National / Science & Health

Team investigates effects of acidification on marine ecosystem

by William Hollingworth


British and Japanese scientists are conducting new research seeking to discover how Japan’s marine ecosystem may be affected by global warming.

They are studying the potential side effects of rising acidity in Japan’s seas caused by increased levels of carbon dioxide in the atmosphere.

Previous studies in the Mediterranean have shown that increased acidification can disrupt the growth of sea organisms, with potentially long-term implications for the marine food chain.

Researchers hope their findings will inform politicians about the importance of cutting greenhouse gas emissions.

Scientists believe the heating of the world’s oceans will impact marine ecology, but less is known about a second byproduct of global warming: acidification.

The world’s oceans are absorbing higher levels of CO2. This dissolves into the seawater and reacts with the water to produce a weak carbonic acid.

The ocean gradually becomes less alkaline and the level of carbonate is reduced. However, calcium carbonate is required by organisms, such as corals and shellfish, to build skeletons and shells.

Some estimates suggest the oceans have become 30 percent more acidic since the Industrial Revolution. And if CO2 continues to be emitted at the same rate by 2100, acidity will increase by about 150 percent.

In order to examine the effects of CO2, the team has sent divers to a spot off Shimoda, Shizuoka Prefecture, where there are several underwater volcanoes that pump out CO2 from vents.

Jason Hall-Spencer, a professor of marine biology at Plymouth University who is working with a team from the University of Tsukuba in Ibaraki Prefecture, said similar studies in Europe showed the “corrosive” effects of CO2.

Around the vents, the diversity in marine organisms declines with none exhibiting the usual array of bright colors due to lower levels of carbonate in the seawater. There are fewer species and they tend to be brown or green.

In addition, corals, which can be an important component in the marine food chain, are not present around the vents because there is not enough carbonate to build their skeletons. As the diversity of plankton and organisms declines, so does the diversity of fish higher up the food chain, scientists believe. Studies have also shown that shellfish tend to get smaller at higher CO2 levels.

However, some marine life actually prospers, including seaweed, anemones, jellyfish, algae and sea grass.

Hall-Spencer said the seawater chemistry is changing in Japan, as elsewhere, but little work has been done on the effects.

Colder and deeper waters naturally have lower levels of carbonate than shallow, warmer waters (home to the tropical coral reefs, for example) so experts believe they will be impacted first as a result of increased acidification.

Hall-Spencer said one of Japan’s main concerns should be the possible effects on coral reefs around Okinawa, where already there is evidence to suggest the combination of warming and acidification is damaging the corals.

He said this could hurt tourism and lead to coastal erosion, as the reefs act as a barrier against strong tides.

However, scientists are keen to stress the sea will remain productive for the marine industry in the future, albeit in a different way. Japan’s seaweed harvesters may benefit from larger yields, for example.

The team is expected to publish its findings later this year, but preliminary observations appear to show corals do not grow well close to the vents. It was a different story for algae, as growth was stimulated at high CO2 levels. But kelp forests near Japan are expected to retreat northward due to the effects of global warming, Hall-Spencer said.

“I don’t want to be too dramatic but I think that in the future you may see a simplification of the marine biodiversity around Japan,” Hall-Spencer said in an interview. “At high CO2 areas in the Mediterranean, there’s a descent toward slimy organisms such as jellyfish and bacteria. But corals and the fish that rely on them are easily impacted.”

He added that there is serious concern among Japan’s scientists about the issue.

“We don’t know what it’s going to do to coastal livelihoods,” he said. “The changes in seawater chemistry have never happened this way before.”

Kazuo Inaba, director of the Shimoda Marine Research Center, part of the University of Tsukuba, said, “I really want politicians to know about ocean acidification and what we think will happen in the future. However, it’s important not to be alarmist and spread any misinformation. A lot of people in Japan rely on the fishing industry.

“One of our major concerns is that increased acidification could disturb some aspects of the marine food chain and impact on fish and mollusks, for example.”