Long-term recovery of mangroves after a major oil spill

A new study from James Cook University TropWATER researchers has tracked the full 30-year recovery of more than 300 hectares of mangrove forests severely damaged by a 1986 oil spill in Central America. TropWATER’s Professor Norman Duke and Dr Adam Canning combined on-the-ground observations with remote sensing to investigate what helped and hindered recovery over the last three decades – providing one of the most comprehensive long-term records of mangrove regeneration. “Understanding how mangroves recover from major disturbances plays a big role in guiding efforts and response strategies for damaged mangrove forests in Australia, not just for oil spills but also for cyclones and other environmental threats,” said Professor Duke.

The 1986 Bahía Las Minas oil spill

In 1986, over 8 million litres of crude oil were spilled in the waters of Bahía Las Minas on Panama’s Pacific coast. The oil spread throughout more than 300 hectares of mangrove forests, killing 69 hectares of mature mangrove trees.

Over 300 hectares of mangrove forests were saturated in crude oil in Bahía Las Minas in 1986. Photo credit: Charles Getter, STRI.

Professor Duke said most research focused on short term recovery, whereas this study was one of the first to investigate long-term recovery of mature mangrove forests – and the findings were encouraging. “Mangroves that were oiled but not killed suffered significant damage in the early years following the spill. But our study found they but had largely recovered within a few decades,” he said. “Where mangroves were wiped out by the spill, recovery was much slower, but these devastated areas have also recovered. It took 15 to 20 years for seedlings to re-establish the forest, and for canopies to close again. “This shows us recovery is possible, but only if environmental pressures remain the same. Recent studies have generally found the frequency of extreme events has increased, threatening to outpace mangrove’s ability to re-establish and recover from damage.”

What this means for Australia and globally

While this study examined oil-damaged mangrove forests in Central America, the methods and findings are applicable to mangrove ecosystems anywhere, including Australia. The team has conducted several assessments of changing mangrove habitats around Australia to track the influences of changes in rainfall patterns, sea level changes, and more frequent and severe tropical cyclones. “These detailed, long-term studies of damaged mangrove habitats provide critical information on the vulnerabilities of tidal wetland ecosystems and their capacity to recover,” Professor Duke said. “By better understanding how mangroves respond to damaging events, we are developing more appropriate and more effective strategies to minimise future impacts from human pressures and extreme climate events. “These strategies include developing practical and more inclusive ways to evaluate and monitor mangrove health day-to-day and in the long-term. This provides more effective expert advice for managers, practitioners, and local communities around the globe.” Read the study in the Bulletin of Marine Science here.