The algae blooms seem to be feeding on nutrients from fertilizer that is carried from farms into the sea.
Source: <a href="http://mobile.nytimes.com/2013/07/06/world/asia/huge-algae-bloom-afflicts-qingdao-china.html">New York Times</a>
BEIJING — In what has become an annual summer scourge, the coastal Chinese city of Qingdao has been hit by a near-record algae bloom that has left its popular beaches fouled with a green, stringy muck.
A group of researchers believe that the algae that washes up around Qingdao originates farther south in seaweed farms along the coast of Jiangsu Province. The farms grow porphyra, known as nori in Japanese cuisine, on large rafts in coastal waters. The rafts attract a kind of algae called Ulva prolifera, and when the farmers clean them off each spring they spread the algae out into the Yellow Sea, where it finds nutrients and warm conditions ideal for blooming.
While farmers have long grown seaweed along the Jiangsu coast, the rafts expanded much farther offshore starting in 2006, which may have contributed to the recent blooms, according to an article published by Dr. Keesing and his colleagues. The answer to curtailing the blooms may lie in disposing of the algae that clogs the nori rafts on land.