Seagrass cover in St. Joseph Bay in 2011.
Seagrass cover in St. Joseph Bay in 2017. Note the bare areas of sand, caused by overgrazing urchins.
Sea urchins grazing on turtle grass in St. Joseph Bay.
Result of urchin overgrazing near Steinhatchee, FL.
St. Joseph Bay, located in Florida’s panhandle in Gulf County, once supported an abundant scallop fishery that has become depleted in recent years. The beds of seagrass, like turtlegrass, that support marine life such as bay scallops, were being overgrazed by an overabundance of sea urchins. This project by FWRI’s Habitat Assessment and Restoration team will jump start natural recovery of seagrass by installing up to 12 exclosures over grazed areas to allow seagrasses to grow without sea urchin grazing pressure. Once the density of seagrass returns to near normal levels, the exclosures will be removed or placed in other bare areas.
In 2020, FWRI scientists secured permits from the US Army Corps of Engineers and the Florida Department of Environmental Protection (FDEP) to install exclosures in one of the heavily grazed areas of St. Joe Bay. Four exclosures were installed and left in place for three months as a pilot scale experiment. Based on the results of the 2020 work, 12 exclosures will be installed in spring 2021. Researchers have also surveyed seagrass and sea urchin abundance along transects every three months, and sea urchins are still abundant and actively grazing seagrass.
Sea urchins have also negatively impacted seagrass beds elsewhere in Florida. In 1973, large aggregations of Lytechinus were seen at a seagrass site in Dixie County, as well as in 2002 in the Florida Keys. Both events caused large seagrass losses of turtle grass and manatee grass. While the current urchin irruption in St. Joseph Bay is similar to those events, it is different in two important ways: First, turtle grass is the most abundant seagrass in St. Joseph Bay, and, because of the physical environment and added stressors in southern St. Joseph Bay, turtle grass might not be able to recover without assistance. Second, previous urchin irruptions have occurred over large areas in deeper water, making human intervention very difficult. Urchin grazing fronts in St. Joseph Bay are in water shallow enough to attempt harvest and relocation. Furthermore, the concentration of urchins along grazing fronts makes manual collection easier than it would be if urchins were dispersed. Areas that have been decimated by urchin grazing are also located in water shallow enough to use exclosures to protect seagrasses during recovery.
This project is a partnership between two state agencies - FWC and the FDEP - that will prevent further losses of seagrasses by mobilizing teams of scientists and agency staff to remove herbivorous sea urchins whose population have irrupted in the past five years. Stakeholder meetings will be conducted to enlist members of the public in urchin control efforts. If legal staff agree, public outreach events including Sea Urchin Roundups will be held to relocate urchins. Following stabilization of urchin grazing fronts in seagrass beds, natural recovery will be enhanced by creating temporary herbivore exclosures and by planting Thalassia seedlings collected from other areas within the Bay. Monitoring of seagrass cover expansion and loss is a key component of the project, and the researchers’ goal is to restore 20% of the seagrass lost within two years. Biologists anticipate improvements in water clarity in response to increased seagrass cover, and turbidity and phytoplankton chlorophyll concentrations will be measured quarterly during the project.
The FWRI researchers involved with this work are Vicki Absten, Allison Patranella, Mike Poniatowski, Laura Yarbro, and Paul Carlson. Jonathan Brucker from FDEP also contributes to this project.
This project aligns with the Gulf of Mexico Program Priority Area II, which is to protect, enhance, or restore habitat, and biologists have designed it to do all three tasks. Researchers will protect existing seagrass from future damage by removing sea urchins, they will enhance and restore grazed areas by using exclosures to give surviving patches of seagrass time to recover without additional urchin grazing, and they will restore lost seagrass area using the exclosures and seedlings collected from turtle grass in other parts of St. Joseph Bay.