Chemosynthetic Ecosystems on the Brazilian Deep-Sea Margin

Abstract

Chemosynthetic ecosystems are fueled by reduced compounds (CH4 and/or H2S), which are important for the chemosynthetic production by microbiota. They comprise hydrothermal vents, cold seeps, and large organic “islands” or patches, such as whale skeletons and wood falls. Despite common along a large range of geological settings around the world, chemosynthetic ecosystems have only been recently found in the Southwestern Atlantic Ocean. This knowledge gap hinders the understanding of the distribution, biogeography, and evolution of chemosynthetic-related fauna. Only one active seep is known in the SW Atlantic at the Rio Grande Cone where anaerobic methanotrophic archaea sustain typical chemosynthetic fauna hosting symbiotic chemoautotrophic bacteria, such as vestimentiferan annelids and solemyid bivalves. However, abundant geological and biological evidence point out that seeps could be frequent along the Brazilian margin. The degradation of the massive organic matter input from a whale carcass and/or large amount of wood increases the concentration of reduced compounds, such as sulfide, which allows chemosynthetic production. As a result, the community established in whale falls or sunken wood resembles those of vents and seeps with part of the fauna relying on the chemosynthetic production. These communities can be common around the world mainly along migratory routes of whales. The Amazon and La Plata rivers are likely to contribute with an abundant quantity of dead wood remains in the SW Atlantic. Despite that, the potential amount of wood was probably negatively affected by the heavy deforestation of the Atlantic rain forest in the last century, reducing the habitat available to wood specialists. The intense exploitation of oil and gas industry along the Brazilian margin as well as the deforestation of Brazilian forests and the pressure on the whale populations could impact indirectly the chemosynthetic communities of this region. Therefore, studies on the chemosynthetic communities of the SW Atlantic as well as the connectivity with other ocean basins are important for conservation efforts in the deep areas off Brazil.