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Red tide found in Clear Water Bay. Photo: SCMP Pictures

Hong Kong fish farmers claim proliferation of red tides is 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.
Glow-in-the-dark blue waves caused by the phenomenon known as harmful algal bloom or

“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.
Dead fish washed up on the banks along the Shing Mun River in Sha Tin. Photo: SCMP Pictures

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.

Gruesome images in the media of large schools of dead fish floating belly up at sea are often victims of this oxygen depletion.

Alas, both the scientific community and government are still struggling to find the exact causes which cause red tides. Like plants, red tides thrive under precise conditions that include the right amount of sunlight, temperature and nutrients.
Dead fish washed up on the banks along the Shing Mun River in Sha Tin. Photo: SCMP Pictures

The finger is often pointed to nutrient discharge in the form of agricultural run-off and waste water from the Pearl River. But the none of this explains the heavy concentration of blooms in and around Tolo Harbour, which alone accounts for more than one-third of algal bloom occurrences.

Fishermen have suspected illegal waste discharges from the Shing Mun River. But environment and fisheries officials have allayed these concerns.

Red tide expert Professor Ho Kin-chung, Open University’s dean of science and technology, attributes the recent spate of red tides to the El Nino phenomenon, which caused water temperatures to be warmer and more saline than usual.

“The El Nino has affected the temperature and timing of water [currents],” he said. “It means warm, saline water was concentrated here for a longer period time before being pushed out west.”

An El Nino occurs when the warm water accumulated in the western Pacific shifts east with the weakening or reversal of westerly winds, causing the eastern Pacific to warm up.

Ho said such conditions – brinier water and warmer waters – were very favourable for rare species of red tide such as the karenia mikimotoi.

Baker said the main driver of red tides was obvious – local sewage, the biggest source of nutrient inputs to Hong Kong waters.

“Very few wastewater treatment plants that are operating at very high levels of nutrient removal. Areas where most Hong Kong people live still use primary or preliminary waste water treatment, or simply removing solid material from the wastewater,” he said.

Baker said the city’s upgraded Harbour Area Treatment Scheme, which connects most of Hong Kong to a central treatment works on Stonecutters Island, was encouraging as it treated waste and removed solids and microbes chemically and in very rapid fashion.
Red tide observed near the waterfront of TST at Victoria Harbour in 2007. It hit the southern waters of Hong Kong and spread to Cheung Chau and Tung Lung Island. Photo: SCMP Pictures

“Nutrient removal is still not 100 per cent and quite low,” he said.

Baker said another possible contributor to nutrient pollution in Tolo Harbour was “atmospheric deposition” or, simply, rain. Last year, Baker’s research team at HKU collected rainwater and measured 25 micromolars of nitrate, which he said was “extremely” high amount and almost on par with what was coming out of a Hong Kong river.

“Twenty five micromoles coming from the sky is pretty scary. This is something like 250 times greater than what you would have in a coral reef in the south Pacific, which is a low nutrient environment.”

Even the industry most affected by red tides could be a possible culprit. Twenty years ago, nutrient loading from local fish farming to the marine environment was significant enough for the AFCD to begin working with the trade to improve husbandry practices, including promoting use of pellet feed instead of trash fish, to reduce the impact of fish farming activities.

Hydrologists such as Professor Jimmy Jiao, of the University of Hong Kong’s school of earth sciences, point to a lesser known driver – groundwater pollution, especially around the Tolo Harbour area.

Jiao, who has studied the matter for over a decade, believes there is clear correlation between polluted groundwater discharge and the formation of red tides in Tolo Harbour.

He pointed to the failure of the government to reduce the frequency of red tides in the area even after a major clean up scheme in the 1980s, which reduced the level of dissolved oxygen and total nitrogen.

“The Tolo Harbour Action Plan carried out in the 1980s reduced river and sewage nutrients by some 82 per cent, theoretically red tides should have decreased by this amount too, but they didn’t,” he said. “They haven’t regulated all possible sources.”

While no government statistics are available on groundwater volumes, Jiao calculated that some 32.5 million cubic metres of groundwater are released into the harbour every year, which is similar in volume to the input from rivers.

In 2005, Jiao’s chemical analysis of the groundwater samples from Sha Tin and Ma On Shan revealed nitrite, nitrate and phosphate concentrations exponentially higher than from river water samples measured by the Environmental Protection Department (EPD).

His latest research has been able to link clusters of red tide occurrences sites in Tolo Harbour and areas with high groundwater discharge. Groundwater is detected by high levels of radium – a naturally- occurring  radioactive substance emitted by igneous rock.

“Based on our preliminary research, we’ve determined that riverine nutrients are not the main contributor to red tides in Tolo Harbour,” Jiao told the Post. “There is a stronger correlation between high groundwater discharges and red tide occurrences.”

Jiao says polluted groundwater, which is metres below ground, can seep into the seas through diffusion, dispersion along freshwater - saltwater interfaces or swept into the sea by tides. Underwater springs formed by “cracks” in geological faults were also potential discharge outlets.

The fractures could be a conduit for groundwater polluted by surface run-off from large areas such as villages, landfills, infrastructure or storm water.

However, Jiao said there was no way to trace where the groundwater pollution is coming from and it was strange for a civilised society like Hong Kong not to have a single information source or monitoring point for groundwater.

“If we don’t start to control this nutrient pollution, it will get worse and more frequent. This is something that is affecting the entire ecosystem,” he said.

A survey published by China’s Ministry of Water Resources earlier this month found that about 80 per cent of groundwater in the mainland’s major river basins was unsafe for human contact.

Baker and Ho echoed Jiao’s concerns. “We can’t control light or temperature easily but we can control the nutrient levels,” said Baker. “If we turn off all the nutrient inputs to the coastal environment, I can say with some certainty that red tides will decrease or completely disappear altogether.”

Both the EPD and AFCD said red tides occur naturally in both “polluted and unpolluted waters” initiated by a combination of natural factors including light intensity, salinity, nutrients, trace elements, water current and motility of algal cells.

The Environmental Protection Department argued that its existing water quality monitoring programme was able to reflect the overall quality of groundwater infiltration and their organic and nutrient loadings.

“Indeed, while some research has suggested submarine groundwater discharge could be a significant source of nutrients to coastal waters for algal growth, [there is a] need for a fuller picture on the nutrient budget in the Tolo Harbour,” a spokesman said.

Tolo Harbour’s “semi- enclosed” nature, poor tidal dispersion and relatively long retention time prevent the effective flushing of nutrients from the harbour, the spokesman added.

The department said the number of red tide incidents in Tolo Harbour had actually decreased from a high of 43 incidents in 1988 to generally below 10 incidents per year in the last decade.

While research interests differ, however, the scientific community is unanimous on one thing. Red tides are indicative of a bigger ecological problem, which warrants greater attention and concern.

“We are turning our ocean into a primordial soup, a microbial soup, ” said Baker. “It’s going to be like what the oceans were like after the emergence of life, a very different ocean, one that totally lacks many of the functions we value as a species.”

Baker points to the degradation and removal of important ecological buffers such as mangroves, wetlands and coral reefs, which have traditionally been served a role natural nutrient removal systems.

“A mangrove forest or a seagrass bed is far more efficient at removing nutrients and maintaining water quality and diversity, boosting fisheries and attracting tourism,” he said. “We need to start thinking more about ecosystems and their biodiversity with respect to the functions and services that they provide to mankind.”


Tidal turmoil

The last time Lee Muk-kan saw anything alive at his Yim Tin Tsai fish farm was before the Lunar New Year. Just two Sabah giant groupers were left swimming in his sea cages.

By then, he had already lost four tonnes of produce – about 7,000 fish – to killer red tides in one of the worst algal bloom outbreaks since 1998.

Fish farmers from at least eight mariculture sites are demanding a full report from the Environmental Protection Department identifying the cause of the red tides that wiped out more than 220 tonnes of produce this winter from Tolo Harbour to Long Harbour in Sai Kung.

“Until we get a satisfactory explanation from the government as to what is causing these red tides, fish farmers do not dare to release a single fish fry into their farms,” he said.

Caused by the rare but toxic and harmful species karenia papilionacea or karenia mikimotoi , it is thought to be the only case of red tide involving fish deaths in the past decade. With no more earnings from raising fish, Lee, like many of his fellow practitioners, have left their farms and resorted to their original roots – going out to sea to catch fish with seine nets.

“For now, we’re still able to eke out a living but we want to know what the problem is,” he said.

The industry believes the red tides are caused by pollution being discharged into Shing Mun River, speculation that the government has dismissed as inconclusive.

The Agriculture, Fisheries and Conservation Department has already doled out HK$2.57 million to some 209 successful applicants through an emergency relief fund, amounting to roughly HK$3,000 to HK$11,000 per farm, depending on the farm’s size and the damage caused.

But farmers like Lee say what they want is not aid but proper compensation.

“Poultry farmers are compensated about HK$30 per culled chicken during an avian flu outbreak,” he said. “Why aren’t we eligible for a single cent?”

Lawmaker Steven Ho Chun-yin, who represents the fisheries sector and is helping affected fishermen take their case to the government, said there was a need to improve the red tide notification mechanism.

The Agriculture, Fisheries and Conservation Department said it would continuously monitor red tide occurrences to minimise the impact on the mariculture industry and the public. The Environmental Protection Department said monitoring at Tolo Harbour between December and January showed no abnormality in terms of organic matter and nutrients.

Ernest Kao