Key drivers for copepod assemblages in a eutrophic coastal brackish lake

The copepod assemblages and abiotic parameters were investigated at 11 stations in a large coastal lake (Lake Manzalah, Nile Delta) from 2009-2010 in order to verify any impacts of eutrophication and salinity on the copepod species composition. The environmental conditions and the copepod assemblages appeared to have changed in comparison with previous studies, possibly because of increasing eutrophication and invasions of non-indigenous species (NIS). The aim of the present study was the identification of species which can be used as ecological indicators of high trophic status. Among the nine copepod species of Lake Manzalah, Acartia tonsa, Mesocyclops ogunnus, and Apocyclops panamensis were reported for the first time. Acartia tonsa, a well-known NIS for the Mediterranean, numerically dominated the copepod assemblages in some portions of the lake. The distribution of Acanthocyclops trajani and Thermocyclops consimilis was insensible to eutrophication because they can stand high levels of nutrients and hypoxia. Compared with previous reports, the copepod assemblage of Lake Manzalah was richer in species. The invasions of NIS, in addition to the heterogeneous progress of eutrophication in the lake, created an environmental mosaic with many species in total, but with single areas suitable for only a small number of them

IMPACT OF VERY WARM TEMPERATURE ON EGG PRODUCTION RATES OF THREE ACARTIIDAE (CRUSTACEA, COPEPODA) IN A NORTHERN AFRICAN LAGOON

The dailyEggProductionRate(EPR)ofthethreeAcartiidaecopepodsnamely Acartia clausi, Paracartia latisetosa and Paracartiagrani in theNorthLagoonofTuniswascomparedtotemperatureandfood availabilityeveryseasonfromMarch,2003toFebruary,2004correspondingtothemajorseasonal peaksoftheirabundanceandovera20-daysperiod.ThedailyEPRwasevaluatedbyassumingadirect correlationwithchlorophyll a, particulateorganiccarbon(POC),andsomeeasilyextractablemacro- molecularcompoundsfromtheseston,suchasproteins,carbohydratesandlipids.Theresultsshowed significantdifferencesinEPRbetweenseasonsandspecies.Temperatureandsalinitynegatively affectedthefecundityof A. clausi and positivelythatof P. latisetosa and P. grani. The A. clausi EPR was supportedbychlorophyll a and sestonicproteinswhilethatof P. latisetosa and P. grani correlated with POCsuggestingthatthesetwotaxafeedonmicrozooplanktonanddetritusmorethanon phytoplankton.Overall,EPRdatashowedpotentialpopulationrecruitmentevidentlythehighestin P. latisetosa in summer, P. grani in autumnand A. clausi in winter.Ourresultsindicatethattemperature and ood quality are the determining factors of both abundance and reproduction of the copepods under study

Physiological and Biochemical Responses in Microalgae <i>Dunaliella salina</i>, <i>Cylindrotheca closterium</i> and <i>Phormidium versicolor</i> NCC466 Exposed to High Salinity and Irradiation

Dunaliella salina (Chlorophyceae), Phormidium versicolor (Cyanophyceae), and Cylindrotheca closterium (Bacillariophyceae) were isolated from three ponds in the solar saltern of Sfax (Tunisia). Growth, pigment contents, and photosynthetic and antioxidant enzyme activities were measured under controlled conditions of three light levels (300, 500, and 1000 µmol photons m−2 s−1) and three NaCl concentrations (40, 80, and 140 g L−1). The highest salinity reduced the growth of D. salina and P. versicolor NCC466 and strongly inhibited that of C. closterium. According to ΦPSII values, the photosynthetic apparatus of P. versicolor was stimulated by increasing salinity, whereas that of D. salina and C. closterium was decreased by irradiance rise. The production of carotenoids in D. salina and P. versicolor was stimulated when salinity and irradiance increased, whereas it decreased in the diatom. Catalase (CAT), Superoxide dismutase (SOD), and Ascorbate peroxidase (APX) activities were only detected when the three species were cultivated under E1000. The antioxidant activity of carotenoids could compensate for the low antioxidant enzyme activity measured in D. salina. Salinity and irradiation levels interact with the physiology of three species that have mechanisms of more or less effective stress resistance, hence different resistance to environmental stresses according to the species. Under these stress-controlled conditions, P. versicolor and C. closterium strains could provide promising sources of extremolyte for several purposes

Key Drivers for Copepod Assemblages in a Eutrophic Coastal Brackish Lake

The copepod assemblages and abiotic parameters were investigated at 11 stations in a large coastal lake (Lake Manzalah, Nile Delta) from 2009&#8315;2010 in order to verify any impacts of eutrophication and salinity on the copepod species composition. The environmental conditions and the copepod assemblages appeared to have changed in comparison with previous studies, possibly because of increasing eutrophication and invasions of non-indigenous species (NIS). The aim of the present study was the identification of species which can be used as ecological indicators of high trophic status. Among the nine copepod species of Lake Manzalah, Acartia tonsa, Mesocyclops ogunnus, and Apocyclops panamensis were reported for the first time. Acartia tonsa, a well-known NIS for the Mediterranean, numerically dominated the copepod assemblages in some portions of the lake. The distribution of Acanthocyclops trajani and Thermocyclops consimilis was insensible to eutrophication because they can stand high levels of nutrients and hypoxia. Compared with previous reports, the copepod assemblage of Lake Manzalah was richer in species. The invasions of NIS, in addition to the heterogeneous progress of eutrophication in the lake, created an environmental mosaic with many species in total, but with single areas suitable for only a small number of them