National Geographic Society Newsroom

Invasion of the Death Stars: Surveying COTS and Coral Health With the Trident ROV

The water is 30 degrees C. The sea is clear and calm and beneath the vessel a garden of colorful coral awaits. Why not go diving?  We are on a reef at Kalapuan Island in the Semporna group of Malaysian Borneo, not our usual dive destination. This island is home to the dive masters, the...

The water is 30 degrees C. The sea is clear and calm and beneath the vessel a garden of colorful coral awaits. Why not go diving?  We are on a reef at Kalapuan Island in the Semporna group of Malaysian Borneo, not our usual dive destination. This island is home to the dive masters, the captains and cooks at the Tropical Reef and Conservation Centre (TRACC) lab on Pom Pom Island. We have been working here for five summers, helping to restore fish bombed corals, reintroducing fish including sharks, and generate a new protected reef for divers to enjoy in a region that has been highly disturbed by human impact. Instead of diving, this time I am staying topside and using the Trident ROV as part of our National Geographic Open Explorer project to survey benthic habitat, and in this case: disease and invasive Crown of Thorn Starfish (COTS).

COTS Removal
Volunteer Diver removing invasive Crown of Thorn from Reef Photo Credit David McGuire

Kalapuan is a largely undeveloped low island, with an old coconut farm, a new high-end resort directed at Chinese tourists, and nearly 800 local people known as the Bajau. These people are the last of the Sea Gypsies. Some live in water houses, others still on the boats they were born on. The village is growing, and the people rely on fish, and most work at fishing to survive. Like much of this region of the world, the population is stretching beyond the limits of sustainable use of the ocean.

Overfishing the reef, and nutrient loads from the village are impacting the adjacent reef system, yet sections of corals still remain in a healthy state. Recently, an outbreak of the predatory starfish the Crown of Thorns (Ancantaster placii) have proliferated at the island Pulau Gaya in the Tun Sakaran Marine Protected Park just 6 Km east of the TRACC home on Pom Pom, and about the same distance north of Kalapuan. Last year a COTS increase was observed on the reef at the Park, an area of high human habitation and impact. Some of the most effective predators on the starfish include titan triggerfish (Balistoides viridescens), and the Maori wrasse (Cheilinus undulates) and Triton snails (Charonia tritonis). These species have been largely overfished, removing predatory regulation on the sea star, and exacerbating other environmental factors impacting the corals.

COTS Removal
Inverted Acroporid Coral consumed by Crown of Thorns Starfish Photo Credit David McGuire

COTS outbreaks have been a problem on coral reefs elsewhere in the world including the Indo-Pacific and the Great Barrier Reef. Earlier this year an outbreak at Swains Reef on the GBR is a repeat of a destructive event in the 1980s. That large-scale epidemic occurred on the Great Barrier reef destroyed thousands of hectares of reefs. These voracious predators can consume live coral at a rate of 5-13 m2 per year day. The starfish prefer branching and table Acprorid corals, the same corals vulnerable to coral bleaching events. In their dives last January the TRACC team observed an increase in COTs on the Kalapuan Reef and began a systematic removal. Last month over 700 COTS were collected off this reef over several dives. So far the outbreak has not reached the house reef where the team has been restoring the fish bombed coral reef since 2013.

We flew the Trident alongside the diver as a test to evaluate the efficacy as a survey tool for COTS. We surveyed 6 transect lines with 5- 1 meter quadrats looking at coral coverage and health and Cots density. In comparison, we flew the Trident alongside six divers screening the reef and removing COTS before the population can proliferate beyond control. In the surveys, we detected one crown of thorn starfish on the live monitor, and after reviewing the footage, we detected one additional.

Buddy and COTS
Removal of COTS is one tool to Defend reef health, Photo Credit David McGuire

The divers collected 27 COTs in their reef survey and cull. While the Trident could enter shallow areas and travel more ground than a diver and spend more time in the water, we could not detect the starfish taking refuge under coral heads. However, the Trident was effective in shallow waters and useful in evaluating coral coverage and disease, bleaching or consumption.

Next- Sea turtles and nocturnal sharks.


Learn more about the Trident surveys adn MPAs and how you can support saving Sabah sharks at

About National Geographic Society

The National Geographic Society is a global nonprofit organization that uses the power of science, exploration, education and storytelling to illuminate and protect the wonder of our world. Since 1888, National Geographic has pushed the boundaries of exploration, investing in bold people and transformative ideas, providing more than 14,000 grants for work across all seven continents, reaching 3 million students each year through education offerings, and engaging audiences around the globe through signature experiences, stories and content. To learn more, visit or follow us on Instagram, Twitter and Facebook.

Meet the Author

David McGuire
A marine biologist and adventurer, David McGuire writes, photographs and explores the natural world, documenting wildlife. As the director of the non profit Shark Stewards as part of the Earth Island Institute, he works to protect threatened sharks and critical marine ecosystems though the non profit Shark Stewards.