Field Research at CO2 Seeps
AIMS researchers are studying three shallow volcanic CO2 seeps (also known as ‘CO2 vents’) in eastern Papua New Guinea, in Milne Bay Province, to observe how ocean acidification is affecting marine ecosystems.
Coral reef and seagrass ecosystems at this site have had a lifetime of exposure to elevated levels of carbon dioxide (CO2) allowing scientists to study them under natural conditions. The seeps also provide a unique opportunity to study how natural tropical marine ecosystems may adapt and how organisms may acclimatise after life-long exposure to high CO2.
Coral reefs in Milne Bay Province at ambient CO2 (top) and one at one of the CO2 seeps exposed to elevated CO2 (bottom). The lack of structural complexity in the coral community leads to substantial losses in reef biodiversity. Photos: Sam Noonan, AIMS.
"The seeps are a ‘natural laboratory’ to study what is occurring in nature when more and more CO2 from the atmosphere dissolves in water," said AIMS research scientist, Dr Katharina Fabricius.
"We have found that ocean acidification will select large boulder-like coral, over branching (bushy) corals that are the home of many species like fish, crabs, shrimps and sea stars. As a result, ocean acidification has a domino effect: as the habitat structure decreases, the animals that live and hide in their nooks and crannies find it far harder to survive, simply because they cannot hide from predators," explained Dr Fabricius.
Swimming along CO2 gradients is like travelling into a future of high CO2 concentrations in a time machine. Scientists use these gradients to identify the ocean acidification tolerance limits for reef dwellers.
Today, tropical seawater has a pH of about 8.1. Benthic foraminifera, which are important producers of sand, are absent below 7.9 pH, a level that may be reached towards the middle of this century. Crustose coralline algae, which are important for coral recovery, are rare below 7.8 pH, while seagrasses are very abundant at a pH lower than 7.7.
Short-term laboratory experiments would not be able to provide such information on changes at the level of whole ecosystems, highlighting the value of collecting in-situ data from the CO2 seep locations.
Since its start in 2010, the AIMS-led CO2 seeps project has grown into a large collaborative study with over 40 researchers from 20 institutions from over nine countries. The work* produced by this team is revealing the fate awaiting tropical marine ecosystems in coming decades if atmospheric levels of CO2 continue to increase.
Reefs in Papua New Guinea are in the same zoogeographic province as the Great Barrier Reef (GBR). Findings from these seep sites are, therefore, directly applicable to the GBR and other Indo-Pacific coral reefs. Predicting future changes and thresholds for reefs under increasing ocean acidification will provide the scientific basis for informed management decisions for the many Indo-Pacific nations that depend on healthy coral reefs for their subsistence, livelihoods and prosperity.
A reef exposed to moderate (left) and high (right) carbon dioxide concentrations at the CO2 seep sites. At high CO2, corals are sparse and sponges and fleshy seaweeds dominate the communities. Photos: Katharina Fabricius, AIMS
*A variety of news articles reporting on the range of ocean acidification work undertaken by scientists at AIMS are listed chronologically below: