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Drive-In Diving: South Florida’s Urban Nudibranchs
By Gabriel Jensen, February 14, 2024 @ 08:00 AM (EST)

Felimare picta is the largest nudibranch in the region, some getting up to seven inches in length, typically living on low reef structure
 

South Florida is best known for its glitzy nightlife, endless condos, engineered canals, and sordid history, but it should also be known as a world-class dive destination for sea slug enthusiasts! Stretching between Jupiter in the north all the way to the world-famous South Beach, the South Florida metropolitan area is bordered by the nutrient-rich Everglades to the west and the thrid-largest reef tract in the world to the east. Well known to local divers, much of the region’s best wildlife can be found in the urban canals and under roadway bridges.

There are endless viral videos of sharks, dolphins, crocodiles, manatees, and goliath groupers taken from dazzled passersby as they jog across bridges or peek into canals, but sea slugs seem to get lost in the cast of underwater characters. Having taken a particular interest in nudibranchs, I was delighted to find that nearly every interesting genus of sea slug prized by photographers in the tropical Pacific was represented by at least one similar species in Florida.

Now, on a quest to save on my cross-Pacific airfare, please join me while we look at the incredible variety of sea slugs thriving just a stone’s throw away from the busy Florida roadsides!
 

Felimida clenchi is a rubble dweller that can be found under the bridges, in the canals, and off the beaches
 

Flabellina dushia is a common find at the Blue Heron Bridge enjoying hydroid and rubble environments

 

Under the Bridges and in the Canals

The most famous and extensively covered dive site in North America is the Blue Heron Bridge. While it is widely regarded as the most accessible place in the region to find sea slugs, there are other bridges that capture most of the same magic and—more importantly—have varying levels of salinity, a key ingredient for finding a variety of sea slugs. Swimming slowly, I’ve discovered that each habitat has its own smorgasbord of slugs.
 

Janolus cf flavoannulatus is an introduced species of nudibranch native to Southeast Asia, now a rare find at various Palm Beach county bridges, including the Blue Heron Bridge. Photographed in the muck with a sparkle background
 

The crown jewel of Caribbean sea slugs, Felimare acriba. This slug can get up to six inches in length and is highly decorated. During summer when nutrient load is highest, local nudibranchs will bulk up and find mates

 

The Wide-Open Prairie

I believe the prettiest sea slugs are the solar-powered cousins of nudibranchs, the sacoglossans. They thrive in the seagrass environments in the intracoastal saltwater “lakes” that form inside the major inlets. Lake Boca, Lake Worth Lagoon, Haulover, and upper Biscayne Bay via Rickenbacker Causeway have seagrass meadows and are all great places to park your ride and suit up for a slug hunt in front of very confused party boats.
 

A seasonal visitor, the photosynthetic Ercolania viridis can only be found on the tumbleweed roots of the calupera algae in fall, under bridges and seagrass meadows. This 8mm subject was imaged using the Nauticam SMC-2 close-up optic

 

Busy Beachsides

The Florida Reef Tract comes within 300 feet of dry land in some parts of Broward County, providing easy shore access to sunlit shallow reefs teeming with sea slugs. The only con is working to get the sand off before heading home.

While the allure of roadside nudibranchs is undeniable, this unique ecosystem must be approached with the same sense of responsibility and conservation as any other habitat.
 

Thuridilla mazda is a semi-common sighting in the seagrass meadows and nearshore reef structures. Their strong pattern hides them well among algae, and it is best to look for them on the sand between fronds

 

Tips for Finding Roadside Nudibranchs

  • Choose the right time: Opt for diving near the high or low slack tides to take advantage of calmer conditions. This is critical around bridges where tidal currents can be extreme.
  • Note what they feed on: This goes for finding nudis everywhere, but knowing what your target sea slug eats means you have a better chance of tuning your focus and spotting them.
  • Bring extra magnification: While there are a few “jumbo hotdog” size nudibranchs in the region, you’ll find there are many, many more beautiful and colorful “pinto bean” or “grain-of-rice” size slugs on each dive. Take advantage of these plentiful tiny subjects by bringing some extra help for your long macro lens.  
  • Prepare for backscatter: Many of these environments suffer from excess nutrient runoff, so visibility can range from 50 feet plus to just past your fins. Bringing light control devices like snoots or artificial backgrounds can help you combat backscatter and separate your subject from the muck.
  • Use a dive flag: These are some of the busiest waterways on the planet, full of jet skiers and pleasure boats ready to end your underwater imaging-making career. Using a flag lets them know to slow down—especially important since most of these dives are so shallow.


Plocamoperous lucayensis exclusively lives on the purple feather bryozoans, which tend to encrust submerged concrete structures. A common find in winter, they will hide during the day and come out at night. A double snooted image from behind and from on top

 

Final Thoughts

The roadside nudibranchs of South Florida offer a unique and accessible opportunity for underwater photographers and marine enthusiasts to explore the ocean's wonders. By diving into these coastal waters, we not only witness the beauty of these often overlooked and underappreciated creatures, but also become stewards of their conservation and the habitats they live in. Let us celebrate the extraordinary treasures that lie just next to our ordinary roadsides!
 

The Atlantic’s version of the famous leaf sheep nudi, the Costasiella ocellifera is a common find if you know where to look. It’s especially prevalent in roadside patches of its Avrainvillea algae home, usually in less than six feet of water
 

To journey along with more of Gabe's South Florida sea slug adventures, please give him a follow on Instagram.

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