Our directory of things of interest

University Directory

How can coral survive at the mouth of the Amazon?

Scientists were surprised to find coral in such murky water Scientists were surprised to find coral in such murky water Yager
29 Apr
The surprise discovery of a 600-mile long coral reef at the mouth of the Amazon river has shocked scientists. Studying such a ‘marginal reef’ could reveal secrets of marine life in low-light conditions

There is a reason why we normally associate corals with clear, shallow waters. They are one half of a symbiotic relationship with zooxanthellae, a microscopic algae, which produces oxygen and other products through photosynthesis. In other words, corals need light to survive and build reefs. So how has an extensive reef been thriving in some of the muddiest waters of the world – the plume of the Amazon river?

‘The plume is huge,’ says Patricia Yager, a Professor of Oceanography and Climate Change at the University of Georgia, who co-authored the paper on the reef discovery. ‘It covers many million square kilometres of the northern tropical Atlantic Ocean. Imagine that huge discharge forming a ten-metre thick layer, which spreads out across the sea.’ The plume is the dense haul of the Amazon river, which carries 1,200 million tons of sediment from the South American continent to the ocean every year. It billows from the mouth of the river, usually spreading northward and skimming ‘like oil on vinegar’ over the saltwater realm of the corals on the sea floor.

Because the reef stretches across the width of the river mouth, in and out of the plume, it offers a spectrum of light-to-dark living conditions

coral2A coral of many colours, dredged from the Amazon reef (Image: Moura)

‘The reef animals are not within the plume water, they are beneath it. However, the plume is dark “tea” coloured – from the organic matter and sediment picked up in the Amazon.’ In other words, light doesn’t penetrate it very well and anything living beneath will struggle to photosynthesise, ‘which is where it gets interesting,’ says Yager. ‘The plume does not shade the reef equally: in the north it is completely covered, while in the south it is covered for just a few months of the year.’

Because the reef stretches across the width of the river, it offers a spectrum of light-to-dark living conditions, she says. ‘The more southerly communities there included hermatypic corals (reef-building corals, that form symbiotically with algae) and rhodoliths (calcareous algae that also photosynthesise). As you move along the the shelf to the north, the community transitions to sponges and filter-feeding invertebrates, until there are no living corals. According to Yager, the northern, darkest communities are likely feeding on detritus floating down from the plume. ‘Though the entire reef is home to many other animals, especially baby fish that use the reef as a nursery ground.’

There is a sense of urgency in studying the species variation across this surprise find, as around 80 leases for oil exploration have been delineated and sold in and around the reef system. ‘Some are are already producing oil,’ says Yager, ‘many of the leases are right on top of where we think the reefs are located. I hope the publicity surrounding the paper will encourage the companies and government agencies involved to take another look at the environmental impact of all human activities around these newly appreciated ecosystems.’

Related items

Subscribe and Save!

geo line break v3

Free eBooks - Geographical Newsletter

Sign up for our weekly newsletter today and get a FREE eBook collection!

geo line break v3

University of Winchester

geo line break v3


Aberystwyth University University of Greenwich The University of Derby




Travel the Unknown

NEVER MISS A STORY - Follow Geographical on Social

Want to stay up to date with breaking Geographical stories? Join the thousands following us on Twitter, Facebook and Instagram and stay informed about the world.

More articles in NATURE...


A look at the contribution of hippos to the savannah…


The new app encourages young children to connect with the…


A type of panel has been invented that can generate…


In the 4th century BC, Aristotle proposed that earthquakes were…


The Chartered Institution of Water and Environmental Management pledges to achieve net…


Earthquakes from time immemorial have attracted the attention of the…


A planned kayaking expedition in Nepal took on a whole…


Scientists from Bristol University are working in conjunction with EDF…


In the 1930s, Charles Richter developed a simple scale for…


Researchers at Colombia University have answered a question that has…


How prepared can any government or city be against a…


Benjamin Hennig creates a series of cartograms to demonstrate the…


Could grey seals singing Twinkle Twinkle Little Star help develop…


Deep sea expert Dr Alex Rogers explains the importance of…


Analysis of coral cores, extracted from coral reefs in the…


Celebrities and animal welfare groups have been expressing their disappointment…


In a series of photographs from his recent trip to…