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Texas wild rice

The Texas wild rice (Zizania texana), an aquatic perennial grass found in the San Marcos River (including Spring Lake and its irrigation waterways) near the city of San Marcos Texas, was abundant when the species was first described in 1933 [1]. By 1967, populations had declined drastically with reports of only one plant in Spring Lake, one in the uppermost part of the San Marcos River, and only scattered plants in the lower 2.4 km of the River [1]. These declines were tied to increased pumping and diversion of Edwards Aquifer groundwater that lowered water levels in the San Marcos River and exposed shallows where Texas wild rice typically grew [2]. In addition, river dredging and damming, riverside construction, and bottomland cultivation destroyed plants, altered stream flows and temperature, and increased siltation [2]. Past seed harvesting had also inhibited successful reproduction [2].

In 1976, a survey estimated 1,131 m2 of Texas wild rice in the San Marcos River, primarily concentrated in the extreme upper and lower segments of the area known as the upper San Marcos River; no plants were found in Spring Lake [1]. Declining numbers of plants, combined with a lack of sexual reproduction (existing plants appeared to be reproducing only vegetatively) led to the listing of Texas wild rice as endangered in 1978 [3]. Critical Habitat was designated in 1980 [1]. A 1986 survey found, however, that coverage had continued to drop to 454m2 [1]. This decline is thought to have been caused by floating debris from Spring Lake (vegetation in the lake was periodically mowed for aesthetic purposes and the debris then allowed to float downstream ), streambed plowing in the city park area, plant collecting, and pollution of the stream [4]. By 1989, conditions had improved and coverage had increased to an estimated 1,005m2 [1]. By 1994, coverage was up to 1,592 m2 and the plant’s distribution extended from the uppermost San Marcos River just below Spring Lake dam (an area where earlier surveys had not found plants) down to an area slightly below the wastewater treatment plant [1].

The first successful attempt at culturing Texas wild rice took place in 1975 when four clones removed from the river eventually produced 1,500 seeds that germinated and produced 500 plants [1]. In 1992 -1993 an attempt was made to transplant cultured wild rice plants into Spring Lake; 183 were planted near the dam and another 500 were planted on the northwest side of the lake [1]. Although at first, there was a slight increase in plants at these sites, numbers later declined [1]. Due to lack of monitoring, population trends at these sites are unknown and it is unclear whether this project was successful [1]. Starting in 1996 fish hatcheries have played a critical role in the conservation of Texas wild rice [5]. About 40 plants are normally kept at the San Marcos hatchery and another 40 plants are maintained at Uvalde National Fish Hatchery in Uvalde, Texas [5]. At both hatcheries, tillers (the product of asexual reproduction that can grow into mature plants) are repotted and eventually transplanted into the river [5].

In recent years there has been an increase in Texas wild rice coverage and it is now abundant in the upper portion of its range, although it is still rare further downstream [6]. Populations are fragmented, however, with large gaps between stands and with sporadic and spotty flowering that could lead to problems with pollination [3]. In one small area (Sewell Park), however, successful seed production was documented in 1998 and continued for several years [3].

In 2000, a breeched dam caused the river to drop and narrow, leaving 25% of the Texas wild rice population either dry or in water flowing too fast [5]. In response, 184 rice plants were transferred to the San Marcos hatchery and another 60 were moved to safer areas within the river [5]. Another recent threat to the species is the invasion of a new exotic plant, water trumpet (Cryptocoryne beckettii). This native of southeast Asia, was introduced into the San Marcos River in 1993 and although efforts have been made to remove it, its growth continues to outpace the removal effort [6].

[1] U.S. Fish and Wildlife Service. 1996. San Marcos and Comal Springs and Associated Aquatic Ecosystems Recovery Plan. Albuquerque, New Mexico. pp. x + 93 with 28 pages of appendices.
[2] Eckhardt, G. The Edwards Aquifer Website. <http://www.edwardsaquifer.net/species.html#Texas%20Wild%20Rice%20(Zizania%20texana)> accessed Arpil, 2006.
[3] Power, P. and F.M Oxely. 2004. Assessment of Factors Influencing Texas Wild Rice (Zizania Texana) Sexual and Asexual Reproduction. 2004 Final Report prepared for the Edwards Aquifer Authority, San Antonio, Texas.
[4] Beaty, H.E. 2001. Texas Wild Rice. In Handbook of Texas Online. Available at <http://www.tsha.utexas.edu/handbook/online/articles/TT/ttt1.html> accessed April, 2006.
[5] Springer, C. 2000. Texas Wild-rice Finds Refuge at Hatchery. Endangered Species Bulletin. XXV(3):34.
[6] Edwards Aquifer Authority. 2004. Draft Edwards Aquifer Habitat Conservation Plan and Draft Environmental Impact Statement. Amended 9/21/04

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