Zooplankton constitutes a sensitive tool for monitoring environmental changes in coastal lagoons; however, the available information on zooplankton communities is not sufficient to optimize their rational management. The relationships between zooplankton distribution and environmental factors were studied in a tropical lagoon to test whether the indicator properties of zooplankton assemblages could be used to monitor water quality, in a context of expected eutrophication provoked by an increasing anthropogenic activity. Twenty-one (21) stations were sampled monthly from January to December 2004. The community was composed of 65 taxa including Copepoda, Rotifera, and Cladocera. Copepoda was the most abundant group (81% of total numbers). The main zooplankton species were Oithona brevicornis, Acartia clausi, and Brachionus plicatilis. The highest zooplankton abundance (171-175 ind. l -1 ) was recorded during the long, dry season (February-April) and the lowest (40-45 ind. l -1 ) during the rainy and the flood periods (June-July). At a spatial level, the lowest abundance was observed in the estuarine zone. During the dry seasons (December-April and AugustSeptember), marine zooplankton taxa were abundant near the channel of Grand-Lahou, and brackish water taxa dominated in the other sites. Multivariate analyses (Co-inertia) showed that the composition of zooplanktonic communities and their spatio-temporal variations were mainly controlled by salinity variations closely linked to the climatic and hydrological context. The role of the trophic state on zooplankton communities could not be clearly evidenced. Our results and a comparison with previous studies in the neighboring, highly polluted Ebrié Lagoon suggest that the ratio between Oithona and Acartia abundance could be used as biological indicator for the water quality.

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The absorption spectra of marine humic substances decrease when they are exposed to a known intensity of monochromatic light at various wavelengths or to a polychromatic source such as sunlight. The results of studies of photochemical bleaching of absorption of marine humic substances are presented and compared to the characteristics of total dissolved organic matter to assess the contribution made by the humic fractions. From the absorbance and apparent quantum efficiency data at specific wavelength and the solar fluxes, a model calculation was used to determine the rates of the change of the photoprocess in the ocean. These parameters were determined for the photochemical degradation of Biscayne Bay (Florida, USA) seawater and humic substances collected in the Gulf of Mexico.

Les variations saisonnières des paramètres physico-chimiques et hydrologiques de la lagune de Fresco ont été mesurées durant deux cycles annuels sur cinq stations. Il en résulte que la température, le pH, l'oxygène dissous et les sels nutritifs sont homogènement répartie sur le plan d'eau lagunaire. La distribution de la salinité et des MES y est hétérogène et permet de délimitée deux zones :-une zone océanique qui se comporte comme une baie avec des eaux peu renouvelées et un faible hydrodynamisme. Elle représente plus des 2/3 de la superficie de la lagune de Fresco ;-une zone continentale où l'influence des apports des rivières côtières Bolo et Niouniourou est très marqué. Les conclusions de cette étude permettent de classer la lagune de Fresco dans le système lagunaire Ebrié.