Water levels in Florida lakes and wetlands fluctuate naturally in an annual cycle driven by discrete wet and dry seasons (June-October and November-May, respectively) (Chen and Gerber 1990).  In the early to late spring in some years, many wetlands, including large portions of the Everglades, become dry (Duever et al. 1994).  These drying events are essential in maintaining the mosaic of different vegetation types required to fulfill the needs of a variety of wetland fauna (Gunderson 1994; Sklar et al. 2002).  Persistence in these wetlands requires life history strategies designed to contend with, or even take advantage of, periodic drying.  Altering the natural hydrologic regime (i.e., the pattern of water level change over time) has compromised the life history of some species, including apple snails.

Although high water can have detrimental effects on apple snails (research is ongoing), clearly a dry down can have serious impacts to an aquatic animal.  We define a ‘dry down’ as the condition in which the water table falls below ground level.  This should be distinguished from a ‘draw down’, which is a controlled (i.e., managed) lowering of water levels that may or may not result in a dry down.   By ‘drying event’ we mean a steady recession of water level that does culminate in a dry down.  The recession rate (how fast the water level drops) may have an important effect on apple snails, but it has not yet been studied.  Research so far has focused on the impacts of dry down duration and timing as they affect apple snail survival and recruitment (i.e., egg laying and hatchling growth and survival) (Darby pers. comm.). 

Dry Down Impacts are divided into two sections, Survival and Recruitment.

 

Dry marsh in the Blue Cypress Water Management Area near Vero Beach.

Literature Cited:

• Chen, E., and J. F. Gerber. 1990.  Climate.  Pages 11-34 in R.L. Meyers and J.J. Ewel, editors.  Ecosystems of Florida.  University of Central Florida Press, Orlando, Florida, USA.

• Duever, M. J, J. F. Meeder, L. C. Meeder, and J. M. McCollom. 1994.  The climate of south Florida and its role in shaping the Everglades ecosystem.  Pages 225-248 in S.M. Davis and J.C. Ogden, editors.  Everglades:  The ecosystem and its restoration. St. Lucie Press, Delray Beach, Florida, USA.

• Gunderson, L.H.  1994.  Vegetation of the Everglades:  Determinants of community composition.  Pages 323-340 in S.M. Davis and J.C. Ogden (eds.), Everglades:  The Ecosystem and its Restoration.  St. Lucie Press, Delray Beach, FL.

• Sklar, F., C. Melloy, R. VanZee, D. E. Gawlik, K. Tarboton, D. Rudnick, S. Miao, and T. Armentano.  2002.  The effects of altered hydrology on the ecology of the Everglades.  Pages 39-82 in S.M. Davis and J.C. Ogden, editors.  Everglades: The ecosystem and its restoration.  St. Lucie Press, Delray Beach, Florida, USA.