Candona Neglecta Research Articles

Palaeoenvironment of the Acheulian Gesher Benot Ya’aqov Pleistocene lacustrine strata, Northern Israel––lithology, ostracod assemblages and ostracod shell geochemistry

The Acheulian archaeological site Gesher Benot Ya’aqov (GBY) is located along the shoreline of a Pleistocene Lake, the GBY Lake, within the Jordan Rift valley. The uniqueness of the site is expressed in its complex sedimentary sequence, rich fossil assemblages, and in the first appearance of lithic technologies not previously seen in Eurasia. The site is reliably dated at the Matuyama–Brunhes geomagnetic polarity chron boundary (∼780 kA), which occurs within the lake sediments. The sedimentary sequence at GBY exhibits a pronounced cyclicity. A single first order cycle begins with a lower conglomerate followed by lacustrine beds, overlain by an upper conglomerate that closes the cycle. Second-order cyclicity is apparent in shifts from littoral to deeper water facies, with five such cycles, identified within the first order cycle. The diatom and ostracod distributions indicate a freshwater–oligohaline environment of deposition for the lower part of the section and oligohaline–meio-mesohaline waters in the upper part of the section. In addition, the C and O isotopes and the Sr/Ca and Mg/Ca ratios of the ostracod ( Candona neglecta) shells exhibit three geochemical zones supporting the paleoecological biozonation. They reflect a cooler period for the lower part of the sequence (interval I), changing into warmer climate at the Matuyama–Brunhes boundary and upward (interval II). Further gradual temperature increase in the upper interval III caused the retraction and desiccation of the GBY Lake.

Zooplankton (Cladocera, Ostracoda), Chironomidae and other benthic faunal remains in sediment cores from nine North African wetland lakes: the CASSARINA Project

Palaeolimnological studies were carried out on sediment cores from nine North African wetland lakes. The lakes represented a variety of habitats ranging from freshwater to mixohaline conditions and with and without direct connections to the sea. Sediment cores were examined for records of recent environmental change during the 20th century period. Faunal remains analysed in the sediments included those of Cladocera, Ostracoda, Chironomidae, Mollusca and, at the sites with marine connections, Foraminifera. Cyprideis torosa littoralis was the most common ostracod, occurring in sediments from the seven sites linked with the sea and also in brackish water Sidi Bou Rhaba. In acid Megene Chitane ostracods were scarce, being represented by a single species (Cypria ophtalmica). Candona neglecta completely disappeared at two sites (Sidi Bou Rhaba and Bokka) during the 20th century. Of the Cladocera, Chydorus sphaericus was common in the moderately mixohaline sites and but Heterocypris salina occurred only where marine salinities were occasionally achieved (in Zerga, Ichkeul and Korba). Microinvertebrate assemblages in the Nile Delta lake cores and to a less extent in Zerga showed a clear response indicative of more fresher conditions occurring during the latter part of the 20th century. However the freshening trend began prior to construction of the Aswan High Dam (mid 1960s). With the exception of the most saline site (Korba), microinvertebrate communiuties at all the CASSARINA sites have experienced major disturbances during the 20th century. Changes in freshwater availability associated with increased human usage of water resources is perceived as a major factor regulating the abundance and occurrence of aquatic microinvertebrate species at these sites

Uptake of phytodetritus by three ostracod species from the Baltic Sea: effects of amphipod disturbance and ostracod density

Three species of ostracods (Candona neglecta, Paracyprideis fennica and Hetero-cyprideis sorbyana) are common in the Baltic proper and often contribute more to the total meiobenthic biomass than any other taxon. An earlier experiment has shown that C. neglecta assimilates more labelled diatoms (Skeletonema costatum) than any other meiobenthic species, and 10 and 100 times more than the other 2 ostracod species, respectively. The uptake of phytodetritus by the 3 ostracod species was investigated in 2 separate experiments with special reference to (1) effects of the presence of amphipods and (2) variable density of ostracods. The amphipods had negative effects on the uptake rate of phytodetritus by ostracods. Mechanical disturbance, which may have caused burial of the phytodetritus, is one plausible explanation. There was no evidence of competition for phytodetritus among the ostracod species, i.e. the absence/presence of C. neglecta did not affect the uptake of phytodetritus by P. fennica and H. sorbyana. A density-dependent uptake of phytodetritus was, however, observed in C. neglecta, where the uptake of phytodetritus was stimulated at an intermediate density [KEYWORDS: C-14 radio-labelled phytodetritus, ostracoda, amphipoda, meiofauna, disturbance, competition]

Cenozoic Ostracoda and palaeoenvironments of the northeastern Tarim Basin, western China

The Paleogene rocks of the northeastern Tarim Basin in western China are composed mainly of reddish gypsum-bearing coarse-grained sediments, and fossils are rare within these clastic facies. However, since the onset of the Himalayan orogeny in the Miocene, continuous uplift of the Tianshan Mountains resulted in the rapid subsidence and appearance of a shallow lake environment. As a result of this, ostracods are widespread in the late Cenozoic rocks of the Tarim Basin. The brackish-water ostracod Cyprideis thrived from the Mid- to Late Miocene; gypsum-bearing sand and mud sediments were also deposited widely in the shallow brackish-water lake environments. This situation is similar to that of the Qaidam Basin, which lies to the south of the Altun Mountains. From the Pliocene onwards, the rates of subsidence and sedimentation increased. The resulting regression of the lake led to disappearance of ostracods from a large part of the basin. To the north of the Kuqa depression, the Tianshan Mountains underwent continuous uplift during the late Himalayan orogeny. As a result, the Quaternary lake deposits have a much greater extent than those of the Pliocene, and extend even further southward than those of the Miocene. Consequently, the brackish-water ostracod Cyprideis became dominant again during the Quaternary. From the end of the Early Pleistocene to present in this area, an abundant and high-diversity fauna of fresh- to brackish-water ostracods appeared alongside abundant Cyprideis. This situation is similar to that of the southern Qaidam Basin, to the north of Kunlun Mountains. The Quaternary assemblages mainly consist of Cyprideis torosa, Candoniella lactea, Candona neglecta, Candona arcina, Cypridopsis vidua, Limnocythere inopinata, Cypris subglobosa, Ilyocypris gibba, Ilyocypris biplicata, Eucypris inflata, Candoniella albicans, Darwinula sp. and Stenocypris sp. Under the extremely arid climate in the Tarim Basin, freshwater originated mainly from snow-melt. This suggests that the Tianshan Mountains to the north were uplifted rapidly to above the snow line during the last million years. The evolution of the ostracod assemblages indicates that the late Himalayan orogeny not only controlled the deposition of biota assemblages but also took an important role in the hydrocarbon accumulation and migration.

Species specific uptake of radio-labelled phytodetritus by benthic meiofauna from the Baltic Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 177:63-72 (1999) - doi:10.3354/meps177063 Species specific uptake of radio-labelled phytodetritus by benthic meiofauna from the Baltic Sea Emil Ólafsson1,*, Helene Modig1, Wouter J. van de Bund2,** 1Department of Zoology, and 2Department of Systems Ecology; Stockholm University, S-10691 Stockholm, Sweden *E-mail: emil.olafsson@zoologi.su.se **Present address: Netherlands Institute of Ecology, Centre for Limnology, Box 299, 3600 BG Maarssen, The Netherlands ABSTRACT: The diatom Skeletonema costatum is one of the dominant phytoplankton species during spring in the northern Baltic Sea. We followed the uptake of radio-labelled S. costatum by all major meiofauna species in a laboratory experiment. The uptake of labelled diatom carbon varied greatly among major meiobenthic taxa and among species belonging to the same class or phylum. Both total uptake and uptake per unit biomass were by far highest in the ostracod Candona neglecta accounting for 46% of the total meiofauna uptake. The total uptake of 14C was significantly different among all 3 common ostracod species, Candona neglecta taking 10 and 100 times more than Paracyprideis fennica and Heterocyprideis sorbyana respectively. Nematodes accounted for over 40% of the total uptake of 14C in the microcosms, of which 84% was taken up by large nematode species such as Paracanthonchus spp. Nematodes with similar buccal cavities and of similar size showed surprisingly large differences in the uptake of the radio-labelled material. There seems to be quite strong selection both for and against the diatom among epistrate feeders as well as among so-called non-selective deposit feeders. Only a small portion of the total meiofauna population was found below 1 cm in the sediment; this was composed almost solely of nematodes. These nematodes assimilated as much 14C per unit biomass as the surface ones did, which contradicts the hypothesis claiming that meiobenthic animals react in 2 ways to phytoplankton sedimentation, with surface feeders directly assimilating sedimented phytoplankton, while subsurface feeders experience a more stable food supply and rely only indirectly on sedimented phytoplankton. KEY WORDS: Pelagic-benthic coupling · Food-web · Meiofauna · 14C radio label Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 177. Publication date: February 11, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Variability in ostracod partition coefficients D(Sr) and D(Mg) : Implications for lacustrine palaeoenvironmental reconstructions

Living and sub-recent ostracods were collected from four lakes and four springs, located in Belgium, France and Spain, characterized by low water Mg/Ca ratios (from 0.08 to 0.65). Valves of ostracods belonging to Cyprideis torosa, Candona neglecta, C. marchica and C. candida have been extensively analysed for their magnesium and strontium contents with respect to calcium. Comparisons of these results are made using the same elements from the waters in which the ostracod valves calcified. Our results offer new and somewhat different interpretations with respect to the uptake of Mg and Sr in the calcitic ostracod valves. These findings include the following. (1) The partition coefficient D(Sr) for ostracods belonging to the same genus ( Candona) is not a constant. The observed variability in D(Sr) values could be due to the rate of biological calcification, although more investigations are necessary to assess the influence of this factor; it is possible that some taxa grouped under the genus Candona belong to a different genus. (2) Even at the species level ( Cyprideis torosa), the ostracod D(Sr) cannot be considered to be constant. At low water Mg/Ca ratio (0.65), our D(Sr) value for C. torosa is higher than those determined by others for C. torosa calcified in evolved marine water. (3) The Mg/Ca ratio of the water appears as a major factor influencing D(Mg) for ostracods. For low water Mg/Ca values (<∼2), D(Mg) drastically increases. This phenomenon is also effective for inorganic calcite, implying a non-biologic effect that could be linked to Mg 2+ adsorption. Consequently, large variations in Mg content of fossil ostracod valves from selected lacustrine sequences, with expected low water Mg/Ca (<∼2), can be due to small variations in water Mg/Ca.

Distribution and population dynamics of ostracodes (Crustacea, Ostracoda) in a karstic lake: Lake Banyoles (Catalonia, Spain)

Qualitative and quantitative benthic samples were collected monthly between December 1986 and December 1987 from several stations at various depths and basins in the karstic Lake Banyoles (Catalonia, Spain), to study the spatial distribution and seasonality of ostracodes. A total of eight ostracode species were found in the lake. Of these, Candona neglecta Sars, Isocypris beauchampi Paris and Cypria ophtalmica Jurine were the most common ostracodes at all depth stations. Darwinula stevensoni Brady & Robertson, Ilyocypris species (I. bradyi Sars and I. gibba (Ramdohr)), Cyprideis torosa (Jones) and Cyclocypris ovum Jurine, on the other hand, were confined to sublittoral and littoral areas of the lake.

Neoechinorhynchus rutili (Müller, 1780) (Acanthocephala) in the whitefish Coregonm nasus (Pallas) sensu Svärdson from the Bay of Bothnia

Abstract. The occurrence of Neoechinorhynchus rutili (Müller, 1780) in the white‐fish Coregonus nasus (Pallas) sensu Svardson from the Bay of Bothnia was investigated in 772 fish obtained as monthly or bimonthly samples during the period July 1975‐January 1977.In both years most parasites were found only in November and December. All of the 402 parasites found were immature and very small. Most of them were in the first third of the intestine, and only a few were attached to the mucosa. No encysted parasites were found in other any tissues. It is thus suggested that the whitefish of the Bay of Bothnia is only an accidental host for N. rutili.A clear correlation was found between the importance of ostracods in the diet and the occurrence of N. rutili. The first intermediate host in the Bay of Bothnia was shown to be an ostracod, Candona neglecta (Sars.).