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Marine Biologists Complete Hardbottom Reef Survey South of Sebastian Inlet


A team of marine biologists from CSA Ocean Sciences completed biological surveys of the nearshore and offshore hardbottom reef South of Sebastian Inlet in July as part of environmental monitoring conducted by the Sebastian Inlet District.

“This type of biological monitoring is extremely important given the environmental significance of the habitats surrounding the inlet,” said Sebastian Inlet District Executive Director James Gray.  “Associated with the District’s periodic, state-mandated sand bypass and beach placement projects, we work closely with our partners at the Florida Department of Environmental Protection (FDEP) through all phases to include the permit-required biological monitoring of the hardbottom along the beaches where sand is placed. We start with a pre-project baseline, monitor immediately post-project, and then conduct three years of annual monitoring thereafter.”

Biologists from CSA Ocean Sciences spent five days gathering data while diving along eight transects, or sections that run perpendicular to the shoreline.  These transects are at 1,000-foot intervals and run from the nearshore to 100 meters offshore within the project area starting near McLarty Treasure Museum and ending just South of Ambersand beach access, an area denoted by Florida Department of Environmental Protection (FDEP) R-monuments R10-R17.  The District’s last project was completed in March 2019.

Biologists conducted quadrat surveys, measured sediment depth to analyze sediment movement along transects, measured algae height and hardbottom relief, and mapped the western edge of the nearshore hardbottom for comparison purposes.  They also collected photos and video of the marine flora and fauna in both the nearshore and offshore habitats.

“July and August are ideal months for conducting hardbottom monitoring each year with clear water and great visibility,” said Gray.

Hardbottom is exposed limestone bedrock in coastal waters within 400 meters from shore, in water depths up to approximately 4 meters or 13 feet. The Florida peninsula is rimmed with this exposed limestone, with a greater prevalence on the East coast.

Hardbottom reefs dissipate wave energy and contribute to shoreline stability by acting as a natural breakwater.  A naturally transitory system, hardbottom regularly experiences cycles of burial and exposure over time.

Nearshore hardbottom typically occurs as shore-parallel bands of exposed rock, and is critically important because it supports diverse biological communities that contain macroalgae, invertebrates, fishes and sea turtles.  Over 1,000 species have been documented in these environments in Florida.  Juvenile endangered green sea turtles can associate with shallow hardbottom for years as part of their development cycle, feeding on the macroalgae and using the structure for shelter.  It also provides an essential fish habitat that includes spawning sites, settlement areas and nurseries for economically valuable and federally managed species like snappers and groupers.

Unique to nearshore hardbottom on the East coast is worm rock, a very important faunal component of this habitat.  Worm rock is composed of colonies of the reef-building sabellariidae tubeworm.  It is soft, made up of sand grains cemented together by a protein-like glue secreted by the worms.  Often referred to as a habitat engineer, much like corals, the worms create these reef-like structures that provide food and shelter to a broad range of other species.

“District Commissioners remain committed to environmental protection and natural resource preservation.  We know from experience that sand bypass and beach renourishment projects can be completed in a way that protects these valuable natural resources,” said Gray. “Every project is carefully designed and planned, appropriate environmental protocols are put in place and the District engages a whole host of partners to ensure no negative impacts.”

Biologists will now analyze the data and submit a report to the District and FDEP.   For a copy of the CSA Ocean Sciences report, once issued, or for more information, call (321) 724-5175.

The Sebastian Inlet District was created in 1919 as an independent special district by act of the Florida State Legislature, and chartered to maintain the navigational channel between the Atlantic Ocean and the Indian River.  The Sebastian Inlet District’s responsibilities include state mandated sand bypassing, erosion control, environmental protection and public safety.  The Sebastian Inlet supports a rich and diverse ecological environment that is unparalleled in North America.  The Inlet is vital not only to the ecological health of the Indian River Lagoon, but it is also an important economic engine for local communities in the region.  Known as the premier surfing, fishing, boating and recreational area on the east coast of Florida, the inlet is one of only five navigable channels that connect the Indian River lagoon to the Atlantic Ocean.

posted: 8/3/2020