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A long hidden chydorid (Chydoridae, Cladocera) taxon, first found as fossil specimens and recently redefined as Rhynchotalona latens (Sarmaja-Korjonen et al., Hydrobiologia 436: 165-169, 2000) is investigated for its biogeography and ecology. Late Holocene sediment sequence from Lake Sylvilampi, NE Finnish Lapland, and R. latens spatial distribution in relation to limno-climatic attributes in Finland were examined. Principal component analyses of fossil cladoceran communities showed that R. latens is mostly affiliated with Alonella excisa-Alonopsis elongata-Alonella nana species pool. Generalized linear modeling of R. latens responses to limno-climatic variation indicated that it prefers acidic, mesotrophic, humic and shallow lakes with organic sediments in NE Lapland and has a north boreal-subarctic climatic affiliation. At the northern end of its geographical distribution (NE Lapland), it reproduces with abundant gamogenesis under environmental stress. The specialized taxon is a benthic detritivore and scraper and has a Holarctic northern-alpine distribution. It is a glacial relict associated with modern analogs of periglacial aquatic environments, and it occurs in semi-aquatic wetlands, lush lake littorals and clear and cold waters. Examination of chydorids as bioindicators, especially those with restricted niches, allow us to understand biodiversity responses of lake littorals under changing limno-climatic regimes.

Cladocera is a primarily-freshwater monophyletic group, an important component of the microcrustacean zooplankton. They inhabit most types of continental fresh and saline water habitats, occurring more abundantly in both temporary and permanent stagnant waters. Cladocera is an ancient group of Palaeozoic origin. About 620 species are currently known, but we estimate that the real number of species is 2–4 times higher. A number of currently-recognised widespread species can be expected to harbour extensive cryptic diversity.

Our objective was to assess the potential of Cladocera from mountain lakes for climate reconstruction. We related Cladocera from surface sediments of Alpine lakes (1,502–2,309 m asl) to 29 abiotic environmental variables using statistical methods. The environmental dataset included water chemistry, lake depth, and bi-hourly water-temperature logs, which were used to assess mean monthly water temperatures, dates of freezing and breakup, spring and autumn mixing. We found 14 different Cladocera of the families Bosminidae, Daphniidae, and Chydoridae. Lakes without Cladocera (eight lakes) were cold and/or ultra-oligotrophic, whereas lakes with planktonic and littoral Cladocera (19 lakes) were warmer and/or less oligotrophic. Lakes with only littoral Cladocera (18 lakes) had intermediate water temperatures/trophy. Changes in Cladocera assemblages were related to changes in climate, nutrients, and/or alkalinity. We found a climate threshold at which Bosminidae disappeared in 95% of the lakes. For climate-change research, we propose studying Cladocera along transects that include climatic thresholds.

Fish predation was tested as a factor mediating the coexistence of Daphnia taxa in the shallow, hypertrophic Lake Blankaart. Naturally co-occurring populations of D. galeata and the hybrid D. galeata x cucullata were subjected to different levels of fish predation in in situ enclosures. In control enclosures without fish, the largest taxon D. galeata rapidly became dominant over the intermediate sized D. galeata x cucullata, mainly as a result of higher birth rates. In enclosures with fish, population densities of D. galeata dropped relative to D. galeata x cucullata, due to higher mortality rates. These results are in concordance with the ‘temporal hybrid superiority hypothesis’, and can be explained by a higher vulnerability of the large and more conspicuous D. galeata to the size selective predation exerted by visually hunting planktivorous fishes. After approximately one month, however, population growth rates of D. galeata and D. galeata x cucullata in the enclosures with fish converged, due to a relative reduction in the mortality rate of D. galeata. This suggests that, in the presence of fish, D. galeata may co-exist with hybrids due to a decrease in its relative vulnerability to visual predation with time. Indeed, both D. galeata and the hybrid showed strong reductions in adult body size in the enclosures with fish, but this size reduction tended to be stronger in D. galeata than in D. galeata x cucullata. In addition, turbidity increased in the enclosures with fish and may additionally have reduced the relative advantage of D galeata x cucullata with regard to mortality caused by visual predation.

Dumontia oregonensis, a cladoceran representing a new family in the Order Anomopoda is described from rain pools in the Agate Desert, Oregon, U.S.A. The proposed family, Dumontiidae, is the newest family within Anomopoda that is not just a reshuffling of already-known species. The general appearance of this novel cladoceran is similar to that of members of the family Macrothricidae. However, a detailed examination of the trunk limbs, particularly of the second pair of limbs, showed that the new species lacks the scraper-setae typically observed in all members of the recently erected suborder Radopoda, to which macrothricids belong. Instead, limb morphology suggests a closer relation of Dumontiidae to the family Daphniidae. Dumontiidae appears to be a ‘missing’ link between the suborder Radopoda and the ‘non-radopodid’ anomopods. The families Daphniidae, Ilyocryptidae, Bosminidae, Moinidae and the new Dumontiidae are similar in that they lack of typical radopodid setae on the second pair of trunk limbs. Further studies on the limb morphology of non-radopodid cladocerans are required to solve the phylogenetic relationships among the members of the order Anomopoda.

Information on the density and diversity of zooplankton from drinking water reservoirs in Mexico is meagre. This is important not only from the point of view of lake management but also for providing clean drinking water for human populations. In the present work, we provide quantitative information on the seasonal variations of zooplankton and selected physico-chemical variables from Valle de Bravo, a large man-made reservoir in the State of Mexico. Based on the nutrient data, this reservoir can be regarded as mesotrophic. However, we found a high density of phytoplankton. Among Cyanophyceae, Anabaena, Microcystis, Nostoc and Oscillatoria were encountered, particularly during the warmer months. Microcystis blooms were observed from June to September. Diatoms dominated the phytoplankton during the remaining months of the year. Among zooplankton, Rotifera comprised the highest number of species. The most common species occurring throughout the year were Keratella chochlearis, Polyarthra vulgaris, Trichocerca capucina, Trichocerca similis, Asplanchna priodonta and Synchaeta pectinata. The highest abundance of K. cochlearis was observed in May at site 5 (340 ind 1−1 ). P. vulgaris occurred in high numbers throughout the year. Both Trichocerca capucina and T. similis were encountered in low numbers (mean annual average: 10 ind 1−1). Among the crustacean zooplankton, Bosmina longirostris occurred in higher numbers (up to 105 ind 1−1) regardless of the time of the year. Copepods were predominantly from the genera Mesocyclops and Megacylops; calanoids were rare. Naupliar stages were dominant during winter months (up to 670 ind 1−1). These results have been discussed from the point of view of Microcystis control in water bodies.

The Albufera of Valencia is a large oligohaline hypertrophic lagoon, regulated by sluice gates according to the needs of the surrounding rice field cultivation. It is in a turbid state with permanent cyanobacterial blooms. A slight improvement was detected after diversion in the 1990s of part of the sewage flowing into it. After sewage diversion, we found that: (1) Chlorophyll concentration and rotifer densities decreased; (2) Rotifer proportions declined, due mainly to a relative increase in cladocerans; (3) Rotifer diversity increased. The two dominants of the 1980s, Polyarthra spp. in the colder period and Brachionus angularis in the warmer one, reverted after sewage diversion to a more diverse assemblage reminiscent of the 1970s, with a higher number of dominant species. In the summer of 1998, both Brachionus calyciflorus and its predator Asplanchna brightwelli, dominant in 1973, became abundant again. In 1998, an increase in the number of dominant species was also observed during water renewal periods, some of these species were new or seldomly found before in the lagoon (Proalides tentaculatus-digitus, Trichocerca pusilla at the end of rice culture, Brachionus variabilis at the end of winter flooding). Another change that indicates an improvement of water conditions is a more distinct and longer clear water phase, which occurs in the water renewal period at the end of winter and involves a Daphnia magna peak. The increased importance of this phase, promoted the flourishment of Brachionus variabilis, a facultative Daphnia epibiont never found before in the lake.

Encysted embryos (cysts) of the brine shrimp, Artemia provide an excellent model system for the study of biochemical adaptation to environmental extremes. Here, we describe an experiment in which cysts of A. franciscana from the San Francisco Bay (SFB), California, U.S.A., were inoculated into experimental ponds in the Mekong Delta region of Vietnam where water temperatures are much higher than the SFB. Cysts produced in each of three successive growing seasons (1996–1998) were collected and examined in the laboratory for resistance to high temperature and relative contents of three stress proteins (Hsp-70, artemin and p26). Thermal adaptation took place rapidly, during the first growing season. The increase in thermal tolerance was reflected in an overall increase in stress protein content, compared to SFB cysts used for the initial inoculation. Also examined were cysts of A. tibetiana collected from a lake on the high plateau of Tibet, PR China, almost 4.5 km above sea level. These cysts were very sensitive to high temperatures, and contained much lower levels of all stress proteins examined, compared to A. franciscana cysts from SFB and Vietnam. Cysts of A. sinica, collected from a hypersaline lake in Inner Mongolia, PR China, were examined in the same fashion and found to be similar to SFB cysts in terms of thermal resistance and stress protein content. The harsh environments in which Artemia are found, and the great diversity of its habitats, world-wide, provide excellent opportunities to relate the ecological setting of an organism to the underlying physiological and biochemical processes enabling its survival.

The Ponto-Caspian predatory cladoceran Cercopagis pengoi was first recorded in the Baltic Sea in 1992 (Gulf of Riga). In 1995 it reached high densities in the eastern Gulf of Finland. Seasonal abundance and distribution of Cercopagis in the Neva Estuary were studied in June—October 1996. Until 21 July densities fluctuated between 0.0 and 4.2 ind m−3. Maximum densities (up to 305 ind. m−3 were observed in August—September, the period of maximum water temperature. On 15 October (surface water temperature 8°C), Cercopagis was still present in plankton at low densities. C. pengoi was present at almost all stations both in the central gulf and in inshore areas along southern and northern coasts. Although Cercopagis was present throughout the water column, its abundance in the upper 10-m was usually higher than deeper down.

Recent studies document diel horizontal migration by large zooplankton in eutrophic shallow lakes. Risk of predation from planktivorous fishes could induce such behaviour. We studied diel horizontal distribution of cladocerans in 31 mainly shallow oligotrophic and mesotrophic New Zealand (NZ) and North American (NA) temperate lakes. In terms of weight, fish catch per net (CPUE w ) in multiple mesh-sized gill nets was similar in the two sets of lakes, while CPUE by number (CPUE n ) was overall higher in the NA lakes. Unlike previous results from eutrophic, temperate lakes, we found no significant diel variations in density in the pelagic and littoral zones, suggesting no diel horizontal migration of zooplankton. In the NZ lakes, Daphnia and Ceriodaphnia were evenly distributed between the littoral zone and the pelagial, while in the NA lakes Daphnia were more abundant in the pelagial and Ceriodaphnia in the littoral zone. In the oligotrophic fishless NZ lakes, large Daphnia carinata dominated, whereas the smaller Ceriodaphnia dubia dominated in lakes with high CPUE’s. In both the NZ and the NA lakes, Daphnia showed no clear correlation to fish CPUE n . However, in the NA lakes, Daphnia occurred at fish CPUE n values at which they were eliminated in the NZ lakes, which may be related to differences in water transparency, reflecting a higher chlorophyll a and humic content in the NA lakes.

We tested the hypothesis that evasive movements by Hexarthra mira reduce adverse effects of interference competition with cladocerans permitting coexistence. To do this we studied the population growth of Hexarthra mira and two non-evasive Brachionus species in the presence of one of either two cladocerans (Daphnia similoides, Ceriodaphnia cornuta) at three food (Chlorella) levels (0.5, 2 and 4 × 106 cells ml-1) at 25°C. The non-evasive, but larger-sized B. calyciflorus was suppressed by D. similoides at all food levels tested, and by C. cornuta at high food levels only. The smaller B. angularis showed similar trends with D. similoides, but with C. cornuta it persisted and increased in population size at the medium and high food levels. Hexarthra was able to coexist with both the cladocerans regardless of food level. However, population growth rate of Hexarthra was affected significantly in presence of D. similoides, but not in the presence of C. cornuta. We suggest that evasive behavior of Hexarthra helps it coexist with large cladocerans by reducing the frequency of its being drawn into their branchial chambers.

The seasonal dynamics of Daphnia populations vary regionally throughout the United States. Within the general pattern, Daphnia increase in abundance after the initiation of the spring algal bloom in all lakes, but their subsequent seasonal patterns differ in various climatic regions. Lakes in regions with cooler summers have large-bodied Daphnia populations that tend to persist throughout the summer, although the species dominance may shift. Regions with warmer summers tend to have large-bodied Daphnia populations that decline or are absent through much of the summer. Still warmer water bodies tend to have medium- to small-bodied species that are abundant during spring, but absent most of the summer. Many central Florida lakes lack Daphnia; if Daphnia species are present, they tend to be small-bodied. Daphnia abundance in these water bodies varies, but seems to be independent of temperature.

From the end of May to November 1995 the succession of rotifers and cladocerans was investigated in Muggelsee with samples taken twice a week. Keratella cochlearis was the only rotifer which was found on every sampling day and this species also showed the highest abundances. During summer, when frequencies of strong wind events were low and water was strongly stratified, three small cladocerans were dominant (Daphnia cucullata, Chydorus sphaericus, Eubosmina coregoni). Food supply was the main limiting factor for Keratella spp. and Synchaeta spp. In autumn, however, when the intervals between strong winds were shorter, rotifers with shorter periods for population development prospered. Zooplankton diversity first increased and subsequently decreased after disturbances. The results do not support the intermediate disturbance hypothesis in its present formulation.

The cyanobacterium Anabaena affinis contains two nucleosides responsible for its toxicity: 9-deazaadenosine 5′-α-D-glucopyranoside (compound 1) and 9-deazaadenosine (compound 2). As expected, a strain of Daphnia pulex inhibited by A. affinis also was inhibited by these nucleosides. Surprisingly, however, a strain of D. pulex coexisting with A. affinis, and not inhibited by it, was equally or more inhibited by the nucleosides. LC50 values for compounds 1 and 2 were, respectively, 1.33 and 0.56 μg ml-1 for the former D. pulex and 0.79 and 0.54 μxg ml-1 for the latter. The resistant D. pulex, which benefits from the ingestion of A. affinis, may have evolved a mechanism to detoxify the nucleosides in its intestine. In contrast, Synchaeta pectinata, which is unaffected by A. affinis, was not inhibited by the nucleosides. High concentrations of compounds 1 and 2 (3.6 and 2.2 μg ml-1, respectively) reduced neither survivorship nor fecundity. The resistance of this rotifer to the dissolved nucleosides may be due to its inability to absorb them across its surface membranes, to its inability to metabolize them into more toxic compounds, or to its lack of a receptor for them. An evolved resistance seems unlikely, as S. pectinata probably does not ingest A. affinis. The effect of A. affinis on natural zooplankton communities should be very different from that of strains of Anabaena flos-aquae producing the alkaloid, anatoxin-a. The A. affinis should be ingested by many cladocerans but not rotifers, and it contains toxins which inhibit cladocerans but not S. pectinata and perhaps other rotifers. The A. flos-aquae is ingested by rotifers as well as cladocerans, and its toxin inhibits both rotifers and cladocerans.

In a field experiment I examined the effect of Chaoborus spp, on the vertical distribution of three rotifer species, Kellicottia longispina, Keratella cochlearis and Polyarthra sp. and on the spatial overlap of these rotifer species with three Daphnia species (D. pulicaria, D. rosea and D. retrocurva). In the presence of Chaoborus, total rotifer abundance increased, while total cladoceran abundance decreased. Patterns of migratory behavior varied among rotifer species. Kellicottia longispina and Polyarthra sp. showed vertical migration, while K. cochlearis did not. Kellicottia longispina mean depth was deeper during the day than during the night. The presence of Chaoborus had no significant effect on its vertical distribution. Polyarthra mean depth was significantly shallower during the day than during the night, but a marginally significant interaction suggests that day-night differences occurred only in the absence of Chaoborus. No vertical migration was observed in any Daphnia species in the absence of Chaoborus. D. pulicaria mean depth was significantly shallower in the presence of Chaoborus, and a marginally significant Chaoborus×time interaction suggests that D. pulicaria migrate upward during the night. The spatial overlap of K longispina with each Daphnia species was not affected by Chaoborus. Keratella cochlearis was spatially segregated from D. pulicaria in the absence of Chaoborus, but the spatial overlap between these two species significantly increased in the Chaoborus treatment. Spatial segregation occurred between Polyarthra and D. pulicaria in absence of Chaoborus, however a significant Chaoborus×time interaction indicated that the spatial segregation occurred only during the day. These results suggest that Chaoborus could have complex indirect effects on rotifer-Daphnia interactions. Rotifer populations could be released from competition due to Chaoborus predation on Daphnia. Chaoborus presence, however, could intensify rotifer-Daphnia competitive interactions by increasing their spatial overlap.

In July and August 1973, I made a number of collections in the Godthab Fjord (now Nuuk) area, partly around the bottom of the fjord, partly in the land area which separates the fjord from the open sea (see Figure 1). The branchiopod fauna of Godthab area has previously been treated by (1894), but he recorded only 10 species from the area, a number of which were unidentified, and there is no information on the location or the type of freshwater from where the specimens were taken.

The transport rate of chalk, clay particles and algal cells (Scenedesmus sp.) through the digestive tract of Streptocephalus torvicornis and Branchipus schaefferi is described under experimental conditions. Differences in transport rate as well as in the degree of digestion at a fixed particle density of algae were found. In S. torvicornis, the transport rate is higher and the digestion of algae lower than in B. schaefferi. These differences might reflect trophic differences related to niche partitioning in these sympatric species.

We examined the relationship between pond duration and life history characters of the clam shrimp Eulimnadia texana, a species inhabiting ephemeral ponds in southwestern North America. Since the shrimp live in temporary habitats, we predicted that there should be high selection pressure on life history characteristics associated with rapid development (e.g., fast growth, early maturity, etc.), rather than selection for increased longevity. Pond duration was estimated using a combination of average monthly rainfall and pond size (surface to volume ratio). Shrimp that live in smaller ponds (high surface to volume ratio) in areas with low average rainfall should, on average, experience a shorter total time available for development than those in larger ponds or in areas of higher rainfall. These shrimp should have an earlier age at maturity, reduced longevity, lower fecundity, and faster growth. Five replicate populations of clam shrimp were collected as cysts from five ponds. These shrimp were raised in a common garden experiment in the laboratory. Daily measurements of growth and egg production were taken and ages at maturity and death were recorded. Shrimp from areas with higher average rainfall had slower growth, higher fecundity, greater longevity, and an earlier age at maturity than those from areas with lower average rainfall. If average rainfall is an accurate measure of pond duration, then the first three of these life history traits differ in the directions expected. However, age at maturity varied in a manner opposite to that expected, being earlier in the ponds with longer duration. Surface to volume ratio was not helpful in further resolving differences in these life history characters.

Daphnia hyalina is a cladoceran present through the whole year except for late summer in Maranhao, a meso-eutrophic reservoir in central Portugal. Apart from the influence of food, both vertebrate and invertebrate predation pressures seem to have an effect on D. hyalina population dynamics. Enclosure experiments were designed to assess the relative importance of both types of predation. After the summer crash, D. hyalina reached higher numbers in the fishless enclosures than in the lake despite of high predation pressure upon juveniles by Acanthocyclops robustus. Fish predation upon the largest individuals, especially large egg bearing females, was responsible for the lower fertility of the open water population when compared with the enclosure population. In the enclosures an increase in tail spine length was observed. The longer tail spine probably offered protection from copepod predation, allowing at least some of the juveniles to coexist with their potential predator and reach the adult stage, less susceptible to copepod predation.

Electrophoretic analysis of 31 populations, ranging from California to Kansas, indicates that the North American tadpole shrimp Triops longicaudatus (LeConte) is actually a mixture of at least two reproductively isolated species. In the central United States, the predominant species is T. longicaudatus, which is found typically in ephemeral prairie pools. In the southwestern United States, the predominant species is Triops newberryi (Packard), which characteristically inhabits large playa pools. The two species coexist occasionally and in sympatric situations they are reproductively isolated from each other. The two species are genetically distinct at a level greater than is typical of conspecific populations. These genetic differences are correlated with subtle morphological differences and profound differences in reproductive biology. Both species represent complexes of bisexual and unisexual populations. Bisexual populations of T. longicaudatus are usually composed of males and females in approximately equal frequencies; bisexual populations of T. newberryi are composed of males in low frequencies and self-compatible hermaphrodites. Unisexual populations of both species apparently consist entirely of self-compatible hermaphrodites.

Cysts of three species of anostracans (Branchipus schaefferi, Chirocephalus diaphanus,and Tanymastigites perrieri), two species of Notostracans (Triops numidicus and Lepidurus apus) and one species of Spinicaudata (Leptestheria mayeti) were collected from the upper 2 cm of dry sediments at intervals along transects from a temporary pool in an arid zone of Morocco and from two ditches in France. The horizontal distribution of viable cysts was patchy and is discussed in relation to several ecological parameters prevailing during the aquatic phase. These include vegetation distribution, depth and morphometry of the pond, dominant wind pattern, and granularity of the sediments.

A study of the structure of the limbs of Bosminopsis deitersi Richard, 1895 was performed. Thestructure is similar in populations from differentregions. According to Meissner (1903), limbs of Bosminopsis differ from those of Bosminastrongly enough to separate Bosminopsis in aspecial family. However, our observations indicatethat the structure of the limbs of Bosmina andBosminopsis is similar, and conform to thegeneral plan of Bosminid limbs. The first limb isstrongly simplified, and the first limb of males isunique among anomopods. Limbs III–V are lessoligomerized than limbs I–II, and are organizedaccording to the chydorid (and macrothricid) type. Thedegree of oligomerization is different in the twogenera. Comparative information on the limb structurein one genus may contribute to the reconstruction ofthe evolution of a corresponding limb in the othergenus. The uniformity of limb structure within eachgenus, and their similarity between both genera isthought to be a reflection of the monotonous lifeconditions in open water.

Anostracans were found living in ephemeral pools in the dark sections of three caves on the As Summan Plateau in Saudi Arabia. Branchipus schaefferi Fischer, 1834 occurred alone in one while it cohabited with Streptocephalus torvicomis bucheti Daday, 1910 in a second cave; fairy shrimps were observed but not collected from the third. None of the specimens demonstrated any of the types of morphological changes typically associated with cave adapted species. This is likely due to continuing colonization of the pools during flooding events.

Like many diapausing crustaceans, anostracans (Crustacea, Branchiopoda) produce encysted embryos capable of surviving the long periods of desiccation typical of their environments. These cysts are far more abundant and are easier to collect than adults and for some applications they are superior to adults as subjects for genetic analysis. Due to the lack of minimal tissue size requirements, PCR-based analysis is the best alternative for genetic study of cysts. We describe a method for the fast extraction of DNA from cysts, yielding template for RAPD-PCR analysis.

Even in the most thorough biomanipulation studies, which covertheresponse of all trophic levels to manipulation at the top ofthefood chain, the mechanisms underlying the success or failureof anexperiment often remain obscure. The case of a small eutrophicLakeWirbel in Poland is an example of how useful it could be toapplydemographic and behavioural analysis of dominant planktonicherbivores to explain the sequence of events followingbiomanipulation measures.At a certain stage of a seven-year (1988–1994)biomanipulationexperiment, rotenone was applied to remove all fish. Followingfishremoval, summer algal biomass in the ‘edible’ fraction ofphytoplankton (

Copepods and protozoans often co-exist in marine rotifer mass cultures. Interspecific interaction between the rotifer Brachionus rotundiformis Tschugunoff and eight other zooplankton species, namely Brachionus plicatilis O. F. Muller (rotifer), Diaphanosoma celebensis Stingelin (cladoceran), Tigriopus japonicus Mori, Acartia sp. (copepod), Euplotes sp., Vorticella sp., an unidentified protozoan species (P1 strain) (protozoan) and Artemia sp. (anostracan) at two developmental stages (nauplii — 0.95 mm, 0 days old; adults — 3.3 mm, 19 days old) were investigated in the laboratory.

For ecology and genetics of the Cladocera to progress more rapidly, it would be beneficial if efforts were concentrated on a single taxon. Daphnia magna is probably the best candidate. But what are the Cladocera? Upon inspection, confusion is found to rage at any level. We do not know whether the group as a whole is monophyletic, the number of families and genera is uncertain, and we have only a faint idea of the total number of species. Neither do we know much about the geographical distribution of most species, which may have been blurred by human dispersal since the appearance of large-scale navigation. Currently, introductions and invasions continue to occur. These are well monitored, but events in the past could also be reconstructed, using the (sub)fossil record. There is thus a good future for the use of cladoceran remains in paleolimnology.

We present observations on the frequency of large branchiopod associations found in north-central Mexico, and in Arizona, USA. Of a total of 25 species involved in these assemblages, 12 were common in both areas. Fifty-eight (43.3%) of the ponds in Mexico, and seventy-eight (47%) of those in Arizona had two or more species present. The combinations of species which occurred with highest frequency were Streptocephalus mackini with Thamnocephalus platyurus for Arizona, and T. platyurus, Triops sp., and Leptestheria compleximanus for Mexico. In Mexico, and Arizona, as in many parts of the world, multispecies assemblages of large branchiopods are a common phenomenon. Therefore, the ‘common rule’ of ‘one-phyllopod-per-habitat’ advanced by Weise (1964) is inconsistent with field observations. Furthermore, since cases of co-occurrence of two or more congeneric species of Anostraca and Notostraca are not uncommon, generalizations about congeners not coexisting remain applicable only for the Spinicaudata and Laevicaudata. On the basis of the literature, and of observations in the field and in the laboratory, we list potential factors contributing to the co-occurrence of several species within a pond.

Chirocephalus ponticus n.sp. (Crustacea: Anostraca) from Turkey is described. The new species is characterized by the form of the second antenna and the frontal appendages of the male. This species seems to be related to C. turkestanicus Daday. Furthermore, analysis of limb structure reveals differences between the three Chirocephalus species previously known from Turkey: C. paphlagonicus, C. vornatscheriand C. diaphanus. New localities for these species are reported.

During the first few weeks of a recurring seasonal period of diel vertical migration in Lake Maarsseveen (The Netherlands), part of the hybrid Daphnia galeata × hyalina population migrated, while another part remained in the epilimnion. In the epilimnion, 0+ perch prey upon daphnids during daytime. Gradually, the number of adult Daphnia in the epilimnion decrease until the epilimnion is nearly devoid of daphnids. The population as a whole may decrease, as in 1991, or may increase as in 1992. Genotype composition, as determined by allozyme analysis, changed substantially within a fortnight in 1992, and one genotype became dominant. Our data are in agreement with the hypothesis that predation on different genotypes (clones) occurs during the beginning of a seasonal period of diel vertical migration, though our data do not allow to exclude alternative explanations.

The Russian Territory known as the Barents Region includes the large islands of Vaigatch and Kolguev, the archipelagos of Franz Joseph Land and Novaya Zemlya, and many small near shore islands in the Barents Sea subregion of the Arctic Ocean. With the exception of Franz Joseph Land, these islands and the Novaya Zemlya Archipelago are inhabited by seven species of large branchiopods: four species of Anostraca, Polyartemia forcipata S. Fischer, 1851, Artemiopsis bungei plovmornini Jaschnov, 1925, Branchinecta paludosa Muller, 1851 and Branchinectella media (Schmankewitsch, 1873); one Notostraca, Lepidurus arcticus (Kroyer, 1847); and two species of Spinicaudata, Caenestheria propinqua Sars, 1901 and C. sahlbergi (Simon, 1886). This is a richer large branchiopod fauna than occurs in other comparable land areas of the Arctic Ocean. The northern most known occurrence of Branchinecta paludosa is at Ivanov Bay on the Novaya Zemlya Archipelago. This report includes some life history observations.

In 1995 the authors studied the effect of different fish communities on the structure of the cladoceran plankton in a shallow hypertrophic lake. After a fish kill of 1991, different fish communities developed in the Kazetta and the outer area of the Kis-Balaton reservoir. In the outer area of the reservoir, the densities of plankton feeding fish species were considerably higher than in the Kazetta. These differences induced changes in the structure and dynamics of the cladoceran plankton. The biomass of small-bodied cladocerans (mainly Bosmina longispina) was higher and the biomass of the large-bodied cladocerans (D. hyalina, D. magna) was lower in the western and eastern part of Kis-Balaton reservoir than in the Kazetta. A peak in cladoceran biomass in the Kis-Balaton reservoir was observed during the summer, close or during a bloom of filamentous cyanobacteria, whereas in the Kazetta a peak was observed during the spring, before the bloom of cyanobacteria. The adult females of D. hyalina were larger and produced more eggs in the Kazetta than in the outer area of the reservoir.

Regional Faunas and Community Assemblages. 6. Distribution, Diversity and Conservation of Anostraca (Crustacea: Branchiopoda) in Southern Africa M.L. Hamer, L. Brendonck. 18. Distribution and Phenology of Large Branchiopods in Austria E. Eder, et al. 3. Community Structure of Branchiopods (Anostraca, Notostraca, and Conchostraca) in the Banat Province in Yugoslavia B. Petrov, D.M. Cvetkovic. 2. The Status of Anostraca, Notostraca, and Conchostraca in Yugoslavia B. Petrov, I. Petrov. 13. On the Presence of the genus Branchipus Schaeffer, 1766 (Crustacea: Anostraca) in Macedonia S. Petkovski. 19. Large Branchiopod Assemblages Common to Mexico and the United States A.M. Maeda-Martinez, et al. 10. New Records of Large Branchiopods (Branchiopoda: Anostraca, Notostraca, Spinicaudata, and Laevicaudata) in Mexico A.M. Maeda-Martinez, et al. 1. Large Branchiopod Crustacea (Anostraca, Notostraca, Spinicaudata) of the Barents Region of Russia N.V. Vekhoff. 12. New Records and Observations on the Anostracan Genus Eubranchipus in California R.E. Hill, et al. Taxonomy and Systematics. 16. On Potentials and Relevance of the Use of Copulatory Structures in Anostracan Taxonomy L. Brendonck, D. Belk. 17. Branchinella madurai Raj (Crustacea, Branchiopoda, Anostraca) Shown by New Evidence to be a Valid Species L. Brendonck, D. Belk. 30. Chirocephalus ponticus n. sp. (Crustacea: Anostraca) and its Affinities to the Other Turkish Species of the Genus L. Beldjal, J. Mertens. 11. Tertiary Envelope Characters Usefulfor Typifying California Anostraca R.E. Hill, W.D. Shepard. Genetics and Evolution. 14. Reproductive Isolation and Genetic Differentiation in North American Species of Triops (Crustacea: Branchiopoda: Notostraca) C. Sassaman, et al. 25. Population Genetic Structure of a California Endemic Branchiopod, Branchinecta sandiegonensis C. Davies, et al. 9. Extraction of DNA from Anostracan Cysts (Crustacea, Branchiopoda) for Use in RAPD-PCR Analysis J.A. Moorad, et al. 28. Gynandromorphism in Anostraca: Multiple Mechanisms of Origin? C. Sassaman, M. Fugate. 27. Anatomical Evidence for Androdioecy in the Clam Shrimp Eulimnadia texana N. Zucker, et al. Ecology. 20. Horizontal Distribution and Abundance of Cysts of Several Large Branchiopods in Temporary Pool and Ditch Sediments A. Thiery. 8. Notes on the Life History of the Clam Shrimp Eulimnadia texana S.C. Weeks, V. Marcus. 23. The Resilience of Anostracan Cysts to Fire M. Wells, et al. 31. Anostracans in Dark Sections of Saudi Arabian Caves D. Belk, W.D. Peters. 15. Feeding Strategy of Two Sympatric Anostraca Species (Crustacea) L. Beladjal, et al. 7. The Effects of Pond Duration on the Life History Traits of an Ephemeral Pond Crustacean Eulimnadia texana V. Marcus, S.C. Weeks. Aquaculture. 4. The Chitin Content of Some Anostracan Species H.M. Cauchie, et al. 5. Evaluation of the Fatty Acid Profiles of Two Fairy Shrimp Species, Branchipus pasai Cottarelli, 1969 and Chirocephalus kerkyrensis Pesta, 1936 (Crustacea

The provision of a refuge from fish predation for large-bodied Cladocera among stands of submerged macrophytes is thought to be an important stabilising mechanism against nutrient-induced phytoplankton increases in clear water shallow lakes. The occurrence of any refuge effect in relation to the seasonal impact of both macrophyte development and recruitment of zooplanktivorous fish was monitored over the summer months (May to September) in three lakes (Cromes Broad, Hoveton Little Broad/Pound End, and Upton Broad) of variable trophic status, fish community structure and nature and extent of macrophyte cover, in the Norfolk Broads in Eastern England. At all sites, Daphnia spp. exhibited a early summer peak of abundance but had declined rapidly by July probably as a result of predation from underyearling fish. In extensive macrophyte stands (Cromes Broad) Daphnia spp. persisted after its elimination in open water, indicating some refuge effect. At sites with macrophyte cover and/or low fish predation pressure, Daphnia spp. was replaced by Ceriodaphniaspp., both with and without Simocephalussp., thus maintaining large populations of grazing Cladocera, apparently capable of exerting a high grazing pressure on phytoplankton. This occurred, even under high predation pressure from a relatively high density of zooplanktivorous 0+ fish (Cromes Broad), consistent with the refuge hypothesis. In addition, at this site, significant positive associations of cladoceran abundance with increasing macrophyte cover were apparent throughout the summer. From information on the distribution of fish it is suggested that dense macrophytes offer the most suitable refuge through provision of predator-free space.

In Artemia franciscana, enriched for 24 h with emulsified lipids, the fatty acid DHA (22:6w3) is unstable. In rotifers the level of DHA can be stabilised by adding algae rich in DHA to the fish tanks. To test this method for A. franciscana,enriched A. franciscana was incubated with the alga Isochrysis galbana, which is rich in lipids and DHA, at six concentrations ranging from 1 to 20 mg C 1−1 at 13–14 °C. After lipid enrichment, A. franciscana contained 15% lipids of which 79% (116 mg g DW−1) were fatty acids. Of the fatty acids, 17% was DHA (19.8 mg g DW−1). After 72 hours incubation with I. galbana, the level of DHA decreased to 1.6–3.2 mg g DW−1, which was a reduction by 84–92%. This was independent of the algal concentration. The amount of total fatty acids decreased to 53–73 mg g DW−1, a reduction by 37–54%, independent of the algal concentration. The rates of loss of the fatty acids, and especially DHA, was greater during the first 24 h at the highest algal concentrations (8, 10 and 20 mg C 1−1). Enriched A. franciscana should therefore not be incubated with high algal concentrations (>6 mg C 1−1) during first feeding of marine fish larvae.

The occurrence of six littoral species of Ceriodaphnia (C. affinis, C. laticaudata, C. megops, C. reticulata, C. rotunda and C. setosa) living at the same time and locality is described. Basic population characteristics were studied in all species coexisting in the field, except for C. setosa, which was too scarce. Abundances, proportions of gamogenetic individuals, mean body lengths and clutch sizes were compared among species. Dissolved oxygen, temperature, chlorophyll-a and total seston volume were measured and related to population changes. C. laticaudata and C. rotunda were closely similar to each other in many features and showed significant differences to other species. C. reticulata and C. megops seem to be similar in some features, while C. affinis was ecologically different.

Observations on distribution, water quality, habitat and avoidance behavior are presented for Eubranchipus bundyi, Eubranchipus oregonus, and Eubranchipus serratus (Chirocephalidae) in California, USA. All three species were previously known within California from single localities. Two new localities for E. oregonus in Tuolumne County and in Humbolt County and 21 new localities for E. serratus in Lassen and Shasta Counties are presented. The E. oregonus localities represent substantial range extensions within California, while the E. serratus localities show a large number of populations within the surveyed area. In occupied pools, pH ranged from 5.5 to 9.0, conductivity from 30 to 150 µS, turbidity (NTU) from 0.8 to 140.0 and total alkalinity from 68 to 128 mg 1−1. Pool size varied from small seasonal pools of a few meters in diameter to large seasonal lakes several kilometers across. Limited survey effort and successful “predator” avoidance by the shrimp may have contributed to the lack of distributional information for these species in California.

Mortality, and whole-body levels of [Na], [Cl] and [K]were measured in adult and naupliar stages of Brine Shrimp, Artemia franciscana, after 24h exposure to a waters of a range of acid (H2SO4)concentrations (pH 8.3 to 4.5). Acid effects were tested in both dilute (20%) and full strength artificial seawater (ASW). All stages showed high sensitivity to acid stress whether tested in 20% or100% ASW. Nauplii were more sensitive than adults in either medium. Mortality in each case was correlated with dramatic changes in whole body [Na] and [Cll but animals in 20% ASW lost [Na] and [Cl] to the environment while animals in 100% ASW gained them from the environment. Clearly animals which ion-regulate in euryhaline media are more sensitive than expected to acid stress which may thus pose a serious threat to sensitive euryhaline habitats.

The cladocerans are a group of Crustacea used as model organisms in many fields of biology. In system-atics, ecology, physiology and genetics, the cladocerans appear as frequently used examples in case studies. Their reproductive system, switching between parthenogenesis and sexual reproduction, makes them particularly suited for studies dealing with genetic and environmentally induced variability. It is on the whole a particularly handy group of animals that can be used for studying almost all kinds of evolutionary processes.

The distribution of the planktonic crustacean Daphnia pulex was tested in a ring-formed flow-through chamber divided into eleven sections. The distribution of the animals under both homogeneous food conditions and in a food gradient were studied. The distribution of repeated registrations of single animals was randomly distributed in a homogeneous, low food environment. Single daphnids exposed to a food gradient tended to reside during 88% of the time at the highest or next highest food concentration, suggesting that daphnids can detect food gradients. When a group of approximately 100 co-occurring animals were given low homogeneous food conditions, they also tended to be randomly distributed. In one out of three cases, however, they were slightly less aggregated than expected from a random distribution. Exposed to a food gradient (0.5–0.0015 mg C l−1), the distribution of the daphnids approximated the ideal free distribution. A very high maximum density in the food gradient (2 mg C l−1) resulted in less strong aggregations than expected from the ideal free distribution.

Eutrophication in Tjeukemeer involved a gradual increase in chlorophyll concentrations from ca. 30 mg m−3 in 1968–69 to 125 mg m−3 in 1976. From 1976 onwards, chlorophyll concentrations remained at a high level fluctuating between 100–225 mg m−3. (1977) hypothesized that small-bodied species will become increasingly abundant and dominant over large-bodied species with increasing eutrophication. We tested this hypothesis using observations from life history experiments on Chydorus sphaericus, combined with data from 25 years of field observations on the population dynamics of cladocerans in Tjeukemeer.