February 11, 2002 (10:30 PM)
Kauai Cave Amphipod
SPECIES CODE: K022 I01
STATUS: Endangered throughout a significant portion of its range on the Hawaiian island of Kauai (65 FR 2357, January 14, 2000). Proposed critical habitat designation is due to the Federal Register on February 15, 2002. Final critical habitat designation is due on August 10, 2002. A total of approximately 4,881 acres on the island of Kauai is proposed for designation as critical habitat.
SPECIES DESCRIPTION: The Kauai cave amphipod (Hawaiian common name 'uku noho ana) is a blind, pale, cave‑adapted crustacean. The animal is 7 to 10 mm (0.25 to 0.4 in) in length and very slender‑bodied, with a translucent outer layer. This species is also distinctive in its lack of eye facets (lenslike division of a compound eye) and pigment, and extremely elongate, spiny, postcephalic (behind the head) appendages.
The Kauai cave amphipod is a detritivore (feeds on organic debris from decomposing plants, animals, and fecal material) and has been observed feeding on rotting roots, sticks, branches, and other plant material washed into the caves; and arthropod fecal material. In large cave passages, most individuals are found on or underneath roots or rotting debris. However, this amphipod does not appear to be particularly gregarious. When disturbed, this species typically moves slowly away rather than jumping like other amphipods (Bousfield and Howarth 1976; Poulson and White 1969).
REPRODUCTION AND DEVELOPMENT: Nothing is known of the reproductive biology of this amphipod, but the vestigial brood plates of the female suggest they give birth to a small brood of large offspring (Bousfield and Howarth 1976; Poulson and White 1969). It has a relatively low reproductive rate; only one young is carried in its marsupium at a time (Bousfield and Howarth, 1976). Development is slow, but the length of the life cycle is unknown. The amphipod’s low reproductive rate makes it vulnerable to novel alien predators and diseases.
RANGE AND POPULATION LEVEL: Originally, the amphipod probably ranged throughout the available subterranean spaces in the Koloa Lava Flow, which covers the lowlands on the southeastern portion of Kauai, Hawaiian Islands, as well as in a limestone cave about five kilometers away from the lava tubes sitting on top of the flow. Subsequent ash deposits and erosion have filled the voids in the upslope portion above about 200 feet elevation, so that the historic range was probably about 15 square kilometers (six square miles). Recent land surface modifications for agriculture, urbanization, and recreation have destroyed more than one half of the historic habitat, including the population in the limestone cave (Bousfield and Howarth, 1976; Howarth 1973; 1983a; 1983b). The current confirmed range (i.e., the area between the known caves) is less than 2000 acres, but suitable habitat is probably larger. These animals are currently known only from a single exposed lava flow which covers approximately 10.5 square kilometers (sq km) (4 sq miles (mi)), and exhibits no covering by erosional sediments.
The Kauai cave amphipod population is divided into several subpopulations (lava tubes). The animal occurs in six small cave segments in the less weathered portions of a single, old (ca 600,000 year‑old) lava flow, as well as in a younger limestone cave that sits on top of the flow (Bousfield and Howarth, 1976). The lava tube segments occur in three groups of one to three caves, which are separated from each other by about one kilometer. The limestone cave and one lava tube in the area have not harbored the amphipod for 20 years and the records are considered historic. It also is presumed to occur in suitable intermediate‑sized voids within the lava flow, but these are not accessible for survey. Howarth (1983c) blocked an entrance with plastic and added water and dead sticks at the end of a dry lava tube not known to harbor cave animals, and within two months the amphipod colonized the cave. The land supporting the Kauai cave amphipod is privately owned, as are adjacent areas with potentially suitable habitat.
Due to the inability to mark amphipods for demographic studies, no attempt has been made to estimate the population sizes of the cave amphipod. The number of individuals which can be censused is fewer than 300. Most of the population lives in inaccessible medium‑sized voids (mesocaverns). Its population has ranged between five to more than 50 individuals in about 120 meters of passage. The other three caves sometimes harbor none or up to 50 individuals especially during wetter periods and if food is available (Nature Serve Explorer 2002).
HABITAT: These animals are restricted to the dark, moist areas of larger caverns and
smaller subterranean spaces or mesocaverns (Howarth 1983a). Specifically, the Kauai cave amphipod inhabits the deep zone and stagnant air zone of lava tubes and intermediate‑size voids (mesocaverns) in pahoehoe lava, as well as similar habitats in a limestone cave resting on top of the lava flow (Bousfield and Howarth, 1976; Howarth, 1973; 1991a). Its lowland (0 to 100 feet above sea level) habitat is warm (between 25 and 30 C) and always in damp to wet areas with calm, stagnant, water‑saturated air (Howarth 1991a), which sometimes contains more than three percent by volume carbon dioxide.
PAST THREATS: These animals and their habitats have been variously affected by: habitat degradation and loss through the removal of perennial vegetation, soil fill, grading, paving, quarrying, and other activities associated with development and agriculture; predation and competition for space, water, and nutrients by introduced, alien animals; biological and chemical pesticide control activities associated with residential and golf course development; and an increased likelihood of extinction from naturally occurring events due to the small number of remaining individuals and populations and their limited distribution.
After 1835, most of the land in the Koloa area with suitable topsoil was used for large‑scale sugar cane cultivation (Hammatt et al. 1988). This activity included the mechanical clearing of stones and boulders and consolidation of smaller field plots. The surface modifications associated with these past agricultural activities greatly reduced underground root biomass through the destruction of perennial vegetation (Howarth 1981; Miller and Burgett 1995), which removes the necessary food base for the amphipod and other cave‑dwelling herbivores (Howarth 1973, 1981, 1982). Large‑scale agricultural practices brought on by the sugar cane industry also increased the amount and mobility of the overlying sediments. As a consequence, the rate of sediment deposition into the underlying subterranean voids increased, eliminating or greatly reducing the amount of available cave habitat (Howarth 1973; Hammatt et al. 1988; Asquith, in litt. 1994).
Thus, with the exception of a narrow 0.5 km‑wide (0.25 mi‑wide) strip of particularly rocky land immediately along the coast, most of the habitat for the amphipod was heavily modified prior to the 1950s. On interior lands, small areas of exposed pahoehoe lava, rock outcrops, and the entrances to lava tubes were generally unsuited for cultivation of crops and were left less disturbed. In areas improved for pasture use, however, some cave entrances were filled or covered (Hammatt et al. 1988; Howarth, in litt. 1977). Significantly, all the known populations of both the Kauai cave spider and amphipod are in areas never used for plantation sugar cane cultivation.
Habitat destruction and loss continues to be a major threat. Two historic populations have been lost and more than half the suitable habitat destroyed in the past 25 years. It has been extirpated from the limestone cave by mining for limestone for cement and from one lava tube that was destroyed during road construction. The amphipod’s population in one other lava tube is tenuous. Currently, the Koloa cave systems are considered to be 1 of the 10 most endangered cave ecosystems worldwide (Culver in litt., 1998).
Koloa is a leeward dry coastal area, which is under intense pressure for tourist developments: golf courses, hotels, and subdivisions (Howarth, 1983a). In the last 5 decades, the Koloa area changed from an agriculture‑based economy to one increasingly dependent on tourism (Kauai Office of Economic Development, in litt. 1994). Approximately 75 percent of the original habitat available for the cave animals is now designated as ``urban'' or ``urban residential'' (County of Kauai, in litt. 1994), and the human population of the Koloa area is expected to double by the year 2015 (KPMG Peat Marwick 1993). This population growth has led to rapid development of homes, condominiums, and resort hotels originally centered along the coastal strip. In recent years, interior lands supporting all but one population of the amphipod have been rezoned from agriculture to urban usage and are undergoing development. The three cave areas are already partly or wholly surrounded by these urban developments, which may have isolated the animals to much smaller areas than the total available habitat. Additional construction is planned. Construction of tourist resorts over the habitat directly and indirectly affect the amphipod by crushing and filling the voids, changing water and food infiltration patterns, and introducing pollutants (Howarth 1983b). Paving the surface above a cave prevents water and food from entering subterranean voids. Adding topsoil filters out food also preventing its movement into deeper voids. The reduced air exchange may further restrict habitat suitability. Changing the environment within the caves, such as by enlarging entrances or creating new ones, will destroy the habitat. The limestone hill containing the cave is slated for complete removal by mining; however, the amphipod disappeared as mining progressed even though some suitable habitat remained. Thus, most of the land that potentially harbored these animals has been highly modified, and an estimated 75 percent of the area has probably been rendered uninhabitable. The remaining habitat, harboring virtually all known populations of the amphipod, is being degraded by current land use or is threatened with degradation and destruction from proposed development.
Direct over utilization of the organisms is not known to be a factor, but unrestricted collecting for scientific purposes or excessive visits by individuals interested in exploring the lava tubes could result from increased publicity associated with listing under the Endangered Species Act.
As the human population grows as a result of the recent creation of these resorts, additional threats from human disturbance, pollution, and alien species introductions are likely (Howarth, 1983a; 1983b). Cave habitats and the native animals living in them are extremely sensitive to human disturbance (Howarth 1983b). Increased human use of caves can result in the direct trampling, intentional or otherwise, of cave animals as well as indirect impacts due to destruction of root systems (Howarth 1982; Culver 1992). In addition to direct habitat destruction, human impacts include the use of campfires (D. Hopper, pers. comm. 1988) as well as introduction of cigarette smoke into the cave environment. Cigarette smoke contains a strong insecticide which, within the enclosed cave, is likely to negatively impact the resident cave animals (Howarth 1982). Both the smoke from cigarettes and fires dries the cave air, and studies and observations have shown that reduced cave humidity is detrimental to cave organisms (Ahearn and Howarth 1982; Howarth 1981, 1982). Such disturbances by human visitation can also promote greater invasion by alien arthropod species, such as cockroaches and their predators, through the introduction of trash (Howarth 1982; D. Hopper, pers. comm. 1998). Howarth (1982) indicated that species diversity and population levels of cave invertebrates are inversely related to human visitation and disturbance.
Several alien spiders including the brown violin spider (Loxosceles rufescens), spitting spider (Scytodes longipes), and Dysdera crocata (no common name (NCN)) have invaded the cave habitats in Koloa (Gerstch 1973; F. Howarth, pers comm. 1994; Asquith, in litt. 1994b), and prey on probably all life stages of the cave amphipod (Howarth 1981). The American cockroach (Periplaneta americana) is abundant in some of the caves (Bousfield and Howarth 1976; Asquith, in litt. 1994a) and probably opportunistically preys on immature cave amphipods (F. Howarth, pers. comm. 1994) and competes for space at amphipod food sources (Asquith, in litt. 1994a).
Insecticide use, coincident with the change to urban land development, poses a serious threat to the cave animals (Howarth and Stone 1993). While plantation‑scale sugar cane cultivation in the Koloa area involves seasonal use of herbicides, intensive usage is generally limited to spot applications of glyphosate (trademark name, Roundup), and generally no insecticides are used (Murdoch and Green 1989). Furthermore, in recent years most sugar cane cultivation in the area has been restricted to land with deep soil, which is generally unsuitable habitat for the cave animals.
Golf courses exist on, or are proposed for, the land directly above or adjacent to all but one population of the amphipod. At least 30 different pesticides are used on golf courses in Hawaii, including insecticides to control pests of turf grass (Murdoch and Mitchell 1975; Murdoch and Green 1989). Most golf courses in Hawaii apply the insecticide chlorpyrifos at the rate of 453 grams active ingredient per 0.41 hectares (1 pound active ingredients per acre), 1 to 3 times per year, but rates and frequency of applications are sometimes much higher (Murdoch and Green 1989; Brennan et al. 1992).
In addition to the use of pesticides on golf courses, pesticide usage on residential property also poses a threat. It is estimated that residential lots use more pesticides per unit area than either sugar cane cultivation or golf courses and that 90 percent of this use involves insecticides. Much of this insecticide is applied directly to the ground for termite control (Hawaii Office of State Planning 1992). With an estimated increase of 4,000 houses in the Koloa area by the year 2015 (KPMG Peat Marwick 1993), residential pesticides are considered a serious threat to the cave animals.
These cave animals are particularly susceptible to pesticides because of their tendency to seek water sources (Howarth 1983a; Asquith, in litt. 1994a). Even if pesticides are not used directly above a lava tube, pesticides that leach into adjacent subterranean caverns with water from runoff or irrigation are serious threats because the animals may be attracted to the water and come into contact with the chemicals. Even if not killed outright, the sublethal effects of both insecticides and herbicides on the cave animals could include reduced fecundity (reproductive capacity), reduced lifespan, slowed development rate, and impaired mobility and feeding efficiency (Messing and Croft 1990).
Biological control agents (living organisms used to control pests) are usually perceived as preferable to the use of chemicals because they represent less of a threat to human health and generally do not stimulate resistance in pests. Some of these organisms, however, attack species other than their intended targets and have caused or contributed to the decline and extinction of several Hawaiian insects (Gagne and Howarth 1985; Howarth 1983b; Howarth 1991b). The nematode Steinernema carpocapsae (NCN) is marketed for use against turf pests and has been petitioned for use on golf courses in Hawaii (Faust 1992). This nematode can infect at least 250 species of arthropods (Poinar 1979), including arachnids such as the endangered Kauai cave wolf spider (Poinar and Thomas 1985). Other biocontrol agents such as Bacillus bacteria, which have been used for mosquito control, have caused serious damage to nontarget species of insects (Howarth 1991b). Unlike most chemical pesticides, biocontrol agents will not break down or decay. Should such biocontrols become established, they will likely remain resident in the area, spread to new areas with suitable host arthropods, and become impossible to eliminate. Lastly, biocontrol agents may undergo great proliferations in the presence of ubiquitous and numerous arthropod pests and other species. The resultant population increase of biocontrol predators or parasites would have devastating impacts on species such as the Kauai cave amphipod, given their restricted ranges and low fecundities. Biological controls have been emphasized for golf course management in the Koloa area (Townscape 1993) and are a potential threat to Kauai cave amphipod.
The small number of populations and small numbers of observed individuals of the Kauai cave amphipod (five populations) increases the risk of extinction from naturally occurring events such as storms or earthquakes.
CURRENT THREATS: The current primary threats to the Kauai cave amphipod are: habitat degradation and loss through the removal of perennial vegetation, soil fill, grading, paving, quarrying, and other activities associated with development and agriculture; predation and competition for space, water, and nutrients by introduced, alien animals; direct or indirect mortality from the use of biological control agents and chemical pesticides; and an increased likelihood of extinction from naturally occurring events due to the small number of remaining populations and their limited distribution.
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