After a first leg in the Tuamotu Islands in early October, Tara continues her route in the Polynesian archipelago with a new component to the coral study, a mission called BioAtoll. Among the 6 new scientists aboard the schooner, Arjun Chennu brought a unique device: the HyperDiver.
In the heat of the mess room, sheltered from wind and ocean spray, Arjun Chennu leans over a strange box. This physicist and ecologist from the Max Planck Institute in Bremen (Germany) is taking part for a few days in the BioAtoll program led by Valeriano Parravicini. Aboard the schooner, this study focuses on the relationship that might exist between the health of a reef’s external slopes and the shape of the island itself. What would be the impact on the health of reefs surrounding the island if the lagoon disappeared? To learn more, Tara set course towards 7 islands with different geological profiles – with or without lagoon, open or semi-closed.
For 2 weeks, Arjun Chennu will provide the mission with the prototype he has been developing for 2 years. Through the watertight housing window appear the HyperDiver’s lenses and sensors – a true underwater scanner. Using a hyperspectral camera, the device will map reefs and provide valuable insights on the biodiversity of these areas: sponges, algae and corals will thus be quantified with high precision. Until now such analyses were conducted by divers. The HyperDiver is expected to deliver faster and more accurate results than those collected visually since the human error rate is estimated at 20% for coral and algae counting operations on the reef.
L’HyperDiver in action 10 meters beneath the surface © David Hannan / Tara Expeditions Foundation
Arjun first tested and fine-tuned the HyperDiver in Papua New Guinea. During his first dives in Polynesia, the scientist faced powerful currents around the islands that made analysis difficult. Ten meters below the surface, he must carry out 30 to 50-meter long transects in a straight line above the reefs, pushing his massive machine in front of him. Along a measuring tape unrolled on the sea floor, Arjun swims back and forth to scan the entire area and thus get a snapshot of the biodiversity present. This operation takes nearly an hour, at the mercy of the Pacific’s whims.
Back on board, the collected data are numerous: images, videos, measurements of depth, vertical drop and light. On the images appear details of the benthos – species inhabiting the ocean bottom – that will have to be counted. Using an algorithm, the HyperDiver is able to identify the species according to the light they reflect. Over the days and dives, this device will record a whole library of life that it can later analyze in a fully automatic way. Moreover, the data collected will enable us to map the reef in 3D and therefore study its shape and structure.
Porites, Turbinaria and Turf algae mapped by the HyperDiver
This new tool will help scientists save valuable time in the face of accelerating ecological disruptions endangering coral reefs. The CRIOBE in Moorea is looking forward in the near future to combining the HyperDiver with the Polynesia Mana project, a Polynesian reef monitoring mission conducted every 2 years. The next dives in Tuamotu waters will test the effectiveness of this scanner, still in the experimental stage, and determine if automation is the future of underwater surveillance.
Pierre de Parscau
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