Groundwater that enters the ocean from nearby land masses has a measurable impact on the “ecosystem metabolism” of coral reefs, according to a study recently published by CSUN Assistant Professor of Biology Nyssa Silbiger and collaborators at the University of Hawai’i at Mãnoa and the Scripps Institution of Oceanography.
Silbiger and her coauthors examined the effects of groundwater contributions to two reef communities in Maunalua Bay, Hawaii, that received groundwater inputs from different onshore watersheds. The team established grids of water sampling sites across each reef, and tracked the water chemistry to estimate how much groundwater input each site received, and how changes in the groundwater input tracked changes in the photosynthetic and calcification activity in the living communities of the reefs. They found that nutrients carried into the ocean by groundwater could enhance photosynthetic productivity — but that the largest observed inputs of concentrated nutrients could also overwhelm that productivity, probably by promoting population booms in non-photosynthetic microbes. Groundwater inputs also shaped the pH of seawater over the reefs, affecting the calcification activity of organisms like corals.
Image: Maunalua Bay, where the study was conducted (Doug Harper, CSUN Today)