water quality evaluation,the results revealed that water quality in Chagan Lake was in β-moderately-polluted category.

Biodiversity patterns of nutrient-rich fish ponds and implications for conservation

Nutrient-rich water bodies are usually expected to host low species richness at the local scale (water body). Nevertheless, they can support a diverse and sometimes unique biodiversity when diversity is considered at a regional scale. This discrepancy between the two scales is well documented for natural water bodies, but little is known about biodiversity of artificial water bodies, like fish ponds. We hypothesise that nutrient-rich water bodies can collectively host high species richness at the regional scale. Thus, these are important ecosystems for the regional conservation of biodiversity. We investigated 84 fish ponds in the Dombes region, France, with five taxonomic groups: macrophytes, phytoplankton, macroinvertebrates, dragonflies, and amphibians. Species richness patterns were determined for alpha- (single pond), beta- (between ponds), and gamma- (regional pond network) levels. For most studied species groups, richness per fish pond and at the regional level proved to be relatively high in comparison with natural ponds in other landscapes. Contribution of alpha-diversity to regional diversity was highest for dragonflies with 41 %, and lowest for amphibians and macrophytes with 16 and 18 %, respectively. For macroinvertebrate families and phytoplankton genera it was intermediate. Contribution of beta-diversity to regional diversity was similar for all species groups with 22-25 %. Furthermore, some ponds hosted a large number of less frequent species and some endangered species, indicating that the conservation of biodiversity of fish ponds must be established at a regional scale.

The influence of mixing frequency and depth on phytoplankton mobility

The influence of mixing frequency and depth on phytoplankton functional group composition (mobile versus immobile species) was studied by enclosure experiments in a shallow, stratified lake. Mixing events were artificially induced at intervals from 2–12 d. The mixing depth was increased from the natural level (4 m) to 6 and 9 m. The mobile phytoplankton in the experiments consisted of cyanobacteria and flagellates. Among the latter, large and rapid swimming species were represented by dinoflagellates. An increase of the relative abundance of gas vacuolated cyanobacteria occurred with increasing frequency of mixing. Additionally Reynolds' hypothesis predicting the occurrence of certain mobile phytoplankton genera in response to the mixing regime could be confirmed for the condition when mixing depth exceeds the euphoric depth.

Comparative functional characteristics of DMSP lyases extracted from polar and temperate Phaeocystis species

Members of the marine phytoplankton genus Phaeocystis (Prymnesiophyceae) pro- duce large amounts of the intracellular osmolyte DMSP and they are known to also produce lyase enzymes that cleave DMSP into the biogeochemically important trace gas DMS. The functional characteristics of DMSP lyase activity in Phaeocystis spp. are not well known. We characterized DMSP lyase activity in extracts from 2 ecologically important species from this genus, the mesophile P. globosa (strain CCMP629) and the psychrophile P. antarctica (strain CCMP1374). Results from whole cell extracts showed that both algal species were potent producers of DMSP lyase, with Michaelis-Menten constant (Km) and maximum reaction velocity (Vmax) values of 1.77 mM and 17.3 nmol DMS min �1 mg protein �1 , respectively, for P. globosa, and 2.31 mM and 28.2 nmol DMS min �1 mg protein �1 , respectively, for P. antarctica. The optimal DMSP lyase activity was recorded at pH 4 and 30°C for P. globosa, and at pH 5 and 20°C for P. antarctica. The half-life of the DMSP lyase of P. globosa was 210 min at 25°C, which was longer than that of the P. antarctica enzyme (61.9 min). First-order kinetic analysis of DMSP lyase thermal denaturation demonstrated that the activation energy, free energy, enthalpy and entropy of denaturation in P. antarctica extracts were lower than for P. globosa extracts, confirming that the P. antarctica DMSP lyase was more thermolabile than the lyase from the temperate strain. Inhibitor tests with metals, a chelator (EDTA) and a serine binding agent (PMSF) suggested that the DMSP lyases from both Phaeocystis species were metalloenzymes with serine and sulfhydryl groups at the active site. The acidic pH optima for the Phaeocystis strains are consistent with findings from other Prymnesiophyceae, and we speculate that this may reflect adaptation to an acidic sub-cellular location for the DMSP lyase.

Effects of diurnal vertical mixing and stratification on phytoplankton productivity in geothermal Lake Rotowhero, New Zealand

Mixing processes in lakes are key factors controlling light availability for phytoplankton growth, but understanding the contribution of mixing is often confounded by other factors such as nutrient availability and species dynamics. Our study examined this problem in a low pH, geothermally heated lake dominated by one phytoplankton genus and lacking the complexity of nutrient limitation, phytoplankton species interactions, or grazing pressure. We hypothesized that the continuous strong convectively driven circulation resulting from atmospheric instability and sediment heating would negate any tendency of thermal stratification, entraining phytoplankton and transporting them away from high surface irradiance that could induce photoinhibition. During our study, water temperatures were considerably warmer than air temperatures, with a diurnal maximum surface temperature of 37.5 °C and minimum of 35.5 °C. Surface heating induced stratification, with a temperature difference of 1–2 °C evident during the day, but there was sufficient heat loss and mixing during the night to erode the stratification and create isothermal conditions. The vertical entrainment velocity driven by convective circulation was on the order of 0.1 mm s−1, but when there was strong solar heating, phytoplankton within the top 0.5 m of the water column still showed depressed photosynthetic quantum efficiencies, as determined with a Pulse Amplitude Modulated fluorometer (PHYTOPAM); however, this depression was less than for phytoplankton cells maintained throughout the day in surface waters with bottle incubations. At other times mixing generated by continuous heating and atmospheric instability meant that phytoplankton did not show photoinhibition; therefore, despite the geothermally driven mixing in Rotowhero, the intensity of solar radiation is still the key mechanism determining the stratification response and resultant photoinhibition of the phytoplankton.Lake Rotowhero provides an excellent natural laboratory to examine the relative time scales of mixing and phytoplankton photoinhibition responses because small changes in solar radiation have such marked impacts on the diurnal stratification and radiation experienced by cells located above the diurnal thermocline.

Contrasting roles of water chemistry, lake morphology, land-use, climate and spatial processes in driving phytoplankton richness in the Danish landscape

Understanding of the forces driving the structure of biotic communities has long been an important focus for ecology, with implications for applied and conservation science. To elucidate the factors driving phytoplankton genus richness in the Danish landscape, we analyzed data derived from late-summer samplings in 195 Danish lakes and ponds in a spatially-explicit framework. To account for the uneven sampling of lakes in the monitoring data, we performed 1,000 permutations. A random set of 131 lakes was assembled and a single sample was selected randomly for each lake at each draw and all the analyses were performed on permuted data 1,000 times. The local environment was described by lake water chemistry, lake morphology, land-use in lake catchments, and climate. Analysis of the effects of four groups of environmental factors on the richness of the main groups of phytoplankton revealed contrasting patterns. Lake water chemistry was the strongest predictor of phytoplankton richness for all groups, while lake morphology also had a strong influence on Bacillariophyceae, Cyanobacteria, Dinophyceae, and Euglenophyceae richness. Climate and land-use in catchments contributed only little to the explained variation in phytoplankton richness, although both factors had a significant effect on Bacillariophyceae richness. Notably, total nitrogen played a more important role for phytoplankton richness than total phosphorus. Overall, models accounted for ca. 30% of the variation in genus richness for all phytoplankton combined as well as the main groups separately. Local spatial structure (<30 km) in phytoplankton richness suggested that connectivity among lakes and catchment-scale processes might also influence phytoplankton richness in Danish lakes.

The legacy of the last cruise of the Carnegie: a lesson in the value of dusty old taxonomic monographs

Large online databases contain a wealth of information from modern oceanographic campaigns. While efforts have been made to “rescue” data from the older literature, the assumption should not be made that all the good data that exist are online, waiting to be downloaded and analysed. Here, I show an example of what can be gleaned from the old literature. Three monographs from the last cruise of the Carnegie catalogued the species of the phytoplankton genus Ceratium, the tintinnid ciliates of the microzooplankton, and the copepod species of the zooplankton. The samples employed were from plankton net tows or a “Pettersson plankton pump” from 160 stations in the North and Central Atlantic, the Central, Southern and Northern Pacific. From each monograph, the species records were keyed into spreadsheets to allow station by station comparisons. Plotting species richness along the cruise track showed roughly parallel changes among the three groups with peaks and troughs corresponding with low and high latitudes. For Ceratium, tintinnid ciliates, and copepods, very similar latitudinal diversity gradients were evident after binning the species richness of each group into 58 bands of latitude. The data extracted from the reports of the last cruise of the Carnegie revealed close correspondence of diversity in planktonic organisms among the protists and metazoan taxa of distinct trophic levels. The group with the most widespread species was the copepods.

Drivers of ciliate and phytoplankton community structure across a range of water bodies in southern New Zealand

The abundance and biomass of phytoplankton and ciliate taxa in lentic fresh waters were related to their resources, physicochemical conditions, potential consumers and water body type in 45 water bodies ranging from deep oligotrophic lakes to swamps, ponds and estuarine wetlands in South Island, New Zealand. Distinct phytoplankton assemblages were related to each water body type. Phytoplankton genera were positively related most strongly to dissolved reactive phosphorus concentrations, and also related positively to the biomass of ciliate consumers. The biomass of ciliate taxa was higher in swamps and ponds than other water body types. Biomass of the ciliate taxa: oligotrichs, prostomatids and Strombidium, was related strongly and positively to the biomass of their phytoplankton resource, and less strongly related to metazooplankton predators: calanoid copepods and Ceriodaphnia dubia. Our findings suggest that resource availability (bottom-up drivers) may be stronger determinants of phytoplankton and ciliate community composition than consumers (top-down effects).

Phytoplankton assemblage of a small, shallow, tropical African reservoir

I measured physico-chemical properties and phytoplankton in the small, shallow tropical reservoir of Oyun (Offa, Nigeria) between January 2002 and December 2003. I identified 25 phytoplankton genera in three sampling stations. Bacillariophyceae dominated (75.3%), followed by Chlorophyceae (12.2%), Cyanobacteria (11.1%) and Desmidiaceae (0.73%). The high amount of nutrients (e.g. nitrate, phosphate, sulphate and silica) explain phytoplankton heterogeneity (p<0.05). Phytoplankton was abundant during the rainy season, but the transition period had the richest assemblage and abundance. Fluctuations in phytoplankton density were a result of seasonal changes in concentration of nutrients, grazing pressure and reservoir hydrology. The reservoir is eutrophic with excellent water quality and a diverse phytoplankton assemblage: fish production would be high. These conditions resulted from strategies such as watershed best management practices (BMPs) to control eutrophication and sedimentation, and priorities for water usage established through legislation. Additional measures are recommended to prevent oligotrophy, hypereutrophy, excessive phytoplankton bloom, toxic cyanobacteria, and run-off of organic waste and salts.

Current Status and Trends in Muskegon Lake, Michigan

A long-term monitoring program was initiated in 2003 to determine the ecological status of Muskegon Lake, a Great Lakes Area of Concern. This paper presents data generated from the first 3 years of the monitoring program, discusses how the data are being used to establish and justify lake restoration targets, and assesses how water quality conditions have changed over time. Between 1972 and 2005, lake-wide averages of total phosphorus and soluble reactive phosphorus from the water surface have declined from 68 to 27 μg/L and from 20 to 5 μg/L, respectively. In addition, average chlorophyll a concentrations have declined from 25 to 6 μg/L over this period, while Secchi disk depths have increased from 1.5 to 2.2 m. Wastewater diversion, and perhaps dreissenid filtering activity, is most likely responsible for these changes. However, nitrate concentrations have increased from 70 to 270 μg/L over the same time period. During 2003–2005, phytoplankton abundance and fish catch were lower in the spring compared to the summer and fall. Microcystis was the most abundant phytoplankton genus; the fish community generally was dominated by round goby ( Neogobius melanostomus) in spring and summer, and sunfishes (Centrarchidae) in the fall. Dreissenid abundance was highly variable over time, but densities were low relative to Saginaw Bay. Approximately 65% of the Muskegon Lake shoreline has been hardened (i.e., physically altered). Overall, the water quality of Muskegon Lake has improved over the past 30 years, but environmental challenges still exist, including contaminated sediments, loss of natural habitat, and invasive species.

Effect of Chemical and Physical Properties of River Water in Shatt Al‐Hilla on Phytoplankton Communities

This paper aims to study the chemical and physical properties in the ecological system of Shatt Al‐Hilla in Babylon Governorate in Iraq and its effect on phytoplankton population. In this context, several limnological parameters were evaluated during the period from December 2003 through November 2004 from four sampling stations sited along Shatt Al‐Hilla. The physical parameters included: temperature, turbidity and electrical conductivity. The chemical parameters included: pH, alkalinity dissolved oxygen, total hardness and the concentrations of nitrite, nitrate, phosphate and sulphate. A total of 154 species were recorded. Ninety‐seven species of the total belong to Bacillariophyceae, 37 species belong to Chlorophyceae, 13 species to Cyanophyceae, 5 species to Chrysophyceae, and 2 species to Euglenophyceae. Bimodal variation of phytoplankton was observed. Five genus of phytoplankton were the highest number of species ( Nitzschia, Navicula, Gomphonema, Cymbella and Scendesmus). Some species was occurred continuously during study period such as, Cyclotella ocellata, Cyclotella meneghiniana, Aulacoseria distans, and Gomphonema abbreviatum. The phytoplankton communities at all sampling sites showed a clear seasonal variation in phytoplankton cell number. However, no significant correlation between total cell number of phytoplankton and nutrient concentration was observed. The study was revealed the city sewage discharge, agriculture and urban run‐off were affecting the water quality of Shatt Al‐Hilla.

Current understanding of Phaeocystis ecology and biogeochemistry, and perspectives for future research

The phytoplankton genus Phaeocystis has well-documented, spatially and temporally extensive blooms of gelatinous colonies; these are associated with release of copious amounts of dimethyl sulphide (an important climate-cooling aerosol) and alterations of material flows among trophic levels and export from the upper ocean. A potentially salient property of the importance of Phaeocystis in the marine ecosystem is its physiological capability to transform between solitary cell and gelatinous colonial life cycle stages, a process that changes organism biovolume by 6–9 orders of magnitude, and which appears to be activated or stimulated under certain circumstances by chemical communication. Both life-cycle stages can exhibit rapid, phased ultradian growth. The colony skin apparently confers protection against, or at least reduces losses to, smaller zooplankton grazers and perhaps viruses. There are indications that Phaeocystis utilizes chemistry and/or changes in size as defenses against predation, and its ability to create refuges from biological attack is known to stabilize predator–prey dynamics in model systems. Thus the life cycle form in which it occurs, and particularly associated interactions with viruses, determines whether Phaeocystis production flows through the traditional “great fisheries” food chain, the more regenerative microbial food web, or is exported from the mixed layer of the ocean.

Qualitative abundance of zooplankton of Bishleri stream of Banihal, Doda (Jammu &amp; Kashmir state)

The main drainage of the Distt. Doda is the river Chenab formed by the confluence of Chandra and Bhaga streams. The other tributaries of the river Chenab are Neeru stream, Kalnei streams, Chatroo stream, Bishleri stream with a number of their tributaries. The present study was carried for a period of two year from January, 2003 to December, 2004 on Bishleri stream by dividing the stream into different stations. A total of 19 genera of phytoplankton were recorded from the stream, out of them, 07 belong to chlorophyceae, 07 to bacillorophyceae, 04 to cynophyceae and 01 to euglenophyceae. Among the phytoplankton, Bacillariophyceae emerged as the largest group

Phaeocystis blooms in the global ocean and their controlling mechanisms: a review

Phaeocystis is a genus of marine phytoplankton with a world-wide distribution. It has a polymorphic life cycle alternating free-living cells and colonies but develops massive blooms under the colony form in nutrient (major)-enriched areas (mostly nitrates) of the global ocean. Among the 6 species, only 3 ( P. pouchetii, P. antarctica, P. globosa) have been reported as blooming species. However, information is lacking on the present-day contribution of Phaeocystis-dominated ecosystems to regional and global marine production as well as to global C and S cycles and on how these might change in the future. As a first step in this direction, this review aims to synthesise knowledge on the physiology, growth and fate of Phaeocystis in the global ocean, and to select relevant parameters for implementing mechanistic models describing Phaeocystis blooms in the global ocean. Missing information concerning the regulation of the most important bottom-up and top-down processes is also identified. The synthesis of published data suggests that it is possible to derive a single unique parameterisation to describe some bottom-up processes for global modelling without consideration of species and location. Most important among these are the temperature-dependence of the maximum growth rates that characterises all three blooming species, and their high adaptation to environmental light. Other processes seem to be more species-(e.g. colony matrix synthesis) or site-related (top-down controls, e.g. grazing parameters). This review also points out that some crucial processes are still poorly described and need further research. For instance, increased knowledge of iron uptake kinetics and iron quotas is of prime importance given the very large recurrent blooms of P. antarctica colonies reported in the HNLC waters of the Southern Ocean.

Observations on colony formation by the cosmopolitan phytoplankton genus Phaeocystis

Few marine phytoplankton have heteromorphic life cycles and also often dominate the ecosystems in which they occur. The class Prymnesiophyceae contains a notable exception: the genus Phaeocystis includes three species that form gelatinous colonies but also occur within their ranges as solitary cells. Phaeocystis antarctica and P. pouchetii are exclusively high latitude taxa, and are notable for regionally tremendous blooms of the colony stage. P. globosa occurs circumglobally, yet its colony blooms primarily are confined to colder waters within its range. Three additional species are warm water forms that have been reported only as solitary cells or loose aggregations that bear little resemblance to the organized colonies of the other taxa. Interpretation of existing data indicates that resource availability (light, temperature and nutrients) by itself is not sufficient to explain this distinction between cold-water colony-forming taxa and warm water solitary cell taxa, nor why colony development in P. globosa is essentially a spatially restricted phenomenon within a much broader geographic range. Colony development by P. globosa in situ has been observed at temperatures ≥20 °C, but only rarely and generally under conditions of seasonally or anthropogenically elevated nutrient supply. Data presented here demonstrate colony development at 20–22 °C in natural plankton communities from oligotrophic waters that were pre-screened through 63 μm mesh (i.e. lacking mesozooplankton and large microzooplankton), but not in unscreened communities containing microzooplankton and >63 μm zooplankton. Reduction of colony proliferation at higher temperatures by mesozooplankton grazing remains as an intriguing possibility that is consistent with available evidence to help explain differences in latitudinal extent of in situ colony development. These data are interpreted within a theoretical framework regarding the potential advantages and disadvantages of the two life cycle stages.

Do distinct water chemistry, reservoir age and disturbance make any difference on phosphatase activity?

Alkaline phosphatase activity was assessed concomitantly with total phosphorus, orthophosphate and phosphomonoester concentrations in two meso-eutrophic reservoirs with distinct age and subjected to different kinds of environmental influence. Differences in conductivity, temperature and pH were found. However, during the study period alkaline phosphatase activity was similar in both reservoirs. Water colour was higher in S. Serrada Reservoir. This fact can be related to (1) reservoir age (2) high internal disturbance (3) large imputs of allochthonous detritus, resulting from the combined effect of grazing, fire and catchment slope. Despite the high water colour recorded in S. Serrada, alkaline phosphatase activity was apparently not inactivated by humic substances. Besides, the obtained results demonstrated that hydrolysis of phosphomonoesters by alkaline phosphatase was not important for orthophosphate regeneration in these reservoirs. Probably orthophosphate was always available to biota. In fact, in the experiments based on Selenastrum capricornutum Printz algal test, similar phytoplankton growth responses were obtained for different phosphorus concentrations. Thus, these results seem to indicate that phosphorus was not a limiting nutrient in either reservoir. Although phosphatase activity was significantly correlated with some phytoplankton genera in both reservoirs, no significant correlations were found between enzyme activity and chlorophyll-a. Significant correlations between phosphatase activity and crustacean zooplankton were only recorded in S. Serrada. In spite of these results there was some indication that the main source of phosphatase might have been bacteria involved in decomposition processes instead of phyto- and zooplankton taxa

Environmental control and limnological impacts of a large recurrent spring bloom in Lake Washington, USA.

A series of statistical analyses were used to identify temporal and spatial patterns in the phytoplankton and nutrient dynamics of Lake Washington, an mesotrophic lake in Washington State (USA). These analyses were based on fortnightly or monthly samples of water temperature, Secchi transparency, ammonium (NH(4)), nitrate (NO(3)), inorganic phosphorus (IP), total nitrogen (TN), total phosphorus (TP), dissolved oxygen (DO), pH and chlorophyll a (chl a) collected during 1995-2000 from 12 stations. Lake Washington has a very consistent and pronounced annual spring diatom bloom which occurs from March to May. During this bloom, epilimnetic chl a concentrations peak on average at 10 microg/L, which is 3 times higher than chl a concentrations typically seen during summer stratified conditions. The spring bloom on average comprised 62% diatoms, 21% chlorophytes and 8% cyanobacteria. During summer stratification, diatoms comprised 26% of the phytoplankton community, chlorophytes 37% and cyanobacteria 25%. Cryptophytes comprised approximately 8% of the community throughout the year. Overall, 6 phytoplankton genera (i.e., Aulacoseira, Fragilaria, Cryptomonas, Asterionella, Stephanodiscus, and Ankistrodesmus) cumulatively accounted for over 50% of the community. These analyses also suggest that the phytoplankton community strongly influences the seasonality of NO(3), IP, DO, pH and water clarity. According to a MANOVA, seasonal fluctuations explained 40% of the total variability for the major parameters, spatial heterogeneity explained 10% of variability, and the seasonal-spatial interaction explained 10% of variability. Distinctive patterns were identified between offshore and inshore sampling stations. The results of our analyses also suggest that spatial variability was substantial, but much smaller than temporal variability.

Ubiquitous ‘benign’ alga emerges as the cause of shellfish contamination responsible for the human toxic syndrome, azaspiracid poisoning

A new human toxic syndrome, azaspiracid poisoning (AZP), was identified following illness from the consumption of contaminated mussels ( Mytilus edulis). To discover the aetiology of AZP, sensitive analytical protocols involving liquid chromatography–mass spectrometry (LC–MS) were used to screen marine phytoplankton for azaspiracids. Collections of single species were prepared by manually separating phytoplankton for LC–MS analysis. A dinoflagellate species of the genus, Protoperidinium, has been identified as the progenitor of azaspiracids. Azaspiracid-1, and its analogues, AZA2 and AZA3, were identified in extracts of 200 cells using electrospray multiple tandem MS. This discovery has significant implications for both human health and the aquaculture industry since this phytoplankton genus was previously considered to be toxicologically benign. The average toxin content was 1.8 fmol of total AZA toxins per cell with AZA1 as the predominant toxin, accounting for 82% of the total.