Contribution à l'étude des modifications hydro-sédimentaires consécutives à la réouverture artificielle de l'embouchure du Comoé à Grand-Bassam

The Bassam artificial inlet was opened (in September 22, 1987) in order to revacuate offshore invasive aquatic plants. This has considerably modified the hydro-sedimentary environment of the lagoonal domain at Grand-Bassam. Tidal currents effect has confered the lagoonal waters an estuarine feature, the saline intrusion (25-35%o) increased beyond the Moossou bridges up to the confluence of the Comoe river. This has led to a cleaning of the river lower course and above all to the bottoms of the lagoon, which were previously confined. The remobilization of mud (from lagoonal bottoms around Bouet Island) evacuated offshore, has exposed lagoonal and oceanic sandy features. This new system remains fragile, with the seasonal (low river-flow) clogging.

Analyse des effets de l'ouverture du chenal de Grand Bassam (estuaire du fleuve Comoé, Lagune Ebrié) sur la macrofaune benthique lagunaire

This paper presents the results of a comparative study of three series of samples collected in the area near the Bassam channel before, six and twenty months after its opening in September 1987. Observed effects are the decrease in the abundance and the modification of the benthic macrofauna composition. These effects appeared to be definitive, without recovery of the most abundant species Corbula trigona. Most differences noted in the population structure are due to the increase of the salinity and at a least degree to the modification of the nature of the sediment.

L'oxygene au large de Grand Bassam (Cote d'Ivoire)

The present paper deals with the variations of the dissolved oxygen content off Grand Bassam (11 miles east of Abidjan, Côte d'Ivoire), during nearly five years (March 1966 to September 1970). Although we find in general the low oxygen values near the bottom, the dissolved oxygen content is at its absolute minimum during the upwelling. There is a good correlation between the Secchi depth and the depth of the well ventilated layer. About 10% of surface irradiance is found at the layer where the dissolved oxygen content equals 80% of the oxygen content found at surface.

Changes in frost frequency and desert vegetation assemblages in Grand Canyon, Arizona

The effect of decreasing frost frequency on desert vegetation was documented in Grand Canyon by replication of historical photographs. Although views by numerous photographers of Grand Canyon have been examined, 400 Robert Brewster Stanton and Franklin A. Nims views taken in the winter of 1889-1890 provide the best information on recent plant distribution. In Grand Canyon, where grazing is limited by the rugged topography, vegetation dynamics are controlled by climate and by demographic processes such as seed productivity, recruitment, longevity and mortality. The replicated photographs show distribution and abundance of several species were limited by severe frost before 1889. Two of these, brittlebush (Encelia farinosa) and barrel cactus (Ferocactus cylindraceus), have clearly expanded their ranges up-canyon and have increased their densities at sites where they were present in 1890. In 1890, brittlebush was present in warm microhabitats that provided refugia from frost damage. Views showing desert vegetation in 1923 indicate that Encelia expanded rapidly to near its current distribution between 1890 and 1923, whereas the expansion of Ferocactus occurred more slowly. The higher frequency of frost was probably related to an anomalous increase in winter storms between 1878 (and possibly 1862) and 1891 in the southwestern United States.

Acoustic tracking of reef fishes to elucidate habitat utilization patterns and residence times inside and outside marine protected areas around the island of St. John, USVI

This technical memorandum describes a developing project under the direction of NOAA’s Biogeography Branch in consultation with the National Park Service and US Geological Survey to understand and quantify spatial patterns and habitat affinities of reef fishes in the US Virgin Islands. The purpose of this report is to describe and disseminate the initial results from the project and to share information on the location of acoustic receivers and species electronic tag ID codes. The Virgin Islands Coral Reef National Monument (VICRNM), adjacent to Virgin Islands National Park (VIIS), was established by Executive Order in 2000, but resources within the monument are poorly documented and the degree of connectivity to VIIS is unknown. Whereas, VICRNM was established with full protection from resource exploitation, VIIS has incurred resource harvest by fishers since 1956 as allowed in its enabling legislation. Large changes in local reef communities have occurred over the past several decades, in part due to overexploitation. In order to better understand the habitat utilization patterns and movement of fishes among management regimes and areas open to fishing around St, John, an array of hydroacoustic receivers was deployed while a variety of reef fish species were acoustically tagged. In July 2006, nine receivers with a detection range of ca. 350 m were deployed in Lameshur Bay on the south shore of St. John, within VIIS. Receivers were located adjacent to reefs and in seagrass beds, inshore and offshore of these reefs. It was found that lane snappers and bluestriped grunts showed diel movement from reef habitats during daytime hours to offshore seagrass bed at night. Timing of migrations was highly predictable and coincided with changes in sunrise and sunset over the course of the year. Fish associated with reefs that did not have adjacent seagrass beds made more extensive movements than those fishes associated with reefs that had adjacent seagrass habitats. In April 2007, 21 additional receivers were deployed along much of the south shore of St. John (ca. 20 km of shoreline). This current array will address broader-scale movement among management units and examine the potential benefits of the VICRNM to provide adult “spillover” into VIIS and adjacent harvested areas. The results from this work will aid in defining fine to moderate spatial scales of reef fish habitat affinities and in designing and evaluating marine protected areas.