Exploring Coral Reef Threats from Changing Ocean Chemistry

A sparsely populated chain of islands in the central Pacific Ocean is providing new clues about the changing acidity of ocean water and its potential impact on the health of coral reefs, a rising threat to already-fragile coral ecosystems.

Nichole Price, a post-doctoral researcher at Scripps Institution of Oceanography at UC San Diego, will present data at the 2012 American Geophysical Union Fall Meeting on groundbreaking research conducted at the Northern Line Islands archipelago during a 2010 expedition and follow-on studies (OS51H-06 · Friday, Dec. 7, 9:15 a.m. · Moscone West 3005). Price's presentation addresses the emerging concern that coral and similar shell and skeleton-building organisms will be among the first to suffer from rising seawater pH due to carbon dioxide uptake, or ocean acidification. Such negative impacts reverberate across coral reef ecosystems and extend to the human societies that depend on them.

Price, Scripps marine ecologist Jennifer Smith and their colleagues tested feedbacks to ocean chemistry at the Line Islands through field deployments of school desk-sized, pyramid-shaped tents over diverse coral reef "footprint" areas. Half of the islands where the tent experiments took place are uninhabited while the others had varying population levels. Sensors within the enclosed chambers detected numerous chemical aspects of reef seawater every five minutes during 24-hour testing cycles. The results revealed details about day-to-day swings in pH and how those natural fluctuations may be affected by the health of the underlying reefs.

Price and Smith found that reefs at uninhabited islands reach a daily pH peak level that can foster healthy coral growth. Reefs off inhabited islands, however, experience night-time pH lows that simulate future acidification and could give rise to degradation where fleshy seaweeds can thrive and overtake the reef.

"The localized human influence and related stressors such as fishing and pollution can change the living function of the reef to compound the impacts due to global change," said Price, who indicated the causes may be rooted at the microbial level, a possibility she and her collaborators are now pursuing.

Price believes their results eventually could help the human inhabitants of the Line Islands as their homes are increasingly threatened by sea-level rise, compounded by crumbling reefs less capable of dissipating oncoming wave impacts. Further, these investigations may provide insight for U.S. coastal areas such as Hawaii and Florida as ocean acidification continues to rise with unclear consequences.

"The juxtaposition of populated islands to those untouched by human inhabitants is striking and a way for us to learn about processes conferring resilience to ocean acidification and perhaps how we can use local management to help ameliorate the problem," said Price. "It gives us hope that maybe local management strategies could help with global issues."

A return trip to the Line Islands, this time targeting the uninhabited southern part of the chain, is being planned for 2013 to further investigate the reefs, ocean acidification and other aspects of coral reef ecology.

Said Price: "We need to learn how these really remote, untouched habitats are behaving so that we have an idea of what a relatively unimpacted reef should look like and how these reefs could behave if we have any hope of conserving or restoring these ecosystems."

"Our work in the central Pacific is helping us to understand how coral reef metabolism varies across oceanographic and anthropogenic impact gradients," said Smith, an assistant professor in the Center for Marine Biodiversity and Conservation at Scripps. "Our data suggest that intact reefs behave in fundamentally different ways than reefs even moderately impacted by local human populations. The most notable differences are a reduction or loss in a given reef's capacity to build calcium carbonate framework in the presence of human inhabitants which will likely have cascading consequences for the long term stability of these reefs and those that depend upon them."

The Gordon and Betty Moore Foundation, the Moore Family Foundation, the Scripps Family Foundation, the WWW Foundation and generous donations to Scripps Institution of Oceanography supported the research.