Julian J. Lewis, Ph.D

Managing Endangered Species: Charting the Course of the Illinois Cave Amphipod with Non-lethal Censusing Julian J. Lewis, Ph.D. Salisa T. Rafail J. Lewis & Associates, Biological Consulting Diane Tecic Illinois Department of Natural Resources Abstract In 1940 the Illinois Cave Amphipod, Gammarus acherondytes, was described as a new species. The only obligate subterranean amphipod of the genus Gammarus in North America, this unique crustacean was described from two caves in southwestern Illinois. By 1988, cave bioin- ventories had revealed Gammarus acherondytes in a total of six caves just southeast of metropolitan Saint Louis. Over time, groundwater quality deteriorated in the area as land use changed. In 1995 Gammarus acherondytes could not be found in two previous sites and was barely present in two others. The amphipod was listed as a federally endangered species in 1998. In 1999 bioinventory by The Nature Conservancy revealed six additional cave populations, two in groundwater basins where the amphipod was previously unknown. As an endangered species, Gammarus acherondytes presented a censusing dilemma. There was no way known to monitor the 12 cave populations of Gammarus acherondytes without killing the amphipods to count them. In 2000 a project was initiated to see if it would be possible to measure the population sizes without killing the tiny endangered animal. Experi- mental census transects were established in several caves. To eliminate sampling prejudice, quadrats were randomly placed within the transects. Using a hand-held 15X microscope it was possible to separate Gammarus acherondytes from three other species of co-occurring cave amphipods. All animals were identified, measured, and released imme- diately back into the stream. The method was painstaking and labor intensive, but successful. Full-scale censusing of the endangered species commenced in 2001. Introduction munities were inspected and appeared intact at that time, but no collections were made. The subterranean amphipod, Gammarus However, over the next 20 years the land use acherondytes, was described by Hubricht and of the area began to change from primarily Mackin (1940) from specimens collected by agricultural and second growth forest into a Leslie Hubricht from Morrisons Cave (Illinois region with an increasing suburban compo- Caverns) and Stemler Cave in the karst of nent. Webb (1995) reported that G. acheron- southwestern Illinois. Bousfield (1958) rede- dytes could no longer be found in Stemler scribed the species but added no new localities. Cave and only small numbers of the am- Based on collections in the mid-1960s, Peck phipods were present in the other sites (Paut- and Lewis (1978) added Fogelpole, ler Cave was reportedly closed by the owner). Krueger/Dry Run, and Pautler Caves to the list Fueled by the growing interest in G. acheron- of localities from which this amphipod was dytes, The Nature Conservancy conducted a known. In 1976, Lewis visited Illinois Caverns bioinventory of caves in Monroe and Saint Clair and Stemler Cave to evaluate the sites for the Counties (Lewis, Moss, and Tecic, 1999). This Illinois Natural Areas Inventory. The cave com- project resulted in the report of six additional 142 2001 National Cave and Karst Management Symposium caves with populations of G. Acherondytes. The fauna During that same year, Gammarus acheron- Aquatic cave communities are usually rela- dytes was added to the U.S. Endangered Spe- tively simple, comprising a handful of species cies List. that can frequently be identified easily, even in During the bioinventory by The Nature Con- the field by the naked eye. Unfortunately this is servancy it became apparent that little had been not the case in western Illinois cave streams in done to provide a basis by which the popula- which there are four species of amphipods that tions of Gammarus acherondytes could be are of approximately the same size and shape. measured. Webb (1995) had collected am- Non-lethal identification of the amphipods was phipods in various parts of several caves using the most challenging part of the project. a biased sampling technique that considered Cave stream communities in the western only the amphipod subset of the total commu- Illinois karst of Monroe and Saint Clair Coun- nity. Lewis, et al. (1999) collected samples in a ties typically comprise an assemblage of spe- similar manner to produce results that could cies: the flatworm Sphalloplana hubrichti be compared to what had already been done. (stygobite); snails Fontigens antroecetes (sty- These samplings of the populations provided gobite); Physella sp. (stygobite or stygophile); little data that could be duplicated to deter- isopods Caecidotea packardi (stygobite); mine the ongoing situation with G. acheron- Caecidotea brevicauda (stygophile); and am- dytes, while killing the endangered animals phipods Gammarus acherondytes (stygobite), that were purportedly being “saved.” Gammarus troglophilus (stygophile), Bactru- Thus was born the raison d’etre for develop- rus brachycaudus (stygobite), Crangonyx for- ing a non-lethal method for estimating popula- besi (stygophile). Detailed analysis of the tions: to provide a yardstick by which the status identification of these animals was presented of Gammarus acherondytes could be meas- by Lewis (2000). ured in the future to see if the situation was getting better, getting worse, or staying the Census transects same. The best method for censusing anything The first priority in the establishment of is to count the entire population. This is obvi- transects was the presence of a landmark felt ously not possible with a cavernicolous inver- to be of an enduring nature, such that a re- tebrate, therefore leading to the alternative of searcher desiring to repeat the census a century examining a subset of the population. Many from now would have an excellent chance of methods are known for preparing population finding the same spot again. For each riffle estimates. We have chosen to use one that was transect, when facing upstream the census start suggested to Julian J. Lewis by cave ecologist point was the point at which the riffle ended Thomas L. Poulson for population biology and pool habitat started on the right-hand side studies in the aquatic communities of the Flint- of the riffle. A square foot (30 by 30 centime- Mammoth Cave System of central Kentucky. ters) Surber sampler was used to collect samples. Randomization of the sample sites was Population Estimate Methodology done by selecting each sample site with a number taken from a random numbers chart (avail- In general, the method consists of counting able in most statistics books). The starting spot and measuring all species present (not just a in the random numbers chart was selected first target organism of interest) in multiple, ran- by random selection on the chart. From the domly-selected quadrats along a series of tran- point selected, the numbers were read down sects. Analyzing the entire community, rather the column and the first two digits used to than merely a population within it, provides a select the sample spot. A flexible plastic tape much more complete picture of what is happen- measure was stretched down the right hand ing in the ecosystem. Concerning measurement side (facing upstream) of the riffle. Using the of the animals, many stygobitic organisms have random number, the first digit was used to populations that are skewed toward older select the number of feet up the tape for the (larger) individuals with fewer juveniles first quadrat. The second digit was the percent- (smaller) or ovigerous females. Although it might age across the stream from the right hand bank. be impossible to glean the exact size of an am- For example, if the first number was 4268, and phipod, an estimate of six millimeters for an the stream was 10 feet wide, the first quadrat amphipod places the animal in a subadult cohort would be placed four feet up the riffle and 20% that obviously differs from a two-millimeter (two feet) across the stream from the right brood release or an 18-millimeter adult. This bank. After the Surber sampler was placed, a provides important information when the entire ruler was placed in the shallowest and deepest community is measured. part of the quadrat and the depth recorded. If 2001 National Cave and Karst Management Symposium 143 the water depth was less than about 2.5 centi- centimeters throughout the transect. The num- meters the animals present were censused in ber of rocks surveyed and an estimate of the situ. If the water was deeper than 2.5 centime- size of the rocks were included in the census ters the gravel was dislodged and animals al- data. lowed to wash into the sampler. All rocks were visually inspected for animals clinging on them. Results Several large plastic beverage cups were carried into the cave and used to wash any The raw data was recorded in the cave and animals or other material clinging onto the then transcribed into a standardized spread- net of the sampler into the plastic container sheet format. On this datasheet is contained the on the bottom of the sampler. Usually 8 to 12 name of the site, the location within the cave washings were adequate. The contents of the of the census area, date and personnel con- sampler were released at streamside into a ducting the census, random numbers used to plastic bowl. On the first day of censusing a generate the quadrats, a description of the four-inch square bowl was used and was im- quadrat microhabitat, and the lengths of all mediately recognized as inadequate in size. animals found. That evening an 8- by 12-inch Rubbermaid Population size of the Illinois Cave Am- plastic bowl was purchased and was found to phipod can be estimated by extrapolating the be an ideal size for carrying into the cave as area sampled to encompass the total area of well as containing the samples.

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