Acidification of the Sea

Student-faculty research published in peer-reviewed journal

by Christine Baksi

April 26, 2012

“Seagrasses help sequester carbon dioxide and slow climate change,” says Associate Professor of Biology Tom Arnold, whose student-faculty research on ocean acidification and its impact on marine ecosystems has been published in Chesapeake Quarterly and the journal PLoS ONE. Photography by National Geographic shows one of Arnold’s underwater field sites.

A Dickinson study of climate change could provide answers as to how coastal ecosystems may respond to elevated carbon-dioxide levels during the next century. The project focused on the phenomenon of ocean acidification, caused by atmospheric carbon dioxide as it permeates the ocean and lowers the pH of seawater. 

The study by Associate Professor of Biology Tom Arnold, Dickinson student researchers and Whitman Miller of the Smithsonian Environmental Research Center, was recently published in the journal PLoS ONE and featured in the recent issue of Chesapeake Quarterly.

By mimicking conditions predicted to occur within the next 100 years in the Chesapeake Bay, researchers found that acidification causes seagrasses, which reduce coastal erosion and serve as nursery grounds for fish and shellfish, to lose their ability to fight disease and consumption. The research sheds new light on the real impact climate change has on seagrasses and calls into question the assumption that high levels of carbon dioxide might benefit these marine plants.

On land, higher levels of carbon dioxide cause plants to produce additional protective chemicals called phenolics, resulting in greater resiliency against disease and consumption; however, the researchers found that higher carbon dioxide in important marine plants such as seagrass, led to a dramatic loss of phenolics.

“We were quite surprised,” said Arnold. “This was different from what has been observed on land.” Arnold and the research team identified nutrient pollution as a potential reason why marine plants respond to acidification differently than land plants. The pollution, or overexposure to nutrients already present in ocean water, causes the plants to grow but lose their natural defenses.

Arnold, a chemical ecologist and visiting professor in the University of Queensland’s Centre of Marine Science, confirmed the discovery by testing seasgrasses exposed to high levels of carbon dioxide near the Island of Vulcano in the Mediterranean Sea. He is continuing his research on Australia’s North Stradebroke Island, the world’s second-largest sand island.

“If ocean acidification stimulates the growth of seagrasses but at the same time reduces their natural defense mechanisms, what does this mean for fishes and turtles and microbes that cause disease? We just don’t know,” said Arnold. “We really need this information before we can predict how seagrasses, and therefore coastal communities, will respond.”