Ecological Archives E096-260-A3

Nathan J. Dorn and Mark I. Cook. 2015. Hydrological disturbance diminishes predator control in wetlands. Ecology 96:29842993.

Appendix C. Periphyton food quality after drying and re-flooding.

Population re-growth of animals following drying events could also be affected bottom-up mechanisms (e.g., phosphorus liberation from sediments; Bostic and White 2006) in addition to predator release and we looked for indirect effects of drying on crayfish growth rates via altered food quality with a juvenile growth assay. One month after re-flooding the LILA wetlands, 32 small juvenile crayfish (mean CL = 5.4 mm CL, SE = 0.05, n = 32) were individually fed bulk periphyton from one of the four wetlands (n = 8 replicates per wetland) to determine whether food quality was better in the dried and re-flooded wetlands. Crayfish were reared in 7.5 L buckets filled with 2 L of well water that were nested water baths outdoors. Bulk periphyton, including algae and invertebrate infauna attached to live or dead aquatic vegetation (Utricularia purpurea or Chara sp.) was collected from each wetland twice weekly and provided to crayfish in 60 mL (wet volume) quantities for three weeks. Leftover periphyton was removed when new periphyton was added. Day zero and day 21 (final) carapace lengths were analyzed with a nested ANOVA to look for effects of drying on crayfish growth. Each crayfish was treated as an independent observation of growth in a disturbed wetland (n = 16 crayfish fed from two wetlands) or flooded/control wetland (n = 16 crayfish fed algae from two wetlands) and wetland macrocosms were treated as the subgroup (denominator error term for treatment effect). Final sizes of crayfish from four wetlands were also directly compared using individual crayfish as replicates and the ANOVA was followed by pair-wise with Bonferroni adjustments for multiple comparisons.

Starting sizes (mm CL) of juvenile crayfish in the periphyton growth assay were not significantly different (F3,27 = 0.02, P = 0.99). Final sizes of crayfish fed algae from disturbed and control wetlands did not differ (Nested ANOVA: F1,2 = 0.28, P = 0.65) although there was variation between wetlands within treatments (F2,27 = 11.91, P < 0.001). When average sizes of crayfish were compared directly across all four wetlands there was significant variation (F3,27 = 8.81, P < 0.001); the growth was slowest in one of the control wetlands (M1 vs. all others, pairwise P values < 0.05) where crayfish only grew to 9.2 mm (SE = 0.2). However crayfish fed algae from the other control (M2) achieved the largest sizes (10.8 mm ± 0.3) and they were not different from crayfish fed algae from disturbed wetlands (P values > 0.4).

Literature Cited

Bostic, E. M., and J. R. White. 2006. Soil phosphorus and vegetation influence on wetland phosphorus release after simulated drought. Soil Science Society of American Journal 71:238–244.

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