In 1964, one Gordon C. Creel penned the most haunting scientific paper I’ve ever read. Couched in his level-headed taxonomic description is the story of a wondrous, totally singular ecosystem — an ecosystem mangled before his very eyes . . . and today all but forgotten.
It was in 1962, halfway through his biotic survey of the Texas Panhandle and South Plains, that Creel arrived at Estelline Salt Spring in Hall County, Texas. Estelline emerged just east of its namesake town, flowing at around 3,000 gallons per minute into a large pool before emptying into the Prairie Dog Town Fork of the Red River. Creel was meticulous about recording habitat data:
The pool is about 65 feet wide at the surface at an elevation of 1742.5 feet above sea level; it narrows downward and is only 20 feet wide at a depth of 25 feet, but farther down widens slightly to the 120-foot depth. At the bottom of the main pool is an opening about 3 feet wide leading into a large cavity completely filled by water. . . The salinity of the water is nearly constant at 43 ‰, and has a temperature that varies from about 64 to 72° F. The 24-hour oxygen cycle ranges from a low of 2.9 PPM at 6 am. to a high of 4.3 PPM. The pH ranges from a low of 5 to a high of 6.
And the species de novo he described? None other than Hemigrapsus estellinensis.
That’s right, a crab. In a hypersaline pool, 800 kilometers from the sea — at the eastern brink of the Texas High Plains, for crying out loud — a crab
“The foreman of the ranch in which the spring is located,” Creel wrote, “reported seeing several crabs in September, 1960; he did not think it unusual.” Creel, we can be thankful, was not inclined to think the same. On February 18, 1962, he captured his holotype, a sexually mature male (USNM 107855), and 15 paratypes: 5 males and 10 females (USNM 107856).
“A number of SCUBA divers,” Creel remarked, “were collecting and charting the spring, disturbing the sediments of the sides of the pool.” This increase in turbidity, he speculated, may have aided his search by altering dissolved oxygen levels and forcing the crabs to the surface. “Not all the crabs seen,” he adds, “were collected.”
Creel took care to keep the crabs alive, presumably for further observation, but the stress of transfer seems to have proven fatal:
The crabs were taken alive to taken alive to the Wayland College laboratory in shallow enamel pans. They were not crowded and could get in and out of the spring water at will. All of them died within 17 hours of collection. During transport the temperature of the water dropped from 64° to 62° F. The campus is about 1500 feet higher than the spring. I doubt that the change in temperature or elevation or oxygen level of the water can account for the death of the crabs.
Creel, undaunted, contrasted the coloration and morphology of his now-dead crabs with what he judged to be their closest relatives, Hemigrapsus oregonensis. Apart from differences in spot arrangement and limb lengths, Creel noticed apparently opposite patterns of sexual dimorphism. (Female H. estellinensis had carapaces up to 18.5 mm long and up to 22 mm wide — larger than those of the H. oregonensis, with corresponding lengths of 17 mm and 20 mm. Conversely, Creel’s largest male H. estellinensis, with a length of 16.4 mm and a width of 19.1 mm, shaped up rather poorly against the largest male (length 23.5 mm, width 29 mm) in his samples of H. oregonensis.)
So why oregonensis? Surely these crabs were derived from marine ancestors in the Western Atlantic? If classification under Hemigrapsus was valid, then they’re the sole testament to that fact. As Creel discovered, all extant species of Hemigrapsus are of Pacific origin.
The accounts of grapsoid crabs by Rathbun (1918, 1924), which also do not mention any populations in this region, were used to establish the generic identity of the Estelline crabs. According to Rathbun (1924) the range of H. oregonensis is from Prince Williams Sound, Alaska, to Todos Santos Bay, Baja California, just south of the United States border. The present geographies would indicate a long isolation of that species from H. estellinensis.
One thing was certain — Estelline Salt Spring and its fauna were by any measure unique. Creel had the foresight to elaborate a little on the other members of H. estellinensis’ community (emphasis mine):
The main spring pool has an algal flora, including Oscillatoria formosa, Lyngbya Bergei, Enteromorpha clathrata, E. intestinalis and about 20 species of diatoms. The algal growth is dense from the surface to about 30 feet deep and becomes less dense farther down. Many invertebrate species occur here, but the most striking was a barnacle. The only fish observed and captured in the pool was a Cyprinodon rubrofluviatilis. The crabs were found only in the main spring pool; the outflowing stream was searched for several hundred yards but no other crabs were found.
I fear it’s not just cirripede aficionados who’ll be frustratingly tantalized by the underlined sentence. The mind just boggles at the thought of what else was scuttling or waving cilia in that pool.
Creel, probably wondering much the same, made a return trip — but, alas, our tale is one of tragedy. Remember those silt-stirring, spring-charting SCUBA divers?
During December 1962 the author and Don Beer explored as much of the spring pool as was safe using SCUBA gear; in 8 days of searching, during which nearly every inch was searched, no further crabs were found. The U.S. Corps of Engineers has been trying for several months to stop the flow of this spring. It appears that much of the native life of the spring is now extinct, including probably H. estellinensis. The only specimens remaining are in the U.S. National Museum. It may be of some interest that two of the females collected laid eggs before they died. The number of eggs was estimated by count-volume to be 8,000 and 3,000 respectively.
And so it goes.
Epilogue: Putting Things in Perspective and Cause for Hope
The aberrant nature of H. estellinensis was further highlighted in Ecology and Classification of North American Freshwater Invertebrates (Thorp & Covich, 2001). It’s first mentioned that Brachyuran crabs, whether introduced or native, occur only “sporadically” in coastal brackish or freshwater systems of North America. The species of note can be counted on one hand:
. . . the portunid blue crab, Callinectes sapidus Rathbun, a xanthid mud crab, Rhithropanopeus harrisii Gould (found in streams of the Atlantic and Gulf coasts and introduced along coasts of California and Oregon), and a grapsid river crab, Platychirograpsus spectabilis Rathbun, introduced from eastern Mexico into the Hillsboro River, Florida.
Then comes some speculation on the origins of H. estellinensis:
This representative of the otherwise marine family Grapsidae* is endemic (probably a Pleistocene relic) to the spring which is located 800 km from the sea at an elevation of 531 m (see Reddell, 1994**).
* genghisprawn: A recent revision by Schubart et al., 2006, has tentatively placed Hemigrapsus within the family Varunidae (still in superfamily Grapsoidea).
** genghisprawn: Reddell’s work, The Cave Fauna of Texas With Special Reference to the Western Edwards Plateau, is available here (PDF). All of the information it provides about Hemigrapsis [sic] estellinensis is from Creel’s paper.
Estelline today (a tiny town of 168 at the 2000 census) still has her “Salt Hole.” The Spring, around 2 miles from the town itself, has fallen into disuse. As of October 17, 2007 (according to Jerry Witherspoon):
The locals used to swim in this pool for many years, and told tales about a diving board, walkway and Sunday outings. It is indeed a jewel and in real need of being opened up and enjoyed by the public in its present form. Otherwise, perhaps a better policy would be to bulldoze the dam-like ring around it and return it to its place among the flats of the Prairie Dog Fork of the Red River as it was originally.
If any other scientists returned to Estelline Salt Spring, their findings remain unknown to me. An entry in the Handbook of Texas Online caught my interest. The brief article, based on Gunnar Brune’s Springs of Texas, Vol. 1 (Fort Worth: Branch-Smith, 1981), may indicate that at least some Spring natives, if not H. estellinensis, have survived the Corps of Engineers’ “chloride control structure”:
Estelline Salt Springs is a group of brine springs less than a mile east of Estelline at the Childress county line in east central Hall County (at 34°33′ N, 100°25′ W). The springs are located on the floodplain of the Prairie Dog Town Fork of the Red River; they became active around the turn of the century when they washed out a funnel in the alluvium. They were used by servicemen stationed at Childress during World War II. In 1964 the United States Corps of Engineers built a dike around the springs to stop the flow and prevent the salt from entering the river. Since then the springwater has apparently grown more saline. Salt minnows or killifish swim in the milfoil growing there, and the surrounding flats support hardwoods and grasses. An endemic saltwater crab was known to live only at these springs, but may not have survived since the springs have been confined.
Fittingly, there’s yet another twist: if the Spring became active only “around the turn of the century,” as we’re led to believe . . . whence its crabs and barnacles?
Brune, Gunnar. “Estelline Salt Springs.” Handbook of Texas Online. 16 Aug. 2008 <http://www.tshaonline.org/handbook/online/articles/EE/rpe2.html>.
Creel, Gordon C. “Hemigrapsus Estellinensis: A New Grapsoid Crab from North Texas.” Southwestern Naturalist 8.4 (Feb. 1964): 236-241. JSTOR. 16 Aug. 2008 <http://www.jstor.org/>.
Ecology and Classification of North American Freshwater Invertebrates. 1991. Ed. Alan P. Covich and James H. Thorp. 2nd ed. New York.: Academic Press, 2001.
“Estelline town, Texas – Factsheet.” American Factfinder. 2000. U.S. Census Bureau . 16 Aug. 2008 <http://factfinder.census.gov/servlet/SAFFFacts?_event=Search&geo_id=&_geoContext=&_street=&_county=Estelline&_cityTown=Estelline&_state=04000US48&_zip=&_lang=en&_sse=on&pctxt=fph&pgsl=010&show_2003_tab=&redirect=Y>.
Schubart, Christoph D.; Cannicci, S.; Vannini, M. & Fratini, S. (2006): Molecular phylogeny of grapsoid crabs (Decapoda, Brachyura) and allies based on two mitochondrial genes and a proposal for refraining from current superfamily classification. Journal of Zoological Systematics and Evolutionary Research 44(3): 193–199. http://dx.doi.org/10.1111%2Fj.1439-0469.2006.00354.x”>10.1111/j.1439-0469.2006.00354.x
Witherspoon, Jerry. “Turkey (Texas, that is) to Quittaque.” Crazyguyonabike: A Place for Bicycle Tourists and Their Journals. 2008. 16 Aug. 2008 <http://www.crazyguyonabike.com/doc/?o=3Tzut&doc_id=3042&v=3A>.