by Navaneeth Dontuboyina (’24) | November 17, 2023
Rising sea levels due to climate change are typically seen as a threat to mangrove ecosystems across the globe. According to the Pacific Islands Climate Adaptation Science Center (PISCASC), “Sea-level rise will eventually flood and kill many coastal mangrove trees.” However, a recent study reveals that certain mangrove forests off the northern coast of Australia have experienced significant growth in the past few decades, and surprisingly, this expansion may be attributed to rising sea levels. Unlike other parts of the world where rising sea levels pose a threat to mangroves, the unique geological history of the Howick Islands in the Great Barrier Reef has created a different narrative.
The Great Barrier Reef boasts ancient coral reef foundations that helped produce wooded islands. These islands are habitats for a diverse range of animals and plants, including mangrove forests, which are a group of trees that live near tropical coastlines and provide many ecological benefits, including homes for birds, breeding grounds for turtles, nurseries for fish, and natural shields during storms and cyclones for coastlines and islands. They also have the ability to absorb carbon dioxide and store it as “blue carbon,” or carbon captured in marine and coastal environments. Furthermore, according to the PISCASC, “human populations on isolated western Pacific islands rely heavily on mangroves for food, building materials, and firewood.”
Because mangroves are integral to the native ecosystem and human population, questions linger about their adaptability to rising sea levels and the potential devastating effects. To address such questions, a team led by environmental scientist Sarah Hamylton from the University of Wollongong investigated how the mangroves on the Howick Islands were responding to rising sea levels and recently published their results in the latest issue of Proceedings Of the Royal Society: Biological Sciences. Through drone-captured aerial imagery captured by drones and on-the-ground assessments of plant diversity and tree measurements, the team estimated that the islands now host nearly 54,000 metric tons of mangroves, which was approximately 10,000 more metric tons than in 1973. The mangrove forest has also expanded its coverage on many islands, such as Bewick Island, where coverage has grown by 50% since 1973.
The flourishing Australian mangrove population is due to the unique geological conditions of the Howick Islands, shaped by the rise and fall of sea levels over thousands of years. The exposed reefs eroded into sediment during periods of lower sea levels, creating an environment conducive to the growth of salt-tolerant mangroves. Thus, the island environment is particularly apt to support mangroves as the ocean rises again. In fact, the study suggests that “as sea level came back down, it wasn’t a suitable mangrove habitat.”
Climate change and rising sea levels have been pushed on the forefront of pressing global problems for the last decade. The UN claims “climate change is the single biggest health threat facing humanity” and rising sea levels are most certainly a contributor to this nefarious title. However, this study highlights that there must be a more dynamic response to the global problem of rising sea levels. Each mangrove and ecosystem across the world is unique and our approaches to accommodating rising sea levels needs to be customized. As Dr. Kelleway, an author of the landmark study, puts it, “We need better consideration of the impacts of climate change and the nuances across different ecosystem types around the country and around the world.”
