Especies Amenazadas En Peligro Extinción Endangered and

of the Edwards Aquifer Region
Endangered and
Threatened Species
Especies Amenazadas y
En Peligro de Extinción
de la Región del Acuífero Edwards
Endangered and Threatened Species
of the Edwards Aquifer Region
A primary source of fresh water for approximately
2
million Texans,
the Edwards Aquifer sustains a unique ecosystem for ten rare aquatic species, including
fish, invertebrates, and one plant. Highly specialized to adapt to living underwater, these
species are protected by federal law because they exist nowhere else on earth. The U.S. Fish &
Wildlife Service (USFWS) has designated eight species as threatened or endangered. Having
an endangered or threatened designation means that the survival of these species will require
i n s i d e f r o n t cov er
special measures to ensure their continued existence because of a small, isolated population
and a delicate or vanishing habitat. The Edwards Aquifer Authority (EAA) is committed to
protecting the Edwards Aquifer, and helps to foster species like the Texas blind salamander,
the fountain darter, and—the only plant on the list—Texas wild rice.
As befits a unique and specialized creature, the Texas blind salamander is known to
live only in the Edwards Aquifer near the San Marcos Springs. Water discharges from the
aquifer through the springs and into the San Marcos ecosystem. The springs are essential
habitat of other endangered species such as the San Marcos salamander and the San Marcos
gambusia, a small fish that some claim is already extinct. Another endangered species, the
fountain darter, lives in both the San Marcos and nearby Comal ecosystems, in the town of
New Braunfels. Comal Springs also contains two unique beetles—the Comal Springs riffle
beetle and the Comal Springs dryopid beetle. Another aquatic invertebrate in the system is
the Peck’s Cave amphipod, a tiny freshwater crustacean that lives in darkness, deep inside
the aquifer. Both the San Marcos and Comal ecosystems flow into the Guadalupe River.
hotel
reach
S p r i n g i n g Fo rt h
The two largest systems of underground springs in the
southwestern United States can be found some 30 miles
apart along the southern edge of the Texas Hill
Country. Both Comal Springs and its slightly
smaller cousin, San Marcos Springs, depend
upon the rain-recharged Edwards Aquifer
for their springflow. At each site, intense
underwater pressure propels water to the surface
through some 200 or more individual orifices.
spring lake
upper spring
run reach
sink
creek
slough
dam
city park reach
landa
lake
reach
old
channel
reach
rio vista dam
new channel
reach
i - 35
T h e Co m a l S p r i n g s aq uat i c ecosyst e m
T h e Sa n Ma r c o s S p r i n g s
aq uat i c ecosyst e m
The Comal Springs originate from the aquifer in Comal County and are located mainly in Landa
Park, a popular public recreational site created in 1898 by the city of New Braunfels, the seat of
Comal County. Landa Park has long been known for its abundant and pure spring-fed pools and
streams. For thousands of years American Indians of the region sought out the springs, and
today Texans enjoy them for swimming, tubing, picnicking, and other recreational activities.
Four major springs and an undetermined number of smaller springs feed the Comal River.
The Comal River is only about three miles long, making it the shortest river in Texas.
It flows directly into the much larger Guadalupe River. Output from the Comal Springs is
impressive. Collectively, they produce the largest average discharge of any spring system in the
Southwest.1 The Comal Springs’ average flow is 287 cubic feet per second (cfs), a figure based on
data recorded from 1933 to 2010.2 The Comal system exhibits excellent water quality, low
bacteria levels,3 and near-constant water temperatures—an annual mean of 74.1°F (23.4°C).
Over the years, several factors have affected the stability of the Comal Springs and Comal River
ecosystem. Chief among these factors are pumping from the aquifer, extensive development
along the lake and river banks, channel modification, and the springs’ natural variability.4
San Marcos Springs, in the city of San Marcos in Hays County, has
historically shown the most environmental stability and the greatest flow
reliability of any spring system in the Southwest.5 It is no wonder that the
area around the springs has been one of the most continually inhabited sites in
the United States: it has been in use by humans for some 11,500 years. Throughout
recorded history, the springs have never ceased flowing. Even during the worst
Texas drought on record, from 1950-56, the flow slowed to 47 cfs but never stopped.
Since then, the annual flow of the San Marcos Springs has averaged 172 cfs.6 The steadiness
of this springflow helps support the rare flora and fauna found in places such as Spring Lake
and the San Marcos River. 7
Spring Lake is the headwaters of the San Marcos River, which, like the Comal, flows on to its
confluence with the larger Guadalupe River. Temperatures in Spring Lake remain nearly constant
year-round at 71.1°F (21.7 C°), and it also features reliable flow and consistent chemistry.8 Construction and
residential development continue to occur along the San Marcos River and, like the Comal, it is a popular
haven for recreation, especially given the 36,000 students attending nearby Texas State University.
cape ’ s dam
historical challenges
T e x a s B l i n d Sa l a m a n d e r
The severe drought of the 1950’s challenged the survival
of several of the Edwards Aquifer’s endangered species.
In 1956, the sixth year of the drought, the hot, dry
conditions caused the aquifer’s water level to drop so
low that from June 13 to November 3, for the first time
in recorded history, Comal Springs stopped flowing.
As a result of the devastating effects of the drought on
Comal Springs, the 1957 Texas Legislature began work
to create a groundwater district to manage the Edwards
Aquifer. Agreement on all details of the Edwards
Underground Water District (EUWD) was completed
in 1959. Of particular note is the fact that the EUWD
was the first groundwater district in Texas that lacked
the ability to propose and enforce rules.
Eurycea rathbuni
t h e ba r e n e c e s s i t i e s
Many of the aquatic dwellers in the Edwards Aquifer
system share similar requirements for living in dark,
cool waters underground. The inhabitants of the
aquifer-fed San Marcos and Comal Rivers need a
reliable food supply, a source of clear and clean water
that maintains a constant temperature, and a wide
choice of protective surroundings, such as undisturbed
sand and gravel substrates, rocky outcrops, and areas
of submerged vegetation for cover. These conditions
are crucial in preserving the future of these endangered
and threatened species.
On the following pages is a list of these eight aquatic
species, plus two candidate species, all of whom call the
aquifer home.
[ endangered ]
large head, slender limbs, unpigmented skin
size: small; 3 to 4 inches in length
h abitat: Edwards Aquifer in the San Marcos area
description: Physical adaptation to its underground, watery
world gives the Texas blind salamander a delicate and otherworldly
appearance. It has smooth, unpigmented, almost translucent skin;
a large, broad head with a strongly flattened snout; long, slender
limbs; and, under the skin, tiny, vestigial eyes. Because of its rarity,
the Texas blind salamander draws considerable scientific interest.
Of all troglobitic—cave-dwelling—salamanders worldwide, the
Texas blind salamander is the most advanced, displaying a large
variety of physical adaptations that well suit it for cave life. Texas
blind salamanders have been observed in caves open to the water,
traveling along submerged ledges within the aquifer. All collections
have occurred in Hays County (close to San Marcos Springs), and,
according to the USFWS, distribution of this species may be limited
to the Edwards Aquifer beneath and near the City of San Marcos
and in an area as small as about 26 square miles.9
appearance:
Texas wild rice
Zizania texana
green, reedy aquatic grass
Size: between 3.3 to 6.6 feet in length;
the linear leaves are about 0.5 inch wide 10
Habitat: San Marcos Springs aquatic
ecosystem
Description: Texas wild rice
exists in only one place: a small
segment of the San Marcos River.
In 1967, the plant was headed toward
extinction, with only a single clump
appearing anywhere in the river.
After a researcher began a long-term
restoration project of the species,
the plant began to again appear in
the water, favoring swift currents,
shallow areas near the middle of the stream, and still
pools of water as much as ten feet deep. Scientists have
confirmed that, for reproduction, Texas wild rice requires
thermally constant temperatures, clear water, undisturbed
stream-bottom habitat, protection from floods, and unimpeded
light. Still, flowering plants are rarely seen. Recreational users
of the river may inadvertently uproot or damage the plant.
In addition, floods can also destroy the plant while low-flow
periods or drought make the plant vulnerable to being eaten
by herbivores or dried out by the sun.
appearance:
P e c k ’ s Ca v e a m p h i p o d
Stygobromus pecki
[ endangered ]
shrimplike, eyeless, unpigmented
Si z e : approximately 1/8-inch in length
Habitat: Comal Springs aquatic ecosystem
Des c r ip t ion : The primary habitat of the Peck’s Cave amphipod,
a soft-bodied freshwater crustacean, is the cool darkness of the
Edwards Aquifer. Specimens have been collected at the Comal
Springs and Hueco Springs orifices and in the Panther Canyon
monitoring well. When found outside of the aquifer, Peck’s Cave
amphipods are typically near the crevices of rocks and in the
gravel near spring orifices.
app ea r a n c e :
[ endangered ]
Sa n Ma r c o s g a m b u s i a
Gambusia georgei
[ endangered ]
dark-bodied, with a dark stripe
along the dorsal fin, and often yellow, yelloworange, or blue markings 11
Si z e : 1.0 to 1.5 inches in length; adult females are
somewhat larger than males 12
Habitat: San Marcos Springs aquatic ecosystem
Des c r ip t ion : The elusive San Marcos gambusia
has always preferred the quiet, shallow, thermally
constant waters of the San Marcos River.
Historically, the fish were found in the upper
portion of the San Marcos River, and—like other
members of the large gambusia family—they
produced live offspring. However, a sighting of
this Texas fish has not been authenticated since
1983, leading to the conclusion that either very
few survive or the species is already extinct.
app ea r a n c e :
Comal Springs dryopid beetle
Stygoparnus comalensis
[ endangered ]
small, brown, with translucent skin and
vestigial (non-functioning) eyes
Size: approximately 1/8-inch in length
Habitat: Comal Springs aquatic ecosystem
Description: The Comal Springs dryopid beetle has a secret
weapon: a mass of small, unwettable hairs on its underside that
enables it to hold a thin air bubble.13 The bubble ensures safe
respiration, much as a tank does for a scuba diver. The beetle
needs its bubble because the variable rate of springflow affects
its breathing; if springflow decreases, dissolved-oxygen levels
decrease as well. Also, because Comal Springs dryopid beetles
can’t swim, their surviving population appears to be restricted
to the headwaters of springs and spring runs.
Description:
Fo u n ta i n da rt e r
Etheostoma fonticola
mottled brown, with dark markings along sides and dark spots at tail,
eye, and dorsal fin 14
Size: usually less than 1 inch, but can be as long as 2 inches
Habitat: Comal Springs and San Marcos aquatic ecosystems
Description: The fountain darter is a tiny perch, as its scientific family name, Percidae,
suggests. Like many of its fellow endangered species, the fountain darter can survive only
if it has a good supply of food to eat, plenty of clean, warm water to live in, and rocks,
pools, sand, and gravel for cover. Young fountain darters prefer thick, overgrown areas
with slow-moving water while adults can be found in all suitable habitats.15 The San
Marcos River has a well-established population of fountain darters, while environmental
conditions created by the record drought of the 1950’s severely affected the fountain
darter population in the Comal Springs aquatic ecosystem. Historical record verifies that
numerous fountain darters were collected there in 1891. However, between 1973 and 1975,
biologists were unable to collect any at all. The most probable cause of the fish’s disappearance was the lack of springflow for five months during the severe drought of 1956. In 1975,
biologists from Texas State University in San Marcos used fountain darters from the San
Marcos River to successfully reintroduce the species to the Comal aquatic ecosystem.16
appearance:
T o o t h l e s s b l i n d c at
Trogloglanis pattersoni
[ ca n d i d at e s p e c i e s ]
tadpole-like head, eyeless, pale pink with
reddish mouth
Si z e : up to 4 inches long
Habitat: the artesian zone of the Edwards Aquifer near,
and underneath, the city of San Antonio
Des c r ip t ion : Like its equally threatened cousin, the
widemouth blindcat, this small catfish does not have
functioning eyes and is troglobitic—that is, cave-dwelling.
The toothless blindcat has highly specialized physical
features that equip it well for underground living. For
example, its build—with a large head overbalancing a
slender body with no air bladder—helps it withstand great
underwater pressure. Also, because the fish is toothless, it
has developed a specialized sucker-like mouth for eating.
Its primary fare is dead invertebrates, which it scavenges
for in the sediment. The current population of the toothless
blindcat is limited to very deep (approximately 984-feetdeep) artesian wells of the Edwards Aquifer that have a
temperature around 81°F. Once, this hardy species was
found as far below the surface as 2,000 feet.
app ea r a n c e :
[ endangered ]
Sa n Ma r c o s s a l a m a n d e r
Eurycea nana
[ t h r e at e n e d ]
small, slender, light brown
with yellowish flecks
Si z e : up to 2.3 inches long
Habitat: San Marcos Springs aquatic ecosystem
Des c r ip t ion : Like the Texas blind salamander,
the San Marcos Salamander is a member of a
lungless salamander family that breathes through
gills. When in danger, the San Marcos salamander
lets its protective coloration kick in; it can change
the hue along its dorsal side from light tan to dark
brown in order to blend in with the color of the
substrate. Some salamanders can perfectly match
the reddish-brown color of the algae in which they
hide. The San Marcos species lives solely near the
headwaters of the San Marcos River. They eat small
aquatic snails as well as insect larvae and pupae.
app ea r a n c e :
W i d e m o u t h b l i n d cat
Satan eurystomus
[ ca n d i dat e s p e c i e s ]
slender, eyeless, whiskered, pinkish in color
Size: up to 5.5 inches long
Habitat: the artesian zone of the Edwards Aquifer, notably in the
Balcones Fault Zone, but has only been collected under Bexar County
Description: Like its cousin the toothless blindcat, the widemouth
blindcat is a troglobitic, or cave-dwelling, catfish, making it one of only
two such species in North America. As its name suggests, it has no eyes;
those organs exist only in vestigial form under the fish’s skin. The species
is unpigmented, making the creature appear pinkish in color—somewhat
incongruously for a carnivore—and the strong jaw and well-developed
teeth give away its food preferences, such as shrimp, amphipods, and
isopods. Because of its highly specialized body and lack of an air bladder,
the widemouth blindcat can withstand water pressure that would crush
other fish. Numerous caverns and fissures in the Texas karst, or limestone, provide natural aquatic habitats. This species has been collected
only from Edwards Aquifer artesian wells over 984 feet deep with a water
temperature near 81°F.
Description:
actual
[ a ppr ox i m ate ]
1
size of species
2
3
4
5
6
T exas Bli nd Salama nd e r
3" to 4"
San Mar cos gambus ia
1" to 1.5"
P ec k’s Cave am p hi p od
approx. 1/8"
San Marcos sa l ama n de r
up to 2.3"
Coma l S p ri ng s d ryop i d b e et le
approx. 1/8"
Comal Springs riffle beetle
Heterelmis comalensis
Coma l S p ri ng s ri f f le b e et le
approx. 1/8"
[ endangered ]
small, flightless beetle 17
Si z e : approximately 1/8-inch in length, with females
slightly larger than males
Habitat: Comal and San Marcos Springs aquatic ecosystems
Des c r ip t ion : A “riffle” is a rocky shoal or sandbar just
below the water’s surface. Hence, these beetles are generally
found near springs orifices (openings in the rock) and in flowing,
uncontaminated waters ranging from one to four inches deep.
They have also been found in spring runs and in spring upwellings
about ten feet below the surface of Landa Lake in New Braunfels
and in the San Marcos ecosystem.18 Both larvae and adult riffle
beetles are entirely aquatic. The adults feed mainly on algae and
detritus scraped from submerged weeds and rocks.19
app ea r a n c e :
Founta i n da rt e r
typically less than 1", can be as long as 2"
Toot hles s b l in dcat
up to 4"
t exas w il d r ic e
[ not pictured here ]
W i d e mo ut h bl i n d cat
up to 5.5"
3.3' to 6.6' feet tall;
leaves approx. 0.5" wide
7
works cited
1 George, W.O. and W.W. Doyle. 1952. Ground-water
resources in the vicinity of Kenmore Farms, Kendall
County, Texas. Texas Board of Water Engineers Bulletin
5204.
2 Edwards Aquifer Authority (EAA). 2003. Hydrogeological
Data Report for 2002. Report 03—2, June 2003.
3 U.S. Fish & Wildlife Service (USFWS). 1996. San Marcos
and Comal Springs and associated aquatic ecosystems
(revised) recovery plan. U.S. Fish & Wildlife Service.
121 pp.
4 Espey, Huston & Associates, Inc. 1975. Investigation of flow
requirements from Comal and San Marcos Springs to
maintain associated aquatic ecosystems, Guadalupe River
Basin. Austin, Texas. Espey, Huston & Associates, Inc.,
Austin, TX.
5 USFWS. 1996.
6 EAA. 2003.
7 McKinney, D.C. and J.M. Sharp. 1995. Springflow
augmentation of Comal Springs and San Marcos Springs,
Texas: Phase 1—feasibility study. Center for Research in
Water Resources Technical Report CRWR 247, Bureau of
Engineering Research, University of Texas at Austin, Texas.
8 USFWS. 1996.
9 Ibid.
references
10 Terrell, E.E., W.H.P. Emery and H.E. Beaty. 1978.
Observations on Zizania texana Texas wildrice, an
endangered species. Bulletin of the Torrey Botanical
Club 105(1): 50 – 57.
11 USFWS. 1996.
12 Schenck, J.R. and B.G. Whiteside. 1976. Distribution,
habitat preference and population size estimate of
Etheostoma fonticola. Copeia 76(4):69 – 703.
13 Chapman, R.F. 1982. The insects: structure and function
Harvard University Press, Cambridge, MA.
14 Gilbert, C.H. 1887. Descriptions of new and little known
etheostomaoids. Proc. U.S. Nat. Mus. 10:47 – 64.
15 Schenck, J.R. and B.G. Whiteside. 1976.
16 USFWS. 1996.
17 Federal Register. 1997. Endangered and threatened wildlife
and plants; final rule to list three aquatic invertebrates in
Comal and Hays Counties, Texas, as endangered. 62 FR
66295, December 18, 1997.
Acronyms
c fs Cubic feet per second
e aa Edwards Aquifer Authority
t pw d Texas Parks & Wildlife Department
u s fws U.S. Fish & Wildlife Service
credits
Jack Unruh
d esi gn & pro d u cti o n : Nancy McMillen
co py wri ti n g: Anne Dingus
i llustrati o n s:
re f e re n c e photo graphy:
Anne John C. Abbott, University of Texas; Ed Oborny,
Bio-West; Randy Gibson, USFWS; Mike Quinn,
Texas Entomology; Glenn Longley, EARDC;
David Bowles; Robert Edwards; Joe N. Fries, USFWS
18 BIO-WEST, 2002. Comal Springs riffle beetle habitat
and population evaluation. Edwards Aquifer Authority
unpublished report.
19 Brown, H.P. 1987. Biology of riffle beetles. Annual Review
of Entomology. 32:253 – 273.
1615 N. St. Mary’s Street
San Antonio, Texas 78215
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WWW. EDW A RDS A QUIFER . ORG
The Texas Legislature mandated the participation
of the Edwards Aquifer Authority and four
other state agencies to work with other regional
stakeholders. Their goal: to resolve a decades-old
dispute regarding the need to manage the aquifer—
depending on its spring flow—for the protection of
federally listed species.
A species, whether plant or animal, can be listed
as either threatened or endangered based on its
biological status and dangers affecting its existence. A threatened species is one that is likely to
become endangered “within the foreseeable future
throughout all or a significant portion of its
range.” Endangered means that a species is
facing extinction within the foreseeable future.
In addition, some plants and animals are listed
as candidate species when there is “sufficient
information on biological vulnerability and threat(s)
to support issuance of a proposed rule to list but
issuance of the proposed rule is precluded.”