Observations on the plankton of some Costa Rican lakes

We sampled 30 lakes in Costa Rica in the wet season (July–August) of 1991 for phytoplankton (with integrated and whole water samples), and 17 for zooplankton (with net tows). Taxa of plankton and community richness were poorly related to geography, morphology, chemistry, and other biota. Neither the zooplankton nor the phytoplankton appeared to influence the composition of the other, and neither were apparently influenced by the presence of fish.Phytoplankton richness reflected primarily sampling method, but also tended to decrease with elevation and with Secchi disk depth, and tended to increase with pH and alkalinity. Chlorophytes were the most abundant division in 14 lakes; these lakes tended to be unstratified, turbid, and located at higher elevation. Diatoms were common in 4 of the 7 lakes with elevated silica (over 30 ppm). Each lake showed at least a 3 : 1 dominance by copepods, cladocera, or insect larvae. Copepods dominated 7 of the 17 lakes, most of which were shallow, turbid, and had low alkalinity. Cladocera dominated 7 lakes that were typically deeper and located at low-to mid-elevations. Insect larvae dominated two small, turbid lakes.     

Pennahia ovata,a new sciaenid from the Bay of Bengal

A new sciaenid,Pennahia ovata, is described from the Bay of Bengal. It differs from its most similar congener,P. anea, in having weakly differentiated teeth on the lower jaw, usually 24–25 dorsal fin soft rays and 18–19 upper+lower gill rakers, a deep body and a long second anal fin spine.     

Competing Effects of Toxin-Producing Phytoplankton on Overall Plankton Populations in the Bay of Bengal

The coexistence of a large number of phytoplankton species on a seemingly limited variety of resources is a classical problem in ecology, known as ‘the paradox of the plankton’. Strong fluctuations in species abundance due to the external factors or competitive interactions leading to oscillations, chaos and short-term equilibria have been cited so far to explain multi-species coexistence and biodiversity of phytoplankton. However, none of the explanations has been universally accepted. The qualitative view and statistical analysis of our field data establish two distinct roles of toxin-producing phytoplankton (TPP): toxin allelopathy weakens the interspecific competition among phytoplankton groups and the inhibition due to ingestion of toxic substances reduces the abundance of the grazer zooplankton. Structuring the overall plankton population as a combination of nontoxic phytoplankton (NTP), toxic phytoplankton, and zooplankton, here we offer a novel solution to the plankton paradox governed by the activity of TPP. We demonstrate our findings through qualitative analysis of our sample data followed by analysis of a mathematical model.     

Comparison of a few systems for the determination of saprobic and trophic degree on the basis of plankton data

A few systems for determining the saprobic and trophic degree are compared. In determining saprobity the saprobic index according to Dresscher & Van der Mark (1976) appears to be in good agreement with the system developed by Zelinka & Marvan (1961). In defining the trophic degree there is an obvious correspondence between the systems of Hutchinson (1967) and Rawson (1956) and the chemical characterization of the water.     

Mechanisms of Rose Bengal inhibition on SecA ATPase and ion channel activities

SecA is an essential protein possessing ATPase activity in bacterial protein translocation for which Rose Bengal (RB) is the first reported sub-micromolar inhibitor in ATPase activity and protein translocation. Here, we examined the mechanisms of inhibition on various forms of SecA ATPase by conventional enzymatic assays, and by monitoring the SecA-dependent channel activity in the semi-physiological system in cells. We build on the previous observation that SecA with liposomes form active protein-conducting channels in the oocytes. Such ion channel activity is enhanced by purified Escherichia coli SecYEG–SecDF·YajC liposome complexes. Inhibition by RB could be monitored, providing correlation of in vitro activity and intact cell functionality. In this work, we found the intrinsic SecA ATPase is inhibited by RB competitively at low ATP concentration, and non-competitively at high ATP concentrations while the translocation ATPase with precursors and SecYEG is inhibited non-competitively by RB. The Inhibition by RB on SecA channel activity in the oocytes with exogenous ATP-Mg²⁺, mimicking translocation ATPase activity, is also non-competitive. The non-competitive inhibition on channel activity has also been observed with SecA from other bacteria which otherwise would be difficult to examine without the cognate precursors and membranes.     

Primary and secondary effects of methabenzthiazuron on plankton communities in aquatic outdoor microcosms

The primary and secondary effects of methabenzthiazuron on plankton were studied in outdoor microcosms (6 m3) for five months. Macrophytes, phytoplankton, zooplankton and the emergence of insects were examined. The herbicide was added to nine of the twelve mesocosms in concentrations ranging from 10 to 3371 μg a.i. l−1 in a single application. The other three ponds were used as untreated controls. Phytoplankton population dynamics fluctuated depending on light intensity, temperature, nutrients, competition and herbicide concentrations. Primary production was temporarily inhibited at test concentrations from 89 to 3371 μg l−1. Cryptophyta (Phytoflagellata) showed also a recovery at the higher concentrations during the study period. Other primary producers did not recover at these concentrations, as expected from the disappearance curve of the active ingredient at these concentrations. This was also indicated by structural indices such as the diversity, eveness and similarity index. The lower concentrations evoked no or only short-term, weak responses. Chemical water parameters were strongly influenced by the absence of macrophytes (Elodea canadensis) at the high application rates, which also caused significant changes in zooplankton communities. No effects were observed on macro-invertebrates and benthic organisms. In conclusion, noticeable effects were detected only at concentrations clearly above the effect threshold known from standard laboratory tests with aquatic primary producers. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of ice duration on plankton succession during spring in a shallow polymictic lake

1. Long-term records of air temperature and ice phenology (ice duration), and phyto- and zooplankton time series (1979–1997) were used to study the effects of ice duration on the successional pattern within plankton communities during spring in a shallow polymictic lake. 2. Water temperature in March was significantly lower after cold winters when compared to average or mild winters. Mean water temperature in April was not significantly different after mild, average or cold winters, but showed an overall significant negative correlation with ice duration. 3. Ice duration affected the timing and the magnitude of the peak abundance of diatoms, rotifers and daphnids during spring, but had no direct effects on the timing and maximum of chlorophytes, cryptophytes, cyanobacteria, bosminids and cyclopoid copepods. 4. Plankton groups which appeared first in the seasonal succession (i.e. diatoms, rotifers and daphnids) reached maximum abundance earlier after mild and average winters. The peak abundance of diatoms was negatively correlated with ice duration, whereas that of rotifers and daphnids was independent of the conditions during the preceding winter. 5. Temperature alone was generally a poor predictor of the timing and magnitude of both phyto- and zooplankton maxima. Turbulence may be important in the timing and the magnitude of peaks in diatoms, while total algal biomass was the most important determinant for the timing of the rotifer maximum. The magnitude of the daphnid maxima were significantly influenced by water temperature in March and April, and by rotifer abundance. The magnitude of the bosminid maximum was correlated with food availability and predation, whereas the timing of the maximum was more closely related to water temperature in May. 6. We conclude that, as a result of the low heat storage capacity of shallow lakes, the effects of winter on planktonic communities are short lived, and soon overtaken by the prevailing weather and by biotic interactions.     

长江口浮游甲壳动物空间分布特征

2010年研究了长江口南、北支浮游甲壳动物的空间分布特征。共采集到浮游甲壳动物50种,其中桡足类39种,枝角类11种。种类数南支高于北支;平均密度北支高于南支,南、北支分别为1.7 ind./L和61.8 ind./L。基于群落相似性矩阵的CLUSTER聚类和MDS分析显示,在群落相似性为40%时,长江口区域浮游甲壳动物群落可分为北支组、南支组1和南支组2共3组。3组的优势种有差异。浮游甲壳动物的平均密度变化趋势为北支组（61.8±22.11 ind./L）〉南支组1（3.07±2.06 ind./L）〉南支组2（0.72±0.45 ind./L）。盐度、潮汐和径流量是影响长江口南北支浮游甲壳动物种类组成、密度和空间分布差异的重要环境因素。     

Microcosm analysis of salinity effects on coastal lagoon plankton assemblages

A microcosm experiment was conducted to assess the effects of salinity on coastal lagoon plankton assemblages. Five salinity levels were replicated four-fold in 3801 fiberglass tanks. Salinity levels used were 0, 8.5, 17, 34 and 51 ppt, or 0, 25, 50, 100 and 150 percent seawater. These were achieved by mixing concentrated lagoon water and tapwater in different proportions. Tanks were inoculated with plankton collected from San Dieguito Lagoon (Del Mar, San Diego County, California) and other fresh and saline waterbodies in the area. Selected physical-chemical variables, phytoplankton, zooplankton, and other invertebrate populations were monitored on five sampling dates over a 114 day period (13 August–5 December 1986).Total phytoplankton abundance increased with salinity, for salinities >17 ppt. Most taxa showed marked effects of salinity, though the pattern of the effects often varied greatly from date to date. Chlorophytes tended to be most abundant at 51 ppt. Pyrrhophytes were most abundant at 0 or 51 ppt, and least abundant at 8.5 or 17 ppt. Cryptophytes increased with increasing salinity. Euglenophytes exhibited no salinity effect on any date. Bacillariophytes were most abundant at 8.5–34 ppt and least abundant at 51 ppt, with individual taxa showing maxima at 0–17 ppt (Navicula, Synedra), 8.5–34 ppt (Surirella, Amphora), and 34 ppt (Cylindrotheca).Total zooplankton abundance decreased with salinity, for salinities > 17 ppt. The dominant taxa were protozoans, rotifers, cladocerans, and copepods, and all but the first group showed strong salinity effects. Protozoan abundance was unaffected by salinity. Rotifers were most abundant at 0 ppt (Keratella, Filinia) or 8.5 ppt (Brachionus). With few exceptions, cladocerans (Alona, Ceriodaphnia, Scapholeberis) were found only at 0 ppt. Abundance of calanoid copepods decreased with increasing salinity, with individual taxa showing maxima at 0 ppt (Diaptomus), 8.5–17 ppt (Pseudodiaptomus, Eurytemora), and 34 ppt (Acartia). Cyclopoid copepods were most abundant at 17 ppt, with individual taxa showing maxima at 0 ppt (Eucyclops), 8.5 ppt (Halicyclops), and 17 ppt (Oithona). Harpacticoid copepods (Cletocamptus, Tachidius) were most abundant at 17–34 ppt. Ostracods and mosquito (Culex) larvae were most abundant at 8.5 ppt and absent at 34 and 51 ppt. Polychaetes generally were most abundant at 17–34 ppt, and water boatmen (Trichocorixa) at 8.5–34 ppt. Various physical and chemical variables also showed significant variations with salinity. Tending to increase with salinity were temperature, ammonia and orthophosphate concentrations. Decreasing with salinity were pH, dissolved oxygen and silica concentrations. The causes and interrelationships of these salinity effects are discussed.     

Nitrogen fixation by periphyton and plankton on the Amazon floodplain at Lake Calado

Nitrogen fixation by periphyton and plankton was measured on the Amazon flood-plain using the acetylene reduction method calibrated with¹⁵N-N₂. The average ratio (± SD) of moles C₂H₄ reduced per mole N₂-N fixed was 3.4 ± 0.7, similar to other studies. Periphyton and plankton had high rates of light-dependent nitrogen fixation, with dark nitrogen fixation averaging 26% of the average rates in the light. The average daily (24 h) rates for periphyton nitrogen fixation in 1989 and 1990 were 1.79 and 0.51 mmol N₂-N·m^–2·d^–1 respectively, which are comparable to summer rates in many temperate cyanobacterial assemblages. Nitrogen fixation was depressed at N0₃^– concentrations as low as 0.5 M, and was below detection limits at concentrations of 4 M, which occurred during periods of river flooding. Planktonic nitrogen fixation rates were high (0.5–0.8 mmol N₂-N·m^–2·d^–1) during the high-water and drainage phases of the annual hydrograph when the floodplain waters were draining towards the river (low NO₃^–), but rates were undetectable (< 0.05 mmol N₂-N·m^–2·d^–1) when there was river flooding (high NO₃^–). Nitrogen fixation by periphyton and plankton in 1989–1990 accounted for approximately 8% of previously reported total annual nitrogen inputs to the floodplain at Lake Calado.     

Phases in the development of riverine plankton: Examples from the rivers Rhine and Meuse

Observations on phyto and zooplankton in two hydrographically different rivers were compared in order to discriminate phases in plankton development. Along the longitudinal axis of the River Rhine a gradual increase in the development of phytoplankton was observed, which reached its maximumca. 100 km before the river flows into its artificial sedimentation area. The development of rotifer populations was slightly retarded as compared with that of phytoplankton and highest population densities were only reached in the sedimentation area. Crustaceans developed in significant numbers, not until the river water had entered the sedimentation area. Development of zooplankton coincided here with a strong decrease in the density of phytoplankton. A similar trend in plankton development was observed in the River Meuse, although in this river the highest densities of phyto and zooplankton already occurred in its middle reaches. The differences in the timing of plankton growth in the two rivers are probably caused by differences in flow regime between both rivers. The River Rhine, which is fed by rainwater and melting of glaciers in the Alps, has a relatively constant discharge. On the other hand, the low discharge of the rain-fed River Meuse combined with an increased residence time of the water as a consequence of large numbers of weirs, allows a full cycle of plankton development long before its discharge into the sea. This phenomenon was also reflected in the silicate cycle in the Meuse, where the consumption by planktonic diatoms and the regeneration of silicate of deposits seem to be important. In contrast, in the main branches of the River Rhine only the effects of silicate consumption were detectable.     

Morphologic variability of the coccolithophorid Calcidiscus leptoporus in the plankton, surface sediments and from the Early Pleistocene

On a global scale, morphological variability of the extant coccolithophorid Calcidiscus leptoporus (Murray and Blackman, 1898) Loeblich and Tappan was investigated in surface sediments and plankton samples and from an Early Pleistocene time-slice (1.8 Ma to 1.6 Ma). In the bivariate space coccolith diameter versus number of rays in the distal shield, Holocene samples follow a single, unimodal morphocline. Sample means of coccolith size and number of elements group in three clusters, I, II and III, which are of biogeographic significance. Clusters II and III coccoliths (mean coccolith size of 5.0 μm and 20.9 elements, and 6.6 μm and 25.6 elements, respectively) are found in a tropical belt extending from 11 °N to 17 °S with an annual minimum sea-surface temperature above 23.5 °C. Cluster I coccoliths (5.8 μm, 20.7 elements) are found in samples outside that belt. The distribution of coccoliths in the surface sediments is tentatively interpreted to be a result of mixing to a varying degree of at least three different morphotypes (‘small’, ‘intermediate’ and ‘large’), which were identified in the living plankton, and which are separated from each other at 5 μm and 8 μm mean coccolith diameter, respectively. A comparison of the surface sediments with the Early Pleistocene assemblages revealed that between 1.6 Ma and 1.8 Ma two morphoclines A and B existed, the first of which persisted until the Holocene in the form of C. leptoporus, while the second comprises only extinct morphotypes including Calcidiscus macintyrei as one end-member. During the Early Pleistocene morphocline A was more homogeneous and no clusters were evident.Morphocline B shows a clear bimodality with a separation of morphotypes at 9.5 μm. Our observations suggest that morphoclines are subsets within the total stratigraphical range of a single species, and represent the global variability of that species in a particular time interval. Morphotypes, which belong to a morphocline, represent the infra-specific variability of that species within the biogeographic and stratigraphic limits of that species.     

Robust parameters confirm predominance of heterotrophic processes in the plankton of a highly humic pond

The conclusions about the role of allochthonous organic matter in the food chains of inland waters are still often conflicting. Here we studied whether the results of specific experiments made in a small pond with very high concentration of allochthonous organic matter could be verified by simple, but robust, basic environmental parameters measured in the field. In summer primary production of phytoplankton could explain only ca. 20% of epilimnetic respiration and <10% of the nutritional requirements of zooplankton. These results agree with those of earlier experimental approaches and unequivocally suggest the major role played by allochthonous nutrition for the plankton in this pond. The roles played by photochemical degradation and anaerobic processes in the transformation of humic compounds available to epilimnetic food web in particular deserve further elucidation.     

Phytoplankton dynamics in relation to hydrography, nutrients and zooplankton at the onset of sea ice formation in the eastern Weddell Sea (Antarctica)

The quantitative and qualitative distribution of phytoplankton was investigated along five North–South transects in the eastern Weddell Sea during the transition from late autumn to winter. Relationships with the regional hydrography, progressing sea ice coverage, nutrient distribution and zooplankton are discussed and compared with data from other seasons. To the north of the Antarctic Slope Front (ASF) a remnant temperature minimum layer was found above the primary pycnocline throughout summer. Surface waters had not entirely acquired typical winter characteristics. While temperature was already in the winter range, this was not the case for salinity. Highest biomass of phytoplankton, with the exception of the first transect, was found in the region adjoining the ASF to the north. Absolute chlorophyll a (Chl a) concentrations dropped from 0.35 to 0.19 g l^–1 . Nutrient pools exhibited a replenishing tendency. Ammonium concentrations were high (0.75–2 mol l^–1), indicating extensive heterotrophic activity. The phytoplankton in the ASF region was dominated by nanoflagellates, particularly Phaeocystis spp.. North of the ASF the abundance of diatoms increased, with Fragilariopsis spp., F. cylindrus and Thalassiosira spp. dominating. Community structure varied both due to hydrographical conditions and the advancing ice edge. The phytoplankton assemblage formed during late autumn were very similar to the ones found in early spring. A POC/PON ratio close to Redfield, decreasing POC concentration and a high phaeophytin/Chl a ratio, as well as a high abundance of mesozooplankton indicated that a strong grazing pressure was exerted on the phytoplankton community. A comparison between primary production (PP) in the water column and the sea ice showed a shift of the major portion of PP into the ice during the period of investigation.     

The influence of macrophyte beds on plankton communities and their export from fluvial lakes in the St Lawrence River

1. To determine the influence of macrophyte beds on plankton abundance within fluvial lakes of the St Lawrence River, planktonic components (macrozooplankton, heterotrophic bacteria, and phytoplankton as chlorophyll- a [Chl- a ]) were sampled in Lake St Francis and Lake St Pierre during summer 1998. We tested the hypothesis that the abundance of planktonic components was higher within macrophyte beds in comparison to the more rapidly flushed open water areas of the fluvial lakes.
2. The large cross channel variation in zooplankton biomass was indeed correlated with the presence of dense beds of submerged macrophytes. Total macrozooplankton biomass was nine-fold greater within the beds (mean=180 μg L−1 dry mass) than in either the open water or areas with only sparse vegetation (mean=20 μg L−1 dry mass).
3. Chl- a and heterotrophic bacterial abundance were also higher in the beds, but only slightly so. There was no difference in total phosphorus or dissolved organic carbon concentrations between areas of dense vegetation, sparse vegetation or open water.
4. Macrophyte beds on the margins of the fluvial lakes allow the development of high planktonic abundance relative to the fast flowing central channel. Macrozooplankton biomass was much higher at the outflows of the lakes (∼50 μg L−1 dry mass) in comparison to the inflows (<20 μg L−1 dry mass). The increase is due to the transfer of organisms from submerged macrophyte beds into the central channel in the downstream quarter of the two lakes where the marginal littoral waters enter central channel waters.
5. Along rivers, shallow fluvial lakes appear to act as sources of plankton which is exported downstream during years of extensive littoral macrophyte development.     

Genetic differentiation among the three Hindu low caste groups of Malda district,West Bengal,India

Three descendants of Koch, Indo-Mongolid populations, have been studied for their 12 genetic markers of blood group, red cell enzyme and serum protein. Distribution of their phenotype and allele frequencies shows some variants apart from their common alleles. Analysis on genetic material reveals very low differentiation coefficient (G_ST) value for the total population, and in the distance measure the Poliya and the Tiyor stand close to each other compared to other populations. Data on ethnohistory of the peoples have been discussed in the light of the results obtained from genetic analysis.     

Interaction among Non-toxic Phytoplankton,Toxic Phytoplankton and Zooplankton: Inferences from Field Observations

We explore the mutual dependencies and interactions among different groups of species of the plankton population, based on an analysis of the long-term field observations carried out by our group in the North–West coast of the Bay of Bengal. The plankton community is structured into three groups of species, namely, non-toxic phytoplankton (NTP), toxic phytoplankton (TPP) and zooplankton. To find the pair-wise dependencies among the three groups of plankton, Pearson and partial correlation coefficients are calculated. To explore the simultaneous interaction among all the three groups, a time series analysis is performed. Following an Expectation Maximization (E-M) algorithm, those data points which are missing due to irregularities in sampling are estimated, and with the completed data set a Vector Auto-Regressive (VAR) model is analyzed. The overall analysis demonstrates that toxin-producing phytoplankton play two distinct roles: the inhibition on consumption of toxic substances reduces the abundance of zooplankton, and the toxic materials released by TPP significantly compensate for the competitive disadvantages among phytoplankton species. Our study suggests that the presence of TPP might be a possible cause for the generation of a complex interaction among the large number of phytoplankton and zooplankton species that might be responsible for the prolonged coexistence of the plankton species in a fluctuating biomass.     

Effects of mineral turbidity on freshwater plankton communities: Three exploratory tank experiments of factorial design

We conducted three exploratory experiments of factorial design on the effects of mineral turbidity in 18 large (7 000 1) fiberglass tanks containing plankton communities derived from Lake Texoma (Oklahoma-Texas), a large reservoir often subject to turbid inflows. Replicate plankton communities developed for 30–45 d in response to 4–9 treatments of planktivorous fish, dead fish, nutrient additions and artificial removal of zooplankton with plankton netting (or combinations of these manipulations). In one experiment we then added three concentrations of kaolin and in the other two experiments we added bentonite or powdered silica to the replicate tank communities. We measured the responses of the diverse plankton communities to the addition of mineral turbidity for an additional period of 30–45 d.Effects of introduced minerals (quality or concentration effects) and food web treatments after mineral addition (fish, nutrients, etc.) were determined by analysis of covariance after observations were adjusted for the value of each response variable at the time of mineral addition. Covariance analysis resulted in a statistical model explaining > 80% of the variance for most response variables. The values of response variables at the time of mineral addition were often the most important source of variation, suggesting the importance of biotic community resiliency to the effects of mineral turbidity. There were few effects of mineral particles on physical or chemical (temperature, conductivity, oxygen, pH), nutrient (nitrate, phosphate, alkalinity) or biotic (algal or zooplankton populations) components of the tank communities. Mineral effects were found for several measures of water clarity (Secchi depth, turbidity, and the concentration of small sestonic particles).     

A study of the relative efficiency of mustard oil cake and urea and the effect of salinity in plankton production in indian fishponds

Augmentation of plankton production in Indian fishponds by application of manure and inorganic fertilisers was studied in laboratory experiments. The effects of the salinity of the medium were also examined.Laboratory trials were made with mustard oil cake and urea on equivalent nutrient bases in media with varying degrees of salinity (0–30 ppt at 2 ppt. intervals). It was observed that Closterium, Fragilaria, Pinnularia and Gyrosigma grew well in the higher salinity range between 24 to 30 ppt. whereas lower salinities ranging from a trace to 8 ppt. are suitable for improved production of Anabaena, Synedra, Navicula, Amphipleura, Amphora and Nitzschia. Comparatively better production of plankton was recorded with urea than with mustard oil cake.     

Diel variation in the vertical distribution of fish and plankton in Lake Kinneret: a 24-h study of ecological overlap

Diel vertical migration (DVM) behaviour is a predator avoidance mechanism observed within many zooplankton species in the presence of zooplanktivorous fish. A 24-h survey was carried out in June 1998 to investigate diel variation in the vertical distribution of fish, zooplankton and phytoplankton (chlorophyll) in Lake Kinneret, Israel. Fish revealed diel variation in vertical distribution but had no spatial overlap with zooplankton, and consequently no apparent influence on zooplankton dispersal. Zooplankton revealed some diel variation in distribution being affected by thermocline and oxycline position and movement of the internal the internal seiche wave. Cyclopoid species closely follow the movement of the seiche wave implying that, due to their greater motility, they are following conditions that are suitable to them. The Cladocera species and small rotifers only partly, which may be part of their phototaxic behaviour. Physical forces like convection, horizontal and vertical forcing probably have a role in contributing to a homogeneous distribution of the plankton by preventing stratification or interfering with the more motile zooplankton which may be attempting to migrate.