Seabed pockmarks associated with deepwater corals off SE Brasilian continental slope, Santos Basin

Abstract

Several factors bear evidence of chemosynthetic ecosystem occurrence in the Brazilian coast; these motivated our investigation to sample three pockmarks located on the continentalslopeoffSE Brazil (26°S and 46°W) at ∼700 m depth. The crater-like features were ∼1 km in diameter and 100 m in depth, and were identified with an echo-sounder (EK-500). They were sampled along two transects using a rectangular dredge. Our main objective was to identify possible evidence of a seep-related community. The surrounding sediments of the pockmarks seem to be filled with coral rubble harboring a rich fauna of metazoans including epilithic and chasmolithic organisms. A total of 9565 organisms were sampled. The most abundant group was the Ophiuroidea, followed by Cirripedia and Polychaeta. A number of new occurrences and new species were registered. The polychaete worm Amelinna was the first record for the Atlantic Ocean, which has been found in reducing habitats such as wood islands. The echo-sounder records also showed the presence of big deepwatercoral mounds associated with the edge of the pockmarks. These features are ∼ 20 m in height and from 180 to 360 m wide. Records of demersal fishes were also registered right above coral mounds. The presence of deepwatercoral mounds at the edge of pockmarks may be related to the flow of the cold, oxygen-rich Antarctic Intermediate Water over the bottom, or else may benefit from the fertilization of the water by the microseepage of hydrocarbons from the sediment. We suggest a more thorough survey in order to map and recognize these environments. Furthermore, our findings may shed some light on new research perspectives concerning the ecology, biogeography and evolution of reducing habitats off the Brazilian coast.