Florida apple snail (Pomacea paludosa SAY) responses to lake habitat restoration activity

Abstract

Water-level drawdown has long been recognized as an effective approach to enhance habitat conditions for aquatic fauna in lakes and impoundments. Although targeted species such as sport fish may benefit, increasingly there are concerns over non-target species. We assessed the impacts of a drawdown of Lake Kissimmee on Florida apple snails. Prior to the drawdown, we found apple snails at significantly higher densities in sites dominated by sandy substrates and emergent macrophytes; no snails were found in sites with deep layers of unconsolidated organic material and dominated by Nuphar luteum. Following the drawdown, some of the sites containing this unconsolidated organic material were also scraped with heavy equipment (e. g., bulldozers) to remove the organic layer. We monitored the response of 31 snails from one site, most of which were stranded in the dry littoral zone during the 1995-1996 drawdown. Mortality rates of stranded snails were high due to the dry conditions of the littoral zone, but also indirectly due to increased vulnerability to predation by several avian species. The survival data was corroborated by the 1996 and 1997 funnel trap data wherein our catch declined by 80% from 1995 (pre-drawdown) levels. The proportion of juveniles also declined significantly, indicating an impact on recruitment. Snail abundance did increase, albeit marginally, in some sites, indicating potential benefits of drawdown and organic substrate removal in some types of littoral zone habitats. However, the timing of drawdown events appears critical, as evident in poor recruitment and relatively low abundance following completion of lake restoration activity. In order to avoid substantial losses to non-target species such as apple snails, we suggest that natural resource managers give greater consideration to the potential negative impacts of deviating from the natural hydrologic regime in terms of timing, duration, and frequency.