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AP Photo/Ng Han Guan
The Red Army battling green algae.

Spewing sewage into the ocean is bad: toxic algae and man-sized jellyfish edition

By Gwynn Guilford in China

Once a swampy backwater of fewer than 20 million people, the Pearl River Delta—the southern swath of mainland China above Hong Kong—now has three times that population. Tens of millions more humans in the Pearl River Delta means many more toilets a-flush, pumping a steady gush of human waste into the South China Sea.

That’s gross—but not necessarily for the reasons you might think. That nutrient-packed sewage is an all-you-can-eat buffet for algae. And since some of those can be toxic to humans, sea mammals, and fish, these algae blooms are a big headache for Hong Kong officials, reports the South China Morning Post (paywall). They’re not the only ones. Scientists are increasingly worried that the causes behind algae blooms are wreaking permanent change to surrounding ecosystems.

In fact, all along China’s coasts algal blooms are bursting more often and more intensely. It’s not surprising; as China’s coastal provinces have powered the country’s economic juggernaut, their populations surged from 243 million in 1952 to more than 700 million (pdf). The agriculture and aquaculture needed to feed these teeming masses add still more organic matter to the streams of waste spilling out of China’s big deltas—the Pearl River, Yangtze and Yellow—and into the sea. Because this waste is packed with nutrients such as phosphorous and nitrogen, which provide a cornucopia for algae gluttony, big algal blooms appear to track with booming coastal populations and economic activity.

"Harmful Algal Blooms in Asia," Patricia M. Gilberg
Change in harmful algal bloom distribution, 1970 vs. 2000.

In July 2013, the biggest algal bloom ever recorded in China covered 28,900 square kilometers (11,158 square miles) of the Yellow Sea—meaning more than three New York City metro areas of ocean was carpeted in green muck—requiring Qingdao city officials to bulldoze 7,335 tonnes (8,085 tons) of beached scum. A similar incident almost shut down the sailing competition of the 2008 Beijing Olympic Games. The army dispatched 15,000 soldiers to remove 1 million tons of algae, costing more than $100 million (pdf, p.9).

A masked female holidaymaker looks on at a beach resort on a scorching day in Qingdao city, east Chinas Shandong province, 3 July 2013. Holidaymakers are flooding to the beach resorts to cool down in the eastern Chinese coastal city of Qingdao as heat waves are sweeping through many parts of China. A group of female swimmers are spotlighted among the others as they dress their heads up with colorful masks, making them look like masked robbers or terrorists. Dubbed as the bikini for faces, the mask is used to protect the face of its user from being tanned by scorching sunlight and stung by jellyfish. Priced at 15-20 yuan (US$2.44-US$3.26) apiece, the mask is quite popular among middle-aged and elderly women.(Imaginechina via AP Images
Imaginechina via AP Images
A Qingdao woman protects her skin from UV rays while surveying the enormous algal bloom, in the background.

The algae’s effect on fish populations varies. Some algae are toxic, killing valuable fish—a big worry for commercial fishermen as well as for China’s fish-farming industry, which contributes more than two-thirds of global aquaculture output. For instance, a particularly nasty ”red tide,” as one type of toxic algae is called, killed 80% of Hong Kong’s fish farm stock in 1998.

"Harmful Algal Blooms in Asia," Patricia M. Gilberg
Harmful algal bloom events in the East China sea (circle represents events, triangle reflects aquaculture production; bars reflect fertilizer consumption.

But the algae that don’t kill fish make them stronger—or fatter, at least. And more plentiful. As little fish chow down on more algae and grow their populations, big fish chow down on more of those little fish—exploding the food chain.

Then come the “dead zones.” As dying fish, fish excrement, and algae sink to the bottom of the ocean, they strip the water of oxygen. (See this fantastic infographic for more.)

Echizen kurage, or Nomura's jellyfish, are caught in a fishing net off the shores of Awashimaura, northern Japan, in this September 26, 2003 file photo. The slimy sea creature up to two metres in diameter and weighing up to 200 kg has Japan's fishing [industry in the grip of its poisonous tentacles, as vast numbers have appeared along the country's coasts since August, clogging and ripping fishing nets and forcing fishermen to spend hours hacking them apart before bringing home their reduced catches]. Picture taken September 26, 2003. ??? USE ONLY (CREDITS: Awashimaura Fisheries Association Coop)
A net full of those man-sized Nomura jellyfish.

Most aquatic life can’t live in water so O2-scarce. But as we’ve discussed before, jellyfish can. Once they appear, jellyfish tend to settle in, keeping fish from returning by eating their food and polishing off their eggs. Scientists think this is a major factor behind explosions of the moon and lion’s mane jellyfish—as well as the man-sized Nomura’s jellyfish—off China’s coasts. Some warn that if nothing changes, this jellyfish takeover could change China’s marine ecosystem for good (paywall).

"Jellyfish blooms in China: Dominant species, causes and consequences.," Dong et al.
Jellyfish bloom distribution: white dot = moon; red dot = Nomura; black = lion’s mane.