Coral core traces 253 years of change at Olowalu Reef
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A 253-year-old coral core from Olowalu Reef has given researchers a record of environmental changes off West Maui dating to about 1760.
The study, published in the journal Coral Reefs, was led by researchers from the University of Hawaii Sea Grant College Program, UH Manoa's School of Ocean and Earth Science and Technology and the U.S. Geological Survey.
Researchers analyzed chemical indicators preserved in a core taken from a massive coral colony to reconstruct changes in sediment, nutrients and other material entering coastal waters from the land between about 1760 and 2013.
Those indicators generally increased over the 253-year record, with some of the largest changes occurring during the 20th century as sugarcane agriculture expanded across West Maui, according to the study.
The coral’s growth record showed that calcification increased through much of the period before beginning to decline around the late 1960s, coinciding with the expansion of sugarcane agriculture.
Plantation workers are shown in a historical photograph provided with a study examining environmental changes at Olowalu Reef. Photo courtesy Alexander & Baldwin
Similar to tree rings, coral skeletons preserve evidence of past environmental conditions as they grow, incorporating elements from the surrounding seawater. Researchers measured that chemistry along the length of the Olowalu core and compared the results with coral growth measurements, historical records of land-use changes and large-scale climate patterns such as El Nino.
The coral recorded both natural climate variability and major changes occurring within the watershed, according to researchers.
"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, Hawai'i Sea Grant postdoctoral affiliate researcher. "Understanding these legacy impacts can help us make better decisions about how we manage these areas moving forward."
Olowalu is shown in this photograph from around 1960. Researchers studying a 253-year coral record found that calcification began declining around the late 1960s, coinciding with the expansion of sugarcane agriculture. Photo courtesy SOEST Climate Resilience Collaborative
Olowalu is one of Hawaii's largest continuous reef systems and an important source of coral larvae for reefs throughout Maui Nui. The study could aid efforts underway across Hawaii to restore watersheds, retain sediment on land and protect downstream coral reefs.
"Records like this can help provide the long-term context needed to support and guide that work," Kekuewa said.
A coral core is shown in an image provided with research examining 253 years of environmental changes at Olowalu Reef. Photo courtesy U.S. Geological Survey