Predation by Acartia tonsa Dana on planktonic ciliates and rotifers

In laboratory experiments, adults and nauplii of the calanoid copepod Acartia tonsa Dana feed on planktonic ciliates and rotifers. Adults have a higher clearing rate for planktonic ciliates and rotifers than for phytoplankton. Adult copepods have a maximum clearing rate of ≈200 ml copepod⁻¹ · d⁻¹ for large ciliates, with lower clearing rates for small ciliates. Nauplii have higher clearance for small than for large ciliates. Addition of ciliates or rotifers to the diet of A. tonsa enhances egg production; this effect is due to improved food quality. Microzooplankton may be an important component of the diet of A. tonsa even when phytoplankton are plentiful. Selective predation by copepods probably influences the population dynamics of planktonic ciliates and rotifers in coastal waters.     

Spring weather determines the relative importance of ciliates, rotifers and crustaceans for the initiation of the clear-water phase in a large, deep lake

Clear-water phase (CWP) is an important event in seasonal planktonsuccession. We examined the influence of all herbivorous zooplanktonon its initiation under different weather and climatic conditionsusing up to 19 years of observations from the large, deep LakeConstance (Europe) and estimates of relative clearance rates.A CWP occurred regularly, even if daphnid biomass was stillvery low. CWP was attributed to strong grazing either by a daphnid-dominatedzooplankton community or by a diverse assemblage consistingof micro- and meso-zooplankton. Both types of zooplankton communitiesoccurred with approximately the same frequency. The timing ofthe CWP was unrelated to the North Atlantic Oscillation (NAO)but correlated with the wind-dependent intensity of deep verticalmixing 3 months earlier, during early spring. Less mixing enabledearly growth of phytoplankton, ciliates and rotifers despitelow temperatures, which prevented daphnid development at thistime. This resulted in enhanced grazing of ciliates and rotifers,which increased the importance of phytoplankton less ediblefor most ciliates, rotifers and daphnids. Ciliates clearly dominatedthe grazing pressure on phytoplankton throughout spring, maintaininghigh biomasses together with the phytoplankton for up to 2 months.A CWP was observed when herbivores grazing on larger phytoplanktondeveloped in addition to ciliates.     

Trophic interactions within the microbial food web in a tropical floodplain lake (Laguna Bufeos, Bolivia)

Whether the primary role of bacterioplankton is to act as "remineralizers" of nutrients or as direct nutritional source for higher trophic levels will depend on factors controlling their production and abundance. In tropical lakes, low nutrient concentration is probably the main factor limiting bacterial growth, while grazing by microzooplankton is generally assumed to be the main loss factor for bacteria. Bottom-up and top-down regulation of microbial abundance was studied in six nutrient limitation and dilution gradient-size fractionation in situ experiments. Bacteria, heterotrophic nanoflagellates (HNF), ciliates and rotifers showed relatively low densities. Predation losses of HNF and ciliates accounted for a major part of their daily production, suggesting a top-down regulation of protistan populations by rotifers. Phosphorus was found to be strongly limiting for bacterial growth, whereas no response to enrichment with Nitrogen or DOC was detected. HNF were the major grazers on bacteria (g-0.43 d(-1)), the grazing coefficient increased when ciliates were added (g- 0.80 d(-1)) but decreased when rotifers were added (g- 0.23 d(-1)) probably due to nutrient recycling or top-down control of HNF and ciliates by rotifers.     

Benthic–pelagic coupling: a comparison of the community structure of benthic and planktonic heterotrophic protists in shallow inlets of the southern Baltic

1. The taxonomic composition, abundance and biomass of heterotrophic protists (ciliates, heterotrophic flagellates (HF), rhizopods and actinopods) in the sediment and water column of shallow inlets of the Southern Baltic was studied under a variety of environmental conditions during 1996–1997. A shallow, highly eutrophic station and a deeper, less eutrophic station were compared.
2. Community biomass ranged from 0.12 to 0.34 μg C cm?3 in the water column and from 1.5 to 105 μg C cm?3 in the sediment. Heterotrophic protists dominated zooplankton biomass at both stations (73% and 84% mean contribution), while they were of minor importance within the zoobenthos. Expressed per unit area, benthic biomass contributed a significant part (44% and 49%) to the total heterotrophic protistan community at both stations.
3. Although the methodology for counting ciliates and HF was focussed on a high taxonomic resolution, the results reveal some general trends in the distribution of heterotrophic protists: protozooplankton biomass was dominated by flagellates (80% mean biomass contribution) at the shallow station and by ciliates (73% mean biomass contribution) at the deep station. In the benthos at both stations, ciliates were the dominant protozoans, followed by the hitherto little‐studied rhizopods (25% and 35% mean biomass contribution) and flagellates.
4. The degree of benthic–pelagic coupling differed between taxonomic groups. Benthic and pelagic communities of ciliates showed little taxonomic overlap. In contrast, many heterotrophic flagellate species were found both in the benthos and in the pelagic. These benthic–pelagic species contributed significantly to the biomass of HF in the water column. The planktonic rhizopod community consisted of a subset of those species found in the benthos.
5. The abundance of benthic and pelagic protists was positively correlated at the shallow station, but taxonomic data indicate that the direct exchange between benthic and pelagic communities was only partly responsible.     

Rotifers as predators on components of the microbial web (bacteria,heterotrophic flagellates,ciliates) — a review

Recent investigations have shown that processes within the planktonic microbial web are of great significance for the functioning of limnetic ecosystems. However, the general importance of protozoans and bacteria as food sources for rotifers, a major component of planktonic habitats, has seldom been evaluated. Results of feeding experiments and the analysis of the food size spectrum of rotifers suggest that larger bacteria, heterotrophic flagellates and small ciliates should be a common part of the food of most rotifer species. About 10–40 per cent of rotifers' food can consist of heterotrophic organisms of the microbial web. Field experiments have indicated that rotifer grazing should generally play a minor role in bacteria consumption compared to feeding by coexisting protozoans. However, according to recent experiments regarding food selection, rotifers should be efficient predators on protozoans. Laboratory experiments have revealed that even nanophagous rotifers can feed on ciliates. Preliminary microcosm and chemostat experiments have indicated that rotifers, due to their relatively low community grazing rates compared to the growth rates of bacteria and protozoans, should generally not be able (in contrast to some cladocerans) to suppress the microbial web via grazing, though they may structure it. Filter-feeding nanophagous rotifers (e.g. brachionids) seem to be significant feeders on the smaller organisms of the microbial web (bacteria, flagellates, small ciliates), whereas grasping species (e.g. synchaetids and asplanchnids) seem to be efficient predators on larger organisms (esp. ciliates). Another important role of rotifers is their feedback effect on the microbial web. Rotifers provide degraded algae, bacteria and protozoans to the microbial web and may promote microbial activity. Additional experimental work is necessary for a better understanding of the function of rotifers in aquatic ecosystems.     

The terrestrial Protozoan fauna of South Georgia

Summary 75 taxa of Protozoa (18 flagellates, 9 naked rhizopods, 20 testate rhizopods and 28 ciliates) were found in 14 samples of mineral materials, peats, soils and guano collected from the sub-Antarctic island of South Georgia. The results confirm the existence of distinct natural communities of protozoan species related to the different classes of habitat in the sub-Antarctic and maritime Antarctic, but suggest that species characteristic of the maritime Antarctic also occur in the sub-Antarctic and species characteristic of bryophyte peats also occur in soils with angiosperm vegetation. The diversity of the fauna of different habitats can be related to degree of soil development and successional stage of associated vegetation. Comparison of the data on the testate rhizopod fauna of South Georgia with those from other sub-Antarctic locations shows a clear trend of faunal pauperization with latitude.     

Trophic coupling within the microbial food web: a study with fine temporal resolution in a eutrophic freshwater ecosystem

• 1 The major components of the microbial food web (dissolved organic carbon, bacteria, protozoa, rotifers and algae) of Priest Pot, a small freshwater pond, were investigated over a period of 5 months. Water samples were collected from the epilimnion every 1–3 days.
• 2 Time series analysis helped identify the trophic relationships within the planktonic community. There were strong predator—prey relationships between both ciliates and large rotifers and the total nanoplankton, between rotifers and small ciliates and between the total microzooplankton community and phytoplankton. Small rotifers and small ciliates probably share the same food resources. The major bacterivores in the system could not be identified with our methods. However, our previous results point to a dominating role of nanoplanktonic (2–20 μm) heterotrophic protists as the main grazers of bacteria.
• 3 Rotifers are the major type of metazoan zooplankton in Priest Pot; crustacean zooplankton are absent from the community. Bacterial production probably reaches rotifers via a variety of pathways: there may be a three-step link from bacteria to bacterivorous nanoplankton, to ciliates and then to rotifers. Furthermore, a strong correlation between the nanoplankton and rotifers suggests a direct link between these components, implying a much shorter pathway. Some of the rotifers in the pond can graze directly on bacteria, and many of the larger planktonic organisms (large ciliates and rotifers) are algivores. The latter two predator—prey relationships suggest an efficient transfer of bacterial and primary production to higher trophic levels.

     

Relative vulnerabilities of natural rotifer and ciliate communities to cladocerans: laboratory and field experiments

SUMMARY. 1. Two experiments with plankton communities from Storrs Pond (NH), one conducted in the laboratory and one in field enclosures, assessed the impact of different cladocerans on rotifers and ciliated protozoa.
2. The smallest cladoceran, Bosmina longirostris , did not depress rotifer or ciliate growth rates while the intermediate sized dadoceran, Daphnia galeata mendotae , reduced ciliate growth rates in the enclosure experiment but had only a marginal effect in the jar experiment. D. galeata mendotae had no effect on any of the rotifers in either experiment.
3. In both experiments the largest cladoceran, Daphniapulex , depressed the growth rates of ciliates and those rotifers known to be vulnerable to interference competition. Polyarthra vulgaris , previously shown to be resistant to cladoceran interference, was the only rotifer unaffected by D. pulex in the field experiment but was depressed by the much higher densities of this cladoceran in the laboratory experiment.
4. Cladocerans did not affect phytoplankton or bacterioplankton abundance in either experiment. Therefore the mechanism most likely to be responsible for the suppressive effect of cladocerans on rotifers and ciliates in these experiments is direct mechanical interference or predation, rather than exploitative competition.     

Chlorella-bearing ciliates dominate in an oligotrophic North Patagonian lake (Lake Pirehueico, Chile): abundance, biomass and symbiotic photosynthesis

1. Large mixotrophic ciliates ( Stentor araucanus , S. amethystinus and Ophrydium naumanni ) were a characteristic component of a temperate, oligotrophic lake in North Patagonia. During a 1-year study, the abundance, biomass and primary production of these large Chlorella -bearing ciliates were compared with those of the total plankton community.
2. Mixotrophic ciliates peaked in spring and from late summer to autumn, accounting for 1.6–43% (annual average: 16.3%) and 67–99% (annual average: 92%) of total ciliate abundance and biomass, respectively. Their contribution to total zooplankton biomass, including flagellates, rotifers, ciliates and crustaceans, was 14–76%, or 47% as an annual average. Endosymbiotic algae accounted for up to 25% of total autotrophic biomass (annual mean: 3.9%).
3. Maximum cell-specific photosynthetic rates of S. araucanus and S. amethystinus at light saturation varied between 80 and 4400 pg C ciliate^–1 h^–1 with high values during autumn and winter, and low values during summer. The depth-integrated rates of photosynthesis (0–40 m) of algal endosymbionts contributed 1–25% to total photosynthesis (annual mean: 6.5%).
4. A comparison of calculated ingestion rates with photosynthetic rates of Stentor indicates that photosynthate produced by endosymbionts generally exceeded heterotrophic food supply of Stentor during autumn and winter, but was much lower during summer, when food supply was high.
5. The mixotrophic ciliates represent an important 'link' between nanoplankton and higher trophic levels within the plankton community because of their high heterotrophic biomass and considerable contribution to total photosynthesis.     

Laboratory experiments on the impact of biofilms on the plankton of a large river

1. Benthic organisms can have a strong effect on the plankton in rivers, although normally only members of the macrofauna are considered as important consumers. In the present study we conducted experiments on four different dates (in December, March, June and September) to assess the potential role of periphytic heterotrophic flagellates (HF), ciliates and rotifers in the control of potamoplankton (bacteria, algae, HF and ciliates). 2. Natural periphyton was established on the walls of circular flow channels by exposing them to river water (River Rhine, Germany). The experimental channels (with periphyton) and control channels (without periphyton) were filled with riverine water and the increase rates of planktonic bacteria, algae, HF and oligotrich ciliates were determined for the two treatments. 3. The abundance of periphytic ciliates and rotifers at the beginning of the four experiments showed large differences with low values in December and March, and high values in June and September. Dominant potential consumers of plankton were the heterotrich ciliate Stentor sp. and bdelloid rotifers. 4. The rates of increase of planktonic algae, HF and ciliates were significantly smaller in the presence of periphyton compared with those in their absence. Significant interactions between the treatment (with and without periphyton) and the time of experiment were found for the planktonic HF and algae, indicating that the impact of the periphyton varied temporarily. The planktonic groups responded differently to the periphyton with the planktonic HF showing the highest loss rate. Significant differences were also found among the loss rates of different HF groups and different diatom size classes. 5. These laboratory experiments demonstrate that periphytic ciliates and rotifers are potentially important consumers of different planktonic groups. The quantitative impact of periphyton on plankton with respect to the selective feeding needs further attention.     

Plankton biomass partitioning in a eutrophic subtropical lake: comparison with results from temperate lake ecosystems

Plankton were sampled for 6 years in a subtropical eutrophiclake in FL, USA, and absolute and relative carbon biomass wasdetermined for bacteria, phytoplankton, heterotrophic and phototrophicnanoflagellates, ciliates, rotifers and crustacean zooplankton.We compared the results with findings from a comprehensive studyof carbon biomass partitioning in eutrophic German lakes withelucidate common patterns and differences. Similarities betweenthe temperate and subtropical systems included: similar seasonaldynamics, with maximal carbon biomass of nanoflagellates andmetazoan zooplankton in spring and phytoplankton in summer toautumn, yearly averaged carbon occurring mainly in the phytoplanktonand phytoplankton accounting for a much greater proportion ofcarbon than bacteria. There also were differences: the Floridalake had lower absolute and relative carbon biomass in crustaceanzooplankton, stronger dominance of protozoa in total grazercarbon biomass, a lower ratio of zooplankton to phytoplanktoncarbon and almost a monoculture of predation-resistant copepods(versus a relatively balanced distribution of carbon among cladocerans,copepods and rotifers in the temperate lakes). The subtropicallake also had 4-fold higher relative biomass of small filamentouscyanobacteria in its phytoplankton, which we attribute to lightlimitation. Although the Florida and German studies did notmeasure biomass of planktivorous fish, the differences observedhere are consistent with a recent hypothesis that fish predationexerts stronger top–down control on the pelagic food webin subtropical lakes than in temperate lakes of similar trophicstatus.     

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.     

Effects of rotifers and ciliates on the growth and survival of Daphnia

Daphnia can suppress ciliates and rotifers through predationand interference competition, but it is not known whether thisproduces any direct benefit to Daphnia. We conducted survivorshipand cohort lifetable experiments to determine whether Daphniacan utilize ciliates and rotifers as food. Three species ofoligotrich ciliates (Halteria grandinella, Strobilidium gyransand Strobilidiumvelox) and one rotifer (Keratella cochlearis)were used. Lifetable experiments were conducted with a basallevel of algae (Cryptomonas sp.), plus either ciliates or rotifers,while survivorship experiments had only the rotifers or ciliates.Densities of 30 H.grandinella ml^–1, 50 S.gyrans ml^–1and 15 S.velox ml^–1 enhanced Daphnia pulex's populationgrowth rate 35–50% over controls with only algae. TenS.gyrans ml^–1 did not produce a significant change inDaphnia's growth rate. Densities of 100 and 300 K.cochlearis^–1 increased Daphnia population growth rates by II and10%, respectively. Both 10 and 50 S.gyrans ml^–1 enhancedDaphnia's survivorship compared to starved controls, but neither100 nor 300 K.cochlearis l^–1 enhanced its survivorship.The amount of enhancement of Daphnia growth rates by rotifersand ciliates is roughly proportional to the death rates imposedby Daphnia. The death rate imposed by Daphnia on rotifers isa function of both algal density and Daphnia size. Per unitbiomass, neither ciliates nor Keratella appear to be as nutritiousfor Daphnia as is Cryptomonas.     

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.     

Mammalian endemism,range size and conservation status in the southern temperate zone

Aim To examine the taxonomic uniqueness, range sizes, endemism and conservation status of southern temperate zone mammals and how factors impacting their conservation differ across hemispheres. Location Land surfaces of all continents (with the exception of Antarctica) and continental islands with an emphasis on the southern temperate hemisphere (land south of the Tropic of Capricorn). Methods We used data from the 2008 IUCN Red List of Threatened Species to characterize conservation status, threats and range sizes to compare northern and southern temperate zone mammals. We assessed the taxonomic uniqueness of the two regions as derived from the EDGE programme. We also conducted a gap analysis by overlapping mammal ranges with protected area coverages for temperate regions. Results Southern temperate species are phylogenetically more unique than in the Northern Hemisphere. The endemics have significantly smaller range sizes and are at a significantly greater risk of extinction (about 50% greater, with 24.7% of species being threatened versus 15.6% in the Northern Hemisphere). Finally, southern temperate endemics are significantly more likely to exist outside protected areas (13.38% versus 3.65%). Main conclusions The southern temperate zone harbours a unique fauna, attributed to the long isolation from the northern temperate zone. Temperate regions are heavily exploited for human activities, especially grazing and agriculture. The Southern Hemisphere is particularly susceptible to disturbance, given the small range sizes of its species and the low degree of protected area coverage. The scenario now is one of regions with numerous endemics under high threat from human activities.     

Microzooplankton feeding behaviour: grazing on the microbial and the classical food web of African soda lakes

We investigated the feeding behaviour of the dominant microzooplankton of saline lakes in the East African Rift Valley. A set of grazing experiments revealed high ingestion rates of the two euryhaline rotifers Brachionus dimidiatus and Brachionus plicatilis and of the large-sized omnivorous ciliates Frontonia sp. and Condylostoma magnum reflecting the unique nature of tropical saline systems. The size spectrum of ingested particles was broad and even included filamentous cyanobacteria such as the commonly dominating Arthrospira fusiformis. Feeding selectivity on cyanobacteria, however, was rather low showing higher values for cryptomonads and small ciliates. Bacterial biomass was favoured by the presence of grazers, as small bacterivorous predators were reduced at an average of 13.9%, showing the cascading effect of large zooplankton on the food web structure. Overall, based on this first-time study of the microzooplankton feeding behaviour in East African soda lakes, a strong structuring effect of rotifers and large ciliates on microbial plankton communities is assumed, especially in times of high consumer biomass.     

A review on the occurrence and taxonomy of heterotrophic protists in extreme acidic environments of pH values ≤ 3

The occurrence and some important taxonomic problems of heterotrophic protists from extremely acidic (pH 3) environments are briefly discussed. Almost all information on the occurrence of heterotrophic protists from extremely acidic environments is restricted to acid mine drainage (AMD) or streams influenced by AMD. Most of the information is provided for ciliates. Very little information is available on the occurrence of flagellates, rhizopods and heliozoa in this environment. Within the ciliates Urotricha, Vorticella and Oxytricha dominate in acidic mining lakes. Actinophrys sp. is the most important heliozoan in these environments. There are many taxonomic problems which are not solved so far. Live observations and taxonomic methods adapted to the extreme chemical matrix are necessary for correct identification.     

Seasonal succession of zooplankton in the north basin of Lake Biwa

To examine the seasonal succession of the entire zooplankton community in Lake Biwa, zooplankton biomass (on an areal basis) and its distribution patterns among crustaceans, rotifers and ciliates were studied in the north basin from April 1997 to June 1998. Seasonal changes in phytoplankton and population dynamics of Daphnia galeata were also examined to assess food condition and predation pressure by fish. From March to November, crustaceans dominated zooplankton biomass, but rotifers and ciliates were dominant from December to February. Among crustaceans, Eodiaptomus japonicus was the most abundant species, followed by D. galeata. Zooplankton biomass increased from January to a peak in early April, just before the spring bloom of phytoplankton, then decreased in mid-April when mortality rate of D. galeata increased. From mid-June, zooplankton increased and maintained a high level until the beginning of November. During this period, both birth and mortality rates of D. galeata were relatively high and a number of rotifer and crustacean species were observed. However, their abundances were very limited except for E. japonicus which likely preys on ciliates and rotifers. In Lake Biwa, food sources other than phytoplankton, such as resuspended organic matter from the sediments, seems to play a crucial role in zooplankton succession from winter to early spring, while zooplankton community seems to be regulated mainly by fish predation from summer to fall.     

Ecology of the active soil microfauna (Protozoa, Metazoa) of Wilkes Land, East Antarctica

Active ciliates, testate amoebae, nematodes, rotifers and tardigrades were examined in fresh and preserved fellfield, moss and ornithogenic soil samples of Wilkes Land. Direct counting was used to investigate abundances, community structures and protozoan diversity. Twenty-six ciliate species (nine first records for continental Antarctica, one undescribed) and five testacean species (three new records) were found. Two Colpoda species were active, further disproving Smith's hypothesis that this genus is absent in continental Antarctica. Animal frequencies varied between habitats but every group occurred in at least 74% of the samples, rotifers (95%) and testaceans (92%) being most frequent. Highest abundances were recorded in moss: 354 ciliates/g dry soil (19 species), 671 testaceans (5 species), 513 nematodes, 1,311 rotifers and 4,607 tardigrades, which thus dominated. Rotifers were most abundant in the other habitats. The microfauna was not randomly distributed because individual numbers were often strongly intercorrelated. Water and organic matter content were relevant environmental parameters; air temperature and pH probably had indirect effects. Received:28 August 1996 / Accepted:23 November 1996