Cascading impacts of groundwater input to coral reefs
by Marcie Grabowski, University of Hawaiʻi at Mānoa
June 26, 2025
Groundwater input to coral reefs directly affects water chemistry and triggers a cascade of changes in the coastal ecosystem, according to a new study led by University of Hawaiʻi (UH) at Mānoa oceanographers. Freshwater from land that flows into the ocean beneath the sea surface, termed submarine groundwater discharge, was found to increase nutrient availability, change acidity of the seawater, and impact the process by which corals build their skeletons. This research, published recently in Ecological Monographs, provides critical insights into the complex interactions between the land and ocean.
“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. “This profoundly influences coral reef health by triggering a cascade of chemical and biological changes that alter the cycling of carbon in these ecosystems.”
The fundamental connection between land and sea through the flow of freshwater is a universal principle recognized as important for coastal health across all cultures. Porous volcanic islands throughout the tropics deliver much of this water through rivers and streams, but a major fraction emerges unseen directly into the coral reefs that ring these islands. This submarine groundwater discharge has long been recognized by Pacific peoples as important, with seeps frequently named and associated with specific communities of algae and fish relevant to subsistence. The new research has helped define the complex interplay of chemistry and biology that makes these inputs so important to the ecology of coral reefs.
Keep reading: https://www.soest.hawaii.edu/soestwp/announce/news/cascading-impacts-of-groundwater-input-to-coral-reefs/
Read the Ecological Monographs paper: https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecm.70020