AsianScientist (July 14, 2017) – They are scenes of mystery, death and destruction. Beachgoers in Hong Kong setting out to enjoy the sun, sand and surf are instead greeted by a sea which has turned a sinister shade of red. On a beach in Singapore, thousands of dead fish of all shapes and sizes are strewn along the shoreline, along with other exotic marine creatures like cuttlefish, and even a sea snake.
In coastal fish farms across Asia, farmers encounter the macabre sight of tons of dead fish floating belly up in their pens. Meanwhile, in Malaysia, several people afflicted with food poisoning symptoms have been admitted to hospital. Three have died and over forty are critically ill. All have indulged in the fresh catches of the day—cockles and mussels.
A microscope is required for the investigation into these bizarre events. The perpetrators at the center of the plot are tiny phytoplankton no bigger than a few micrometers in size, known as dinoflagellates and diatoms.
Dinoflagellates and diatoms are among the most common phytoplankton in the ocean. They are important primary producers in coastal water ecosystems, synthesizing organic compounds from carbon dioxide using sunlight.
Dinoflagellate cells are enclosed in an intricate covering consisting of armor-like plates known as theca. Many dinoflagellates also produce light on their own and put on breathtaking bioluminescent light shows, bursting into flashes of neon blue light when disturbed by sudden movements in the water. Like their dinoflagellate cousins, diatoms are encased in geometrically-intricate silica cell walls, called frustules, captivating scientists and artists alike.
However, a dark side lies beneath their beauty. When conditions are favorable, dinoflagellates and diatoms multiply rapidly to form harmful algal blooms (HABS) that color the oceans red, giving rise to the term ‘red tides’—a misnomer because these algae also come in hues of green, yellow and brown, depending on the color of the pigments in the cells.
An increase in dissolved nitrogen and phosphorus—essential nutrients for algal growth—can encourage phytoplankton to grow out of control. Warm and calm waters, surface runoff into oceans, high sunlight intensities as well as low salt concentrations are also conducive for algal growth. An algal bloom can stretch for several kilometers and there can be as many as 500,000 cells in a single milliliter of water. At high cell concentrations, phytoplankton block and prevent sunlight from reaching other aquatic life.
Suffocating fishes, poisoning humans
When the algae die, they are broken down by bacteria and fungi, a process which consumes oxygen and produces ammonia. The depletion of oxygen and build-up of ammonia from decomposing algae can result in the sudden large-scale death of fish and other aquatic creatures. According to Dr. Hans Eikaas, head of environmental technology and chemistry at DHI Water & Environment Pte Ltd, ammonia irritates fish gills and the algae clog the gills, suffocating fish in the process.
Some dinoflagellates and diatoms have an even more lethal mode of operation. Algal blooms may be dominated by species which produce potent neurotoxins that are harmful to humans and animals. Some algal toxins kill fish directly while others accumulate in shellfish. Like carefully concocted poisons, these toxins are tasteless, odorless, heat resistant and rapidly absorbed by the body. On par with chemical warfare agents like ricin, used in assassination attempts during the Cold War, a few milligrams of the most powerful dinoflagellate toxin, saxitoxin, can kill an adult human.
When unsuspecting humans eat toxin-contaminated seafood, they ingest these powerful algal neurotoxins, resulting in four main kinds of shellfish poisoning: amnesic shellfish poisoning (ASP), diarrheal shellfish poisoning (DSP), neurotoxic shellfish poisoning (NSP) and paralytic shellfish poisoning (PSP), aptly named after the symptoms they produce.
Memory loss, vomiting, diarrhoea and paralysis appear within a few hours after the infected shellfish are consumed. Dinoflagellate toxins block the transmission of signals in the nervous system, causing DSP, NSP and PSP. Victims of PSP, one of the most deadly types of shellfish poisoning, gradually lose control of their muscles. As their diaphragms fail, victims suffocate when their lungs cannot expand. Death soon follows if the paralysis is untreated.
Another deadly form of shellfish poisoning, ASP, is caused by domoic acid, produced by the diatom Pseudo-nitzchia. Unlike dinoflagellate toxins, domoic acid causes neurons to fire wildly and kills by overstimulation, leading to memory loss. There are no known antidotes for shellfish poisoning and current supportive treatments only relieve symptoms.
Algae across Asia
While HABs are natural occurrences, they have become more rampant in Asia in the past decade. In 2014, Hong Kong experienced the highest number of ‘red tides’ in 26 years: 35 cases triggered by 16 algal species—five of which are toxic—in a six-month period. In the first quarter of 2016, there were more HABs than any year in the same period over the last decade.
Annually, massive fish kills caused by HABs result in losses amounting to billions of dollars in the Asian aquaculture industry. Fish deaths have been reported in Hong Kong, Japan, the Philippines and Singapore. In 2015, thousands of dead fish washed up on Pasir Ris beach in Singapore, and farmers lost over 600 tons of farmed fish. In the land of fish head curry and delectable stir-fried seafood, where fishermen pray to deities for bountiful catches, these losses threaten the livelihoods of many who depend on the ocean.
Cases of PSP have been reported in almost all regions of Asia since 2000. From 2001 to 2013, there were several outbreaks of PSP in Malaysia after the consumption of toxin-tainted shellfish, and several victims have succumbed to the poisoning.
The increase in HABs in Asia has been linked to nutrient runoff into oceans from the increased use of nitrogen- and phosphorus-containing fertilizers during farming. Warmer water—a result of climate change and El Niño weather—is another key factor which promotes HABs.
Scientists fight back
Despite understanding the conditions which encourage algal growth, the precise combinations of factors which encourage the proliferation of phytoplankton remain an enigma. Scientists also do not fully understand why phytoplankton produce toxins and what triggers them to do so. Toxic algae can wipe out fish stocks and poison humans at low cell densities, giving the impression that HABs are silent assassins which strike suddenly without warning.
Algal blooms can develop quickly over large areas, so cooperation between scientists and other authorities is required to stop these swift killers from claiming their next victims. During a bloom, satellite imaging is used to track the spread of the algae so that authorities can warn farmers to isolate their fish stock. Through careful management of nutrient-laden discharges from farms, the number of algal blooms can be reduced. To prevent outbreaks of shellfish poisoning, the public is also advised not to consume seafood during periods when HABs are expected.
The best way to arrest these algae in their tracks is to forecast algal blooms before they occur. Weather conditions and water quality parameters such as nutrient concentrations are regularly monitored by environmental agencies to predict the likelihood of a bloom. Visual examination and molecular biology techniques developed in recent years are used to identify as well as monitor phytoplankton numbers.
To capture phytoplankton, seawater is passed through filters which retain the algal cells. Scientists then identify the captured phytoplankton by looking at their unique characteristics under the microscope. By sequencing the DNA of the phytoplankton suspects or using molecular probes that bind to specific algae, scientists are able to pinpoint the offending phytoplankton more accurately and correlate algal blooms to environmental factors.
Using these techniques, the ‘red tides’ in Hong Kong have been traced to various species of dinoflagellates and diatoms that surge during periods of warmer water as well as nutrient pollution. Preliminary findings point to Karlodinium veneficum, a dinoflagellate associated with massive fish kills as the cause of the 2015 HAB in Singapore. Alexandrium minutum and Pyrodinium bahamense were two dinoflagellate species responsible for the shellfish poisoning in Malaysia.
In the ongoing battle against algae, researchers at the Tropical Marine Science Institute and the Singapore-MIT Alliance for Research and Technology Centre for Environmental Sensing and Modelling (CENSAM) in Singapore have developed a robotic kayak that measures the quality of seawater and identifies algae in a few hours instead of days. According to Mr. Tawfiq Taher, senior research manager at CENSAM, the robot is designed to be resilient to extreme weather conditions and is able to collect more data as compared to traditional methods.
With the help of science, the algal culprits have been brought to justice. The seas are clear once again and beachgoers frolic in the waves. All over Asia, people tuck into shellfish and other gastronomic delights from the ocean. On a perfect day like this, it is difficult to imagine that the next HAB may be lurking around the corner, waiting to erupt at the right conditions. No one knows for sure when or where it will appear. What we can do is to be prepared.
This article won second place at the 2017 Asian Scientist Writing Prize.
Click here to see photos of the the prize presentation ceremony held on July 7, 2017.
Also, look out for the other winning entries to be published in a compilation coming out later this year.
———
Copyright: Asian Scientist Magazine; Photo: Shutterstock.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.
