By John Walsh
Have you ever been beautifully dressed up with nowhere to go? Such is the life of the spotted salamander (Ambystoma maculatum) which spends most of its life beneath ground emerging but for a brief time to mate before returning to its subterranean and solitary existence.
Unlike it’s more abundant and fully terrestrial relative, the red-backed salamander ( Plethodon cinereus ), the spotted is hard to overlook. A monster by comparison, stretching upwards of 7 inches or more, the spotted possesses a striking black background punctuated with large yellow dots. The spotted has several notable close relatives all distinguished by a similar lifestyle. Commonly known as the mole salamanders in recognition of their below ground (or fossorial) existence, members of the family Ambystomatidae are unique to North America and are represented by a single genus comprising some 32 currently recognized species. However, only three of these are known to inhabit the Blue Hills. Along with the aforementioned spotted salamander, which is the most common of our local mole salamanders, the Blue-spotted (A. laterale ) and the Marbled (A. opacum ) may also be found in the Reservation. The blue-spotted is distinguished by possessing small blue spots or flecks on a dark background, an appearance reminiscent of vintage blue speckled enamelware. The marbled, as its name suggests is distinguished by having a stockier build with grey or white bands on a black background.
However, it’s that party once a year that really sets these mole salamanders apart. With the first warm rains of early spring (typically late March through April), these critters temporarily vacate their underground quarters during the night and clandestinely make their way to a nearby vernal pool. These pools typically form in depressions that fill with water during the fall and winter, yet are shallow enough to fully dry out as the summer goes along. By drying out completely these pools thus are not able to sustain populations of fishes that might otherwise prey on tasty salamanders and their eggs. While this might be an effective mechanism to reduce fish predation, it means that salamanders are racing the clock. The race begins with the salamanders reaching these pools where the males place packets of sperm (spermatophores) on submerged surfaces followed by females who take up the spermatophores. The activity can get frenzied with these breeding congresses, as they are known, sometimes involving hundreds of individuals. The female then deposits the fertilized eggs in masses that can contain varying numbers of individual eggs depending upon the species. These egg masses can readily be distinguished from most other amphibian species as they have a smooth appearance due to a gelatinous cover. The masses may also take on a green coloration due to the growth of symbiotic algae that may both provide oxygen and camouflage for the developing eggs. Incubation typically lasts a month or so with the larvae undergoing a rapid metamorphosis in which the external gills of their aquatic stage give rise to the features needed for their terrestrial futures as mature salamanders. They then usually emerge from these drying pools during the summer months and then disperse to surrounding upland habitats. It should be noted that while this scenario is true for both the blue-spotted and spotted salamanders, their marbled cousins go through much the sequence but during the fall, instead of the spring and summer months. This strategy has its advantages resulting in an advanced state of growth for marbled larvae that overwinter in these pools allowing them to prey on their newly hatched relatives in the spring.
Like amphibians globally our own populations are at risk. Although spotted salamander populations are relatively secure, the blue-spotted is listed as a species of Special Concern by the state of Massachusetts. The marbled is at even greater risk and is currently listed as Threatened by the state. This greater level of endangerment may, in part, reflect the fact that our state is at the northern limit of its natural geographic range. However, the range of threats to all of these critters is daunting. Leading the list is unquestionably habitat loss, degradation and fragmentation. Pollution including road runoff and acid precipitation, coupled with road kill as they migrate across roads on their way to breeding pools, also add significantly to the toll. Climate change and mosquito control methods that act to reduce potential food sources for the salamander may add to the burden. Although vernal pools and associated wetlands do offer some degree of legal protection with additional protection afforded species such as the blue-spotted or marbled under the Massachusetts Endangered Species Act, this may not be enough. Research, for example, has indicated that while many of these salamanders spend most of their lives within a few hundred feet of their breeding pools, many others may travel from thousands of feet distant. Thus, not only must such pools be recognized and protected, but significant swaths of adjoining upland habitat may require similar protective measures as well to be fully effective.
In any case, if this spring you are all dressed up and ready for a night on the town yet find your plans dampened by wet weather, take heart for in scattered vernal pools and wetlands throughout the Blue Hills the party is just beginning.
Friends of the Blue Hills Board member, John Walsh, is an educator and naturalist.