Sebastian News

Marine Biologists Complete Survey of Nearshore and Offshore Hardbottom Reef South of Sebastian Inlet

A team of marine biologists from CSA Ocean Sciences completed field surveys last week as part of environmental monitoring of the hardbottom reef South of the Sebastian Inlet following the completion of the Sebastian Inlet District’s state-mandated sand bypass and beach placement project.

“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.  “We also have biologists from Ecological Associates, Inc. (EAI) that will be monitoring the beaches for the entire 2019 sea turtle nesting season to document sea turtle nesting activity and assess any escarpments or changes in the profile.  We know from experience that beach renourishment projects can be completed in a way that protects these valuable natural resources.”

The project began on January 20 and phase I beach operations concluded on March 26 with an estimated 110,000 cubic yards of beach-quality sand placed onto a 1½ mile stretch of downdrift beaches 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 sand was dredged from the inlet’s sand trap, a 42-acre submerged depression that collects sand that migrates into the inlet.

Beach profiles were built according to specifications designed by coastal engineers and authorized by permits.  The Sebastian Inlet District works with coastal engineers, marine biologists and partners at the FDEP, Army Corps of Engineers (USACE) and Florida Fish & Wildlife Commission (FWC) in permitting, planning and conducting all beach renourishment projects.

Biologists from CSA Ocean Sciences spent several days gathering data while diving along nine transects, or sections that run perpendicular to the shoreline, at 1,000-foot intervals and up to 100 feet offshore within the project area.

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 flora and fauna in both the nearshore and offshore habitats.

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.

“Sand is in constant, natural motion along our coast as an ephemeral system,” said Gray.  “Coastal Engineers anticipate and design for the sand to naturally transport, along the project area.”

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.

“We work closely with FDEP through all phases of our beach renourishment to include the permit-required biological monitoring of the hardbottom, ” said Gray.  “FDEP standardized monitoring protocols required for comparison purposes to ensure nearshore hardbottom habitat protection.  We start with a pre-project baseline, monitor immediately post-project, and then conduct three years of annual monitoring thereafter.”

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.

Marine Biologist and team leader Chip Baumberger of CSA Ocean Sciences completes a quadrat survey.