The Tampa Drill - Eupleura tampaensis (Conrad, 1846)

By Marlo F. Krisberg

The Tampa Drill - Eupleura tampaensis (Conrad, 1846)     Dr. R. Tucker Abbott in his Guide to Field Identification Seashells of North America (1974) and Dr. Harald Rehder in the Audubon Society Field Guide to North American Seashells (1981) report the Tampa Drill as found on the West central coast of Florida. Rehder describes its habitat as "on mud flats intertidally" and Abbott as "on mud flats and near oyster beds." Both agree that its favorite food are the small mussels of the genus Brachidontes. Rehder suggests that the Tampa Drill may also prey on small oysters.

((hold mouse pointer over the image to see a ventral view))

     In 1995 Paula Mikkelsen et al. published a paper in the Bulletin of Marine Science entitled "Molluscan Biodiversity in the Indian River Lagoon, Florida." The paper recorded mollusks collected from the Indian River lagoonal system from 1974 to 1994. The lagoon extends along Florida's east coast from Ponce Inlet (Volusia County) to Jupiter Inlet (Palm Beach County). Although Mikkelsen's data were based upon 4,503 records from 1,150 collecting stations throughout the lagoon, no record of the Tampa Drill was found until early 1993 when I found a few small empty shells in the Banana River in Brevard County. Within a few months of further exploration, I had found living populations, small in number, small in specimen size and limited in distribution. By 1995 I had identified the limits of this sparse distribution and never found more than two "largish" specimens. In discussions with other collectors around Florida since then, I have encountered one other who has found the Tampa Drill on Florida's east coast. That find was in the Banana River.

     I have collected the Tampa Drill on Florida's west central coast and always found it in muddy, intertidal areas among oyster beds. Alas, there are no longer any oyster beds in the Banana River. It is not an "intertidal" habitat since there is no open exchange of water to the ocean. Nor are there many (if any) mud flats along shorelines due to the extensive development. However, there is one thing that the Banana River does have which fits with Abbott's and Rehder's observations. The second most common molluscan species Mikkelsen reported in the Indian River lagoon and which I found in large and pervasive numbers in the Banana River, was the Scorched Mussel, Brachidontes exustus (Linnaeus, 1758). The Scorched Mussel attaches to the base of seagrasses, rocks, and any other debris in the water. I think it can be safely concluded that the essential habitat ingredient required by the Tampa Drill is a tasty menu of Brachidontes.

     During 1998 I have briefly reexamined some areas in the Banana River and have observed the Tampa Drill to be plentiful and consistently larger than those observed in 1993 to 1995. I believe the Tampa Drill (eggs, veligers or juveniles, all of which are adapted by the intertidal environment to survive extended direct exposure to the air and sun) was probably transported to seafood restaurants in the Port Canaveral area with oysters from Florida's west coast in the mid-to-late 1980's time frame. This would be after the local commercial oyster fisheries had died off in the 1970's. The oyster shells and other debris transported therewith were probably, on occasion, disposed of in the Banana River by transporters, restauranteurs, or "carryout customers" tossing oyster shells into the river from their boats and river-front picnic areas or backyards. Some of the Tampa Drill "passengers," in one form or the other, survived and multiplied. It is apparent that it is now well established and flourishing.

     The remaining questions are "Are there enough or any predators (besides shell collectors) in the Banana River to limit the Tampa Drills' population; and, will the Tampa Drill eat itself to extinction or reach a sustainable balance with the Scorched Mussel?"

The Tampa Drill - Eupleura tampaensis (Conrad, 1846)

Banana River specimen | digital image by the author

*Adapted from an article published in The Capsule, Vol. 30, No. 5, May-June, 1998; newsletter of the Astronaut Trail Shell Club.