Surveying the least human influenced marine environment on Earth

Image: Endemic Chagos Anemonefish - Notice they have no black stripe framing the white bands.


We have just finished our 3rd day of surveying the Chagos Archipelago on board the British Indian Ocean Territory (BIOT) research vessel. So far the expedition has made its way from Diego Garcia, along the Great Chagos Bank before cruising through the Peros Banhos atoll. Charles Darwin utilized the first charts of these islands when he hypothesized his classic and original theory of atoll formation. It is a real privilege to be onboard the vessel conducting these important large-scale surveys of the archipelago’s pristine coral reefs, which have been spectacular in the first three days of our expedition.



A Pristine Baseline to Study

According to scientific literature Chagos has one of the lowest human influenced marine environments of anywhere in the world. This makes the area extremely interesting to science. With nearly zero human impacts such as coastal development, overfishing and marine pollution, scientists can make comparisons between pristine Chagos and sites that are under direct pressure from the modern day influences of humans. Also we can attempt to measure the impact that global drivers such as ocean acidification, ocean warming and increased storm frequency have on pristine coral reef ecosystems which are devoid of human influences.



Sharks, Anemonefish and a Manta Ray

On dives so far we have encountered a variety of sharks including, grey reef sharks (Carcharhinus amblyrhynchos), tawny nurse sharks (Nebrius ferrugineus), and even small silvertips sharks (Carcharhinus albimarginatus) investigating our activities. The sharks come cruising up from the depths (below 30m) where it usually dwells to investigate the retrieval of the SVII camera.


Another significant observation was the Chagos anemonefish (Amphiprion chagosensis). This relative of Nemo is distinguished by its lack of black bands and uniform coloured fins and is only found within the Chagos Archipelago.


At the end of a dive on the outer reef of the Great Chagos Bank, Dr. Ben Neal and I were greeted by a reef Manta Ray (Manta alfredi), catching the underside of its belly perfectly in the SVII, the unique pigmentation is like a finger print for Manta Rays and could be used to one day identify the individual.



A healthy reef (that is still in recovery)

Aside from the amazing fish life we have been encountered a very healthy reef largely made up of huge Acropora table corals (mainly Acropora  cytherea) fighting for space on the reefs amongst mounds of massive Porties ssp colonies. Chagos was severely hit by the 1998 mass bleaching event caused by the 1997 El Nino Southern Oscillation (ENSO), where there was thought to be a 90% loss in coral cover (Sheppard et al. 2008). A study 8 years later provided evidence that coral reefs were on a steady road to recovery, more than reefs affected by pollution, overfishing and habitat degradation. It has been wonderful to witness these reefs bouncing back from such an event, however there is always a risk such an event could happen again in the near future. This makes the protection of the area vital, as it is one of the only natural measures for coral reef recovery left in the world.


Sheppard, C. R. C., A. Harris, and A. L. S. Sheppard. 2008. Archipelago-wide coral recovery patterns since 1998 in the Chagos Archipelago, central Indian Ocean. Marine Ecology Progress Series 362:109-117.