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= Gammarus pecos (Pecos amphipod) =

Gammarus pecos, commonly known as the Pecos amphipod, is a species of crustacean in the family Gammaridae. It is endemic to Pecos County, Texas in the United States, where it is known from only two locations: the Diamond Y Spring system (sometimes known as Wilbank Spring) and Leon Creek.

Gammarus pecos is classified as a vulnerable species by the IUCN Red List. A portion of the spring and cienega habitat inhabited by this species is now protected as part of the Diamond Y Spring system, a nature reserve, owned by the Nature Conservancy.

Description
Amphipods generally have two antennae, thirteen body segments, and seven pairs of legs. The first two legs on an amphipod are used for grabbing food. Amphipods also have three tail appendages referred to as uropods that are connected to the end of their abdomen. Gammarus pecos has red or green bands along its body. Male Gammarus pecos can grow to 12-14mm, while females grow to 9-11mm.

Life History
There is little information available on the life history of Gammarus pecos. But there is plenty of information on its order, Amphipoda. Most amphipods have a life cycle of 1 year, and will breed from February to October. Breeding is dependent on water temperatures. Higher temperatures increase reproductive rates. If the conditions are good for breeding, a male amphipod will attach to a female and remain there for up to seven days. While the male is attached, the female continues to swim and eat like normal. The eggs are stored within the female amphipod’s marsupium, also known as a brood pouch. Amphipods generally only produce one brood, but some species can produce more than one. These broods typically contain between 15 and 50 amphipods.

Diet
Gammarus pecos are detritivores, which means they feed on dead or decaying matter at the bottoms of their aquatic habitats. They also feed on algae and certain vegetation.

Mating Behavior
Male amphipods use their antennae to sense pheromones released by females during mating season. During mating, the male will latch on to the female until she molts. When the female is ready to molt, the male will push sperm into the female’s marsupium. The female releases the eggs from the marsupium.

Feeding Behavior
There is not much information available on the feeding behavior of Gammarus pecos, but amphipods typically feed by using their two front legs to grab and rip off pieces of their food.

Habitat
Gammarus pecos occur only in desert spring outflows. These amphipods are commonly found in vegetation, on or under rocks, and around gravel sediments.

Gammarus pecos is only known to inhabit the Diamond Y Spring system in Pecos County, Texas. The Diamond Y Spring system contains seeps, desert springs, and ciénegas. The Diamond Y Spring system also contains a diverse community of springsnails, amphipods, and other invertebrates.

Range
Gerald A. Cole and E. L. Bousfield were the first to collect samples of Gammarus pecos in the Diamond Y Spring system in 1964. Cole and Bousfield first observed Gammarus pecos in southeastern New Mexico and western Texas. According to the 5-year review released in 2019, the U.S. Fish and Wildlife Service used genetic testing to confirm that Gammarus pecos is endemic to the Diamond Y Spring system. Even within the Diamond Y Spring system, their range has been reduced by the loss of spring outflow. It is possible that the lowering of the water table caused the loss of spring outflow. Because it is a small crustacean, it is unlikely that it will expand outside of its current range.

Population Size
Despite the lowering of water outflow among certain parts of the spring system, Gammarus pecos has a locally abundant distribution. Adequate spring sites and the lack of disturbance within those areas may explain this abundant distribution. The U.S. Fish and Wildlife Service has not done a lot of research on population trends of Gammarus pecos.

Past and current geographical distribution
Gammarus pecos has a very restricted range. It is located in spring systems in the Diamond Y Spring system. Historically, researchers generally believe it is only found there. Some researchers believe it may be found in springs in the nearby area such as the Comanche and Leon Springs in Pecos County.

Major Threats
There are many factors that led to the decline in Gammarus pecos population size. Groundwater pumping is one of the most significant reasons responsible for this decline. In Texas, there is a law that allows people to use any groundwater that they can pump from their property. This law, known as the Rule of Capture law, often saps groundwater from nearby reserves. People often use groundwater for irrigation and maintaining livestock. Second, Texas is a hotspot for harvesting natural resources such as oil, which can lead to contamination of the surrounding water.

Listing under the Endangered Species Act (ESA)
In 1984, the ESA identified the species as a potentially threatened species. In 1989, 1991, and 1994 the agency reviewed the listing. Gammarus pecos was listed as endangered by the ESA in July of 2013.

5-Year Review
Gammarus pecos is a small freshwater crustacean that lives in the Diamond Y Spring system. The Service identified the Gammarus pecos as a candidate for listing in the May 22, 1984, Endangered or Threatened Wildlife and Plants, Annual Notice of Review (49 FR 21664). The 5-year review did not assign a Species Recovery Priority Number and there is no current Recovery Plan for Gammarus pecos. Additionally, the review stated that there has not been a systematic survey on population and demographic trends since 2003 and there are no new changes to taxonomy.

Threats
First, climate change threatens Gammarus pecos. The 5-year review stated that researchers believe that human driven climate change will impact the population of Gammarus pecos in the future. The biggest factor will be the increasing frequency of extreme temperatures which can have a rippling effect on the species’s habitat. Future climate change may also affect water quality.

Second, there are over 200 oil wells within a 2.5-mile radius of the Diamond Y Spring system. These wells may affect future water quality.

Third, decreased groundwater due to pumping threatens the population of Gammarus pecos. Between 1948-1979, most of the water pumped from Rustler Aquifer in Pecos County was for oil extraction. After 1980, irrigation became the primary use for groundwater from the Rustler Aquifer in Pecos County. The yearly average rate of water pumping of the Pecos County aquifer between 2010 and 2017 is over ten-times the average amount pumped each year from 1937 to 2009.

Researchers believe that the pumping of groundwater has lowered the water table. Springs are dependent on a high-water table because springs output water that falls down hills due to gravity. If the water table is too low, then the spring will not have a flow of water, causing it to dry up. The Diamond Y Spring system's discharge has declined drastically since 1950. Water flow has decreased in many areas and in some locations, water has completely dried. Decreased spring outflow due to groundwater pumping leads to fewer, more unstable habitats.

Fortunately, as far as conservationists know, there is no market for Gammarus pecos because they are not desirable to buy and sell. There are no invasive species that directly interact with Gammarus pecos in the Diamond Y Spring system, as well as no non-native competitors or predators.

Species Status Assessment
As of April 29th, 2022, there is no species status assessment on the U.S. Fish and Wildlife Service website.

Recovery Plan
As of April 29th, 2022, there is no recovery plan listed on the U.S. Fish and Wildlife Service website.