A Sea of Change

March 13, 2012


Having grown up in Zhoushan, one of the largest fishery areas on the coast of the East China Sea, Academy scientist Dr. Ling Ren can’t hide her surprise at the changes there. Three decades of rapid urbanization and development accompanied by dramatic population increases have changed the face of this formerly peaceful fishing community. During the past 15 years, the once-bountiful fish supply has decreased drastically—in part because of pollution-induced algae blooms.

Harmful blooms of phytoplankton, a type of algae that floats on water surfaces, are appearing repeatedly along the coast of Zhoushan. Phytoplankton, which grow naturally over time, are the foundation for the aquatic food web, Ren says. When light, temperature, and nutrient conditions are ideal, phytoplankton populations can grow explosively, a process called bloom. Yet certain species tend to thrive in the presence of pollution, and their blooms can be harmful.

Pollution can cause certain toxin-producing phytoplankton blooms that are harmful to fish and humans who consume contaminated seafood. Humans also can become ill from airborne toxins. Even when some blooms don’t produce toxic substances, the increased algae may get stuck in fish gills, causing the fish to suffocate and disrupting the food supply.

"Phytoplankton blooms happen as a result of eutrophication, or excessive input of nutrients like nitrogen and phosphorus," explains Ren. "Eutrophification is common in coastal areas where large populations of people live. In Zhoushan, large amounts of nutrients from improper disposal of untreated sewage, untreated or mistreated industrial wastes, and excessive fertilization of crops are dumped into the coastal area."

Although nutrients are essential for photosynthesis, excessive nutrient input causes the process to occur too quickly, resulting in rapid growth of massive phytoplankton populations. These blooms sink to the bottom of the sea where they decompose and consume oxygen. The condition of hypoxia occurs when oxygen levels fall too low to sustain animal life.

"Hypoxia stresses crabs and other bottom feeders because these animals need oxygen to survive," says Ren. "They will either flee or die off, leaving a ‘dead zone’ where life once existed."

Ren explains that this problem occurs throughout the world, including on the northern Gulf of Mexico, where she spent three years studying the relationship between hypoxia and phytoplankton blooms during her postdoctoral research.

In Zhoushan, the effects of phytoplankton blooms extend through the food chain. Small animals graze on the algae, the larger fish eat those animals, and soon the harmful toxins accumulate in the local fish supply. Fishermen have told Ren that the decreased availability of healthy fish combined with the health risk posed by toxic food challenges their ability to provide for residents.

As a result, fish market shoppers have witnessed rising prices. "I wanted to get inside this problem and find out more about its relationship to human activity," she explains.

So in 2009, Ren took to the seas—literally. In collaboration with scientists from Zhejiang Ocean University (ZJOU), she began a project that aims to evaluate the status of the ecosystem and biodiversity in the Zhoushan Fishery area, re-examine how phytoplankton blooms affect fish resources, and provide a scientific basis for coastal management and ecological restoration measures. The three-year project is funded by the Chinese Ministry of Science and Technology. Ren’s role is to study the biodiversity of phytoplankton and human-induced nutrient input on phytoplankton growth.

Last November, supported partly by the Cotswold Foundation, Ren embarked on a field trip with graduate students. They collected samples at 11 stations throughout the coastal area before returning to the University for four weeks to analyze these and other samples that the students had collected during the year. This analysis uncovered the presence of a phytoplankton called Pseudo-nitzschia that may cause shellfish poisoning in humans.

Ren also set up microcosms (small-scale experiments to recreate the conditions that spur algae blooms) to study the nutrient inputs on phytoplankton, and she trained Chinese graduate students to carry out the experiments and take monthly phytoplankton samples from the study area. She will return to China this November to check their progress. She also will return to the sea to take new samples.

"People can see algae blooms; they wonder why they happen and what causes them," she adds. "I hope the information I find can support waste removal in the area and help develop information for coastal management strategies."

Ren recently received funding to study phytoplankton blooms in the Barnegat Bay area of New Jersey. During the three-year funding period, she hopes to learn how phytoplankton blooms are related to human activity and how these blooms are affecting the long-term ecology of the bay.

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