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Marine Lab Studying Oyster Growth in Caloosahatchee

December 6, 2023
Oyster Growth

Earlier this year, the SCCF Marine Laboratory deployed bags of oysters in the Caloosahatchee Estuary along the flow of the river to understand how changes throughout the estuary affect oyster growth and survival.

The study was a collaboration with Florida Gulf Coast University (FGCU), which is an ongoing partner of the SCCF Marine Lab for a bimonthly oyster spat survey.

Unfortunately, despite placing oysters at five sites, only one site could be studied over the study’s full 16 weeks due to rampant barnacle growth.

“Barnacles covered our living oysters, potentially competing for food and space for new oysters to settle and grow. This made it difficult to accurately measure and count oysters,” said SCCF Marine Lab Research Assistant Isabella McDonnell.

Rampant barnacle growth occurred over the course of the study. Pictured here is a group of oysters before and after 16 weeks at the base of the river. 

Advanced barnacle settlement, density, and growth could be partly due to Hurricane Ian, which stirred up nutrient-rich sediment, McDonnell said.

“Like oysters, barnacles are filter feeders, surviving and thriving from nutrients within the water. Barnacles may have also thrived due in part to decreased predation and feeding competition, as the hurricane likely altered the food web,” she said.

The team tracked the settlement of oyster larvae, growth, and mortality rates from the site at the base of the river, near Shell Point. FGCU students also collected larvae samples and counted the number of juvenile oysters settled. Overall, the number of oysters increased, and the average height decreased as new spat settled. 

FGCU students sample oyster larvae while SCCF Marine Laboratory Director Eric Milbrandt deploys a PVC ‘T,’ where oyster shell strings and bags containing living oysters are hung.

By tracking oyster growth over the summer, insights into their lives within the estuary can be better understood. This work will also provide a baseline for future studies within the estuary.

“We can use this data to learn more about how oysters grow and track correlations with freshwater releases into the estuary. The more healthy oyster reefs we have, the more water is being filtered, improving water quality,” McDonnell said. “In upcoming years, methods can also be tweaked to decrease barnacle growth. And, for our own sake, we hope that barnacles take a backseat.”

Importance of Oysters

  • Oysters are a valuable resource in marine environments. The reefs they build are home to many marine species of varying ages, creating habitats with intricate food webs.
  • Oysters improve water quality. A single oyster filters 50 gallons of water a day, removing some nutrients and pollutants as they feed.
  • Oyster population health is one way to monitor the general health of the ecosystem.
  • Oyster reefs have been declining globally, and many reefs are at risk.

The Caloosahatchee is not immune to oyster declines and is known to experience dramatic changes due to varying levels of freshwater flow from Lake Okeechobee and the surrounding watershed. Freshwater from the river changes the salinity of the water and contains higher levels of nutrients, which can negatively impact oysters by decreasing reproduction, growth, and survival.

Learn more about SCCF’s oyster restoration and research >>


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