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Arkansas's Karst: Salamanders Call it Home

Arkansas Natural Heritage Commission - Friday, March 29, 2019

by Dustin Lynch, ANHC

Arkansas’s cave and karst habitats are home to a disproportionately high number of sensitive and rare species and comprise an amazing part of our state’s natural heritage. Limestone caves associated with karst topography provide habitat for several species of salamanders, although some utilize these habitats more than others do.

The Grotto Salamander (Eurycea spelaea), is a species endemic to the Ozark Highlands. This species has one of the most unusual life cycles of any vertebrate animal. Like most salamanders, they begin life as aquatic larvae with adaptations such as external gills and tail-fins. Grotto Salamanders are thought to lay their eggs attached to rock surfaces in the pools of caves. After hatching, the larvae [troglophiles (see Underground tales: karst)] may dwell in cave streams, but they are often washed out into small springs and streams on the surface where they are more frequently encountered. The larvae (pictured at left) have fully functional eyes. Usually heavily pigmented, they range in color from brown to dark gray, generally with a pattern of spots and streaks.

After two to three years of life in these small surface streams, the Grotto Salamander larvae undergo an amazing metamorphosis to adulthood as they migrate back into the caves (pictured at right). Like most other salamanders, they lose specific aquatic features such as external gills and tail fins, but Grotto Salamanders undergo additional changes. Their pigmentation fades and their eyelids fuse shut, leaving them blind. The adults appear pinkish-white in color with long slender tails and small, nonfunctional eyes that may appear as darkened spots beneath translucent eyelids. The adults are true troblobites (Underground tales: karst); they are confined to the darkness of wet limestone caves for the rest of their lives.

Adult Grotto Salamanders (pictured at left) feed on cave-dwelling invertebrates such as small insects, while the stream-dwelling larvae feed on a variety of aquatic invertebrates, which are typically more abundant in surface streams than those in caves. Recent studies have revealed that the Grotto Salamander may actually represent a complex of three different, genetically distinct species, all of which can be found in disparate portions of the Ozark Highlands in northern Arkansas.

There are several other species encountered dwelling in caves, most often in or near cave entrances, or in the “twilight zone” where some light still penetrates the cave environment. The striking Cave Salamander (Eurycea lucifuga) ranges in color from yellowish-orange to bright red and is covered in black spots (pictured at right). Although this species prefers to live in the twilight zones of caves, they can also be found above ground near springs or under logs and stones in moist environments. Eggs are typically laid in cave pools, and the aquatic larvae may be found in springs on the surface near caves. The larvae usually transform in about a year, although this varies with local conditions.

The same environments where Cave Salamanders are encountered are also home to the Dark-sided Salamander (Eurycea longicauda melanopleura). This species is slender, with a very long tail, dark striped sides, and a broad middorsal stripe that is typically greenish-yellow and covered in black spots (pictured at left). These salamanders also begin life in cave pools but after hatching normally migrate to surface springs where food is more abundant.

The Western Slimy Salamander (Plethodon albagula) is another species encountered both on the surface of karst habitats as well as in the twilight zone of caves and mineshafts (pictured at bottom right). It is black to bluish-black above with numerous white or silvery-white flecks and a pale underside. It differs from these other species in one key way – this species has no aquatic larval stage. Eggs are deposited in moist environments rather than in the water, and hatch directly into tiny terrestrial juveniles.

Cave-dwelling species such as these salamanders inhabit our most fragile natural ecosystems and are therefore vulnerable to a variety of anthropogenic threats (caused or made by humans) including direct human disturbance, contamination and pollution, and changing land use.

All photos by Dustin Lynch, ANHC.








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