Biology and Distribution of Mangrove Crabs in the Wouri River Estuary, Douala, Cameroon

Abstract

Crabs appear as the most important group of mangrove epifauna. Their distribution seems influenced by some biotic and abiotic parameters. To verify the interactions between crab populations and relevant environmental components, six mangrove sites around the city of Douala (3°40' - 4°11'N and 9°16' - 9°52'E) were selected. During six months, four 25-min independent time-biased samples methods were conducted in the plot of 4 × 4 m 2 delimited inside each zonation throughout transect. The distance from plot to water and its groundwater salinity, temperature, conductivity and pH were measured. The individual sex, fresh weight and carapace size were determined. 3016 individuals were harvested (57% of females). Perisesarma kamermani was the most abundant (29%) while Chiromates angolense was the most frequent (13.47%). Cardisoma armatum was only found in Pandanus zone. Crab species number was positively correlated with tree, suggesting that the mangrove vegetation is important to the crab fauna as a habitat and food supply. Sex ratio showed a significant difference for Chiromates buetikoferi 1:2.34 ( χ 2 = 33.21) and for Perisesarma huzardi 1.36:1 ( χ 2 = 39.98). Portunus validus live closer to water between 5 - 20 m while Cardisoma armatum was found 70 m away from water. Portunus validus was present exclusively in high salinity zones whereas Perisesarma kamermani dominate in low salinity zone. This baseline ecological study of crab mangroves is important for monitoring, management and conservation of mangrove ecosystems.