[Hydrological and edaphic structure of an oyster-farming site: Duna Blanca (Bay of Dakhla, south Morocco)]. / Structure hydrologique et edaphique d'un site ostreicole: Duna Blanca (la baie de Dakhla sud du Maroc).

Morocco shelters lagoons, estuaries and bays along its paralic coasts which are among the most productive in the world. The Bay of Dakhla is the longest and the most important site in Morocco due to its halieutic richness. In fact, this bay is an ecosystem with great potential in terms of aquaculture, mainly shellfish farming, and shelters favorable zones for tapiculture, mytiliculture and ostreiculture, in accordance with ecological planning. A hydrological study (temperature, salinity, chlorophyll "a", suspended matter and organic matter) was conducted on a breeding project of the cupped oyster (Crassostrea gigas) installed on the Duna Blanca site since April 2003. A seasonal follow-up of sediment structure was carried out involving granulometric and metallic studies. The hydrological sampling was performed monthly on the surface and at the bottom, during spring tides, low tide and high tide. The results confirmed that the site encompasses a wealth of nutritive elements and a significant chlorophyll-rich biomass. A gradient of hypersalinity is well correlated with seasonal variation of the temperature. The sedimentary structure ranges from muddy-sandy to sandy type. The metal concentrations in the sediments never exceeded the toxicity thresholds. However, the site's production potential cannot be limitless and could be affected by the extension and installation of new conchylaceous farms.

Structural analysis of Gigartina pistillata carrageenans (Gigartinaceae, Rhodophyta).

The chemical structure of carrageenans produced by the gametophytic and tetrasporophytic life cycle phases of Gigartina pistillata has been determined by permethylation analysis, IR and 13C NMR spectroscopies. The chemistry of the galactans varies according to the biological phases of the plant, the gametophytic alga produces heterogeneous kappa-iota type carrageenan containing minor amounts of nu-carrabiose. The tetrasporophytic alga synthesizes a complex sulfated galactan composed of lambda-, xi-, pi-carrabioses and sulfated carrabioses containing 3-linked galactopyranose 2,6-disulfate.