L'écosystème pélagique de la côte atlantique marocaine est influencé par la variabilité spatio-temporelle de l'upwelling. L'évolution des paramètres physico-chimiques et biologiques ainsi que leur corrélation et leur regroupement par l'analyse en composante principale nous ont permis de subdiviser le littoral atlantique en quatre zones de remontées : deux zones situées au nord de Cap Juby (28 • N), caractérisées par une activité estivale et deux zones situées au sud, actives en permanence avec une intensité variable.

No abstract

No abstract

The study of the Oualidia lagoon aims to establish the state of knowledge of the environment of this ecosystem after the construction of an inner dam in 2011 and the ecological functioning of the lagoon. For that, several campaigns were carried out between February 2011 and October 2012 and were the subject of a seasonal monitoring for the collection of the main biotic and abiotic parameters of the environment of this ecosystem. During the construction of the inner dam on 2011, a hydrological variability was marked in summer by low oxygen levels and maximum temperature variation between the two tides. Since the completion of the construction of the inner dam, there has been a significant increase in nutrients, mainly nitrogenous elements, and an increase in turbidity caused by an improvement in hydrodynamics, which has particularly increased of the sandpit modified the morphology and moved on south, creating a new main channel structure in 2011. This hydrodynamic was manifested on the upstream area by a decrease of the sedimentary organic European Scientific Journal June 2018 edition Vol.14, No.18 ISSN: 1857 -7881 (Print) e -ISSN 1857 94 matter due to the trapping of fine sediments in the inner dam. At the immediate level of the upstream area (Slikkes and Schorres), the hydrodynamic is relatively low, which has reduced the sedimentation rate on the upstream of the lagoon. The Oualidia lagoon is situated in a littoral zone influenced by the enrichment in deep cold waters loaded with nutritive salts, which invade it during the high tide, and would be, consequently after construction of the inner dam, protected from any confinement of the ecosystem.

The Oualidia Lagoon is a semi enclosed marine ecosystem connected to the Atlantic Ocean of Morocco and exposed to human activities, mainly agriculture and oyster farming. The present study aims to characterize the spatio-temporal variation of the phytoplankton assemblage and to highlight the effect of the main environmental parameters on this important planktonic component evolving in a vulnerable anthropized ecosystem. For this purpose, a field survey was carried out during four seasons in 2011 to determine the biotic (phytoplankton, chlorophyll a) and abiotic (temperature, salinity and nutrients) variables during low and high tide periods. Results highlight an established spatial variation of physicochemical parameters especially at low tide, with contrasted environmental conditions between the upstream and downstream zones. The phytoplankton diversity and abundance were characterized by a pronounced seasonal pattern. The Oualidia Lagoon is a nutrient rich ecosystem, especially in its upstream part. We also showed that both planktonic diversity and abundance were maximum in autumn and summer. The phytoplankton richness is governed by two main factors: the seasonality of nutrient enrichment and the regular supply of Atlantic seawater. Nitrate and ammonium were the main environmental abiotic factors determining the development of phytoplankton populations. The dynamic of phytoplankton in the Oualidia Lagoon is highly influenced by marine waters incoming from the Atlantic Ocean especially during the upwelling season. Finally, potential harmful algal species belonging to different genera such as Pseudo-nitzschia, Alexandrium, Prorocentrum, Dinophysis, Ostreopsis, Karenia, Coolia, Gonyaulax, Gymnodinium, Dictyocha and Chattonella were encountered showing a potential in this ecosystem to develop noxious blooms.Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. Highlights► The spatio-temporal variation of phytoplankton assemblage (biodiversity and abundance) was driven by environmental constraints from both land and sea. ► The taxonomic richness was dominated by typical marine species. ► The inventoried taxa were dominated by diatoms and dinoflagellates when considering both species number and density. ► Potential Harmful Algal Blooms species, belonging to different genera such as Pseudo-nitzschia, Alexandrium, Prorocentrum, Dinophysis, Ostreopsis, Karenia, Coolia, Gonyaulax, Gymnodinium, Dictyocha and Chattonella were encountered. ► The warm season (August and October) showed the highest values of phytoplankton species diversity and densities particularly upstream.