Notes on the structure and the use of Neosarmatium meinerti and Cardisoma carnifex burrows in a Kenyan mangrove swamp (Decapoda Brachyura)

Abstract

Burrow distribution and morphology were investigated in Neosarmatium meinerti and Cardisoma carnifex, two species sharing the same environment in a Kenyan mangrove swamp. Burrow structure and occupation ratio were also analysed. The sizes and shapes of the burrows are consistently variable in both the species. Most of the burrows have a simple linear shape, that in few cases can be complicated by the presence of bends, rooms and accessory branches. Bends are due to obstacles found while digging the burrows, the rooms and the accessory branches are probably used to store food. In accordance with the fact that C. carnifex is larger than N. meinerti, the burrows of the two species significantly differ in terms of both diameter and volume. For N. meinerti burrows there is a strong correlation between the carapace width and the entrance size, and with the volume, but not with the linear length. Thus length is not related to crab size but varies depending on the substrate, the presence of roots and the depth of the sea water level. An interesting finding is that some crab burrows are occupied by the fish Acentrogobius simplex as a temporary refuge, probably aiding its survival in shoal periods.