2016 was an exciting year for oceanographers with the discovery of a new coral reef. Not just any reef though; this particular reef is destined to alter scientific knowledge, rewriting the textbooks of what we know about these incredible ecosystems.
Typically reefs are known to occur in clear, salt-water at depths that sunlight can reach, with the most studied and widely recognised being tropical shallow reefs such as the Great Barrier.
The newly discovered Amazon reef is over 600 miles long, stretching from French Guinea to Brazil’s Maranhao State, and covers 3,600 sq miles. Aside from its scale what makes this reef so important is it contradicts the conditions considered essential for coral reefs to establish.
The reef is located at the mouth of the Amazon where the murky freshwater of the river meets the saltwater of the Atlantic ocean. Freshwater is less dense than saltwater so sits on top in a separate layer and slowly mixes. These are known as plumes and were typically thought incapable of harbouring coral reefs, as the coming together of water would drastically affect pH, salinity, sedimentation and light penetration; all factors correlated with the lack of coral reefs in other river plumes around the world.
By Mario Roberto Duran Ortiz Mariordo (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons
The Amazon holds one fifth of the worlds’ freshwater and is the largest river by discharge of water, shifting an incredible amount of sediment and debris, resulting in some of the muddiest water on Earth. This makes the presence of this reef even more remarkable as, relative to other reefs, the discovery of one existing under the most opaque plume in the world will provide key insight into the adaptability of reefs.
The Amazon plume is a dynamic system and the paper published about the reef found that differences in conditions affected the biodiversity along the reef shelf. The south of the shelf was exposed to more sunlight allowing for the growth of photosynthesising organisms and hard corals, whereas northwards the plume is more established, giving rise to softer corals, sponges and filter feeders that can survive under low light feeding off of particulates delivered from the plume.
Prior to the its discovery it was assumed that any reef under these conditions would be impoverished of biodiversity, but after its discovery the Greenpeace ship Esperenza launched a submarine and found more than 60 species of sponges and 73 species of reef fish.
By Philip Terry Graham [CC0], via Wikimedia Commons
Of course, by some macabre serendipity, this area of ocean is earmarked for BP oil exploration. Coral reefs are the most fragile habitat on Earth, vulnerable to the slightest oceanic changes let alone when humans start disturbing the ocean floor in search of energy. What’s more troubling is the unknown nature of this reef; as it’s the first of its kind discovered, and exists in such a niche environment, it could be more susceptible to such disturbance. If that’s the case we might not have enough time to fully understand its scientific significance, so all must be done to protect it.