Energy budget and ecological role of mangrove epibenthos in the Caete estuary, North Brazil

Epibenthic community structure, somatic production and energy flow were studied in the Caete mangrove estuary in North Brazil on for 3 representative strata: high intertidal forest (F), small creeks in the forest (SC) and open mudbanks of large intertidal creeks (LC). Seven decapod crustaceans and I gastropod accounted for > 95 % of total epifaunal biomass, with highest values in the forest followed by large and small creeks (228.2, 103.6 and 69.7 kJ m(-2) respectively). The leaf-consuming crab Ucides cordatus was clearly dominant in the forest, followed by the fiddler crabs Uca rapax and U. vocator. The large creek stratum was strongly dominated by the fiddler crab U. maracoani, while in the small creek 4 species (Uca cumulanta, U. maracoani, Pachygrapsus gracilis and Eurytium limosum) contributed similar quantities to total biomass. Per area somatic production (P) and respiration (R) was highest in the large creek, followed by the forest and small creek stratum. Based on the contribution of each stratum, total biomass (332.8 kJ m(-2)), production (455.8 kJ m(-2) yr(-1)) and assimilation (2959.6 kJ m(-2) yr-1) were estimated for the whole area. While the herbivorous feeding guild with U. cordatus was the most prominent in terms of biomass (75 % of the total), the detritivorous fiddler crabs and P. gracilis clearly dominated in terms of respiration and somatic production (60 and 90 % respectively). Carnivores (Eurytium limosum and Thais coronata) contributed < 2 % to the epibenthic energy budget. A system picture emerges whereby energy flow is strongly dominated by herbivorous and detritivorous species, Both guilds probably promote mangrove primary production by (1) conserving nutrients in the system, (2) enhancing nutrient remineralization, and (3) oxygenizing the soil through their burrowing and feeding activities. A resulting positive feedback loop between mangroves, crabs and bacteria could explain the very high mangrove productivity and the high efficiency with which mangrove primary production is assimilated by the crabs (almost 15 %).