FISH ASSEMBLAGE STRUCTURE IN SHALLOW WATERS OF THE MELLAH LAGOON (ALGERIA): SEASONAL AND SPATIAL DISTRIBUTION PATTERNS AND RELATION TO ENVIRONMENTAL PARAMETERS

Background. Southern Mediterranean lagoons are poorly studied. The Mellah Lagoon is the only coastal lagoon in Algeria. Characterized by low anthropogenic pressure it has a crucial environmental and socioeconomic role because of its fishing activities and conservation status. The spatial and temporal variations of fish assemblage structure in relation with the environmental parameters were investigated. This study contributes to a better understanding of the functioning of the Mellah Lagoon, thus providing useful data regarding its conservation and management. Materials and methods. Sampling was carried out monthly during one year at four stations with a beach seine of 3-mm mesh. Environmental variables were measured during each sampling. Canonical correspondence analysis (CCA) and cluster analysis were used to assess environmental influences on fish spatio-temporal assemblages. Results. A total of 11 fish species representing 8 families were collected and examined: Aphanius fasciatus (Valenciennes, 1821); Atherina boyeri Risso, 1810; Liza saliens (Risso, 1810); Liza aurata (Risso, 1810); Mugil cephalus Linnaeus, 1758; Mugilidae gen sp.; Pomatoschistus marmoratus (Risso, 1810); Diplodus sargus sargus (Linnaeus, 1758); Sparus aurata Linnaeus, 1758; Syngnathus abaster Risso, 1827; Anguilla anguilla (Linnaeus, 1758); Hyporhamphus picarti (Valenciennes, 1847). Resident species presented the highest abundance values, accounting for 96% of the total number of fish captured, while marine migrant species that use the lagoon as a nursery ground contributed the most to the community species richness (7 species). Atherina boyeri (87.59% of total catch by number) was the most abundant species. Environmental parameters measured were uniform across the whole lagoon. However, temperature and salinity showed a seasonal pattern. The CCA analysis based on species abundance indicated the absence of clear spatial and temporal patterns in fish assemblage. The majority of the species had mean values of distribution in relation to environmental variables. Conclusion. The fish assemblage of the shallow water (< 1.5 m) of the Mellah Lagoon is characterized by a small number of species dominated by resident species. The low species richness, the dominance of resident species, and the weak spatial and temporal patterns in the fish assemblage are mainly the result of a high degree of confinement because of the low freshwater inputs from the wadis and the limited tidally-driven exchanges between the lagoon and the sea. To maintain high biodiversity and a sustainable fishery in the lagoon, it is necessary to develop a management plan which would facilitate a proper water exchange between the lagoon and the sea and would promote colonization of the lagoon by marine species.