In aquatic ecosystems it is known that water depth affects habitat structure and predator-prey interactions. In shallow highly vegetated wetlands it is unknown whether water depth management might affect predator-prey interactions and population limitation. Consistent with proposed management regimes for the Florida Everglades we are investigating effects of water depth (i.e., hydro-pattern treatment) in four experimental subtropical wetlands by altering wet season depths +/- 60 cm (n=2; 8 ha each). We hypothesized that as permanently flooded wetlands become deeper and more lacustrine the populations and prey-limiting effects of fully aquatic predators (e.g., fishes) on macroinvertebrate prey will increase. Densities of crayfish (Procambarus fallax) were quantified over two years with throw trap sampling. Large-bodied fish populations were quantified with trap nets. We conducted a study of predation risk in a single season using a tethering assay; juvenile (10-15 mm carapace length) crayfish were tethered (n=120) across four wetlands over six nights and were checked for losses to predators each morning. Crayfish densities and predator abundances through time were analyzed using a repeated measures analysis of variance. The survival data were analyzed with a proportional hazard model.
Results/Conclusions
Mean crayfish densities did not differ by hydro-pattern treatment from 2018-2019. Crayfish densities between the replicate wetlands were consistently low (1.69/m2). Large-bodied fish catch rates did not vary by hydro-pattern. There was no difference in crayfish risk of mortality by predation in the dry season, but local, small scale, stem density raised the risk of crayfish mortality. The lack of effect of hydro-pattern on crayfish density, predator abundances, or mortality risk suggest predator-prey interactions and environmental carrying capacities may be unaffected by the 60 cm wet season depth variation in perennially flooded wetlands, or that the effects will take longer to manifest (e.g., if the vegetative structure changes).