Vertical migration, hatching rates, and distribution of egg stages in freshwater zooplankton

In shallow, thermally stratifield lakes, the developing eggs carried by pelagic crustacean zooplankton are exposed to regularly alternating higher and lower temperatures during daily vertical migration. Rate summation techniques for determining the duration of egg developiment suggest that (1) the distribution of egg stages in the population will not change because of the alternating temperatures, and (2) the majority of young animals will not be hatched or released in the warmer, upper waters of the lake. This latter result is probably positively adaptive, but it may be brought about entirely mechanistically by the more rapid development in warmer waters.     

Biogeography and ecology of freshwater diatoms in Subantarctica: a review

Subantarctica is situated between the Antarctic and the Subtropical Convergence and consists of the islands in the southern Atlantic, Indian and Pacific Oceans. Diatoms are an important component of all Subantarctic aquatic, moss and soil habitats. Taxonomic studies reveal a high diversity and species richness in both the present-day and the fossil diatom flora. Planktonic diatoms are almost completely absent. A similarity analysis of the diatom composition from different localities in the southern zone (below 40°S) resulted in a biogeographical zonation. Three regions could be formed, based on their diatom composition: Subantarctica, Maritime Antarctica and the Antarctic Continent. The diatom communities in the different regions are all characterized by a high proportion of cosmopolitan species. A second feature of the southern diatom floras is the decreasing diversity when moving southwards.     

Influence of light quality and gassing on the vertical migration of diatoms inhabiting the Wadden Sea

Diatoms inhabiting the Wadden Sea show a rhythmic migration pattern, which is superimposed by the tidal rhythm. In addition to light intensity, light quality has a pronounced influence on the upward-directed migration, thus giving some information on the nature of the relevant photoreceptors. Maximum diatom migration occurred when sediment surfaces were illuminated with blue light. The cell densities in blue light exceeded those of white light control experiments 1.8-fold. Furthermore, we registered a minor peak in the red light region, which reached approximately 60% of the white light controls. Cryptochrome and/or phototropin may thus be involved and act as photoreceptors for the vertical migration pattern. Flushing sediment surfaces of freshly mixed Wadden Sea sediments with air, O₂, CO₂ or N₂ did not show a significant influence of O₂ on the upward migration. The disappearance of diatoms from sediment surfaces which were flushed with CO₂ is most probably caused by the acidification of the sediment bed.Communicated by E. Rachor     

Development of molecular tools for the detection of freshwater diatoms

This study was undertaken to develop a reliable and reproducible procedure for the detection and quantitative determination of diatoms in environmental samples. A comparative study of seven different DNA extraction kits was carried out to establish conditions for analysis of diatom containing samples. The best performers were identified using both standard and real-time PCR. We show that the yield of diatom DNA is generally quite low when using commercially available extraction kits; in addition, a new protocol was devised to obtain samples suitable for DNA amplification without the need to perform all the steps required for DNA extraction. This method was tested on environmental samples spiked, in a wide range of total cell mass, with the rarely occurring diatom Neidium affine together with a highly species-specific oligonucleotide designed on the small subunit (SSU) rRNA gene. Thus, we propose a fast and effective procedure that, combined with the use of species-specific oligonucleotide probes can detect minute amounts of a spiked diatom within a complex diatom community. This study provides experimental conditions for a fast and accurate detection of diatoms, and demonstrates the feasibility of the use of molecular tools in the evaluation of water quality.     

Vertical distribution and diel migration of rotifers in a Parana River floodplain lake

The vertical distribution of zooplankton rotifers in the open waters of Laguna El Tigre was investigated. Rotifers showed a relatively uniform distribution throughout the water column. This pattern of distribution was maintained during the year and did not show variations in relation to hydrologic phases of inundation and isolation of the lake. Diel vertical migration of rotifers from the limnetic and the littoral area was investigated too. In littoral area rotifers exhibited a reverse migration, whereas in the limnetic the movements were less conspicuous. Horizontal migration was observed too, and there were interactions between horizontal and vertical distribution. Predation and competition offer a possible explanation.     

Vertical, lateral and longitudinal movement of zooplankton in a large river

1. The spatial distribution and movement patterns of zooplankton in large rivers are little known compared with those in lake environments. We conducted a series of studies in the Ohio River (U.S.A.) during the low flow period to assess diel vertical (DVM), longitudinal and lateral movement of crustacean zooplankton. 2. The dominant large zooplankter, the copepod Eurytemora affinis, showed a consistent vertical migration pattern of daytime ascent and night‐time descent during all sampling periods – the reverse of the most common migratory pattern of zooplankton in lakes. The cladoceran Bosmina migrated in a similar way in two of the three sampling periods. Surveys taken longitudinally in the river showed similar trends for both taxa. 3. During the lateral surveys, E. affinis was significantly more abundant in the shallow littoral zone during the night than in the daytime. The combination of vertical and lateral movement patterns along with the diel distribution of zooplanktivorous fish suggest that these movements are a predator‐avoidance mechanism. 4. Sampling programmes in large rivers should consider that larger zooplankton such as E. affinis may not be randomly distributed in the river channel and behaviours such as diel vertical migration may be just as evident in river habitats as in lakes.     

An ecological study of three freshwater ponds of hyderabad-India IV. the phytoplankton (diatoms,euglenineae and myxophyceae)

Data on the ecology of Diatoms, Euglenineae and Myxophyceae in three freshwater ponds, differing in chemical composition and algal flora, situated in the vicinity of Hyderabad-India are presented. An attempt has been made to isolate various genera into groups, as their multiplication depended on particular ranges of a single chemical factor or set of factors. Several species could be separated into seasonal forms as they occur in particular periods of the year. Others could be grouped under indifferent forms as these are neither influenced by fluctuations in chemical factors nor by seasonal changes.     

Twofold effect of blue light on a circadian rhythm in Acetabularia

Abstract

The circadian chloroplast migration in Acetabularia mediterranea was monitored by continuously measuring the transmission of the cells near the apex. Under continuous red light the amplitude of the rhythm decreased rapidly within a few days. However, circadian changes of chloroplast density were still detectable even after 28 days of red light, indicating the persistence of the rhythm. When blue light was added after red light preirradiation of several days phase shifts were observed which were expressed as advances as well as delays. The period of the rhythm proved to be strongly dependent on the intensity of the continuous blue light which was given in addition to red light. Different red light intensities did not change the period. The occurrence of both effects indicates that the sensory transduction of blue light photoreception in Acetabularia works in two different ways: quanta counting processes and processes of light intensity measurement.     

Distribution of epipelic diatoms in artificial fishponds along environmental and spatial gradients

Although epipelic diatoms play a key role in primary production of many ecosystems, many aspects of their biodiversity, ecology and geographical distribution are poorly understood. The present study is based on sampling of 45 man-made fishponds in the Czech Republic covering an environmental gradient from oligo/dystrophic highland ponds within protected areas to the eutrophic/hypertrophic lowland ponds used for intensive fish production. Diatom distribution patterns assessed using biomass and species composition variables were assessed along environmental and geographical gradients. In total, 185 epipelic diatom taxa were found in the investigated samples. The differences in species composition between sites were correlated with environmental parameters, but not with the geographic distance of the localities. This pattern might suggest that niche-based control, rather than the effect of dispersal limitation, is the main driving force in the species composition of epipelic diatoms in fishponds. The alpha-diversity of sites correlated with altitude, nitrogen and chlorophyll a concentrations but did not correlate with the area of the ponds. The significant relationships between local abundance of species and their regional occupancy were very similar to previous studies of diatoms in boreal streams. In addition, these data concur with patterns known for multicellular organisms suggesting that in this respect diatoms may not differ from groups of organisms with larger body sizes. Handling editor: J. Padisak     

Cladistic analysis of some freshwater araphid diatoms (Bacillariophyta) with particular reference toDiatoma andMeridion

Interrelationships of the ribbed araphid diatoms have been reinvestigated using a cladistic analysis of a revised morphological dataset. The presence of silicified transapical ribs has previously been used to distinguish between different groups and its ability to serve as a distinguishing feature is reevaluated. The importance of valve symmetry, not fully appreciated in a previous paper, is examined. The evolution of heteropolarity, and its importance in taxonomy appear more complex than is implied by a simple dichotomy dividing groups of species into heteropolar and isopolar forms, involving an inferred evolutionary transformation from one condition to the other. This analysis proposes a close relationship betweenDiatoma, Fragilariforma, Asterionella, Distrionella, Meridion, Tabellaria, andTetracyclus. It also confirms the sub-division ofDiatoma into two closely related taxa. The genusMeridion, however, should not include both heteropolar and isopolar species in a single genus. Although the species are closely related, the isopolar species are more closely related toTabellaria andTetracyclus than they are to the heteropolar species ofMeridion.     

Gymnodinium helveticum Penard F. Achroum Skuja a case of phagotrophy

Gymnodinium helveticum f. achroum in Blelham Tarn was occasionally noted to exhibit phagotrophy. Various algae were observed inside Gymnodinium cells. The seeding of an experimental enclosure with dead Lycopodium spores resulted in some of the Gymnodinium cells containing a spore.

From the results, it is suggested that this dinoflagellate exhibits non-selective and non-predatory phagotrophy.     

Vertical foodweb structure of freshwater zooplankton assemblages estimated by stable nitrogen isotopes

Although theoretical foodweb models predict the presence of only three to four trophic categories, estimation of “potential” vertical foodweb structure from species lists and inferred feeding interactions suggest that as many as 7 trophic categories can occur in the pelagic foodwebs of North American glaciated lakes. A compilation of data on the nitrogen isotopic composition of zooplankton from 46 Canadian Shield lakes suggested the average existence of one “realized” trophic category in addition to that of filter-feeding, herbivorous cladocerans. When phytoplankton, planktivorous invertebrates, and plantivorous and piscivorous fish are included, the vertical foodweb structure in the pelagic zones of these lakes are greater than those hypothesized from some theoretical models.     

Cytoplasmic free calcium in single cells of centric diatoms. The use of fura-2

Summary Cytoplasmic free calcium concentration has been measured in centric diatoms using Fura-2. Cells hydrolysed Fura-2 acetoxymethyl ester and accumulated free Fura-2 in the cytoplasm. The [Ca²⁺] distribution in two species (Coccinodiscus concinnus andGuinardia flaccida) has been mapped using digital image analysis.Abbreviations [Ca_cyt²⁺] Cytoplasmic free calcium concentration - Quin-2/AM Quin-2 acetoxymethyl ester - Fura-2/AM Fura-2 acetoxymethyl ester DMSO dimethyl sulphoxide - CCTV closed circuit television     

Circadian rhythms of demand-feeding and locomotor activity in rainbow trout

Under free-running conditions, most rainbow trout displayed circadian feeding rhythms, although the expression of circadian rhythmicity depended on the experimental condition: 16·7% of fish under constant dim light (LL dim), 66·1% under a 45 :45 min light-dark cycle (LD pulses), and 83·8% under constant light (LL). Under LD pulses, the period length of the free-running rhythms for feeding was significantly shorter (21·9 ± 0·7 h, n =8) than under LL (26·2 ± 0·3 h, n =10). Period length for locomotor activity under LL was 25·8 ± 0·6 h ( n =4). Under LD conditions, the daily demand-feeding profile was always confined to the light phase and chiefly composed of two main episodes, directly after lights on (light elicited) and in anticipation to lights off (endogenous). Contrasting to feeding, the diel locomotor activity profile varied remarkably: a diurnal activity pattern at the bottom, while a clearly nocturnal pattern at the surface. These results contribute to a better understanding of feeding and locomotor rhythms of rainbow trout, providing evidence for the existence of a biological clock involved in their circadian control. This finding contrasts with the previously recorded lack of an endogenous oscillator in the pineal organ driving the rhythmic secretion of melatonin, which suggests different locations from the pineal for the circadian pacemakers in this species.     

Uncertainty in ecological status assessments of lakes and rivers using diatoms

The EU’s Water Framework Directive requires all surface water bodies to be classified according to their ecological status. As biological communities show both spatial and temporal heterogeneity, expressions of ecological status will, inevitably, have an element of uncertainty associated with them. A consequence of this environmental heterogeneity is that there is a risk that status inferred from one or more samples is different to the true status of that water body. In order to quantify the scale of temporal uncertainty associated with benthic diatoms, replicate samples were collected from sites across the ecological status gradient in lakes and rivers in the UK. Variability (expressed as standard deviation of temporal replicate samples from a single site) could be described using a polynomial function and this was then used to calculate the risk of placing a water body in the wrong ecological status class. This risk varied depending on the distance from the class boundaries and the number of replicates. Based on these data, we recommend that ecological status is determined from a number of samples collected from a site over a period of time.     

Epiphytic diatoms in two freshwater maritime Antarctic lakes

SUMMARY.

• 1 An ecological study of two small maritime Antarctic lakes on Signy Island, South Orkney Islands, was undertaken from January 1986 to March 1987. Analysis of diatom counts from the lakes provided examples of oligotrophic and mesotrophic ecosystems.
• 2 A diverse community of 104 epiphytic taxa was identified. Twenty-eight taxa had a percentage abundance greater than 1% in both lakes. Distinctive dominant taxa were identified from each lake.
• 3 A variety of ordination techniques was performed on the abundance data and a principal components analysis demonstrated differences in the diatom assemblages between the two lakes. Clear separations of sites and species were evident between the lakes, and accounted for the greatest percentage variance.
• 4 Species composition varied with depth within each lake and was also important in influencing changes in assemblage composition between sites.
• 5 A redundancy analysis indicated that species composition was correlated to concentrations of nitrogen and phosphorus but the total variance accounted for by the four physical and chemical factors measured was low (24%).

     

SEM observations of some noteworthy diatoms from the Ikpoba reservoir,Nigeria

ABSTRACT

Eighteen taxa of diatoms from the Ikpoba reservoir, southern Nigeria are listed in this report. They belong to the genera Cymbella, Stenopterobia, Eunotia, Brachysira, Frustulia, Navicula, Pinnularia, Stauroneis and Surirella. The occurrences and distribution of the algae are indicated. Two of these taxa occurred very frequently, six frequently and four occasionally. Five taxa had rare occurrences while one was very rare. They were compared with national as well as regional records.     

Valve formation in diatoms and the fate of the silicalemma and plasmalemma

Summary In two species of the diatom genusMelosira the inner profile of the silicalemma fuses with the plasmalemma covering the older part of the cell at, or slightly before, maturity of the new siliceous cell wall component. Subsequently, the outer profile of the silicalemma and the remainder of the plasmalemma are cut off. Though there are indications that the valves may continue to add silica after this time the wall component now lies to the outside of a membrane which must,de facto, be considered the plasmalemma. When cingula move apart as development continues the membrane fragments are allowed to disperse and it is thought unlikely that they contribute to the formation of an organic investment of the siliceous components of the frustule.