The Florida Crown Conch
By Phil Poland
Shell Point, Lee County, Florida (left 73.5 mm. and right 83 mm.)
| It's my
conclusion, certainly simple, shared by some, and bound to annoy
others: We've got one species of crown conch, Melongena
corona (Gmelin, 1791), in Florida.
Ecological factors are powerful and may account for the spectrum
of variation in this familiar species.
A number of forms have been identified. Species and subspecies names have been applied. Some of the named taxa follow:
--Melongena corona bicolor (Say, 1827): a dwarf form usually associated with the southeast edge of the Keys. It is typically found in tide pools. Dr's. William Clench and Ruth Turner (1956) recognized this form as a species extending from the Dry Tortugas to Biscayne Bay. More recently, John Tucker (1994) extended the range for this snail, treating it as a species, from the Dry Tortugas to Matanzas Inlet near St. Augustine.
--Melongena corona altispira Pilsbry and Vanatta, 1934: the smaller forms, excluding M. c. bicolor, found on the east coast from Cape Sable to Matanzas Inlet. Clench and Turner considered this snail a subspecies of M. corona. Tucker considered it to be M. bicolor. The famous (and confusing) holotype is a high-spired aberration.
--Melongena corona johnstonei Clench and Turner, 1956: an elongate form from northwest Florida to Alabama. Clench and Turner, and Tucker recognized this form as a subspecies of M.corona, extending from Panacea, Florida to Gulf Shores, Alabama.
--Melongena corona corona (Gmelin, 1791): the west coast snail according to Clench and Turner, and Tucker.
--Melongena corona sprucecreekensis Tucker, 1994: a large form limited to the area of Spruce Creek Estuary near Daytona Beach.
--Melongena corona aspinosa Dall, 1890: a nearly spineless variety living in Florida Bay at the northwest edge of the Keys.
Other interesting and unnamed varieties include the heavy and elaborately spined snails from the Goodland area in southwest Florida, and large forms on the east coast.
Until fairly recently, I pigeonholed all our forms into the prescribed subspecies. I went back and forth on M. c. bicolor (Say) and M. c. aspinosa Dall, the two main Keys forms, as to whether they should be considered species. I nagged folks for their opinions, which varied considerably. The more populations of Melongena I found, the more difficult it became for me to segregate them.
A brief account of my frustrating effort to find the distinctions between subspecies follows:
On a visit to Mexico Beach in the panhandle, I had no problem identifying M. c. johnstonei. At Adams Beach in Taylor, County, 106 miles to the east, I found another large form, just a little bit squatter. Is it M. c. johnstonei?
Many Cedar Keys specimens look very much like Ft. Myers forms.
Taking a canoe into the mangroves east of Marco Island in southwest Florida, I found a form that really stands out. This form, with large basal spines and up to four rows of them on the shoulder, looks like a distinct variety, the product of isolation. But is it? Three miles of paddling brought me to small mangrove islands near the open Gulf. Here, with the clean sand between the roots of red mangrove, were specimens identical to those collected at Sarasota with short spines on the shoulder and little or no basal spines.
A very thorough and knowledgeable collector with whom I correspond had seen dwarfs that were indistinguishable from east coast M. c. bicolor, and that had been collected in a lagoon at Mullet Key near St Petersburg. I checked it out. At the northwest end of Mullet Key, a small lagoon (not the one my friend had meant, it turns out) connects to the Gulf by way of a small intermittent stream. There are no oysters or other large bivalves in the lagoon. The Melongena were indeed small and similar to those I had seen on the east coast that had fed on Batillaria. These dwarfs were eating Anomalocardia, a small brackish water bivalve, and Cerithidea, a marsh snail. They reached old age, but never 60 mm. On the sand flats few hundred yards to the west at the edge of the Gulf, several young 80 to 100 mm specimens were found, one eating a Macrocallista nimbosa, a sunray clam. Again, geographic isolation couldn't be an issue.
These were some problems on the Gulf coast.
On the east coast, I had begun finding large forms, up to 145 mm. All were associated with oysters in mangrove habitats and ranged from Lake Worth in Palm Beach County to the Indian River in Brevard County. I was alerted to John Tucker's new species near Daytona Beach and checked it out. Some of the specimens I found looked like forms I'd gotten from the Pensacola area.
Over the years, I'd found small crown conchs that I'd labeled M. c. altispira at inlet areas on the east coast. This made sense when comparing my shells with the plates in Johnsonia, (Clench and Turner, 1956).
On a visit to Sebastian Inlet in 1995, I found a tremendous die-off of catfish. A feeding frenzy involving all the local Melongena was taking place. On previous occasions, I'd found large Melongena on the oyster bars in the Indian River. On this day in the Inlet, between the State Road AlA bridge and into the Indian River, over a distance of about one and a half miles, thousands of crown conchs had gathered. Large oyster habitat forms, as large as 150 mm, were found together with the 40 mm M. c. altispira forms I'd found previously near the bridge. There were plenty of size intergrades. The range of form with regard to spine development and coloring was not related to size. Geographic isolation was not a factor here. Diet seemed to be the key.
Things went smoothly in the Keys until I looked too closely. I'd found the typical M. c. bicolor, feeding on Cerithium and Batillaria, in silty environments and in the tide pools near the southeastern edge of the Keys. My experience has been that basal spines are not rare within this group, and that color patterns exhibited are not greatly different from those in most other populations of M. c.
After reading Dr. Edward Petuch's (1988) Neogene History, which touched on Dall's M. c. aspinosa, I revisited the spot along U.S. 1, near the Monroe/Dade County line, where I'd found a nearly spineless variety in the past. I found live specimens to 78 mm, and a dead 96 mm specimen in nearby Blackwater Sound. Prey included Polymesoda, another small bivalve, and Cerithidea . I thought maybe this was a distinct species.
A search for other gastropods brought me to the edge of Florida Bay further into the Keys. Several dead Melongena, looking like hybrids of M. c. bicolor and the larger M. c. aspinosa, caught my eye and induced me to visit the very difficult habitat of silt and red mangrove that fringes the northwest side of the Keys. At Sugarloaf Key, I found the live snails ranging in form between the two. I found a similar range of forms at Plantation Key, over 60 miles to the northeast.
What I would like to find are Melongena populations in areas to the north and west of the Keys. Unfortunately, I have no material from the area between Chokoloskee, in southwest Florida, and Blackwater Bay, just south of Florida City. Do any of you permitted researchers, park rangers or crocodile poachers have any specimens from these areas? If you do, or even if you just want to kibitz on the subject, please contact me.
Rumor has it that results from DNA analyses comparing several M. c. forms may be forthcoming. That will be interesting!
Clench, W. J. and Turner, R. D. 1956. The Family Melongenidae in the Western Atlantic, Johnsonia vol. 3, no. 35.
Petuch, E. J. 1988. Neogene History of Tropical American Mollusks, The Coastal Education & Research Foundation (CERF), Charlottesville, VA.
Tucker, J. K. 1994. The Crown Conch (Melongena: Melongenidae) in Florida and Alabama with the Description of Melongena sprucecreekensis, n. sp. Bull. Florida Mus. Nat. Hist., Biol. Sci. 36(7): 181-203.