Monoraphidium Contortum Research Articles

Vertical niche separation of phytoplankton: large-scale mesocosm experiments

Vertical distribution patterns of Heterocapsa triquetra, Mesodinium rubrum, Aphani- zomenon sp., Anabaena lemmermannii, Monoraphidium contortum and chlorophyll a were analyzed in large-scale mesocosms extending throughout the euphotic layer and manipulated with low and high levels of mineral nutrient additions. Using an ordination method, quantitative comparisons of the variability in the vertical distribution due to species differences, to experimental treatments, and to inter-annual variation were made. The inter-specific variance component was largest. The signifi- cance of inter-specific differences was verified by a randomization test. There was also significant inter-annual variability in the species-specific vertical distribution patterns, but the inter-annual effect was less pronounced than the differences between species. Differences in the nutrient loads to the mesocosm did not have significant effects on species-specific vertical distribution patterns. The results demonstrate that the vertical segregation patterns of phytoplankton are species-specific and robust, not overly sensitive to changes in environmental conditions, but appear to be persistent bio- logical phenomena. The implications of these findings to co-existence, competition, and diversity in the plankton are discussed.

Phytoplankton community structure in the lower reaches of a Mediterranean river (Aliakmon, Greece)

Phytoplankton communities from the lower reaches of the Aliakmon River, Greece, have been studied over a period of one year. Seasonal phytoplankton dynamics was described on the basis of its species composition and abundance, biomass and chlorophyll-a concentrations. Phytoplankton assemblages comprised diatoms (mainly Cyclotella meneghiniana, Nitzschia palea and Fragilaria ulna), cyanobacteria (mainly Pseudanabaena limnetica, Aphanizomenon sp. and Limnothrix cf. redekei) and green algae (various species of Scenedesmus and Chlamydomonas, Coelastrum microporum and Monoraphidium contortum). Many benthic diatoms were also present. An important growth of euglenophytes was observed during summer, mainly Lepocinclis steinii, L. ovum, Euglena intermedia, E. viridis and Phacus caudatus. The spring maximum of centric diatoms extended into the summer. The qualitative and quantitative composition of the phytoplankton is compared to communities of other European rivers. With regard to phytoplankton assemblages, Aliakmon resembles more the relatively fast-flowing, individual-poor European rivers. Its widely varying discharge volume, turbidity and shallowness, seem to be the main factors controlling phytoplankton communities in its lower reaches.

Variaciones espaciales y temporales del fitoplancton en un lago subtropical de Argentina

Species composition, biomass and diversity of the phytoplankton in a subtropical lake (27°29'S; 58°45'W) were studied from February 1995 to March 1996. One or two samples were taken monthly in the limnetic and the littoral area. Cell counts were done by the Utermohl method (1958). Phytoplankton biomass varied among 2.38 and 45.59 mm3.m-2 with a mean value of 12.11 (±10.52) mm3.m-2. The population density oscillated among 0.3x106 and 4.7x106 ind.cm-2. Cyanophyta was the dominant group all the year contributing among 25% and 83% of the total biomass. Cylindrospermopsis raciborskii, Aphanizomenon sp. and Microcystis aeruginosa were the dominant species. The Chlorophyta, second group in importance, contributed among 8% and 50% being Botryococcus braunii the dominant species. Bacillariophyceae, Xanthophyceae, Euglenophyceae and Cryptophyceae they did not surpass 20% of total biomass. Chrysophyceae and Dinophyceae they did not surpass 5% of total biomass. Chlorophyll a content ranged between 0.7 and 8 µg.L-1 reflecting the annual variation of phytoplankton biomass. Phytoplankton density diversity varied among 0.34 and 3.69 bits.ind-1. Biomass diversity varied among 1.04 and 2.92 bits.µm3, with a similar variation in the depths of the lake. The lowest biomass and the highest diversity were always found in the littoral zone. CStrategists, with a high SA/V ratios prevailed in density (Monoraphidium contortum, M. tortile, Chlorella vulgaris and other small flagellates of Chlorophyta) while SStrategists (with a low SA/V ratios) such as Microcystis aeruginosa and Botryococcus braunii prevailed during the greater part of the year. Cylindrospermopsis raciborskii and Aphanizomenon sp. were dominant in density and biomass when the temperatures were superior to 20°C and the solar radiation surpassed 20 MJ.m-2. The RStrategists (Aulacoseira italica and Gymnodinium sp.) prevailed during great unstability of water column. Phytoplankton biomass was positively correlated with rain falls 10 days before each sampling (r = 0.772; p < 0.01; g.1. = 30). During the period that prevailed the filamentous Cyanophyceae an increase in the heterocysts frequency was observed in coincidence with a period of notorous drought.

Effect of selenium on the growth of some selected green and blue‐green algae

AbstractAn algal assay procedure using microplate technique was carried out to assess the effect of selenium on the growth of some green and blue‐green algae. Sodium selenite pentahydrate (Na2SeO3.5H2O) and selendioxide (Se2O4) were tested as selenium. The test algae were Selenastrum capricornutum, Scenedesmus obliquus, Chlorella sp., Monoraphidium convolutum, Monoraphidium contortum, Monoraphidium griffithii, Anabaena flos‐aquae, Micro‐cystis aeruginosa, and Oscillatoria agardhii. The blue‐green algae are toxin‐producing strains. Cell number and in vivo chlorophyll fluorescence were the growth parameters of green and blue‐green algae respectively. Dose‐response curves quantify the selenium toxicity in terms of EC50. The lowest selenium concentrations giving no detectable growth (EC100) were visually inspected. The test algae showed distinctly different responses to various selenium treatments. Selenium at concentrations &lt; 0.1 mg L−1 stimulates, to varying degrees, the growth of all the green algae with one exception: S. capricornutum was dramatically inhibited at all treatments. O. agardhii, A. flos‐aquae and M. aeruginosa showed marginal growth stimulation up to 0.1 mg Se L−1, 1.0 mg Se L−1 and 3.2 mg Se L−1 respectively. In terms of EC50, the compound selendioxide was more toxic to greens than sodium selenite. The reverse was indicated for the blue‐greens. In general, the EC50 presented a wide range (0.08–7.2 mg Se L−1), with the lowest values reported for S. obliquus and the highest for M. aeruginosa. All the test algae, except S. obliquus, maintained observable growths at higher selenium levels (EC100&gt;1.0&lt;100mg Se L−1).

Population dynamics and ecology of subdominant phytoplankton species in a shallow hypertrophic lake (Albufera of Valencia, Spain)

Long-term population dynamics and ecology of the abundant but non-dominant phytoplankton species of the shallow hypertrophic lake the Albufera of Valencia (Spain) are described for the period 1980–1988. The lake is used as a reservoir for the surrounding ricefield cultivation. It is continuously dominated by three filamentous blue-green algae, Planktothrix agardhii, Pseudanabaena galeata and Geitlerinema sp. Horizontal differences of the phytoplankton were less important than annual and seasonal variations. An annual increasing trend was observed for Planktolyngbya subtilis, Planktolyngbya contorta, Cylindrospermopsis raciborskii, Microcystis incerta, Nitzschia palea var. tenuirostris and Rhodomonas lacustris var. nannoplanctica, whereas Anabaenopsis elenkinii, Scenedesmus acuminatus, Scenedesmus quadricauda and Cyclotella meneghiniana showed an opposite trend. This pattern seems related to the increase of nitrogen and phosphorus loading in the lake and certain hydrological changes occurred in the latter years of the study. Seasonal pattern of the subdominant species showed the presence of Cyclotella meneghiniana, Scenedesmus species and Chlamydomonas spp. in spring, during moderate water renovation rates and phosphate availability. Periodicity shifted to blue-green algae and Nitzschia species in summer and early autumn, during reduced phosphate levels and initial low but later high water renewal. Autumn and winter species, such as Monoraphidium contortum, Nitzschia gracilis, Rhodomonas lacustris var. nannoplanctica and Cryptomonas erosa, were mainly related to light intensity and temperature. Although the lake has a typical hypertrophic phytoplankton assemblage, the general seasonal variation of the species is similar to that often described in temperate lakes. Diatom species composition differs to that cited in other shallow hypertrophic lakes of Europe.

Photolithotrophy, photoheterotrophy and chemoheterotrophy during spring phytoplankton development (Lake Pavin)

In order to determine the relative importance of autotrophic and heterotrophic activities in both bacterial and phytoplanktonic communities in an oligomesotrophic lake, the size fractionation by differential filtration and the use of a bacterial inhibitor (gentamycin) were combined. The study was carried out at Lake Pavin during the spring planktonic bloom. Photosynthetic and photo- and chemoheterotrophic activities were measured from the assimilation of NaH(14)CO3 and glucose-(3)H, using a double labeling technique. The bacterial community was at low cell concentration (0.6 to 7 × 10(5) cells ml(-)) and represented very low biomass values (0.9 to 11.5 μgC liter(-1)). The abundance of the phytoplankton varied between 0.5 and 1.8 × 10(6) cells liter(-1), and biomass values ranged between 19 and 118 μgC liter(-1). The diatom Melosira italica sp. subarctica (O. Mueller) was the largely dominant species in the meta- and hypolimnion. Inorganic fixation by photolithotrophy (mean value: 1.66 mg C m(-3) hour(-1)) largely predominates over assimilation by photoheterotrophy (mean value: 0.93 μg C m(-3) hour(-1)) or chemoheterotrophy (mean value: 2.42 μg C m(-3) hour(-1)). However, because of the considerable underestimation of heterotrophic assimilation due to the experimental methods used, and because of the spatial and temporal separation of photolithotrophic and photo- and chemoheterotrophic activities, it is likely that the fixation of organic carbon by microalgae plays an important role in the survival of species and/or in competitive interactions, as the results with Monoraphidium contortum (Pasch. et Korschik.), the prevailing species in the epilimnion, would suggest.

Interactions between Phytoplankton, Zooplankton, and Fish in the Nutrient Rich Shallow Lake Hjarbæk Fjord, Denmark

AbstractIn the shallow, nutrient‐rich dammed‐up lake Hjarbæk Fjord the balance between phytoplankton, zooplankton, and fish was completely disturbed during the summer period. Extensive growth of small blue‐green algae (Oscillatoria cfr. trichoides, Pseudanabaena galeata) and chlorococcal green algae (Scenedesmus spp., Monoraphidium contortum, Actinastrum hantzschii) induced a pH rise to 10.5 in July. Fish were driven into the rivers, and many that did not escape died. After the fish had disappeared daphniae multiplied explosively and grazed away the major part of the phytoplankton. Ammonia concentrations rose and oxygen concentrations dropped to noxious levels for highly sensitive fish in August–September. Larger phytoplankton species (Aphanizomenon flos‐aquae, Pediastrum boryanum, Pandorina morum, a. o.) were not grazed by the daphniae and gave rise to a maximum of copepods in September. Fish returned to the lake in October, when pH, ammonia, and oxygen levels had normalized.

AUTECOLOGY OF AN ULTRAPLANKTONIC SHADE ALGA IN LAKE TAHOE2

ABSTRACTThe ultraplanktonic green alga Monoraphidium contortum Korm. in Lake Tahoe (California‐Nevada) demonstrated several ecological and physiological attributes of a genetically adapted shade species. Monoraphidium contortum achieved maximum biomass during deep mixing in winter when light availability was at a minimum. During stratification it was found in maximum abundance in the deep euphotic region, 100–150 m. This species was also distributed through the deep aphotic zone where, despite prolonged darkness, it remained capable of immediate photosynthesis when re‐exposed to light levels in the euphotic zone. The spirally twisted cells were grazed by two calanoid copepods in Lake Tahoe as readily as much larger‐celled phytoplankton species of less complex morphology. Slow growth rates in combination with high susceptibility to copepod grazing may effectively exclude M. contortum from the upper 75 m, where it was rarely recorded. In culture it showed a marked incapacity to adjust to ‘sun’ conditions but was well adapted to low light regimes. Under a wide range of irradiances, photochemical capacity, photosynthetic capacity and growth rates were low, but cellular pigment content remained high. The ratio of Pmax to respiration was at the lower end of the range for shade plants. Genetically distinct sun and shade populations of phytoplankton may play a determining role in major shifts of community structure over depth and time in Lake Tahoe.