Abstract
The objective of this study was to describe the marine ecosystem off northeastern Brazil. A trophic model was constructed for the 1970s using Ecopath with Ecosim. The impact of most of the forty-one functional groups was modest, probably due to the highly reticulated diet matrix. However, seagrass and macroalgae exerted a strong positive impact on manatee and herbivorous reef fishes, respectively. A high negative impact of omnivorous reef fishes on spiny lobsters and of sharks on swordfish was observed. Spiny lobsters and swordfish had the largest biomass changes for the simulation period (1978-2000); tunas, other large pelagics and sharks showed intermediate rates of biomass decline; and a slight increase in biomass was observed for toothed cetaceans, large carnivorous reef fishes, and dolphinfish. Recycling was an important feature of this ecosystem with low phytoplankton-originated primary production. The mean transfer efficiency between trophic levels was 11.4%. The gross efficiency of the fisheries was very low (0.00002), probably due to the low exploitation rate of most of the resources in the 1970s. Basic local information was missing for many groups. When information gaps are filled, this model may serve more credibly for the exploration of fishing policies for this area within an ecosystem approach.
Highlights
Ecosystem models are representations of complex systems that attempt to depict their main components and the interrelations among these components
The present study aims to describe the marine ecosystem off northeastern Brazil, representing the East Brazil Large Marine Ecosystem (LME), and will allow for the comparison with other previously modelled regions
The mixed trophic impact (MTI) analysis allows for a better understanding of the impact of one group over the others
Summary
Ecosystem models are representations of complex systems that attempt to depict their main components and the interrelations among these components. Modelling requires the proper definition of the ecosystem to be studied This is a difficult task, in the marine realm, due to the absence of fixed boundaries. Longhurst (1998) proposed a hierarchical classification for the oceans, in which the most general levels are the biomes, subdivided into fifty-seven provinces One of these provinces is the Guianas Coastal Province. The northeast sub-region, the object of this study, is characterised by rocky substrates and low primary production due to the influence of the warm North Brazil and Brazil currents. This sub-region corresponds to the East Brazil Large Marine Ecosystem (LME) (Sherman et al, 2007). LMEs have been proposed as a conceptual framework for ocean management (Sherman, 1993) and their use should facilitate the comparison of the results obtained here with the ones obtained in other studies
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