Vernal Pools: Physical Characteristics and How They Affect Breeding Success of Amphibians

Ben Klein

Description of Research
Previous studies have found vernal pools are critical for reproduction in several amphibian species (Smith 1956, Shoop 1965, 1968). Vernal pools are temporary bodies of water that form in spring after snowmelt and usually dry in mid to late summer (Petranka 1998). Pools provide the necessary habitat for these amphibian species to breed with little predation from fish (De Graaf et. al. 1983). Many studies have found particular pool characteristics important to breeding success, particularly temperature and pH (Petranka 1998). Previous studies have estimated wood frog (Rana sylvatica) and spotted salamander (Ambystoma maculatum) breeding success to determine habitat quality. The purpose of my study was to document the physical characteristics of vernal pools and estimate the breeding success of these two species at the Huntington Wildlife Forest (HWF) in the central Adirondacks, in upstate New York.

Wood frogs and spotted salamanders were chosen for this study because of their relatively high abundance and their sensitivity to local disturbance (Petranka 1998). The wood frog ranges from northern Georgia to treeline in Alaska, and breeds from March to July at temperatures of approximately 10 degrees Celsius (Smith 1956). The spotted salamander ranges from Nova Scotia through the eastern United States and as far west as Kansas and Texas. Populations of spotted salamanders have been declining in recent years (Petranka 1998). They are a nocturnal species, and are generally considered fossorial (Petranka 1998). The breeding season of the spotted salamander is from March to mid-April.
The objectives of this study were to 1) document the physical characteristics of the pools at the Bureau Brothers Turn (BBT) study site, 2) quantify breeding success of the vernal pools by counting wood frog and spotted salamander egg masses and emergents, and 3) compare these results to other vernal pools at HWF. I tested the null hypothesis that there would be no difference in pool characteristic variables between BBT site pools and pools at other sites at HWF.

This study was conducted at Huntington Wildlife Forest, a 15,000 acre research area owned by the State University of New York College of Envrironmental Science and Forestry. The two sites at HWF were quite similar in their make-up. One site, the BBT site, was situated in the central portion of the property, while the other sites were scattered throughout the southern part of the property. Both sites were mixed northern hardwood forest, and lay between the elevations of 550 and 650 meters.

Various physical characteristics and evidence of breeding were recorded during sampling. Physical characteristics measured included: pool length, width, depth, temperature, pH, substrate type (mud/silt, leaf litter, or vegetation), and percent cover of emergent vegetation, cyanobacteria, and tree canopy. To estimate breeding success, egg masses, tadpoles/larvae, and emerging metamorphs were surveyed. Any other frog species, adult or otherwise, seen in the pool was also recorded.

Pool depth (P=0.014), length (P<0.001), and width (P=0.044) were significantly different at BBT pools compared to other HWF pools (Table 1). Average water depth for BBT pools was 14.1 cm (standard deviation=6.3), compared to 38.8 cm (standard deviation =11.7) outside the BBT site. Average length for BBT pools was 6.40 m (standard deviation =2.77), compared to 18.08 m (standard deviation =1.84) outside the BBT site. Averagewidth for BBT pools was 3.51 m (standard deviation =1.62), compared to 6.16 m (standard deviation =1.30). All other variables tested were not significantly different (Table 1).
No breeding success was observed at the BBT site. No egg masses, tadpoles, or metamorphs were observed during pool sampling. Additionally, breeding behavior was not observed in adult frogs or salamanders found in the BBT pools. Breeding success, however, was observed at the other pools at HWF used in this study (Endriss 2001).

Physical characteristics of vernal pools appear to be strongly related to the breeding success of spotted salamanders and wood frogs (Seale 1982, Brodman 1995). Shoop (1974) found water depth important to breeding success. Pools at BBT were shallower than a threshold suggested by Seale's (1982) study for significant amphibian egg deposition. In my study, shallow pool depth could be due to a lack of precipitation in HWF - April and May were particularly dry at HWF in 2001. Average length and width of BBT pools was also less compared to pools in Seale's study (1982). Conversely, the other pools sampled at HWF, that successfully supported amphibian eggs, tadpoles/larvae, and metamorphs, were consistent in depth, length, and width with Seale's (1982) study pools. Therefore, my study suggests vernal pool depth and size are important in determining breeding success in wood frogs and spotted salamanders.

About The Author: Ben Klein
I am currently an undergraduate at SUNY-ESF, majoring in Wildlife Science, minoring in secondary education. Research interests include carnivore ecology, and raptor ecology. Other interests are rock and ice climbing, mountaineering, backpacking, and fly-fishing. After graduation, I plan on attending graduate school out west and then hopefully working as a wildlife biologist or wildlife interpreter in a National Park.