Nitrate impacts on the Florida apple snail, Pomacea paludosa

Nitrate pollution in springs in Florida has been suggested as a possible reason for declining populations of the Florida apple snail, Pomacea paludosa (Say). No correlation was found between snail density and nitrate concentration measured in six Florida springs. In laboratory studies examining short-term acute impacts of nitrate, adult and juvenile snail 96 h LC₅₀ values could not be determined due to low mortality rates despite nitrate concentrations > 500 ppm. Juvenile snail growth was affected with EC₅₀ values of 504 and 622 ppm nitrate, in two trials, respectively. Juvenile survival during the 14 d growth study fell below 50%, but again nitrate levels were very high (> 500 ppm). Given that snails exhibited little to no response to nitrate concentrations orders of magnitude greater than those found in Florida springs, we suggest that other factors, possibly including natural differences in habitat structure or changes in structure related to exotic plant invasions, may help explain the observed declines in apple snail abundance.