Abstract:
Seagrass beds are found in most of the world's seas except the Antarctic and provide important ecosystem services to both the marine system and local users. Despite recent and sporadic studies, the distribution and ecology of seagrass ecosystems along the West African coast are still poorly understood. In this context, this study compared two seagrass communities on the West African mainland (Bétenty, Senegal) and on an island (Gamboa Bay, Cape Verde). Species assemblages, biomass and physico-chemical parameters were compared. Descriptive statistics were used to identify differences in biological data according to local abiotic factors. Three species: Cymodocea nodosa, Zostera noltei and Halodule wrightii (the only one present in Gamboa Bay (GB). The southern limit of Z. noltei was confirmed to be in Bétenty and not in the PNBA of Mauritania. The species were distributed according to the type of sediment, which was sandy with the largest grain size in Gamboa [66.54 to 950.3 μm] and sandy muddy in Bétenty. Cover and DW were more than 4 and 6 times higher, respectively, in Bétenty than in Gamboa. Furthermore, temperatures, pH and salinity were within species tolerance at both sites, but Gamboa had low water clarity and its seagrass leaves were tiny (LL= 4.1 ± 0.03 versus 6.5 ± 2.4 cm) and covered by filamentous epiphytes. High nitrate concentrations were found at both sites. These abiotic differences could explain the absence of the temperate species C. nodosa and Z. noltei on the island. Unsustainable fishing practices in the case of Bétenty and urbanization in Gamboa were identified as the main threats.
Description:
A Thesis submitted to the West African Science Service Center on Climate Change and Adapted Land Use and Universidade Técnica do Atlântico, Cabo Verde in partial fulfillment of the requirements for the Master of Science Degree in Climate Change and Marine Science
