By Santhosh Pavagada
On a sunny April morning, the Alliance Air flight lifted off from Kochi, bound for the Lakshadweep Islands. My mind buzzed with thoughts, my excitement barely contained as I stayed glued to the window, not wanting to miss a thing. The sea below shimmered, broken only by the occasional vessel. We passed an island, and soon the descent began.
The stretch between that first glimpse of land and our touchdown at Agatti was breathtaking – the ocean unfolding in brilliant shades of blue, each one blending effortlessly into the next. As we approached the runway, the water turned a vivid turquoise, revealing everything beneath its surface, a living canvas dotted with dark coral patches and the slow, graceful movement of turtles.
Lakshadweep, a remote archipelago of 36 islands, including 12 atolls, was the chosen site for our experiments. Just a metre or two above sea level, these islands share a deep, timeless bond with the sea, their people, and the region’s rich biodiversity. The Habitats Trust, in collaboration with REEF, is working on a long-term conservation strategy here. My visit was part of one such ambitious effort: an innovative project to explore and monitor the region’s mesophotic reefs.
It was my first time on these islands, and with minimal marine exposure, every moment felt new, and every scene utterly captivating. The evocative turquoise blue I had admired from the air was now right beside me, edged by dazzling white sand. From this vantage point on the beach, the distant waves formed a soft semi-circle, and the sea shifted dramatically from turquoise to deep cobalt beyond the reef. It wasn’t long before Abhishek Jamalabad’s explanation of atolls – he leads the Marine Programme at The Habitats Trust – came flooding back to me.
Mesophotic reefs support significant fish diversity and biomass but are understudied. The Habitats Trust is working to develop effective methods to understand these vital, hard-to-reach zones. Photo: Digant Desai/Sanctuary Photolibrary.
How is the ocean floor observed, and how easy or difficult is it to document life here? A couple of hours in, after a few interactions with our partner team members, I was given a briefing and handed a snorkelling kit. The moment I began making sorties face-down, the surprises began unfolding all along the way. But, to explore deeper sites, and get closer to the seabed, one needs to dive. While snorkelling and diving are popular recreational activities for tourists, researchers use the very same techniques to survey marine ecosystems, understand and assess biodiversity and study interactions… all to derive meaningful conservation strategies.
Coral reefs are among the most biodiverse ecosystems on Earth. The services they provide and the roles they play are critical, both ecologically and socio-economically. That said, our understanding of coral reefs and other ecological components in the Lakshadweep archipelago remains limited, both in terms of extent and scale.
Traditionally, monitoring coral reefs or assessing their status and health has involved divers equipped with cameras and samplers, a practice still widely followed, not just for corals but for fish data as well. While this method allows for detailed information collection, it has significant limitations in terms of scale and efficiency. Human divers are physiologically limited, which constrains how deep and how long one can stay underwater. The deeper you go, the less time you have, which directly impacts the amount of data that can be collected. Typically, dive surveys are conducted up to depths of 25 to 30 m. and at these depths, one can stay underwater for 10 to 15 minutes. Most of our understanding of coral reefs therefore tends to come from within this range and with the stated limitations.
However, there is a vast, largely unexplored region beyond these diveable depths. These deeper regions are known as mesophotic zones in the context of coral reefs. They are dimly lit areas that extend roughly from 30 to 150 m., and are characterised by the presence of various sunlight-dependent corals that thrive in low-light conditions.
Technology is a vital ally to overcome human limitations and deepen our understanding of lesser-known zones. Subsea technologies, particularly robots capable of operating underwater, are proving to be invaluable tools. They are revolutionising marine studies across the globe by offering unprecedented access to the underwater world. Broadly, the suite of subsea vehicles and robots used for research includes submarines, subsea capsules, autonomous underwater vehicles (AUVs), autonomous underwater gliders (AUGs), and remotely operated vehicles (ROVs). Each of these tools offers different capabilities and outcomes, while also demanding varying levels of resources and logistics.
In our pursuit to study the deeper regions of the sea, at THT, we have chosen ROVs as our preferred tool. They are relatively easy to deploy and can be manoeuvred from shallow waters to deeper sites. This first visit to Lakshadweep was aimed at testing the feasibility of using an ROV to explore and monitor coral reefs, particularly within the mesophotic zone.
The one we chose for our initial trial was IROV Tuna, an indigenously developed industrial ROV. Having been exposed to terrestrial surveys using cameras and drones for years, I was surprised by the sheer volume of equipment that arrived at the field station. The number of components to be assembled, along with the range of accessories it required, was overwhelming. The ROV was tethered, which meant it could live-stream data in real time, and therefore required displays and laptops to watch the feed.
To study deeper sea regions, The Habitats Trust team used remotely operated vehicles (ROVs), which are relatively easy to deploy and navigate from shallow to deep waters. Over two years, they’ve collected data across several Lakshadweep islands and are now refining methods and extracting insights. Photo: Santhosh Pavagada.
With arrangements in place, the entire team boarded the survey boat to begin the trials. Onboard, the cabin was converted into a mini control station, while much of the deck space was taken up by the ROV and its equipment. The otherwise ordinary tuna fishing boat had now become a sophisticated marine research vessel. The ROV was equipped with two cameras, one up front and another below, together with a side-scan sonar, imaging sonar, a depth and temperature sensor, and an underwater positioning system. The side-scan sonar helps interpret ocean terrain, and the imaging sonar assists in detecting objects ahead. This fully loaded ROV was operated using a joystick – yes, the kind we once used to play video games. Piloting it required careful monitoring of incoming data from all sensors and delicate maneuvering of the vehicle accordingly.
Using this setup, trials were conducted at five different locations around Agatti Island during the first visit. The chosen sites included terraced regions, gentle slopes, and drop-offs.
For each trial we had to contend with sea conditions such as surface currents, underwater currents, wind, turbidity, and tether drag, plus the constant motion of the vessel. Nothing stays still, and unlike on land, there are no fixed physical references on the ocean surface. A welcome relief from these challenges was the live video feed from the ROV, which offered intriguing sub-surface views. On the fourth day of the trials, the ROV reached a depth of 100 m. at a site featuring a gentle slope that offered fascinating views. We observed hard corals and a variety of fish in the shallower sections, but their presence thinned out beyond 45-50 m. Everything we saw during these trials marked a first-ever observation for this island at such depths!
Following these successful deployments, the team delved into the collected data to extract ecological insights and assess the technical capabilities of the equipment. It soon became evident that a higher-capability ROV would be needed to capture more stable footage while negotiating underwater currents. Additionally, newer payloads were considered, including 4K cameras instead of HD, a laser scaler for size reference, a longer tether, and better alignment of the bottom camera. With these adjustments, surveys have been conducted at different sites over the past two years. We have collected around 15 to 20 hours of mesophotic zone (up to 190 m.) visuals along with environmental data from Agatti, Andrott, and Kalpeni islands in Lakshadweep, as well as from a submerged bank located north of the archipelago. During our recent surveys, we attempted systematic data collection following standard survey techniques. We are currently extracting insights from the collected data and working to standardise this method for further exploration and monitoring of the fascinating mesophotic zone.
Coral reefs, and the incredible diversity of fish and other marine life they support, are vital ecosystems with global and regional significance. Hosting roughly 25 per cent of all marine species, they play a crucial role in sustaining fisheries-based livelihoods, trade and food security. Reefs also protect coastlines and islands from erosion and storm surges, while offering spectacular tourism opportunities. However, coral reefs have come under growing threat in recent decades. While anthropogenic pressures such as infrastructure development and over-extraction remain serious concerns, climate change is causing increasingly severe and widespread impact. Vast stretches of dead or bleached corals, visible during snorkelling around these islands, are a stark reminder.
Although corals in shallow waters are relatively easier to observe and monitor, much less is known about their presence and condition in deeper regions. Emerging research suggests that mesophotic reefs may be extensions of shallower reefs, with some overlap in community composition. These deeper reefs have been shown to support significant fish diversity and biomass, and may even host substantial reef-building coral populations. They could play a critical role in the recovery of upper reef zones post bleaching events or other disturbances. Yet, mesophotic reefs remain comparatively understudied. Current efforts are focused on developing effective methodologies to expand our understanding of these vital but hard-to-reach zones.
Santhosh Pavagada is the Tech4conservation lead at The Habitats Trust. He holds an engineering degree and a Masters in Applied Ecology and Conservation.
