Biomass flow structure and resource potential of two mangrove estuaries: insights from comparative modelling in Costa Rica and Brazil

Abstract

Trophic models were compared for mangrove fringed estuaries in Costa Rica (Gulf of Nicoya, at the Pacific shore) and Brazil (Caete estuary, NE of Belem) in order to evaluate biomass and energy flow distributions, productivity and fisheries potential, and to obtain guidelines for conservation and management of these systems. As the same network modelling approach (ECOPATH II) and a similar number of system compartments were used, a comparison based on the network models seemed attractive. Differences in biotic structure, energy flow and resource productivity’s between both systems and their causes were assessed. They proved to be substantial and largely due to differences in topography, tidal regime and mangrove cover between both systems. While the Gulf of Nicoya is exposed to semidiurnal tides and an efficient daily water exchange between the mangrove stands and the gulf and thus to a strong mangrove matter export to the gulf water, the mangrove forest of the Caete estuary is flushed each fortnight only and the largest part of the mangrove production thus remains within the forest. This is reflected in great differences in food web structure and the amount and type of resources produced in both systems. In the Gulf of Nicoya, detritus matter exported from the mangroves to the estuary feeds an aquatic food web with shrimps and other aquatic detritivores in the centre of the web, while in the Caete estuary, most energy remains in the benthic domain of the mangrove forest where it is transferred to an enormous biomass of leaf consuming mangrove crabs, the principal resource of this system. Findings imply that generalizations among mangrove systems need to be tempered with caution and differences in trophic relationships among systems must be considered. Rev. Biol. Trop. 54 (Suppl. 1): 69-86. Epub 2006 Sept. 30.