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     

Recent ecosystem dynamics in nine North African lakes in the CASSARINA Project

An integrated multi-disciplinary study of nine North African lakes (CASSARINA) aims to establish ecological baselines and to explore responses to 20th century human impacts on their ecosystems. Water chemistry measurements (1997–1998) demonstrate a wide range from dilute oligotrophic to calcareous freshwaters and from mildly brackish to hypersaline lagoons. The biota are consequently highly diverse. Aquatic ecosystem responses to environmental stress over the last 100–200 years in all nine lakes are summarised by detrended correspondence analysis (DCA) of plant and animal macrofossil, zooplankton, diatom, and pollen data from short sediment cores. DCA proved to be a powerful tool for summarising multi-proxy sediment records and ecosystem dynamics. Compositional changes measured by the DCAs have been very large and rapid, often over a few decades; as great as climate-controlled late-glacial changes over 2000 years and larger than most Holocene (11000 years) changes. These results emphasise the strength of human impact on the lakes and the surprisingly great resilience and dynamism of their ecosystems. The DCA summaries for the most recent decades indicate ecosystem disequilibrium in all the lakes, implying that their future stability is uncertain and that large or damaging changes may soon occur if the stresses are maintained. Thresholds have recently been passed in 3 lakes. During the project, Merja Bokka (Morocco) was drained and cultivated. The unique acid Megene Chitane (Tunisia) is in danger of drying up permanently due to water extraction. Freshwater diversion from Garaet El Ichkeul (Tunisia) has dramatically altered its wildlife habitat, as reed-marshes were replaced by salt-marsh and bare mud within 20 years. In contrast, the ecosystems of the Delta lakes (Egypt) have responded dramatically to the year-round inflow of fresh irrigation water controlled by Nile dams and the rise in the freshwater table due to inadequate drainage in the flat delta. The Project has demonstrated remarkably rapid responses by the lakes to environmental stresses. In particular, it highlights the threats to wetland-lake ecosystems in North Africa if uncontrolled exploitation continues.     

Recent environmental change in North African wetland lakes: diatom and other stratigraphic evidence from nine sites in the CASSARINA Project

All nine wetland lakes in the CASSARINA North African suite of sample sites have been disturbed strongly by human activity during the 20th century. Dated lake sediment core were used to provide evidence of the extent of recent environmental change at each site. Sedimentary diatoms at seven sites were useful for inferring salinity change trends during the last century. At two sites preservation problems severely degraded the sedimentary diatom record. Sediment core integrity was otherwise established.Lithostratigraphic measurements indicated some site specific changes in soil erosion and sediment composition but, for the Egyptian Delta lakes, no physical signal synchronous with Aswan High Dam construction was found. Sedimentary diatom assemblages were generally site characteristic and halophilous taxa were common. At two sites planktonic diatoms indicated some recent eutrophication but generally the assemblages were more indicative of salinity changes. Diatom-inferred salinity trends for the seven sites typically indicated that reductions in water salinity occurred sometime during the early or mid 20th century.Rather than climate, hydrological modification of water resources is implicated as the primary driver of salinity changes during most of the 20th century. In the western North African region these modifications were mainly local land drainage and water diversion programmes to alleviate winter flooding and/or promote summer water availability. In the Delta region, the Nile has been intensively exploited since antiquity and intensively so from the late 19th century to release more fresh water for agriculture. Here, diatom records indicate that freshening began well before the Aswan High Dam but salinity fluctuations have tended to diminish during the latter part of the 20th century. A small reversal in the water freshening trend in the 1980/90s was possibly a response to land subsidence/sea-level change or to reduced freshwater supply.Freshwater supply to the sites is generally diminishing as former freshwater surpluses switch to deficit. One site (Merja Bokka, Morocco) became completely dry in 1998 as agriculture encroached and Megene Chitane, the only acid lake in Tunisia, is currently affected by excessive inflow abstraction. At the beginning of the 21st century, eight of the nine CASSARINA sites persist as viable but modified aquatic ecosystems. They nevertheless continue to support valuable aquatic biodiversity, especially in the Delta sites and in Chitane. The modern diatom communities are clearly tolerant of considerable environmental change but the remaining sites are increasingly threatened by major hydrological disturbance. Base-line floristic data for the late 20th century are given but continuous biomonitoring combined with effective management is needed urgently to help conserve North Africa's diminishing natural wetland lake resources.     

Some observations on the age and growth of thin-lipped grey mullet, Liza ramada Risso, 1826 (Pisces, Mugilidae) in three North African wetland lakes: Merja Zerga (Morocco), Garâat Ichkeul (Tunisia) and Edku Lake (Egypt)

Age and growth characteristics of the thin-lipped Grey Mullet (Liza ramada) were investigated in three North African wetland lakes: Merja Zerga (Morocco), Garâat Ichkeul (Tunisia) and Edku Lake (Egypt). Age structure of the mullet populations was very similar in all three study lakes. Small differences in growth were indicated, especially for the Moroccan population, where growth tended to be slower than for the other two populations. The fastest growth was observed in the Edku population while the best condition was observed in the Ichkeul population. Compared with some European populations, the sampled North African populations have faster growth and better condition factors.     

FIMM, a database of functional molecular immunology: update 2002

FIMM database (http://sdmc.krdl.org.sg:8080/fimm) contains data relevant to functional molecular immunology, focusing on cellular immunology. It contains fully referenced data on protein antigens, major histocompatibility complex (MHC) molecules, MHC-associated peptides and relevant disease associations. FIMM has a set of search tools for extraction of information and results are presented as lists or as reports.     

Some characteristics of the prostaglandin synthesizing system in rabbit kidney microsomes.

The prostaglandin synthesizing system in rabbit kidney microsomes was characterised using a radiometric assay. Three prostaglandins (F2alpha, E2 and D2) were formed form (1-14C)arachidonic acid, a small amount of prostaglandin A2 was also detected but this was formed non-enzymatically. Biosynthesis was stimulated by reduced-glutathione and 1-adrenaline and was inhibited by aspirin-like drugs. The enzyme system was sensitive to small changes in pH. There were substantial differences in drug sensitivity and optimal reaction conditions between this prostaglandin synthesizing system and the one from bovine seminal vesicles.