Vernal Pools

EPHEMERAL LIFE IN THE PIONEER VALLEY

For inquiries contact: Monica O'Guinn , Entomology Department, University of Massachusetts, Amherst, MA 01003

VERNAL POOL CONTAINING WATER IN THE SPRING

SAME POOL SITE, DRY IN THE SUMMER

Vernal pools provide a habitat for many plant, invertebrate and vertebrate species. These aquatic habitats are often overlooked as important wetland resources and thought of as merely the residual effects of winter. Webster defines vernal as "belonging to, or appearing in spring". Snowmelt and ephemeral are terms used interchangeably with vernal. Vernal pools characteristically appear as the ground thaws and snow melts following the winter season. In Massachusetts, these temporary wetlands generally dry up by July but a few exist until September.

VERNAL POOL IN THE SPRING

SAME POOL SITE IN THE SUMMER

Unique characteristics of these aquatic habitats make ephemeral life attractive to organisms capable of rapid development. Vernal pools possess elevated nutrient levels from organic matter buildup throughout the year. This promotes rapid development. which is crucial for the success of each organism.

Vernal pools vary in size, shape, depth, diversity among organisms (plant and animal) and duration of existence, but possess overall qualities that categorize these wetlands as "vernal pools". They all lack fish, generally last for two or three months and dry up at some point during the year.

Vernal pools have been characterized by the Massachusetts Division of Fisheries and Wildlife as "biological" or "facultative" based on whether organisms rely exclusively upon these temporary habitats for survival (biological) or utilize vernal pool habitats as well as permanent aquatic habitats (facultative). The existence of the wood frog (Rana sylvatica), the Ambystoma species of salamander, and fairy shrimp (Anostraca) depends entirely on the presence of vernal pools. Occupancy by these specific animals and others make a vernal pool "biological".

Of course, environmental conditions determine the success of any given species each year. A snowy, cold winter coupled with a rainy, wet spring will ensure propagation of vernal pool animal species. A mild winter followed by a fairly dry spring will have adverse effects on each organism.

Vernal pools are equally attractive habitats to pests as well as the publicly favorable species of organisms. Mosquitoes are considered by most to be one of the biggest pests known to man. "Spring hatch" mosquitoes, primarily from the genus Aedes, hatch sometime in March, pass through four larval instars, a pupal stage and emerge as adults around mid-May. Under optimal rainy conditions, tremendous numbers of adults will emerge to make outside activities unbearable. Three to fours days following emergence, female mosquitoes will seek out victims in order to obtain their first blood meal. Even with reptile, amphibian and insect predation, startling numbers of mosquitoes emerge from Massachusetts vernal pools each year.

Vernal pools exist almost everywhere. These unique wetlands are common in the river flood plain. The diversity of organisms alone make these ephemeral pools worth further study, exploration and protection from destruction. The Massachusetts Division of Fisheries and Wildlife has established guidelines for the certification of these aquatic habitats. The booklet covers general information, plant and animal species found inhabiting these wetlands, procedural information for certification and required forms. Certification may assist in diverting development projects away from these wetlands, therefore protecting them. Contact any local office for further guidance.

References:

DesMeules, Mark P. and Nothnagle, Gustav. 1997. Where life springs ephemeral. Natural History. 5/97. pp. 44-47.

Guidelines for the Certification of Vernal Pool Habitat. The Commonwealth of Massachusetts, Division of Fisheries and Wildlife, Natural Heritage and Endangered Species Program. (617) 727-3151

Stone, Janice S. 1992. Vernal pools in Massachusetts: aerial photographic identification, biological and physiological characteristics and state certification criteria. University of Massachusetts, MS thesis.