New occurrence records for stygobiontic invertebrates from the Edwards and Trinity aquifers in west-central Texas , USA

We report new occurrence records for stygobiontic invertebrates from the Edwards and Trinity aquifers in Blanco, Hays, and Travis counties of central Texas, USA. Our collection includes seven species from four families: Caecidotea reddelli (Steeves, 1968), Asellidae; Crangonyx nr. pseudogracilis Bousfield, 1958, Stygobromus balconis (Hubricht, 1943), Stygobromus bifurcatus (Holsinger, 1967), and Stygobromus russelli (Holsinger, 1967), Crangonyctidae; Sphalloplana mohri Hyman, 1938, Kenkiidae; and Cirolanides sp., Cirolanidae. Specimens of Caecidotea reddelli and Crangonyx nr. pseudogracilis are new records for Hays County and Travis county, respectively. Specimens of an undescribed species of Cirolanides were collected from a well in Hays County and from two localities in Travis County.


Introduction
The Edwards and Trinity aquifers in west-central Texas are some of the most biologically diverse aquifers in the world, home to at least 68 described species of endemic groundwater-obligate (stygobiontic) invertebrate species (Hershler and Longley 1986, Bowles and Arsuffi 1993, Hutchins 2018, Külköylüoğlu et al. 2017a, 2017b, 2017c, Camacho et al. 2018, Külköylüoğlu 2018, Külköylüoğlu and Gibson 2018).Of these species, 52 are in the Edwards (Balcones Fault Zone) Aquifer (hereafter, Edwards Aquifer), 18 are in the Trinity Aquifer, and 23 are in the Edwards-Trinity (Plateau) Aquifer.Seventeen stygobiontic invertebrates have been recorded in the Austin-Round Rock Metro Area (Table 1).The Edwards Aquifer is also the primary source of water for the city of San Antonio and other communities in central Texas (Gibson et al. 2008), which are currently experiencing rapid development and growth (Pendall et al. 2015).As new pumping wells are drilled for agricultural and municipal use, increased demands are placed on these aquifers, threatening regional groundwater biodiversity and ecosystem services.Documenting the stygobionts endemic to these aquifers is necessary to refine our knowledge of their distributions, thereby informing conservation and management of natural resources within the Edwards and Trinity aquifers.Furthermore, monitoring stygobiontic communities can prove useful in detecting changes in the water quality of these aquifers (Gibson et al. 2008), which many Central Texans rely on for drinking water, agriculture, and recreation.

Sebidae
Seborgia relicta Holsinger, 1980 present new occurrence records for seven species, including three new county records, from groundwater wells and springs in the Edwards and Trinity aquifers.Long-term monitoring of groundwater wells using bottle-traps allows a unique opportunity to sample a variety of locations over long periods of time with minimal effort (Hutchins andOrndorff 2009, Fenolio et al. 2017).In addition, we give a brief synopsis of known distributions of those species and relevant literature.

Sampling sites
Seventeen sites were sampled in and around the Barton Springs segment of the Edwards Aquifer and its catchment area in the Hill Country portion of the Trinity Aquifer in Blanco, Hays, and Travis counties (Figure 1).Most sampling took place in 2010-2011 and again in 2015-2018.We also report a handful of other specimens collected opportunistically over the past two decades (Table 2).

Trap designs
We sampled springs using cotton mophead "traps" lodged into spring outlets (modified per methods in Holsinger and Minckley 1971, Hershler and Longley 1986, Gibson et al. 2008, Huston et al. 2015).We separated the mopheads into individual strings, tied them into loose bunches, and securely wedged them into the spring outlets using rocks to keep them in place (Figure 2).The size of the mop bunches was determined by the size of the spring outlet, ideally filling a large portion of the outlet, to maximize the volume of water flowing through the trap.Where possible, we placed multiple clumps of mophead material into the spring outlets at various locations.We checked mops for invertebrates after approximately two weeks by removing them from the spring outlet, quickly placing them in a large handheld net and flushing water through the net to dislodge any invertebrates from mophead strands.We also searched through the strands by hand after flushing.Specimens were collected and stored in 99% ethanol.Five groundwater wells were sampled using a funnel trap fashioned from 1-L plastic water bottles with the top cut off and inverted into the bottle (Fenolio et al. 2017).We baited the traps using pistachio nuts, dried Mysis shrimp, Slim Jim (Conagra Brands) pieces, or catfish bait (Catalpa Worm: Little Stinker (Acme Tackle Company); Cricket: Berkley Gulp! Alive! (Berkley Fishing)).Traps were set between 0-10 m above the bottom of the well (Table 3).Wells were sampled every two weeks from September 2010   2).

New Occurrence Records
Caecidotea reddelli (Steeves, 1968)  Caecidotea reddelli is a stygobiontic isopod about 10 mm in length that occurs throughout central Texas in springs, caves, and wells in Bell, Burnet, Coryell, Dallas, Henderson, Hill, Limestone, Palo Pinto, Panola, San Augustine, Tarrant, Travis, and Williamson counties (Steeves 1968, Mitchell and Reddell 1971, Lewis and Bowman 1996, Lewis 2001, Hutchins 2018).Caecidotea reddelli is known from both the North Balcones Fault Zone and the adjacent part of the Gulf Coast Plain Province directly to the northeast in Dallas and Henderson counties (Lewis and Bowman 1996).Mitchell and Reddell (1971) showed an additional locality in Hays County (their fig.30) but without further explanation, and there is no associated voucher specimen (Reddell, personal communication to TJD and BDN, 21 September 2017).Therefore, we present our specimen of C. reddelli collected from Red's Spring in Hays County as a new county record for this species.Well No. 5850411 (30.18667, -97.84917).One specimen collected 4 December 2017 by BDN.Identified by Benjamin F. Schwartz.

Cirolanides nr. texensis (Isopoda, Cirolanidae
These specimens are part of the Cirolanides texensis species complex, which needs revision (Ben Hutchins, Texas Parks and Wildlife, personal communication to BDN on 12 July 2018).These specimens represent a distinct lineage of Cirolanides related to C. texensis (Benedict, 1896) that warrants species-level designation, to be described elsewhere (Benjamin F. Schwartz, Texas State University, personal communication to BDN on 15 December 2017).All specimens were collected from a Hays County well and a cave and nearby well in Travis County.Crangonyx pseudogracilis is recorded in the east-central United States and southern Canada (Zhang and Holsinger 2003).Diaz and Alexander (2010) noted specimens of Crangonyx sp.collected in samples from the spring-fed San Marcos River, Hays County, Texas.Groundwater-adapted populations with reduced eyes and reduced pigmentation have been recorded in Comal and Kendall counties (Gibson et al. 2008).Specimens collected from Old San Antonio Spring and Treadwell Spring also show these stygobiontic adaptations.

Stygobromus russelli
ter Sprouse (Zara Environmental, LLC) for specimen donations.Finally, we thank the many landowners and managers who provided access to lands under their care, including: Jared Holmes and the Bamberger Ranch; Reed and Holton Burns (Charro Ranch); Kevin Theusen (City of Austin); the owners of Camp Ben McCulloch; Brandon Crawford, John Karges, and The Nature Conservancy of Texas.The views presented herein are those of the authors and do not necessarily represent those of the U.S. Fish and Wildlife Service or the City of Austin.

Figure 1 .
Figure 1.Sample Sites.Sampling map showing the extent of the Barton Springs Segment of the Edwards (Balcones Fault Zone) Aquifer and its hydrozones in Hays, Travis, and Blanco counties, Texas, USA.Sampling sites are numbered as follows: 1 Bamberger Ranch Spring 2 Red's Spring 3 Emerald Spring 4 Bello Spring 5 Ben McCulloch Spring 6 Sky Ranch Tract -State Well No. 5857507 7 Sweetwater Spring 4 8 Sweetwater Spring 1 9 Hays County Ranch Tract -State Well No. 5849939 10 Old San Antonio Spring 11 Ed's Crossing Tract -State Well No. 58499SH 12 Blowing Sink Cave 13 Blowing Sink Tract -State Well No. 5850411 14 Barton Creek Greenbelt -State Well No. 5842820 15 Cold Spring 16 Eliza Spring 17 Treadwell Spring.Boundaries of aquifer hydrozones courtesy of the Barton Springs Edwards Aquifer Conservation District.Wells are identified primarily by the Texas Water Development Board (TWDB) well-numbering system (Nordstrom and Quincy 1999).

Figure 2 .
Figure 2. Mophead in spring outlet at Cold Spring, Travis County, Texas, USA.

Table 1 .
Stygobiontic invertebrate fauna recorded in the Austin-Round Rock Metro area, Texas, USA.

Table 3 .
Well Information.Data on sampled wells collected in the field and from the TWDB database.Tract names correspond to City of Austin WQPL tracts.The depth of trap in State Well No. 5857507 (Sky Ranch Tract) was not recorded.Water depth measurements were taken in the fall of 2017.