New research led by University of Hawaiʻi Sea Grant College Program (Hawaiʻi Sea Grant), UH Mānoa School of Ocean and Earth Science and Technology (SOEST), and U.S. Geological Survey analyzed a 253-year old core from a massive coral colony at Olowalu Reef off West Maui to reconstruct how Olowalu has changed over time, what has driven those changes, and what restoring healthy connections between land and sea may mean for the reef's future.
The study, published in Coral Reefs , analyzed the coral core from approximately 1760 to 2013 which provided a rare glimpse into the conditions that began before large-scale changes to the West Maui landscape following Western contact occurred, and continued through plantation agriculture and modern coastal development.
Chemical indicators associated with sediment, nutrients, and other land-derived inputs generally increased over the 253-year record, with some of the largest changes occurring during the twentieth century as sugarcane agriculture expanded across West Maui. At the same time, the coral's growth record showed that calcification increased through much of the record before beginning to decline around the late 1960s, concurrent with sugarcane expansion.
Coral skeletons
Like the rings of a tree, corals build their skeletons incrementally over time. As they grow, elements from the surrounding seawater become incorporated into their skeletons. By measuring this chemistry along the length of the Olowalu core, the researchers were able to reconstruct how conditions affecting the reef changed over generations.
"One of the important lessons from this study is that some of the changes that occurred on land more than a century ago can still provide important context for what we see on reefs today," said Samuel Kekuewa, Hawaiʻi Sea Grant postdoctoral affiliate researcher. "Understanding these legacy impacts can help us make better decisions about how we manage these areas moving forward."
Researchers paired the chemical record with measurements of coral growth, historical records of land-use change, and large-scale climate patterns such as El Niño. The coral recorded both natural climate variability and major changes occurring within the watershed. The research occurring at Olowalu is particularly important because it is one of Hawaiʻi's largest continuous reef systems, and an important source of coral larvae for reefs throughout Maui Nui.
"Across Hawaiʻi, there is already a large amount of work being done by the community to restore watersheds, retain sediment on land, and protect the downstream coral reefs," said Kekuewa. "Records like this can help provide the long-term context needed to support and guide that work."
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