Cephalopodcast

Florida Surf Clams (aka, Coquina, Donax variabilis), © Jason Robertshaw

What the Shell Is That? is my series on beachcombing and tidal life. Living on the west coast of Florida, it is mostly about shells, but can also be about other flotsam, fauna and even flora.

Note:
This is a bonus, double-feature entry. You get the WSIT #5 and Cephalovlog #4 combined in one.

Florida Surf Clams (aka, Coquina, Donax variabilis)

Date: 6 April 2008
Location: Siesta Key, Sarasota, Florida, U.S.A.
All along the surf.

Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Order: Veneroida
Family: Donacidae
Genus: Donax
Coquina Clams (Donax variablis)

Report:
Surf clams, also called Coquina, are bean-sized (2 cm), colorful bivalves that make their living in one of the most challenging habitats, the surf zone. They are filter feeders, extending their siphons into the water as it washes over them. As the wave pulls back out, they are often exposed at the surface and have to quickly put their muscular foot down to scoot back beneath the sand. It seems like a very energetically expensive way to make a living and it’s surprising they get enough nutrients from just filtering bacteria and algae out of the water (but still further proof that even the tiniest mollusks are tough enough to whip any echinoderm’s hiney).

The clams, in turn, are an important food source for shorebirds. People seem to like them too, but personally I have never eaten them before. The shells of these animals also accumulate over time and mix with other sediment to form a consolidate material called Coquina rock. It is used as a building material throughout Florida.

Something else that was remarkable, and requires more investigation, was the presences of hundreds of small marine worms. You can see a close up in the video about half way through. These worms would suddenly appear in the hundreds, wriggling after a wave wash, only to disappear instantaneously beneath the sand.

Cephalovlog #4: 60 Second Surf

I borrowed the Sanyo Xacti E1 from work for a field test. This little camera is immersible to 5 meters. I did not need to send it that far down to video these little guys, as they are in the wash zone of the beach. Video was edited in iMovie and scored in Garageband. Note, this is not time-lapse footage. The clams really do dig that fast.

Donax me

References

• Ruppert, Edward and Richard Fox. Seashore Animals of the Southeast. Columbia: University of South Carolina Press, 1988. pp. 158.
• Witherington, E., Blair and Dawn Witherington. Florida’s Living Beaches. City: Pineapple Press (FL), 2007. pp. 109.

Additional Links

• YouTube: Cephalovlog #5
• Wikipedia: Donax
• Wikipedia: Coquina rock
• SeashellGuide.com: Coquina: Catching “Butterflies”
• FL Fish and Wildlife Research Institute: Coquina Clams