Removing harmful corals which invade coral reefs in Phu Quoc


Button Polyps, an invasive coral, are causing negative ecological impacts on coral reefs. They invade areas of hard corals, block them from being exposed to sunlight, and cause them to starve.
In the past few years, based on observations about coral reefs in Phu Quoc that OnBird has made, we have found a kind of invasive coral which is a true “coral killer”, now one of the greatest threats to coral reefs in Phu Quoc.
Button Polyps corals as well as other Zoanthid species readily proliferate, become overgrown and colonize other corals, forming large, tightly attached colonies that are difficult to thin out.
Removing harmful corals from a barrel sponge at a coral reef, Phu Quoc Island, Vietnam
Removing harmful corals from a barrel sponge at a coral reef, Phu Quoc Island, Vietnam
Button Polyp Corals are colonial animals with multiple individual polyps attached to a piece of live rock or coral rubble known as Moon Polyps, Encrusting Anemones, or Sea Mats.
Over time with proper conditions, Button Polyp Corals will grow out with more and more colonies being produced and over time can create a mat or carpet-like appearance. Recently, the Button Polyps Coral has dramatically increased in abundance and now dominates over hundreds even thousands of meters of coral reefs in Phu Quoc Island, which displaces hard corals and other typically-dominant biota in the process. This strong development is a coral-reef-killing culprit as the Button Polyps Coral blanketed many parts of coral reefs in Phu Quoc regardless of alive or dead corals, squeezing out all other sessile invertebrates. As they blank almost the surface of underwater objects: stony corals, dead corals, alive hard corals…thereby hard coral areas do not have a chance to grow because the symbiotic algae zooxanthellae hosted within coral tissues can not be exposed to the sunlight to produce necessary nutrient for corals to grow and develop their skeleton as well as build the reef.
The zooxanthellae cells can not carry out photosynthesis to produce sugars, lipids (fats) and oxygen… which corals use to grow and carry out cellular respiration then leads to the coral’s starvation and death.
Button Polyp Coral is blanketing a cabbage coral at a coral reef in Phu Quoc Island, Vietnam
Button Polyp Coral is blanketing a cabbage coral at a alive coral reef in Phu Quoc Island, Vietnam


Button Polyp Coral a kind of harmful coral is now invading and putting coral reefs in Phu Quoc under threat without bringing a chance to recovery as they will gradually invade and then blanket any area, even damaged coral areas, and dead coral areas which are actually supposed to be new placements for baby coral larvae to attach on to regrow. Button Polyp Corals grow rapidly and will crowd out their neighbours including any sessile life, corals. Once they take over the area of coral reefs, hard corals will be killed gradually and can not reproduce.
Many coral reefs are now in a very serious situation as they do have not much chance to regrow, and reproduce, for example, coral reefs at Dam Ngang Island, May Rut, Mong Tay, Hon Xuong are now seeing a fast-growing area of Button Polyp Corals, they cover every surface of objects underwater so healthy coral areas will gradually disappear forever.


To protect hard coral areas in Phu Quoc that are now under threat by the rise of Button Polyps Coral, the OnBird Phu Quoc team has been conducting activities to remove the invasive or harmful coral from the coral reefs in Phu Quoc Island. “OnBird underwater warriors” are equipped with proper gears (wetsuit, glove and knife) to remove these harmful corals from alive coral clusters and dead coral areas toward which new corals can attach and develop. This reef cleaning is a usual activity as we do it on almost every snorkelling excursion if the water conditions are favourable.

Please note: this coral is a species of Zoanthid coral (e.g. Palythoa species and Zoanthus species) that can contain a highly toxic, naturally occurring and potentially lethal substance known as Palytoxin which is poisonous to humans. The poisons exist in the coral as protection from predators in nature. Thereby, please don’t touch or remove them by yourself.

OnBird underwater warriors are equipped safely for these special tasks: removing ghost nets, removing harmful invasive corals, and removing harmful algae from coral reefs in Phu Quoc Island, Vietnam.