Reefs rarely found in such muddy waters
Researchers made a surprising discovery in the murky waters of the Amazon River: a huge reef measuring about 9,500 square kilometres, stretching from French Guiana to the northeastern Brazilian state of Maranhão.
The extensive reef was located at the plume at the mouth of the Amazon River, specifically the muddy mixture where the fresh water of the Amazon mixes with the salty seawater of the Atlantic Ocean. Previously, it was assumed that no reefs could develop at such locations as the waters were less salty and acidic than the seawater.
Nevertheless, during a 2012 oceanographic study of the region, the researchers managed to dredge up various reef organisms during their investigation. They returned two years later to further their exploration and documentation of the site. It was only in April 2016 that they made their findings public in the journal Science Advances.
The reef is about 80 kilometres off the coast at a depth of up to 120 meters. It is one of the largest reef systems in the world with a total length of 970 km and an area of about 9,500 square kilometres. Scientists found 61 sponge species, 73 species of fish, spiny lobsters and brittle stars there.
Due to the low-light conditions, there are few corals there. Instead, the reef consists mainly of sponges and rhodolith, a red algae that resembles coral. The rhodolith can survive in low-light conditions as it does not photosynthesise, but instead gets its energy from the oxidation of minerals, through a process called chemosynthesis.