Responses of Plethodontid Salamanders to Stream Acidification and Acid Mine Drainage in the Pennsylvania Central Appalachians
Open Access
- Author:
- Rocco, Gian L
- Graduate Program:
- Wildlife and Fisheries Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 27, 2007
- Committee Members:
- Robert P Brooks, Committee Chair/Co-Chair
Dr Robert F Carline, Committee Member
Walter Matthew Tzilkowski, Committee Member
Alan H Taylor, Committee Member - Keywords:
- Pseudotriton
Eurycea
Desmognathus
acidification
Appalachians
stream
Plethodontidae
salamander
Gyrinophilus
in situ - Abstract:
- Low pH and dissolved heavy metals are toxic to amphibians by disrupting ionoregulatory mechanisms that cause loss of body sodium. Stream salamanders of the family Plethodontidae can occupy small, northern Appalachian streams in large numbers and are important vertebrate components. In the Pennsylvania central Appalachians, up to seven species comprise a streambank assemblage. The northern two-lined (Eurycea b. bislineata), longtail (E. longicauda), northern spring (Gyrinophilus p. porphyriticus), and northern red (Pseudotriton r. ruber) salamanders (subfamily Plethodontinae) have aquatic egg-laying habits and extended aquatic larval stages (1-4 yr). The mountain dusky (Desmognathus ochrophaeus), northern dusky (D. f. fuscus), and Appalachian seal (D. monticola) salamanders (subfamily Desmognathinae) have terrestrial egg-laying habits and shorter larval stages (3 mo - 1.5 yr). Differences in life history and nesting habits were hypothesized to favor terrestrial nesters in acidified streams because of greater exposure to stream toxicity in more aquatic forms. Three investigations were completed, each focusing on resolving separate but related questions. The effect of acidification on stream salamander abundance and distribution was initially addressed by sampling for stream salamanders along an acid-alkaline gradient. The direct effects of stream toxicity was investigated subsequently by in situ exposure of aquatic nesters, assemblage members most likely to be affected. The hypothesized benefits of terrestrial habits and life history were investigated in terrestrial nesters by simulating adverse nesting environments in the laboratory. Investigations subsequent to the field study were intended to compare survival of taxa that exhibited different distribution patterns but shared similar nesting habits and life histories. Assemblage response in the field (abundance, species and life stage composition) was investigated in 1997-1998 by plot-sampling for salamanders in 14 Pennsylvania Central Appalachians streams representing acid mine drainage-contaminated (AMD), episodically acidified, non-acidic, and non-acidic-high alkalinity conditions. Acidic streams favored the mountain dusky and northern spring salamanders, adult or terrestrial stages, and low abundance. The northern two-lined and northern dusky, aquatic larvae, and higher salamander abundance were favored in non-acidic streams. Ordination by correspondence analysis (CA) grouped the above taxa similarly and along the axis most highly correlated to the acid-alkaline gradient sampled. Removal, by partial canonical correspondence analysis (CCA), of variation tied to stream physical habitat failed to eliminate significant associations with water chemistry. Low abundance of the northern dusky, a terrestrial nester, and persistence of the northern spring, an aquatic nester with an extended aquatic larval stage, in acidic streams, were inconsistent with the proposed general hypothesis that survival favored terrestrial nesting and shorter aquatic larval stages. The direct effects of stream toxicity were investigated by in situ exposure of northern spring and northern two-lined salamanders in AMD-contaminated reaches where sampling had revealed low abundance. Survival, changes in body water content and total body sodium were examined as response variables in 1998 and 1999 by 19-d, 48-hr, and 12-hr in situ exposures in reaches of varying AMD-contamination. Testing of the northern spring was limited to the 48-hr exposure. Exposures were conducted in southwestern and central Pennsylvania streams using wild-caught larvae and metamorphs. Most northern two-lined larvae and metamorphs survived the 19-d (weak AMD) and 12-hr (strong AMD) exposures. Survival in the 48-hr exposure favored lower AMD-contamination, larger and older larvae, metamorphs, and northern spring larvae. The proportion of body water was lower after 19-d and 48-hr exposures, relative to controls, but increased initially during the 12-hr exposure. Total body sodium was lost in all exposures. The northern dusky and mountain dusky are both terrestrial nesters. In acidic streams, the northern dusky declined, whereas the mountain dusky persisted. Absence of an aquatic larval stage, as reported in the early literature, was hypothesized to favor survival in acidic streams. Survival in hatchlings of both species was examined in the laboratory by exposure to treatments simulating acidic, dry, and normal nesting environments. Hatchlings were collected in nests from southwestern and central Pennsylvania. Early transformation was observed in only 2 (<1%) of the original 302 northern dusky hatchlings collected and before the experiment began. Hatchling survival was lowest in acidic and dry treatments. Hatchling size and their origins also affected survival. A single mountain dusky nest was found; all 10 hatchlings transformed within weeks of hatching and survived the 51-d exposure irrespective of container treatment. Based on the findings of the three investigations, reduced abundance and distribution of stream salamanders is attributed to the direct effects of acidification. Persistence in acidic streams by the life-history route was possible by early transformation, the bypassing of the aquatic stage. Natural acid tolerance aided survival in one aquatic nester. The impact of stream acidification was anticipated to be considerable in stream salamanders lacking either mechanism.