Biodiversity of Freshwaters - Freshwater Ecology: Concepts and Environmental Applications - page 189

organisms found in groundwaters can be accidental wanderers from sur-
face waters, can occur mostly in groundwaters and have some adaptations
to the subsurface life (stygophile), or can be specifically adapted to life in
groundwaters (stygobite) (Gibert et al., 1994). Adaptations to life in
groundwater habitats include loss of eyes and pigmentation, increased
length of sensory appendages, slowed metabolic rates, long life histories,
and production of few large eggs.
Apparently, dispersal ability is low in groundwater fauna (Strayer,
1994), probably contributing to endemism. For example, little recovery of
some North American hypogean invertebrates occurred following the last
glaciation. In some cases, the species found in groundwaters can vary over
small spatial scales. Diversity of ostracods in the groundwater (hyperheos)
near the Sava River (Croatia) varies considerably across a 135-m transect
moving away from the river channel (Rogulj et al., 1994). Studies of sub-
terranean crustacean species found in subsurface streams in a Virginia
karst aquifer indicated the importance of spatial scale (Fong and Culver,
1994; Culver and Fong, 1994). These authors demonstrated unique species
assemblages that varied at scales from individual rocks to differences be-
tween pools and riffles. Greater differences were found among different
branches of the streams, and the greatest differences were found in adja-
cent subsurface drainage basins.
Rivers with extensive hyporheic systems in very permeable or chan-
nelized aquifers can have a unique biota associated with the subsurface wa-
ter (Marmonier et al., 1993; Dole-Olivier et al., 1994; Popisil, 1994; Ward
and Voelz, 1994; Hakenkamp and Palmer, 2000; Boulton, 2000). In a fas-
cinating series of studies on groundwater communities in a gravel-bed river
system, numerous aquatic insect larvae and other invertebrates were doc-
umented up to 2 km from the river channel (Stanford and Ward, 1988).
Some of these species are unique stoneflies that spend their entire nymphal
life cycle underground (Stanford and Gaufin, 1974). Hyporheic habitats
may be constant enough to provide refugia for ancient taxa of cladocerans
over evolutionary time (Dumont, 1995).
The data available on biodiversity of hypogean animals suggest that a
tremendous number of undescribed species exist. The difficulties encoun-
tered in sampling these organisms, coupled with the documented spatial
variation in distributions of the animals, make it highly probable that
species will be missed unless areas are sampled intensively. Despite what
we do not know about the distribution of these species, many are highly
susceptible to human-caused pollution of groundwaters. Thus, the use of
groundwater invertebrates as bioindicators of contamination has been sug-
gested (Malard et al., 1994), particularly as indicators of low O 2 condi-
tions (Malard and Hervant, 1999).
Some temporary pools are also centers of endemism. Such pools are
isolated from other aquatic habitats and require special adaptations in the
form of desiccation resistance. The vernal pools of California are examples
of this because they provide habitat for highly endemic plant communities.
In addition, when 58 of these vernal pools were sampled, 67 species of
crustaceans were found and about half these were endemic, mostly fairy
shrimp (King et al., 1996). Such pools with endemic plant and crustacean
communities have been described in dry habitats throughout the world
(Thorne, 1984; Belk, 1984).