Brachyuran crab community structure and associated sediment reworking activities in pioneer and young mangroves of French Guiana, South America

Abstract

This study in French Guiana evaluates the changes of crab assemblages and their bioturbation activities between mangrove early stages (pioneer and young mangrove) and within stages by taking their spatial heterogeneity (tidal channels, flat areas, pools) into account. The results show differences in crab assemblage structure between and within the early stages of mangrove in relation to microhabitat and sediment characteristics. The sediment reworking rates are a function of the biomass or density of particular species (Ucides cordatus, Uca cumulanta) and burrower functional groups. Crab species or functional interactions mediate changes in sediment reworking rates suggesting the need to consider entire benthic communities rather than single species. This study suggests that the role of the microhabitat in determining the biologically-induced sediment reworking rates depends on the age of the mangrove. Feeding activity results in a sediment turnover of 11.7 ± 9.7 gdw m−2 day−1 and 6.8 ± 3.0 gdw m−2 day−1 in the pioneer and young mangroves, respectively. Burrow maintenance excavates 40.5 ± 7.4 gdw m−2 day−1 and 251.3 ± 419.7 gdw m−2 day−1 in the pioneer and young mangroves, respectively. Upscaling to the studied area (Sinnamary estuary: 6 km2), shows that 500 tons.day−1 and 20 tons.day−1 of sediments could be excavated and pelletized, respectively, during the spring tides of the dry season. Thus, biological sediment reworking would greatly contribute to the sedimentary dynamics of the Guianese mangroves under Amazonian influence.