Groundwater directly affects water chemistry in coral reefs and triggers a cascade of changes in the coastal ecosystem, according to a new study led by University of Hawaiʻi at Mānoa oceanographers. The researchers describe the effect as a "Goldilocks scenario"—too much groundwater has a negative impact, and when the input is "just right," the reef benefits.
Freshwater from land that flows into the ocean beneath the sea surface, termed submarine groundwater discharge, was found to indirectly affect the ecosystem by changing the acidity of the seawater and impacting the process by which corals build their skeletons. One finding, however, was that researchers discovered that groundwater discharge increased nutrient availability to help reefs thrive. This research, published in Ecological Monographs , provides critical insights into the complex interactions between the land and ocean.
"One idea we hope this research can communicate is the natural role of groundwater in feeding healthy reefs," said Craig Nelson, study co-author and faculty in the UH Mānoa Daniel K. Inouye Center for Microbial Oceanography . "Runoff and springs bring subsidies of nutrients and organic matter that can help reefs thrive, and the complex interplay this work illuminates demonstrates that some reefs are adapted to these inputs."
"Submarine groundwater discharge is a widespread and underappreciated land-sea connection that delivers terrestrial nutrients and carbon to coastal ecosystems," said Nyssa Silbiger, lead author of the study, associate director of the Uehiro Center for the Advancement of Oceanography , and associate professor in the Department of Oceanography at the UH Mānoa School of Ocean and Earth Science and Technology (SOEST). "This profoundly influences coral reef health by triggering a cascade of chemical and biological changes that alter the cycling of carbon in these ecosystems."
Cascading impacts at Moʻorea reefs
Silbiger and collaborators studied two coral reef sites in Moʻorea, French Polynesia that were chosen based on surveys indicating fresh groundwater, as well as discussions with local fishers with historical knowledge of the island. The research team measured water quality parameters that can change directly in response to the groundwater input as well as change indirectly in response to altered biological activity of the coral reef community.
Nutrients from submarine groundwater boosted the productivity of both photosynthetic algae and corals which, in turn, changed seawater acidity and altered the calcification of coral skeletons. Defining this complex exchange between organisms and the chemistry of the seawater around them is crucial for developing a more holistic understanding of how reefs work.
"We show that adding new nutrients to the coastal ocean alters the metabolism of coral reef ecosystems, thereby changing the patterns of uptake and release of carbon," said Silbiger. "This highlights a chain reaction where enhanced biological activity, fueled by submarine groundwater discharge, directly affects the acidity of the water and, subsequently, the ability of reefs to grow."
Informing management of Pacific coral reefs
The authors hope that their work can help emphasize the importance of keeping groundwater free of contaminants for the benefit of both land and ocean ecosystems.
"These findings are vital for protecting coral reefs across the Pacific from land-based pollution and informing sustainable land management," said Megan Donahue, study co-author and director of the Hawaiʻi Institute of Marine Biology in SOEST. "Understanding these cascading effects allows us to predict how coral reefs respond to a changing world and provides a framework to connect ecosystem ecology to land-based activities."
See the entire story on SOEST's website .
—By Marcie Grabowski
The post Groundwater discharge found to alter coral reef ecosystems first appeared on University of Hawaiʻi System News .
