ABSTRACT
The coastal zone of Benin is the interface between the marine environment and the straightforward continental environment. It is constituted of sandy cords, lagoon system, lakes and flood plains. This zone shelters a population of about 3 million inhabitants that is more than 30% of the Beninese population. As all coastal regions of the world, this zone remains very sensitive to climatic changes (global elevation of the sea level, perpetual variations of the weather marines conditions) and to human activities (large inland dams, harbour infrastructures, urbanization) that drive to the rupture of the equilibrium in this coastal environment with enhanced risks of beach erosion as the main consequences. This study monitors the evolution of the Beninese shorelines around Cotonou and underlines the causes mainly human that negatively affect this naturally fragile environment. Natural factors (tempests and erosive processes) and human actions (building of the port of Cotonou (1962) then Lome (1967) and hydroelectric dams on Volta (1966) and on Mono (1987) rivers) aim the coastal evolution of the Benin. They procreate, on the sandy cords at East of ports and rivers mouths, an erosion about 10 m linked to the reduction of provisions in sand and the fragilisation of cords by farms, steps and of anarchic occupations.
ABSTRACT
Leatherback sea turtles (Dermochelys coriacea) nest on dynamic, erosion-prone beaches. Erosive processes and resulting nest loss have long been presumed to be a hindrance to clutch survival. In order to better understand how leatherbacks cope with unstable nesting beaches, I investigated the role of beach erosion in leatherback nest site selection at Playa Gandoca, Costa Rica. I also examined the potential effect of nest relocation, a conservation strategy in place at Playa Gandoca to prevent nest loss to erosion, on the temperature of incubating clutches. I monitored changes in beach structure as a result of erosion at natural nest sites during the time the nest was laid, as well as in subsequent weeks. To investigate slope as a cue for nest site selection, I measured the slope of the beach where turtles ascended from the sea to nest, as well as the slopes at other random locations on the beach for comparison. I examined temperature differences between natural and relocated nest sites with thermocouples placed in the sand at depths typical of leatherback nests. Nests were distributed non-randomly in a clumped distribution along the length of the beach and laid at locations that were not undergoing erosion. The slope at nest sites was significantly different than at randomly chosen locations on the beach. The sand temperature at nest depths was significantly warmer at natural nest sites than at locations of relocated nests. The findings of this study suggest leatherbacks actively select nest sites that are not undergoing erosive processes, with slope potentially being used as a cue for site selection. The relocation of nests appears to be inadvertently cooling the nest environment. Due to the fact that leatherback clutches undergo temperaturedependent sex determination, the relocation of nests may be producing an unnatural male biasing of hatchlings. The results of this study suggest that the necessity of relocation practices, largely in place to protect nests from erosion, should be reevaluated to ensure the proper conservation of this critically endangered species. Rev. Biol. Trop. 58 (4): 1237-1246. Epub 2010 December 01.