Mesophotic reefs at the Amazon River mouth: an inconvenient truth

Did you know that there’s a reef near the mouth of the Amazon River?

Reefs off the Amazon River mouth at ~180 m depth, close to the Brazil-French Guiana border. They’re, thriving from abundant nutrients but with less light and more suspended sediment.

Our group has recently been involved in the study of the mesophotic reefs that are at the outer shelf where the Amazon River discharges into the Atlantic Ocean. Mesophotic means that the reef is composed of organisms that use photosynthesis to grow and organisms that don’t need light to grow.

Although evidence of a reef system in the region has been presented since the ‘70s, a simplistic view remained that the Amazon River plume prevented reef development. The existence of this reef system is now incontestable, due to results from scientific cruises performed in cooperation with the Brazilian Navy in 2014 and 2017, as well as with Greenpeace, in 2017 and 2018.

The  area is also facing potential threat from new oil & gas exploration, resulting in conflicting interests between environmental conservation and exploration of natural resources. Although oil companies themselves recognize the reef existence and its relevance, there have been unscrupulous people trying to convince the authorities and general public that the reef does not even exist (aka fake news).

Our mission is to better understand this reef system and how it survives so close to the Amazon River plume. The plume carries much suspended sediment, which decreases the light reaching the sea bed. We are working to understand the dynamics of suspended sediments of the Amazon River and the sedimentary and oceanographic mechanisms that enable this reef system to exist.