Fish farmers claim red tides worst ‘unnatural disaster’ to hit industry in years

Hong Kong has seen 29 days with red tide sightings in the first three months of the year, more than any year in the same period over the last decade

On April 1, a thick brownish-white froth floating off Shek O beach caused a stir among residents and tourists. Smartphones at the ready, they flocked to the shoreline to capture the morbid spectacle, braving the putrid stench.

Scenes like these are common in Hong Kong come springtime. Algal blooms, also known as “red tides”, are a natural phenomenon, according to the Agriculture, Fisheries and Conservation Department (AFCD).

Peaking between March and June, the department has received more than 80 reports of red tide this year, six of which have been confirmed as actual cases.

Red tide season appears to have struck early, too. According to the Post’s review of data from the department’s red tide monitoring network, Hong Kong has seen 29 days with red tide sightings in the first three months of the year, more than any year in the same period over the last decade.

While formations of algal blooms are indeed completely natural, scientists believe their frequency and persistence are anything but.

“They are correct when they say they are formed naturally by natural organisms. But it’s their abundance and occurrence, which is extremely unnatural,” said ecologist Dr David Baker, an assistant professor at the University of Hong Kong Swire Institute of Marine Science.

“Red tides are associated with the Pacific Northwest of the US where you have upwelling conditions that provide the nutrients to cause red tides. In that case, it’s a very natural phenomenon.”

There were 55 reports of red tides last year, nine which the department was able to confirm. The year before that, 2014, went on record for the most confirmed reports – 23 out of 99 – in nearly a decade.

“There are few other places where you have red tides occurring so often throughout the year ... and in a very unusual environment where it is not the natural upwelling off the continental shelf that is providing the nutrients but really human waste.”

Algal blooms are areas of seawater discoloured by large concentrations of microscopic algae. Depending on the species, they can appear murky brown rather than red and are often associated with inorganic nutrient pollution from sewage and fertilisers.

Their key defining nature of a red tide is eutrophication, the excess of nutrients in the water and their composition, which is dominated by nitrogen and phosphorous. Like plants, they thrive on photosynthesis – the conversion of light energy into chemical energy. 

Red tides can be harmful to marine life. In December to February, more than 220 tonnes of fish died off across mariculture zones as a result of red tides formed by the toxic karenia papilionacea or karenia mikimotoi, a rare but harmful species. It was the first massive fish kill to hit in more than a decade.

Fish farmers claim this is the worst “unnatural disaster” to hit their livelihoods in years. More than 200 fishermen had to apply emergency relief fund, costing the government HK$2.57 million.

Even non-toxic “harmless” species such the omnipresent akashiwo sanguinea or the noctiluca scintillans – famous for its spectacular bioluminescent glow – can suffocate and kill fish due a process called hypoxia, which sees large concentrations of algae cells sink to the ocean floor when they die, consuming all oxygen as they decompose.

Source: South China Morning Post

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