Hundreds of thousands of tourists visits Green Island each year to enjoy scuba diving and snorkelling among its beautiful reefs, but no sewage treatment exists so an average of 1,500 tons of untreated sewage is flushed into the sea on a daily basis.

According to The China Post , no sewage treatment project has been prepared for the island since land can’t be procured for a sewage plant. Researchers now fear that the untreated sewage is to blame for the spread of the so called “Black Death” among the corals.

Chen Jhao-lun, a senior research fellow at the Academia Sinica who has studied the coral
reefs, describes the affected colonies as being covered slowly with a piece of black cloth.
“As this black sponge which multiplies itself covers the colonies, it shuts off sunlight to stop
photosynthesis by coral polyps,” Chen explains. The polyps die and no new corals are formed.

The “Black Death”, a type of necrosis, typically manifests in the form of black lesions that gradually spread across the surface of an infested colony.

However, very little is known about the Black Death and some researchers think that other factors, such as changing water temperatures or overfishing, might be to blame – not the untreated sewage. It is also possible that a combination of unfavourable factors have tipped the balance of the reef, causing the disease to go rampant. Temperature does appear to be a key variable associated with outbreaks, but it remains unknown if a temperature change alone is capable of causing this degree of devastation.

Molecular studies on lesions have not been able to identify a likely microbial pathogen, and according to Chen, the black layer might actually be an opportunistic second effect rather than the causative agent of the coral mortality. Montipora aequituberculae corals seem to be especially susceptible to the disease, but at least five other coral species from three different genera have been affected as well.

When Chen surveyed the water of Green Island last year, only four colonies off Dabaisha or Great White Sand showed signs of Black Death. In April this year, Chen found 24 affected colonies – six times as many as last year. If nothing is done to remedy the problem, Great White Sand near the southernmost tip of Green Island may have only dead colonies in five to six years, Chen predicts.

Green Island
Green Island is known as one of the world’s best spots for scuba diving and snorkelling. Located roughly 16 nautical miles southeast of Taitung on east Taiwan, Green Island used to house a concentration camp for political prisoners. Today, it is instead famous for its rich coral reefs.

(The picture is not from the green island but rather the great barrier reef)