FAU researchers measured aragonite saturation – a key indicator of water’s ability to support calcifying organisms like clams and oysters – throughout the Indian River Lagoon.
Photo Credit: Courtesy of Florida Atlantic University
Scientific Frontline: "At a Glance" Summary
- Main Discovery: Elevated nutrient runoff, freshwater discharges, and harmful algal blooms are accelerating coastal acidification in Florida's Indian River Lagoon, resulting in critically low levels of aragonite saturation necessary for shell-building organisms to survive.
- Methodology: Researchers performed a comprehensive spatial survey of the entire lagoon alongside weekly monitoring at three distinct central sites—an urban canal, a river mouth, and a natural reference area—between 2016 and 2017 to measure water chemistry and correlate aragonite saturation (\(\Omega_{arag}\)) with environmental stressors.
- Key Data: The study established a strong positive correlation between aragonite saturation and salinity, with data showing that nutrient-dense northern regions and freshwater-impacted southern areas consistently exhibited saturation levels insufficient for healthy shell development.
- Significance: Depleted aragonite levels inhibit the growth and structural integrity of calcifying species like oysters and clams, making them more vulnerable to predation and disease, which threatens the stability of the entire estuarine food web and local economy.
- Future Application: These findings provide a baseline for new ecosystem management strategies focused on controlling nutrient inputs and freshwater flows, supported by real-time pH and \(\mathrm{CO_2}\) monitoring via the upgraded Indian River Lagoon Observatory Network of Environmental Sensors (IRLON).
- Branch of Science: Marine Biogeochemistry and Estuarine Ecology
- Additional Detail: This research represents the first complete documentation of aragonite saturation distribution across the entire Indian River Lagoon, identifying specific "hotspots" where local anthropogenic pressures amplify global ocean acidification trends.
Florida’s Indian River Lagoon (IRL), one of the state’s most ecologically productive estuaries, is facing a growing but invisible threat that could reshape its marine ecosystems. Over the past decade, the lagoon has suffered severe degradation caused by nutrient pollution, excessive freshwater runoff, harmful algal blooms (HABs), and declining water quality. These changes have led to the loss of tens of thousands of acres of seagrass and have negatively impacted shellfish, fish, dolphins, manatees and other key species.
A new study from Florida Atlantic University’s Harbor Branch Oceanographic Institute now reveals that these pressures are also contributing to coastal acidification, a chemical shift in the water that threatens the ability of shell-building marine organisms to grow and thrive.
Many marine animals, including oysters and clams, rely on a mineral called aragonite to build shells and skeletons. Scientists measure the water’s ability to support aragonite using aragonite saturation \(\Omega_{\text{arag}}\).
To understand these changes, FAU Harbor Branch researchers studied the IRL from 2016 to 2017, measuring \(\Omega_{\text{arag}}\) and other water chemistry factors. They examined how nutrients, freshwater inputs, and other environmental conditions affect the lagoon’s ability to support shell-building marine life.
The study used two approaches. First, researchers conducted a broad survey across the lagoon, from nutrient-rich northern areas to southern regions affected by freshwater inflows. Second, they did weekly sampling at three central sites with different salinity and land-use conditions: an urban-influenced canal, a river mouth affected by urban and agricultural runoff, and a relatively natural reference site with strong ocean exchange.
Results of the study, published in the journal Marine Pollution Bulletin, revealed clear patterns. Northern sites with high nutrient concentrations and frequent HABs had lower aragonite saturation. Southern sites, influenced by freshwater discharges, also had lower \(\Omega_{\text{arag}}\), primarily due to reduced salinity and dilution of aragonite. In the weekly surveys, \(\Omega_{\text{arag}}\) was positively correlated with salinity and negatively correlated with nutrient levels, confirming that both freshwater input and nutrient pollution play a role in controlling water chemistry.
“For shell-building organisms, the consequences are clear,” said Rachel Brewton, Ph.D., co-author and an assistant research professor, FAU Harbor Branch. “When aragonite saturation drops, growth slows and shells become weaker, leaving animals more vulnerable to predators, disease and stress. Over time, this can disrupt the food web, affecting fish, dolphins, and the human communities that rely on these species. Shrinking shellfish are more than a curiosity – they’re a warning for the entire ecosystem.”
This research provides the first comprehensive documentation of aragonite saturation throughout the entire IRL, filling a critical gap in our understanding of coastal acidification in shallow estuaries. Prior studies focused on nutrient pollution, algal blooms, or freshwater inflows, but none had examined how these factors interact to impact the water’s chemistry and the health of shell-building organisms.
“Coastal acidification occurs when carbon dioxide, \(\mathrm{CO_2}\), from the atmosphere or from biological processes, such as microbial activity associated with decaying algae, dissolves in seawater. This \(\mathrm{CO_2}\) reacts with water to form carbonic acid, which lowers the water’s pH and reduces the amount of carbonate ions available for shell-building,” said Brian Lapointe, Ph.D., senior author and a research professor, FAU Harbor Branch. “In addition to atmospheric \(\mathrm{CO_2}\), nutrient pollution from urban runoff, agricultural sources, and wastewater can fuel algae growth. When these algae die and decompose, the process produces more \(\mathrm{CO_2}\), further acidifying the water.”
Other factors, such as freshwater inflows from rivers and canals, also influence aragonite saturation by diluting the water and lowering salinity and mineral concentrations. In shallow estuaries like the IRL, where water circulation is slower than in the open ocean, these effects are amplified, creating localized hotspots where shell-building organisms are especially at risk.
The results have broader implications. Estuaries worldwide are experiencing similar pressures from population growth, land-use changes, stormwater runoff, and nutrient pollution.
“By identifying the environmental conditions that lower aragonite saturation, we can start to develop strategies to mitigate coastal acidification,” said Megan Conkling, Ph.D., first author and research scientist at FAU Harbor Branch. “Managing nutrient inputs and freshwater flows more carefully could help protect oysters, clams, seagrass, and other critical species. Our work provides a roadmap for designing restoration and mitigation efforts, not just in Florida, but in estuaries around the world.”
The study also emphasizes the importance of ongoing monitoring. FAU Harbor Branch’s Indian River Lagoon Observatory Network of Environmental Sensors (IRLON) has been upgraded to track pH and \(\mathrm{CO_2}\) levels, which allows scientists to calculate aragonite saturation in near real-time. This IRLON data can help forecast future changes, identify vulnerable species and habitats, and guide targeted management actions.
“Protecting the Indian River Lagoon requires understanding not just what we can see on the surface, like algae blooms or seagrass loss, but also the invisible chemical changes affecting marine life,” said Conkling. “This study provides essential insight into one of the less visible but critical threats facing estuaries today.”
Funding: This research was supported by the Harbor Branch Oceanographic Institute Foundation through the Saves Our Seas Specialty License Plate Program awarded to Lapointe.
Published in journal: Marine Pollution Bulletin
Title: Coastal eutrophication and freshwater inputs drive acidification in the Indian River Lagoon, Florida
Authors: Megan Conkling, Rachel A. Brewton, Bret R. Kaiser, Kristen S. Davis, Mingshun Jiang, and Brian E. Lapointe
Source/Credit: Florida Atlantic University | Gisele Galoustian
Reference Number: mb020326_01
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