The function of mangrove transition zones on the population structure and fishery of the mangrove crab Ucides cordatus on the Brazilian Amazon coast

Transitional areas provide many benefits and advantages for several species according to shifts in environmental conditions. Because mangrove crabs (U. cordatus) seem to benefit from the ecotone between mangrove (M) and estuarine várzea (V) forests on Marajó Island, eastern Amazon coast, we investigated whether crab population structure varies in response to shifts in vegetation and fishing pressures. Generalized linear models revealed that crabs are larger and heavier at Furo do Saco (FS), where estuarine várzea trees dominate the landscape, and have higher density and biomass at Praia do Goiabal (PG), where the landscape is dominated by mangrove trees. Multivariate models also indicated that the distance between villages and crabbing sites turns transition zones into difficult access for crabbers and shelters for larger and more commercially profitable resources. The combined analysis of both biotic (crab and vegetation) and fishery variables highlighted the role of transition zones as a key environment for demographic maintenance and species conservation, guaranteeing the natural stocks and other ecological advantages for the sustainable fishery of mangrove crabs for future generations.