Aaron O'Dea

Staff Scientist

Smithsonian Tropical Research Institute

Long-term monitoring is essential to understand how marine ecosystems function but we only have a few decades of data, at the most. That’s not enough to properly document natural or human-driven change and variation in the seas. 

“Documenting the sea’s past helps us place modern day changes in proper context, provide clues about what can be done to promote resilience in marine ecosystems, and make more informed predictions about the future,” says Aaron O’Dea, a staff researcher at the Smithsonian Tropical Research Institute in Panamá.

Fossil, archeological and historical records can extend our understanding of ecological, evolutionary and environmental changes in tropical marine environments. Much of Aaron’s work focuses on coral reefs, which are home to an astonishing proportion of the world’s biodiversity and vital to the well-being of about a billion people. Aaron and his team take coral reef cores at sites around the globe to create records of change that stretch back thousands of years.
These records can reconstruct what conditions were like before major human impact. “Ideas of what was pristine are often limited to a single idealised state, such as an impenetrable rainforest or a coral reef teaming with fish,” says Aaron. While such places of course existed, there must have been variation too. “We need to move away from preconceptions of how things were and instead use rigorous ecological approaches to quantify the full gamut of variation in the past if we are to establish informed conservation objectives.”

Extending ecological and environmental records back in time can also reveal how coral reefs function. For example, with MarineGEO post-doc Katie Cramer, the team used parrotfish teeth preserved in a 3,000-year-long span of fossil reef to show that when more parrotfishes are on the reef, the reef grows faster. It was only possible to see the pattern with the long-term data.

Past events are also useful for forecasting the future. “A lot of things have happened in the past – warming, acidification, sea level rise and even catastrophic losses of whole ecosystems. We can use these to observe how life responds and help predict what will happen in the future,” says Aaron.
The team extract coral and mollusc skeletons, the fossilised otoliths and teeth of reef fishes, dermal denticles of sharks, the spicules of sponges and the spines of echinoids - “anything that leaves a good fossil record,” remarks Aaron. They are also exploring the use of ancient DNA in reef sediments to provide insight into those components of reef ecosystems that do not leave a fossil record