Final Comprehensive Conservation Plan - U.S. Fish and Wildlife ...

Hakalau Forest National Wildlife Refuge
Comprehensive Conservation Plan
in deep, extensive interconnect passages or small voids. Species diversity tends to increase with the
age of the cave; however, individuals can disperse to younger, more recent caves (Howarth et al.
2007).
Obligate and facultative cave animals often have unique characteristics because they have adapted to
subterranean habitats. Morphological adaptations include a loss or reduction of eyes, pale coloring,
wings, and longer appendages. Behavioral traits have also evolved as efficiency tactics in these
energy-poor environments. These include slow movements, a lower metabolism, a circadian rhythm,
and consuming large amounts in a single feeding. It is difficult to find cave animals because of their
cryptic behavior. Many of the cave species are rare; however, the only two endangered cave species
occur on the island on Kaua„i (Howarth 1983, Howarth et al. 2007).
Species within these caves receive their energy from several different sources: deep-rooted plants;
surface animals that accidentally fall or are washed into the caves; oozes deposited by percolating
ground water and reworked by microorganisms; and other organic material such as flood debris.
Plant roots are the primary energy source for cave species. In particular, the pioneer „ōhi„a tree is a
key food species, because it is the first to colonize young lava. Plant roots also provide shelter and
building materials for cave animals (Howarth et al. 2007).
In addition to invertebrates, rare and unusual plants can occur in lava tube skylights. These plants
may thrive in moist microclimates and survive due to protection provided by the steep rock walls of
the tubes making these sites unavailable to grazing ungulates. Cave ecosystems can also contain
minerals, as well as cultural and paleontological remains (USFWS 1997). The twilight zone was
often used by early Hawaiians for specialized uses, such as for water catchment or shelter (Howarth
and Stone 1998). Archaeologists have found artifacts and prehistoric features within caves
throughout the islands (Ziegler 2002). To date no cultural sites have been found in lava tube systems
at the KFU. There are no known lava tube systems at the HFU.
Cave habitats on the KFU are extensive. A reconnaissance survey of these caves was conducted by
Dr. Howarth and Stone in 1998. Four distinct cave systems consisting of 22 cave entrances were
found at the unit, although only three systems were surveyed. The caves are of intermediate age (less
than 4,000 years old) and have a thick overburden of rock and soil. Most entrances occur as vertical
pits. The cave passages explored by Howarth and Stone were primarily in twilight and transition
zones, which are characteristic of caves that have multiple entrances. However, a few other areas
likely enter deep zone habitats, where the specialized cave-adapted animals thrive (Howarth and
Stone 1998).
It is estimated that only about 20 percent of the caves have been mapped (Ball, pers. comm.).
Although caves throughout the site have only been partially surveyed, they are known to support rare
and unusual species adapted for life in subterranean ecosystems. Some resident species have
persisted because the caves are generally inaccessible to ungulates (USFWS 2002b). Additional cave
features likely occur that have surface openings not large enough for humans to enter. The cave
locations at the KFU are kept confidential under U.S. cave law (Howarth, pers. comm.).
Due to the cryptic nature of the species, relatively few arthropods were seen during the 1998 KFU
survey. Endemic cave fauna and evidence observed by Howarth and Stone included the following:
cave carabid ground beetle (Mecyclothorax? sp.), Schrankia root moths, a Carposina fruit moth
(probably gracillima), Linyphiid spider webs, and trails of the native Limonia crane flies. In addition,
Chapter 4. Refuge Biology and Habitats 4-81