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FAU researchers measured aragonite saturation \u2013 a key indicator of water\u2019s ability to support calcifying organisms like clams and oysters \u2013 throughout the Indian River Lagoon. <\/p>\n
\n Study Snapshot: Florida\u2019s Indian River Lagoon is facing growing environmental stress from nutrient runoff, freshwater discharges, and harmful algal blooms. In addition, increasing atmospheric CO2 is causing acidifying waters, which make it harder for shell-building organisms like oysters and clams to grow and maintain their shells. When the water can\u2019t support shell growth, these organisms become stressed, and their shells can even start to dissolve.<\/p>\n
A new study by FAU\u2019s Harbor Branch Oceanographic Institute measured aragonite saturation \u2013 a key indicator of water\u2019s ability to support calcifying organisms \u2013 throughout the lagoon. The research found that areas with higher nutrients and lower salinity have lower aragonite levels, putting shellfish and other marine life at risk. This is the first study to map these conditions across the entire lagoon and provides critical information for future monitoring and restoration efforts.<\/p>\n
Florida\u2019s Indian River Lagoon (IRL), one of the state\u2019s 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.<\/p>\n
A new study from Florida Atlantic University<\/a>\u2019s Harbor Branch Oceanographic Institute<\/a> 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.\u00a0<\/p>\n Many marine animals, including oysters and clams, rely on a mineral called aragonite to build shells and skeletons. Scientists measure the water\u2019s ability to support aragonite using aragonite saturation (\u03a9arag).<\/p>\n To understand these changes, FAU Harbor Branch researchers studied the IRL from 2016 to 2017, measuring \u03a9arag and other water chemistry factors. They examined how nutrients, freshwater inputs, and other environmental conditions affect the lagoon\u2019s ability to support shell-building marine life.<\/p>\n 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.<\/p>\n Results of the study, published in the journal Marine Pollution Bulletin<\/a>, 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 \u03a9arag, primarily due to reduced salinity and dilution of aragonite. In the weekly surveys, \u03a9arag 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.<\/p>\n \u201cFor shell-building organisms, the consequences are clear,\u201d said Rachel Brewton<\/a>, Ph.D., co-author and an assistant research professor, FAU Harbor Branch. \u201cWhen 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 \u2013 they\u2019re a warning for the entire ecosystem.\u201d<\/p>\n 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\u2019s chemistry and the health of shell-building organisms.<\/p>\n \u201cCoastal acidification occurs when carbon dioxide, CO\u2082, from the atmosphere or from biological processes, such as microbial activity associated with decaying algae, dissolves in seawater. This CO\u2082 reacts with water to form carbonic acid, which lowers the water\u2019s pH and reduces the amount of carbonate ions available for shell-building,\u201d said Brian Lapointe<\/a>, Ph.D., senior author and a research professor, FAU Harbor Branch. \u201cIn addition to atmospheric CO\u2082, nutrient pollution from urban runoff, agricultural sources, and wastewater can fuel algae growth. When these algae die and decompose, the process produces more CO\u2082, further acidifying the water.\u201d<\/p>\n 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.<\/p>\n The results have broader implications. Estuaries worldwide are experiencing similar pressures from population growth, land-use changes, stormwater runoff, and nutrient pollution.<\/p>\n \u201cBy identifying the environmental conditions that lower aragonite saturation, we can start to develop strategies to mitigate coastal acidification,\u201d said Megan Conkling, Ph.D., first author and research scientist at FAU Harbor Branch. \u201cManaging 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.\u201d<\/p>\n The study also emphasizes the importance of ongoing monitoring. FAU Harbor Branch\u2019s Indian River Lagoon Observatory Network of Environmental Sensors (IRLON<\/a>) has been upgraded to track pH and CO\u2082 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.<\/p>\n \u201cProtecting 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,\u201d said Conkling. \u201cThis study provides essential insight into one of the less visible but critical threats facing estuaries today.\u201d<\/p>\n