Differential effects of increased salinity on growth and survival of a native and a nonnative apple snail species.
The purpose of this study was to directly compare the effects of increased salinity on growth and survival of both species. Knowledge gained will provide baseline data concerning the potential impact of predicted saltwater intrusion into wetlands on both native Pomacea paludosa and nonnative P. maculata collected from Florida, USA, in 2013 and 2014. Twelve snails from each species were randomly assigned to one of five treatments with five replicates each: control, 2, 4, 8 and 12 ppt. It was shown that at 4 amd 8 weeks, there was a significant effect of species, salinity and the interaction between the two on survival. There was a significant difference in P. paludosa survival after 4 weeks with 0% survival at a salinity of 12 ppt. Survival was high (93-98%) and no difference was seen at salinities <8 ppt. Significant differences were observed in native snails after 8 weeks, with lower survival at 4 ppt (71.6%) and 8 ppt (31.5%) compared to <2 ppt (90-95%). There was a significant difference in survival in P. maculata after 4 weeks with lower survival at 8 ppt (67%) and 12 ppt (0%) compared to <4 ppt (95-100%). Significant differences were found between treatments in nonnative snails after 8 weeks with no survival at 8 ppt (0%), compared to high survival (91-98%) and no significant differences at <4 ppt. At 4 weeks, significant interactions were seen in growth rate between species, salinity and the interaction of the two. By 8 weeks, a significant difference was seen between species reared at <4 ppt, but not between salinity and the interaction of the two. Weekly growth rate of P. paludosa was significantly different between treatments in all weeks, with snails reared at 8 ppt exhibiting slower growth. No differences in growth rate were seen among native snails cultured at lower salinities except in week 2 between the control and 4 ppt treatment. The weekly growth rate of P. maculata was significantly different between treatments in weeks 1 through 4, with snails at 8 ppt exhibiting slower growth. By week 8, no nonnative snails remained in the 8 ppt treatment and growth was similar between snails reared in the remaining treatments. different salinities for 8 weeks. These findings suggest that the native apple snail may be more tolerant to saltwater intrusion than the nonnative apple snail. Growth and survival of both species were hindered at salinities greater than 4 ppt, with P. maculata being more adversely affected at higher salinities. The ability for both species to survive and grow following short-term exposure to less-than-optimal salinity suggests that P. maculata will continue to thrive in the same environments as P. paludosa.