Rotifer occurrence in relation to oxygen content

Information on the distribution of 204 species of planktic, periphytic and benthic rotifers from diverse waters in south and central Sweden was analyzed for details on relationships to the oxygen content of the environment. No sign of truly anoxybiontic appearance was traced, although some species may be encountered in high abundance at low O₂-values. Most cold-stenothermal species prefer an environment rich in oxygen, but there are a few exceptions. For the warm-stenothermal species no really close connections with oxygen exist. Several species combine a tolerance of low oxygen content with a preference of high Pt-values. No such connections were traced between oxygen content and trophic degree.     

Rotifer occurrence and trophic degree

Information on the distribution of planktic, periphytic and benthic rotifers from diverse waters in south and central Sweden was analysed for details on relationships to the trophic degree. Three factors were combined in order to get an estimation of the trophic degree: tot-P-content, electrolytic conductivity and content of dry matter. Indicators of oligotrophic and eutrophic environments are enumerated. As far as the planktic species are concerned, the results are largely compatible with those of earlier investigations (while the non-planktic forms were previously less known in this respect). Some eutrophy indicators have been reported as typical of saprobic environments.     

Relation to habitat in rotifers

Rotifera should be especially suited for an analysis of habitat relations because this group contains such a high number of species, inhabiting diverse environments. Furthermore, rotifers are to a large extent cosmopolitan, implying that ecological barriers, rather than geographical, are decisive of their distribution. In this review a short characterization of the rotifer fauna in different habitats is given, whereby macroenvironments and microenvironments are reported separately. The macroenvironments are classified as follows: harmonious lakes and ponds, arctic and antarctic waters, hot springs, hypertrophic-saprobic environments, mires, strongly acidic waters, saline waters, temporary water bodies, subterranean waters, running waters, oceans, terrestrial environments. The following microenvironments are distinguished: macrophytes (housing periphytic rotifers), open water (with planktic forms), minerogenous sediments (with psammon and hyporheos), organogenous sediments, other organisms (i.e. parasites and epizoans).Many rotifers are more or less euryecious, while relatively few are strongly restricted in their choice of habitat. In extreme environments a low number of species is found, but often a high number of individuals within these species. These rotifers are usually primary consumers, and for natural reasons extreme environments are characterized by a low number of trophic levels.In environments with a high species number the separate species differ very much in their morphology, making it difficult to find common traits which may be interpreted as adaptations to the respective habitats. The most apparent adaptations ought to be found among the planktic rotifers, and these adaptations seem to constitute largely a protection against predators. Rotifers in extreme environments are usually not very apart in a morphological or taxonomical respect, with their most close relatives living in normal habitats and sometimes euryecious (an apparent exception from this rule is formed by the class Seisonidea). Adaptations to deviating chemical and physical environments may develop relatively rapidly (seen from a geological perspective), while the more fundamental changes (occurring during a longer period of time) seem to be a response to biotic factors (e.g., the development of different types of trophi for facilitating food collection).     

On choice of substrate and habitat in brachionid rotifers

Information on the distribution of 28 rotifers of the family Brachionidae from diverse waters in south and central Sweden was analyzed to reveal their relationships to substrate and habitat. Some brachionids are preferably planktic, others periphytic and/or benthic. Some non-planktic habitats are utilized more than others, but there is no evidence of a chemical attraction from any substrate. Instead, some substrates seem to be avoided, possibly depending on a poorer flora of periphytic algae. Besides substrate type, the following factors are found to be important for creating separate ecological niches in the brachionid family: temperature, oxygen content, trophic degree, chemical environment, food choice and sensitivity to predation. It is possible to delineate separate ecological niches for all brachionid rotifers, implying that Hutchinson's ideas about the plankton paradox are contradicted. Some species are specialists, other are generalists, the latter being characterized by a great morphological variation. The species are adapted in different ways to their preferential habitats, as regards foot, egg-carrying, protrusions and other lorical structures etc. Longer spines, for instance, are generally found in more transparent water, being a supposed protection against visual predators.     

The effect of food on protein content in rotifer and cladoceran species

SUMMARY. 1. The protein content of individuals of four species of cladoceran and two species of rotifer in eight ponds was measured over several time periods. The protein content in coarsely filtered water, which includes particulate (less than 31 μm for cladoceran and less than 10μm for rotifers) and dissolved proteins, was also analysed to estimate the amount of food available to the animals.
2. A positive relationship between protein content of individuals and protein in the food was found for all the species. The increase in protein content of the animals was less pronounced when food was more abundant.
3. When food concentration was lower, a greater reduction in protein content was observed in two species of rotifers than in four cladoceran species. Moreover, when comparing among species of Cladocera, the reduction in protein content at low food concentrations was more marked in the small-bodied than in the large-bodied species. These results are consistent with the size-efficiency hypothesis.     

Taxonomic studies of planktic species of Anabaena based on morphological characteristics in cultured strains

Fifty (50) strains of planktic species of Anabaena (cyanobacteria), including collections from Japan and China and from different culture collections, were induced to form akinetes at low temperature (15 °C). Their morphologies were then observed and described. Fourty seven strains successfully formed akinetes and these were classified into 20 species comprising seven with straight trichomes and 13 with coiled trichomes. Three strains, which did not form akinetes, were separated into two taxonomic groups, but could not be identified to any described species. In addition, a key to the planktic species of Anabaena described in the study is presented.     

Bile salt-dependent lipase in larval turbot, as influenced by density and lipid content of fed prey

Turbot larvae were fed three different densities of rotifers (1000, 3000 and 7500 rotifers 1⁻¹) with a low lipid level (< 15% of dry weight) or 7500 rotifers 1⁻¹ with a high lipid level (∼30% of dry weight). The larval consumption of rotifers increased with increasing prey densities and the content of bile salt-dependent lipase (BSDL) in larvae was correlated positively with the ingestion rate from days 6 to 8. This suggests that BSDL synthesis was stimulated by the amount of ingested prey in the early larval phase. However, growth was highest in larvae receiving the medium prey densities, which indicates that the larvae were not able to digest properly the ingested prey at the higher density. No significant effect on the BSDL content was seen in turbot larvae fed rotifers with a high or low lipid content.     

On limnic micro-crustaceans and trophic degree

A large material of planktic and semiplanktic microcrustaceans from different types of waters in south and central Sweden was computerized. The more frequent species were ranked according to phosphorus content (tot-P), electrolytic conductivity and content of suspended matter, searching for correlations with the trophic degree. With few exceptions, species indicating oligotrophy are found at lower factor values and those indicating eutrophy at higher values concerning all the abiotic factors considered.     

The genetic diversity of planktic foraminifera and the global distribution of ribosomal RNA genotypes

Fossil planktic foraminifers in the ocean sediments play an unparalleled role in our understanding of the oceanographic environment in the past. An in depth knowledge of their diversity, ecology and biogeography in the modern ocean lies central to the interpretation of the fossil assemblages. In comparison with their benthic counterparts, planktic foraminifera have a very limited diversity of around fifty extant morphospecies. Their morphospecies diversity peaks in the sub-tropics and decreases steeply towards the poles. Traditional species concepts have partitioned morphological types into distinct species (morphospecies) based on test shape, but genetic studies show that individual morphospecies are actually complexes of several discrete genetic types (genotypes). Many of these genotypes have distinct ecologies and novel adaptations that are consistent with species-level classification, indicating that the true diversity of planktic foraminifers has been greatly underestimated. Although planktic foraminifera are clearly capable of long-distance dispersal, they may be constrained by both physical and ecological barriers that vary according to the evolutionary history and ecology of the individual genotypes within a morphospecies. These differences lead to diverse biogeographies. Here, we provide an overview of the genetic and biogeographic data available to date for the planktic foraminifera and present global biogeographies highlighting the distribution of genetic types in the eight planktic foraminiferal morphospecies for which detailed molecular evidence is available.     

Miocene biochronology and paleoceanography of the North Pacific

Biostratigraphic correlation based on microfossil datum levels, directly or indirectly tied to the paleomagnetic time scale, provides a high resolution time control for the Miocene in the equatorial and middle latitude North Pacific. Faunal changes and abundance fluctuations of planktic foraminiferal species combined with the oxygen Pacific. Faunal changes and abundance fluctuations of planktic foraminiferal species combined with the oxygen isotope record of foraminifers, reveal the paleoclimatic and paleoceanographic history. The planktic foraminiferal assemblage change in the early Miocene, extinction of Oligocene fauna and rise of a highly diverse Neogene fauna, appears to be related to increased water mass stratification in the world oceans presumably resulting from the establishment of circum-Antarctic circulation. An increase in the siliceous productivity in the eastern equatorial Pacific region between 20 and 18 Ma suggests that the vertical and horizontal circulation was intensified at that time. Climates cooled rapidly during the middle Miocene between 14 and 13 Ma suggesting the growth of a major east Antarctic ice sheet. Paleoclimatic conditions remained generally cool, although oscillating, during the late Miocene. In the late early to middle Miocene faunal provincialism developed between low and middle latitudes, and by late Miocene time a distinct provincialism similar to the present was established.     

Kinetics of n-3 fatty acids in Brachionus plicatilis and changes in the food supply

Moderately starved rotifers exhibited a two-phased increase in n-3 fatty acids when they were fed a diet rich in these fatty acids. The first 20–30 min of enrichment, the increase in n-3 fatty acids was primarily due to increased gut content. The subsequent slow increase was due to an incorporation of n-3 fatty acids into rotifers tissues. Saturation was achieved before 24 h of exposure and the saturation level was independent of the initial content of n-3 fatty acids in the rotifers.Starvation and limited feeding of the enriched rotifers for additional 4–8 h at 10–20 °C did not affect the accumulated fatty acids significantly. This was found for rotifers with high and low initial content of n-3 fatty acids. The n-3 fatty acids were assimilated with high efficiency from the feed and were not metabolized faster than other groups of fatty acids.Enriched rotifers retained their nutritional value for a sufficient period after enrichment to serve well as live feed for marine fish larvae.     

Dictyonema Hall and its importance for the evolutionary history of the Graptoloidea

Dictyonema retiforme has been regarded as the benthic ancestor to the planktic Graptoloidea, represented by the earliest planktic Rhabdinopora flabelliformis and its descendants. The revision of the type material of Dictyonema retiforme, the type species of the genus Dictyonema, from the Silurian of New York State shows compound stipes formed by the complexly growing and overlapping tubular thecae of acanthograptid type. The connections between adjacent stipes are formed by thecal tubes or thecal bridges and not by dissepiments. Thus, the species has to be transferred to the Acanthograptidae and cannot be regarded as being related to the early planktic Graptoloidea. The tubarium meshwork of Dictyonema is phylogenetically unrelated to the meshwork of the planktic Rhabdinopora, and represents a case of convergent evolution. The origins of the planktic graptoloids lie among members of middle to upper Cambrian Dendrograpidae, as can be seen from the thecal style and the triad budding patterns with regularly developed bithecae in this group.     

Estimating lacustrine zooplankton species richness and complementarity

Literature and original information reveals that lakes at any latitude may be expected to lodge + 50 spp. of cladocerans, against + 150 spp. of rotifers in the temperate, and + 210 spp. in the tropical zone. Collector's curves can be used to estimate the number of species present at any point in time in a lake. Hyperbolic regression and Chao's non-parametric estimator were used to extrapolate from species numbers observed to true numbers present. Estimates for rotifers were better (had lower variances) than for cladocerans, and both were better in the temperate than in the tropical zone, where more species co-exist than in the temperate zone but where many more species are rare. Approximate numbers of samples required to approach true instantaneous species richness were calculated. However, a test in a (sub)tropical lake in Brasil where such an asymptotic number of samples was collected and examined failed to reduce the variance, while recording a number of species higher than predicted. We conclude that seasonal succession was still significant here, and that more research is needed to determine the minimum number of sampling repeats needed for a full census.Lakes with an ATBI (All Taxa Biological Inventory) for rotifers and cladocerans were compared by a complementarity index. This revealed geographic gradients between lakes, strong for cladocerans, but less so for rotifers. It is argued that this mainly reflects a difference in the state of taxonomic advancement between these two groups, and that the theory of cosmopolitanism must be abandoned for both.     

An update to modern taxonomy (2011) of freshwater planktic heterocytous cyanobacteria

It is essential for the modern taxonomic classification of cyanobacteria to be continually updated in accordance with revisions based on molecular sequence comparisons and combined with morphological features, ecophysiological characters and other biochemical and molecular markers (“polyphasic approach”). Several genera, which are characterized by their planktic life form and contain indicator species important for the evaluation of aquatic biocenoses in majority of water bodies are recognized in the monophyletic group of heterocytous cyanobacteria. Current taxonomic revisions (and nomenclatoric consequences) of the specific contents of these heterocytous cyanobacterial generic units are covered by this article. Among these genera, 12 contain only planktic species, three remaining genera contain both planktic and non-planktic species. Comments and suggestions for future research are stressed especially in the ecologically distinct genera, which includes species dominating in the plankton of various reservoir types.     

Associations of Rotifera in the zooplankton of the lake sources of the White Nile

Plankton samples for rotifers were collected by means of vertical hauls with phytoplankton nets at eight stations on Lake Albert during the course of a year. Similar hauls were taken from Lakes Kyoga, Victoria, George and Edward in October and November. The rotifers found in the samples are listed and some estimates of their abundance and seasonal occurrence in Lake Albert are given. The most important planktonic rotifers are Keratella tropica and several species of Brachionus . Other species may also become locally or temporarily abundant; Lecane bulla becomes numerous in samples taken near vegetation after disturbance by rough weather, or where blue-green algae are abundant.
The associations of rotifers at the stations on Lake Albert and in the other lakes have been compared by means of the Sorensen Index and the index of diversity. The highest diversity is found in situations with a high rate of flow, as at the mouth of the Victoria Nile, where the extra species are non-planktonic forms swept into suspension by the current. This high diversity is associated with low numbers of individuals per unit volume. In Lake Albert rotifers are most consistently present and abundant at the mouth of the River Semliki, where the rate of flow is moderated by a large reed swamp. The middle of Lake Albert is poor in rotifers, and this may be related to the sparseness of planktivorous fish coupled with competitive elimination of the rotifers by larger crustacean zooplankters.
The associations of rotifers in Lakes Kyoga and George are similar, and resemble one another more than they resemble the associations in their neighbouring deeper lakes. The association in Lake Kyoga also resembles the associations found in water of a similar depth at the northern end of Lake Albert.     

Associations of Rotifera in the zooplankton of the lake sources of the White Nile

Plankton samples for rotifers were collected by means of vertical hauls with phytoplankton nets at eight stations on Lake Albert during the course of a year. Similar hauls were taken from Lakes Kyoga, Victoria, George and Edward in October and November. The rotifers found in the samples are listed and some estimates of their abundance and seasonal occurrence in Lake Albert are given. The most important planktonic rotifers are Keratella tropica and several species of Brachionus . Other species may also become locally or temporarily abundant; Lecane bulla becomes numerous in samples taken near vegetation after disturbance by rough weather, or where blue-green algae are abundant.
The associations of rotifers at the stations on Lake Albert and in the other lakes have been compared by means of the Sorensen Index and the index of diversity. The highest diversity is found in situations with a high rate of flow, as at the mouth of the Victoria Nile, where the extra species are non-planktonic forms swept into suspension by the current. This high diversity is associated with low numbers of individuals per unit volume. In Lake Albert rotifers are most consistently present and abundant at the mouth of the River Semliki, where the rate of flow is moderated by a large reed swamp. The middle of Lake Albert is poor in rotifers, and this may be related to the sparseness of planktivorous fish coupled with competitive elimination of the rotifers by larger crustacean zooplankters.
The associations of rotifers in Lakes Kyoga and George are similar, and resemble one another more than they resemble the associations in their neighbouring deeper lakes. The association in Lake Kyoga also resembles the associations found in water of a similar depth at the northern end of Lake Albert.     

A form-function analysis of photon capture for seaweeds

A large material of planktonic and semiplanktonic micro-crustaceans from various type of waters in south and central Sweden was computerized. The more frequent species were listed according to pH-preference and relation to humic content measured as mg Pt/l. Species indicating oligotrophy have their optima just below the neutral point, eurytopic ones around this level, while the eutrophic species Daphnia cucullata and D. magna were closely correlated with higher pH-levels. No really extreme pH-preference was observed. There is no link between trophic indication and the ranking list for humic content. Most planktic species occur at lower humic contents and semiplankters at higher.     

轮虫和枝角类的种间竞争及其影响因子研究进展

轮虫和枝角类是浮游动物群落的重要组成部分和优势类群,它们之间的竞争互作是调节水生态系统结构和功能的主要动力之一。普遍的观点认为,轮虫和大型枝角类难以共存,往往被竞争排斥,而和小型枝角类可以共存;实际上,轮虫和枝角类的种间竞争结局存在一定的不确定性。介绍了轮虫和枝角类的种间竞争方式及其相对重要性,对影响轮虫和枝角类种间竞争结局的因素,包括温度、食物、相对起始密度、个体大小、食物临点、耐饥饿能力、捕食及竞争者和捕食者释放的化感物质等,进行了系统的梳理和分析,并提出了今后亟待解决的科学问题和研究切入点。     

The Unitary Association method in biochronology and its potential stratigraphic power between benthic and planktic organisms: A case study on foraminifers from Paleocene–Eocene strata of southern Egypt

Although foraminifers have been extensively used for biochronology, no quantitative evaluation of the quality of their application is available. In this work we apply a quantitative approach – the Unitary Association (UA) method – to evaluate the relative quality of planktic and benthic foraminifers in biostratigraphy. Based on 12,321 specimens belonging to 65 planktic and 132 benthic foraminifer species in 117 samples from the Paleocene–Eocene strata of the Kharga-Baris Oases (Western Desert, Egypt), the potential stratigraphic resolution power of benthic foraminifers is quantitatively assessed and compared to planktic foraminifers. The UA method accounts for superpositional contradictions between sets of coexisting taxa and generates unitary associations, which are conceptually similar to Oppel zones. The analysis produced fifteen unitary associations for the Paleocene–Eocene benthic Foraminifera of the studied sections, instead of three classical zones; most of these unitary associations are easily identified by the restricted occurrence of a single species. Although planktic Foraminifera have a higher seriation reality leading to a more robust biozonation, benthic Foraminifera have a higher stratigraphic resolution, at least at such regional scale. Furthermore, there was a significant positive correlation between the number of unitary associations and the number of species (R = 0.78 for planktic and 0.70 for benthic foraminifers; both with p < 0.001). These results corroborate that quantitative techniques may lead to a higher resolution in biochronology, even when applied to poor biochronological markers. Moreover, in contrast to simple spatiotemporal analyses, the Unitary Association method can accurately assess the stratigraphic potential of a given taxonomic group.     

Oxygen isotopic evidence for the depth stratification of tertiary and cretaceous planktic foraminifera

Oxygen isotope analyses of Tertiary and Cretaceous planktic foraminifera indicate that species have been stratified with respect to depth in the water column at least since Albian time. There is a relationship between morphology and depth habitat. Species with globigerine morphology have consistently occupied shallower depths than have species with globorotalid morphology. Biserially arranged species occupied both shallow and deep levels in the water column. On the average, it appears that ancient species with shallow habitats have been more susceptible to dissolution and have been preserved less well than species dwelling in deeper habitats. This relationship is similar to that observed for Recent planktic foraminifera. Comparison of carbon isotope ratios of adult and juvenile forms indicates that either the source of the carbon found in the shell or the carbon isotopic fractionations which occur during calcite secretion change during the development of individual foraminifera. The carbon isotopic ratios do not provide a reliable means for reconstructing the depth habitats of ancient species. Temperature-depth profiles for tropical Tertiary oceans have been reconstructed from the isotopic temperatures of planktic and benthic foraminifera. The vertical thermal structure of Oligocene oceans resembled that of modern oceans most closely. Those of Paleocene and Maastrichtian times differed most from that of modern oceans.