Activite Photosynthetique Du Phytoplancton Dans Le Barrage Hydroelectrique D\'ayame I (Côte D\'ivoire)

L\'activité photosynthétique du phytoplancton du barrage hydroélectrique d\'Ayamé I a été suivie au cours de six campagnes de mesures sur deux stations (Bakro, Ayamé) afin d\'évaluer son évolution spatio-temporelle et d\'identifier les variables qui la contrôlent. Les mesures de la productivité photosynthétique du phytoplancton ont été effectuées dans la couche euphotique (0-3 m). Les résultats montrent une variabilité temporelle de l\'activité photosynthétique dans les deux stations du lac. Les productivités phytoplanctoniques sont maximales à Bakro et à Ayamé en début de saison des pluies (respectivement 0,35 et 0,81 mg.C.m-2.j-1) et minimales en saison sèche (respectivement 0,18 et 0,43 mg.C.m-2.j-1). Les productivités phytoplanctoniques ont été positivement corrélées aux nitrates (r > 0,8 ; p 0,6 ; p < 0,05), ce qui souligne l\'importance des nutriments dans la productivité du phytoplancton.Photosynthetic activity of phytoplankton in the hydroelectric reservoir of Ayamé I was studied during 6 data acquisition campaigns at two stations (Bakro, Ayamé). The main objective was to monitor spatial and temporal changes in phytoplankton productivity and identifiy potential variables responsible for the changes. Phytoplankton photosynthetic activity was determined in the euphotic layers (0-3m) of the lake. Results show changes in photosynthetic activity with time in the two stations. Maximum concentrations of carbon assimilation were observed during the begining of the rainy season (0.35 and 0.81 mg.C.m-2.j-1 ) and minimum activity during the dry season (0.18 and 0.43 mg.C.m-2.j-1) at Bakro and Ayamé, respectively. The phytoplankton productivities correlated with nitrate (r > 0.8 ; p 0.6 ; p < 0.05) which underscores the importance of nutrients in phytoplankton productivity. Keywords: Activité photosynthétique, phytoplancton, barrage hydroélectrique, Côte d'Ivoire.Agronomie Africaine Vol. 19 (1) 2007: pp. 63-7

Twee eeuwen mariene biologie in België

In Belgium, with its rather small and monotonous coastal line and without much sea commerce going on, only a very slight interest in marine science existed before 1800. During the nineteenth century, however, marine biology became one of the main topics for research among Belgian scientists. This was largely due to the efforts of the Louvain professor Pierre Joseph Van Beneden (1809-1894) and his son Edouard (1846-1910), professor in Liège. Around 1900, their leading rôle was taken over by Gustave Gilson (1859-1944), who largely succeeded in shaping Belgian oceanography around a well-defined research programme focusing on the Mer Flamande. Apart from Gilson, some other researchers such as Désiré Damas (1877-1959) and Paul Pelseneer (1863-1945) contributed to the study of marine science in Belgiu

Études préliminaires de la distribution spatio-temporelle du phytoplancton dans un système fluvio-lacustre africain (Bassin Bia ; Côte d'lvoire)

Les échantillons examinés mensuellement de novembre 1996 à octobre 1997 proviennent de divers endroits du système fluvio-lacustre de la Bia : deux sites dans le lac (Bakro et Ayamé) et deux dans le système fluvial dont un en amont (Bianouan) et un en aval (Aboisso). La structure et la dynamique du phytoplancton ont été appréciées. En amont du barrage, le peuplement est marqué, presque toute l'année, par une relative abondance des Diatomées Aulacoseira granulata et Fragilaria virescens. Dans le lac, l'évolution du peuplement phytoplanctonique est plutôt fonction des deux grandes saisons de I'année. Les Diatomées, principalement, Asterionella formosa, Aulacoseira granulata et A. granulata var. angustissima dominent le peuplement en saison sèche. Pendant les périodes pluvieuses de I'année, les Cyanophycées Microcystis aeruginosa, Anabaena spiroides constituent la composante majoritaire du phytoplancton dans les échantillons. En aval du barrage hydroélectrique, la dynamique du phytoplancton observée est plus ou moins semblable à celle ci-dessus décrite dans le système lacustre. Les variations des paramètres physico-chimiques enregistrées dans les différentes stations semblent peu influencer la densité du phytoplancton. Elle apparaît plutôt déterminée par le régime hydrologique de la rivière

Twee eeuwen mariene biologie in België

Two centuries of marine biology in Belgium In Belgium, with its rather small and monotonous coastal line and without much sea commerce going on, only a very slight interest in marine science existed before 1800, During the nineteenth century, however, marine biology became one of the main topics for research among Belgian scientists. This was largely due to the efforts of the Louvain professor Pierre Joseph Van Beneden (1809-1894) and his son Edouard (1846-1910), professor in Liege. Around 1900, their leading role was taken over by Gustave Gilson (1859-1944), who largely succeeded in shaping Belgian oceanography around a well-defined research programme focusing on the Mer Flamande. Apart from Gilson, some other researchers such as Desire Damas (1877-1959) and Paul Pelseneer (1863-1945) contributed to the study of marine science in Belgium

Intraspecific density dependence in the dynamics of zooplankton under hypertrophic conditions

Intraspecific interactions may limit population growth of small cladoceran taxa under food-rich, hypertrophic conditions. Multiple-regression models significantly explained a large proportion of the variation in the body size adjusted fecundity and population growth rate of crustacean zooplankton taxa in a shallow, hypertrophic lake. The results of partial correlation analyses suggested exploitative competition to have only limited significance in determining the zooplankton dynamics. The analyses also revealed strong negative relationships between biomass and both body size adjusted fecundity and population growth rate within most taxa. Most of these relationships cannot be explained by food shortage or predation and suggest alternative mechanisms such as chemically mediated, intraspecific interference competition or life history shifts

Winter distribution of phytoplankton and zooplankton around some sandbanks of the Belgian coastal zone

The distribution of phytoplankton and zooplankton around three sandbanks (Gootebank, Westhinder and Buitenratel sandbank) off the Belgian Coast was investigated in February 1994. The abundance of phytoplankton taxa was significantly different between the sandbanks. Community analysis using TWINSPAN resulted in a clear separation of clusters corresponding to the different sandbanks. The zooplankton community analysis, on the contrary, showed a rather indistinctive division of the sandbank stations. This was due to the omnipresence of three dominant copepod species (Temora longicornis, Pseudocalanus elongatus and Centropages hamatus). When these species were excluded from the analysis, a clearer distinction between the different sandbanks was found. The observed differences in phyto- and zooplankton species distribution could be explained by the position of the sandbanks. Westhinder is positioned further from the coast than Buitenratel, while Gootebank has an intermediate position. Buitenratel and Gootebank harbour typical coastal plankton communities, while the plankton community over Westhinder is clearly influenced by the Atlantic current penetrating the southern North Sea from the English channel. More phyto-benthic species were found at Buitenratel than at Gootebank, probably because of its limited depth. Thus, the Belgian coastal zone, which is considered as one box in most spatial descriptions of the North Sea plankton, in fact harbours heterogeneous plankton communities at the end of winter

The relevance of size efficiency to biomanipulation theory: a field test under hypertrophic conditions

The superiority of large zooplankton in suppressing phytoplankton growth has often been inferred from the Size Efficiency Hypothesis (S.E.H.). The S.E.H. has originally been formulated to account for the competitive superiority of large to small zooplankton under food limiting conditions. Extrapolation of its predictions to the suppression of phytoplankton by zooplankton under high food availability, should be done with care. In an attempt to assess the relevance of the S.E.H. to biomanipulation theory in hypertrophic systems, a fish exclosure experiment was carried out in which the efficiency of two differently structured zooplankton communities in reducing phytoplankton biomass was examined. By inoculating part of the enclosures with laboratory grown Daphnia magna, a community dominated by this large cladoceran species could be compared with a community mainly consisting of Bosmina and smaller Daphnia species. After the exclusion of fish, there was an exponential increase of total. zooplankton biomass. Phytoplankton growth was efficiently suppressed to equal levels in both treatments, though there was a difference in timing: chlorophyll-a levels in the enclosures inoculated with D. magna dropped one week earlier than in non-inoculated enclosures. The time-lag was even more pronounced when large phytoplankton was considered. In accordance with the S.E.H., the time lags could be explained by differences in population growth potential as well as by differences in zooplankton grazing rates (indirectly measured as the minimal zooplankton biomass needed to suppress phytoplankton growth) and food particle size range