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The Socorro isopod: Endangered but important (commentary)

  • The Socorro isopod is an endangered crustacean endemic to the thermal water of a spring in the state of New Mexico.
  • Its population is relegated to just three small habitats, like a concrete pool built by the state to collect the hot water the isopods live in.
  • “There is lot of attention paid to what are called charismatic megafauna [but] the Socorro isopod that is native to a spring that is smaller than most people’s offices doesn’t get the news or the attention grabbing headlines that some of the others do. But their plight is the same.”
  • This article is a commentary. The views expressed are those of the author, not necessarily of Mongabay.

Near the city of Socorro in the state of New Mexico lies a small spring. It is only here where one of the most endangered isopods, the Socorro isopod (Thermosphaeroma thermophilum), lives. Also known as the Socorro sowbug, they are a species of isopod commonly referred to as roly-polies, or woodlice. They are not insects but actually are crustaceans, more closely related to crabs and shrimp than insects. The Socorro isopods are brown and live underwater in a thermal spring with temperatures ranging from 77 to 91 degrees Fahrenheit.

Socorro isopods are important omnivores in their ecosystem. Like their terrestrial counterparts, Socorro isopods consume detritus, which is dead and decaying matter such as leaves, dead plants, and rotting wood, that can accumulate in the water. They also feed on algae. In ponds and other bodies of water, if there is an overabundance of algae, the algae produces toxins that kill fish and birds and are even harmful to humans. So, Socorro isopods, despite their limited range, play an important role within their ecosystem.

Today, if you visit the native spring where they still live, you will see concrete pools and lighting set up around the spring vent, because the spring was used as a bathhouse in the early 1900s. “Where the concrete infrastructure exists, everything flows through it and those tanks just kind of guide the water. It hasn’t been problematic to our knowledge for isopod persistence, and going in there and doing any type of renovation or removing the concrete lining might actually be more detrimental,” Dan Trujillo, aquatic biologist for the New Mexico Department of Game and Fish, explains.

Isopod illustration via New Mexico Department of Game and Fish.

The U.S Fish and Wildlife Service lists the species as endangered while The International Union of Conservation for Nature (IUCN) lists the species as “extinct in the wild” but according to Trujillo, the species can still be found in their native habitat. Parts of the spring were modified in the 20th century to supply water to the city of Socorro. The wild isopods live in two small concrete pools with an interconnecting pipe and a narrow stream under the pools.

Currently, the main threat is the disruption of the thermal water that they depend on. Socorro isopods live in water and depend upon it for their survival so if there is a threat to the city of Socorro’s water supply or the thermal spring then that is considered a big threat. In August 1988, the wild population became extinct due to tree roots blocking the valve control system (for surface discharge), a pipe that fed water into the spring. The spring dried up completely and all the wild isopods died with it. In September that same year, the problem was fixed and the water flow was re-established. A captive population from University of New Mexico was then introduced into the spring. This incident led to the creation of the Socorro Isopod Propagation Facility (SIPF) to help preserve the species. Construction for SIPF was completed in 1990. Built by the city of Socorro and resources agencies, SIPF houses a captive population of Socorro isopods and allows researchers to study their captive propagation, genetics, and life history. In September 1990, 600 isopods were first introduced into SIPF. A November 2021 survey of the tanks indicated isopod densities to be around 1514 isopods/m2.

According to Dan Trujillo, the population is  “pretty stable.” Currently, isopod populations exist in three different places: the native spring which they still inhabit, the SIPF, and the Albuquerque bio-park. “The population at the Albuquerque bio-park is actually several. There are a couple of tanks and in each of those tanks is maintained a self-sustaining population. So, in general because of that I would say they are secure,” Trujillo states.

However, the native spring is still privately owned. The U.S. Fish and Wildlife Service have not been able to reach a long term conservation agreement with the landowner. In accordance with the private landowner’s request not to release confidential data regarding the specific location of the wild isopod population, the species’ wild habitat is referred to in papers, studies, and articles as “the thermal spring” or “native habitat” and so on.

Socorro isopods primarily consume detritus and algae. Surprisingly, they also eat each other: they are known cannibals and devour smaller ones within the population. Males are larger than females, reaching lengths around ½ inch, while females only grow to ¼ inch. Males are very protective of their mates and will form a breeding pair that can stay together many days while swimming around their habitat. As stated by Trujillo, “a large male isopod will actually clasp and grab on to a smaller female isopod and kind of tuck her in between all of his legs and swim around with her and hold her there until she is ready to mate. When I have handled them and sampled them, I have found breeding pairs in that condition regularly, so it’s a common and well-documented behavior.” This behavior is known as “mate guarding.”

A Socorro isopod. Image by Bronwyn H. Bleakley via Creative Commons, CC BY-SA 3.0.

Researchers initially believed that Socorro isopods in captivity diverged morphologically and genetically from their native population due to their captive environment. However, further research has indicated that this is not the case. “Some of our preliminary data from the genomics study indicates that the populations are more closely related than we previously thought. And so the three populations at the native spring, the Albuquerque bio-park, and SIPF have actually maintained some semblance of similarity, despite being separated for over a decade,” Trujillo explains.

Trujillo emphasizes the need to raise awareness for species like this. “There is lot of attention paid to what are called charismatic megafauna, you know, grizzly bears and polar bears and the like, but you know an animal that is like the Socorro isopod that is native to a spring that is smaller than most people’s offices doesn’t get the news or the attention grabbing headlines that some of the others do. But their plight is the same. There are things that people have done to habitats that have essentially altered them forever,” Trujillo states.

The Socorro isopod is just one of many endangered isopod species. There is the endangered Lee County Cave isopod, which is endemic to a single cave system in Virginia, and also lives underwater. The vulnerable Madison Cave isopod is another underwater, cave-dwelling isopod that lives in limestone caves throughout Virginia and West Virginia. And then there’s the beautiful, critically endangered, spiky yellow woodlouse, which is only found on the island of Saint Helena.

Each of these species plays an important role within their environment, whether that be nutrient recycling in a dark cave, or consuming the spores of tree ferns high up in the peaks of Saint Helena’s cloud forest. More work must be done to understand Socorro isopods to ensure their survival for the future.

Can we save the spiky yellow woodlouse, one of the most endangered isopods? (commentary)

Citations:

Lang, Brian. “The Role of Controlled Propagation on an Endangered Species: Demographic Effects of Habitat Heterogeneity among Captive and Native Populations of the Socorro Isopod.” Nau.edu, 2005, https://www2.nau.edu/~shuster/isopod/Pubs/Lang%20et%20al.%202006.pdf

Inland Water Crustacean Specialist Group. “Thermosphaeroma Thermophilum.” IUCN Red List of Threatened Species, 1 Aug. 1996, https://www.iucnredlist.org/species/21741/9315891

Lang, Brian. “Wildlife Notes – Socorro Isopod.” Wildlife.state.nm.us, New Mexico Department of Game & Fish, 2003, https://www.wildlife.state.nm.us/download/education/conservation/wildlife-notes/aquatic/Socorro-isopod.pdf