When storms disrupt life underwater

Spoorthy Raman explores the reasons behind the surfacing of noodle-like worms in Malpe and many such events.

Every year, about two or three severe tropical cyclones ravage parts of India’s 8,000-km-long coastline. As solid gusts of winds blast the shores, torrential rains cause devastating floods leaving behind a trail of destruction after the landfall. Lives are lost, structures damaged, and cities inundated.

When cool air blows over warmer oceans in the tropics, it heats up, picks up moisture and rises. Soon, cooler air from the surroundings swirls to fill the gap, gets heated and rises to form clouds. Over time, this system of clouds grows, and the wind spins faster and faster, with gusts over 100 km/hour. A tropical cyclone is born.

Between 1970 and 2019, 117 tropical cyclones pounded India’s coast and claimed over 40,000 lives. While a cyclone’s toll on land is conspicuous, its effects on underwater marine life, especially as the storm races towards land, are almost invisible. So, how do tropical cyclones affect marine ecosystems?

“Tropical cyclones can profoundly affect marine ecosystems,” says coral ecologist S Sureshkumar from the Kerala University of Fisheries and Ocean Studies, Ernakulam. “The most devastating aspects underwater are the strong winds and storm surges. These can cause physical damage to coral reefs, seagrass beds, and other habitats, disrupting the delicate balance of marine ecosystems.”

Winners and losers

The impact of a tropical cyclone depends on its ‘force’—or how hard it hits the coast and at what depth. Weaker cyclones only perturb life forms that live in shallow waters, like crabs or seagrass.

However, severe tropical cyclones can uproot kilometres of vegetation and sea life from the seafloor and along the coast. While massive-but-mobile life forms, like whales, sharks, and most fish, can move away from a cyclone’s path without being hurt, sedentary life forms, like corals or plants, bear the brunt. 

“Coral reefs, seagrass beds and mangroves are among the most affected ecosystems due to their proximity to the coast,” says Sureshkumar. “The strong currents and storm surges can physically break or dislodge corals, leading to extensive damage. The sediment and debris stirred up by the cyclone can also smother corals, further affecting their health and growth.”

A 2020 study, which Sureshkumar co-authored, revealed the damage that the 2017 tropical cyclone Ockhi caused to coral reefs in Lakshadweep’s Kavaratti island. Ockhi originated near Sri Lanka and moved northwards in the Arabian Sea, passing through the many coral atolls in Lakshadweep. Once the cyclone moved on, the corals in the region showed tissue damage, and the cyclone’s force uprooted many stable reefs from the ocean’s depths.

In June 2023, beachgoers in Karnataka’s Malpe were startled to find piles of noodle-like materials on the beach. Scientists identified it as shells of cellophane tube worms—a marine worm found on the seabed. Considering the mass die-off of the worms that happened on the heels of the tropical cyclone Biparjoy’s movement, experts speculate that the force of the cyclone may have played a role in it. “Such events can be attributed to the disruption of habitats and changes in ocean currents caused by cyclones,” says Sureshkumar.

The churning of the ocean and the addition of freshwater due to rain and floods also decrease the salinity of the water and reduce the volume of dissolved oxygen. When scientists studied the aftermath of the 2019 severe tropical cyclone Fani in the Bay of Bengal, they found a decrease in dissolved oxygen—a condition that could suffocate marine life.

Mangroves, which defend coastlines from storm surges and coastal flooding, also suffer from the wrath of tropical cyclones. “Mangroves and coral reefs have a more profound impact than sandy or rocky shores,” says marine biologist Deepak Apte from Srushti Conservation Foundation, Pune. A recent report from his organisation found that after the 2020 tropical cyclone Nisarga hit Maharashtra, it damaged mangroves and increased shrubby vegetation on the coast.

Domino effect

When cyclones ravage marine ecosystems, the impacts cascade into other ecosystems and human communities. For example, when corals die en masse, they leave many fish communities and crustaceans that depend on the corals for food, starving. Cleaning up mass die-offs on beaches, like the marine worms that washed up in Malpe, is often expensive. Artisanal and small-scale fishers who depend on fish found closer to the coast may also suffer without the necessary ecosystem to support fish.

“Coastal communities heavily depend on marine ecosystems for their livelihoods, including fishing, tourism, and coastal protection,” says Sureshkumar. “Cyclone-induced damage to these ecosystems can lead to reduced fish stocks, loss of tourism revenue, and increased vulnerability to coastal erosion and flooding, affecting the well-being of local populations.”

Precarious future

Marine or terrestrial ecosystems continuously change and evolve based on many drivers that alter their constituents’ physical and chemical composition. Cyclones are one such driver. “Earth has always seen violent events since its formation. Such extreme events help in creating new systems,” says Apte.

Tropical cyclones are predicted to be more frequent and intense as the planet warms. India’s east coast experienced more devastating cyclones than the west coast for decades. But, in the last two decades, the Arabian Sea has become a hotspot for severe tropical cyclones. “Increased frequency on the west coast is a warning sign,” says Apte, calling for a rethink on how we develop our coasts.

Proactive steps like creating marine protected areas, reducing pollution and other factors that create additional stress on the ecosystems, and implementing sustainable fishing practices can help bolster the recovery capacity of ecosystems and support coastal communities in adapting to cyclone impacts, he adds.