By lisa D. Mickey
As a participant in the Indian River Lagoon National Estuary Program’s shellfish
restoration grant to the University of Florida, Riverside Conservancy is helping spread
the word about the role clams play in improving the lagoon’s health.
The Conservancy has worked with Dr. Todd Osborne at the University of Florida’s
Whitney Laboratory in St. Augustine since 2021 on Osborne’s IRL Clam Restoration
Project. That program is focused on how hard clams (Mercenaria mercenaria) work as
filter feeders to improve water clarity and thereby, help improve overall water quality.
“Dr. Osborne’s clam restoration program in Brevard County has been a great example
of public/private partnership efforts to restore the Indian River Lagoon,” said Kelli
McGee, Riverside Conservancy’s Executive Director.
“Riverside Conservancy is proud to help expand this program into Volusia County,”
added McGee, who has been speaking to local groups about the role clams play in the
ecosystem. Conservancy staff have also brought newly found adult clams from the
Mosquito Lagoon to Whitney Lab for inclusion in the breeding program.
Staff and student interns at Riverside Conservancy regularly sample water quality in the
lagoon and post monitoring results on the center’s website.
Osborne’s IRL Clam Restoration Project looked at how the lagoon’s compromised water
quality contributed to the loss of the IRL’s hard-clam fishery (also known as Quahogs)
and how the clam fishery was once a key component in the state’s seafood industry.
Since the 1980s, widespread commercial and residential development around the IRL,
as well as overharvesting of hard clams alongside seagrass decline, have combined for
a detrimental recipe in a lagoon system economically valued around $7.64 billion per
year.
Osborne observed that without clams in the lagoon to work as filter feeders, water in the
lagoon is more turbid (cloudy) -- shading out and ultimately killing seagrass. In turn,
decaying seagrass contributes to reduced dissolved oxygen upon which healthy fish
and shellfish populations depend.
So, in the spring of 2019, Osborne and a team of researchers embraced the concept of
“natural selection” after collecting a few large remaining hard clams that had outlived
recent harmful algal blooms and low-oxygen events in the IRL.
They took these “super clams” back to Whitney Lab, where they were spawned. The
progeny was then collected and reared in the lab’s hatchery, a land-based nursery and
in a field nursery. After about 8-12 months -- with the clams each measuring around
one-inch in size -- the clams are moved to restoration areas.
Osborne and his team began out-planting some four million clams to aquaculture lease
areas throughout the IRL in the fall of 2019. They worked with participating lease
holders to offer additional protection from harvesting.
The baby “super clams” were spread into the lagoon waters and then protected by
cover nets to help reduce natural predation during their first years of growth by such
species as stingrays, fish and other mollusks.
Even at one year, the planted clams begin to filter water immediately at the rate of three
gallons per clam per day – eventually capable of filtering 20 gallons of water per clam
each day two to four years later.
“Hinging on our belief that natural selection is working … we’re counting on the
survivors that we can find in the Indian River Lagoon to be exceptionally well adapted to
the environmental insults they have survived thus far,” said Osborne of his clam
spawning program.
“We’re hoping that the expression of these genes that have allowed them to survive will
make them suitable to help us restore the IRL by being able to do what they do so well
– filter water – and to continue to do so in the [estuary] system,” he added.
Osborne calls oysters and clams “players in the game” of balancing nutrients between
algae and other organisms and he states it is his project’s goal to reintroduce a missing
member of its ecosystem.
“We’re reintroducing clams, and especially these clams that are adapted to this
ecosystem the way it is now,” he added. “[This] should be a huge step in the right
direction for improving our water quality and that relates back to seagrasses and to the
health of the [lagoon] system itself.”
Osborne believes if his “super clams” can help improve the lagoon’s water quality by
improving its water clarity, then seagrasses can more easily be reestablished, providing
habitat and food sources for other species in the system. He admits “there’s a long way
to go,” but believes the new “frontier colonies are moving us toward better water
quality.”
And with “super clams” laying the bottom-dwelling foundation for the challenged Indian
River Lagoon, Osborne sees a true possibility for a trickle-up effect by this magnificent
mollusk.
Want to learn more? Visit https://www.indianriverclamrestorationproject.org/