Riffling through the reefs: Can India's coral beds be saved?

One of the stated aims of the research was to study coral bleaching.

What is coral bleaching?

If you keep abreast of travel trends, a trip to Lakshadweep will surely be on the cards. The island offers magnificent underwater views of coral reefs. Over the past decade, they have been losing their myriad hues and turning white. This is coral bleaching.

When seawater temperature exceeds 29 degree Celsius for more than three to four weeks, corals start turning white. This is primarily because microscopic unicellular algae called zooxanthellae leave the coral polyps due to a rise in water temperatures, explained Dr Deepak Apte, marine ecologist and former director of the Bombay Natural History Society. “After the algae leaves, corals appear white. It is because of zooxanthellae that coral polyps get different colours. Under normal circumstances, without zooxanthellae, coral polyps are translucent without any colour,” he said.

“This loss leads to the bleaching effect and, if prolonged, can cause coral mortality,” said Apte, “however, coral bleaching doesn't immediately result in coral death.”

Over the last two decades, the Indian Ocean's sea surface temperatures have consistently been above 28°C, particularly during peak summer (April to June), leading to frequent coral bleaching events. For example, Lakshadweep experienced four bleaching events within 10-12 years, significantly more than it has in the past. “Fortunately, except for two incidents, these events didn't cause major coral mortality due to the brief duration of elevated sea surface temperatures, allowing corals to regain zooxanthellae,” said Apte.

How does C-Bot work?

According to Pramod Kumar Maurya, the project's principal scientist from CSIR-NIO, the AUV is a first of its kind in India, though similar systems exist globally. “C-Bot is designed to autonomously navigate predetermined paths, capturing images and recording environmental parameters affecting coral health, such as temperature,” Maurya said.

While underwater, communication with C-Bot is limited to acoustic modems, using sound waves instead of electromagnetic waves, which are ineffective underwater. This technology, though slower compared to terrestrial communication methods, effectively transmits data.

Once surfaced, C-Bot can quickly transmit its gathered data via radio frequency. “This technology significantly enhances coral monitoring efficiency compared to traditional methods involving divers and human intervention. C-Bot's ability to georeference each image and video add precision to coral health assessments,” added Maurya.

With a battery life allowing for 4-5 hours of operation and a depth capability of up to 200 metres, C-Bot is particularly adept at exploring regions where corals typically reside, around 10-60 metres deep. “This advancement in technology not only reduces human effort but also increases the scope and frequency of underwater expeditions, crucial for assessing coral health,” said Maurya.

Currently a prototype, C-Bot represents NIO's commitment to innovation, following its first AUV, ‘Maya’. “In 2006, India got its first autonomous underwater vehicle ‘Maya’ and transferred the tech to Larsen & Tubro but the device, being an axisymmetric UAV (like a torpedo), could not hover or stop in one place to collect information. The C-Bot is a much more evolved version with higher capacity of this AUV and offers advanced capabilities such as hovering and stopping to collect detailed information, making it a more evolved and capable research tool,” added Maurya.

Beyond coral research, C-Bot's potential applications include aiding the Navy in bathymetry studies and exploring hydrothermal vents (environments with extreme conditions where understanding active biology is crucial).

Experts welcome C-Bot’s capabilities

Traditionally, underwater divers were responsible for ground-truthing coral bleaching, a task often hindered by turbulent ocean conditions. “The introduction of C-Bot, as an autonomous machine capable of performing these tasks underwater, is seen as a substantial improvement. This innovation is expected to provide continuous data and monitor microclimatic changes, key factors in identifying the triggers and tipping points of coral bleaching,” said Dr Dhriti Banerjee, director of the Zoological Survey of India.

Apte echoed that C-Bot will allow near real-time monitoring of corals at various depths. “Currently, our knowledge of corals is restricted to scuba depth up to 50 metres. We need to examine coral reef connectivity of shallow and deep water reefs and their characteristics,” he said.

Dr EV Muley, former director general, Union environment ministry and former national coordinator for the United Nations Global Coral Reef Monitoring Network highlighted that globally such AUVs were being regularly used. “Underwater imagery through georeferencing has become a common technique by several countries in the face of climate change. We must scale such prototypes at the earliest,” he said.

Combating coral bleaching: Strategies for India

In India, corals are protected under Schedule 1 of the Wildlife Protection Act, 1972. The country hosts five primary reef structures: the Gulf of Mannar (Tamil Nadu),the Gulf of Kutch (Gujarat), the Andaman and Nicobar Islands, the Malvan coast in Sindhudurg (Maharashtra), and parts of Goa, along with Lakshadweep. With the Indian Ocean warming faster than the global average, as reported by the Intergovernmental Panel on Climate Change (IPCC), up to 90% of coral reefs could disappear by 2050, even if global warming is limited to a 1.5-degree Celsius increase. Along with this, local dangers include marine pollution, overmining of corals, bottom trawling, blast fishing, and coastal infrastructure development.

The key to addressing the escalating issue of coral bleaching is robust monitoring, enabling us to understand and respond effectively, said Dr Banerjee. “Maintaining the cleanliness of ocean waters is critical. This includes efforts to treat effluents, control oil spills, and reduce ocean acidification. Given the vast scale of coral bleaching, our mitigation strategies must be equally expansive,” she said.

Muley added that the climate stressors in the form of El Nino are aggravating the changes in sea surface temperature. “One thing is sure, nothing much can be done to contain the impact on corals due to climate change beyond monitoring. Shifting or translocation is not a solution, as it takes thousands of years for reefs to form. Only regular monitoring will help to understand and assess the trend,” he said.

An India Australia Training and Capacity Building Programme was launched from 2003 - 2006 with 170 scientific scuba divers. Those scuba divers are now present across reputed institutes, including NIO carrying out coral monitoring across the Indian Ocean region. “Such capacity building programmes are the need of the hour as technology develops, taking monitoring to the next level,” said Muley.

Are corals adapting to warming oceans?

Recent research indicates corals are adapting to increased temperatures, with Lakshadweep corals increasingly hosting the more resilient Clade D (a type of zooxanthellae). In Lakshadweep, most bleaching occurs in mid-May, just before the monsoon, which helps in recovery. Conversely, Gulf of Kutch corals show higher temperature tolerance with minimal mortality, likely due to their intertidal nature and the prevalence of Clade D, which offers more resilience. In contrast, Lakshadweep corals predominantly host Clade C algae, which is more susceptible to higher temperatures, said Apte.

However, this has a downside: Clade D corals grow slower than Clade C. “This suggests that, over centuries, slower-growing corals might dominate as reefs adapt to elevated temperatures. Still, frequent high temperatures challenge recovery potential, emphasising the need for long-term reef monitoring,” added Apte. “Having worked in Lakshadweep for over three decades, I've observed that corals are faring well despite predictions. However, factors beyond temperature, like eutrophication from nutrient loads in Lakshadweep lagoon and reef fish harvesting, also impact coral health. Therefore, a comprehensive understanding of combined stresses — nutrient load, fish harvesting, sea surface temperatures, and human activities — is crucial for coral conservation.”

"As biological organisms, reefs might adapt to warmer temperatures, a hypothesis that warrants further study to understand potential adaptive mechanisms. They might adapt to warmer temperatures at some point given their continuous exposure to thermal stressors,” said Banerjee.

As we confront global-scale coral bleaching and dire predictions of total reef loss, the remarkable recovery of the Great Barrier Reef post-2020's bleaching event, one wonders: What might contribute to coral resilience that we have yet to understand?