Dry Disturbance and Fish Reduction Produce Enhanced Crayfish Densities in a Freshwater Wetland

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1 Dry Disturbance and Fish Reduction Produce Enhanced Crayfish Densities in a Freshwater Wetland Nathan J. Dorn Florida Atlantic University Davie, FL Mark I. Cook South Florida Water Management District West Palm Beach, FL

2 Water depth (cm) Average slough water depths in the Everglades from two locations ( ) Sediment level Apr-05 Apr-06 Apr-07 Apr-08 Apr-09 Apr-10 Apr-11 Date

3 Hydrologic Pattern Ecosystem Function Hydrologic Pattern Wading Bird Nesting Success Observation: Supranormal wading bird nesting years were associated with severe droughts (low water levels) in the previous 1-2 years. Frederick and Ogden (2001) Wetlands 21:

4 Hypothesis: Drought conditions (dry disturbances) enhance secondary production in the year(s) after the drought. Dry Disturbance Predatory Fish Populations - CRAYFISH Prey Production (P. fallax) + Resource Enhancement

5 A. Experimental evidence that predatory fish limit wetland crayfish (Procambarus fallax) recruitment. B. Experimental evidence that drying (and fish reduction) enhances crayfish density. C. Patterns of crayfish density and hydrologic variability in Everglades sloughs

6 Evidence that sunfishes limit crayfish recruitment. Lepomis marginatus Lepomis gulosus Kellogg and Dorn (2012) Oecologia

7 Slightly Larger Experimental Units Loxahatchee Impoundment Landscape Assessment (LILA) Replicate 8 hectare wetlands

8 Control (M1) Control (M2) Dried (M3) Dried (M4) BACI (before-after control-impact) design Experiment Dried two wetland macrocosms and reduced large fish in Response variables: 1)Fish predators (Catch-Per-Unit-Effort) 2)Crayfish densities (throw trap sampling)

Simulation of Drought and Fish Reduction Water Depth Stage (ft) 17 Before After Sampling event 16

9 Simulation of Drought and Fish Reduction Water Depth Stage (ft) 17 Before After Sampling event Sediment level (deep slough) Feb-08 Aug-08 Feb-09 Aug-09 Feb-10 Jul-10 Jan-11 Jul-11

10 Fish netting followed by rotenone application.

11 Did the manipulation significantly reduce predatory fish catches? Measure of Fish (predator) activity-density = Standardized catch per night

12 Large Fish (> 5 cm SL) abundance TRT x Time(Period): P< Before After Mean Predatory Fish Catch night control dried 0.1 Mar-09 Sep-09 Mar-10 Sep-10 Mar-11 Date

13 Did the densities of crayfish change in response to the manipulation?

14 Crayfish Density TRT x Period: P< Before After control dried Mean Crayfish Density (#/m 2 ) Mar-09 Sep-09 Mar-10 Sep-10 Mar-11 Date

15 Mean Carapace Length (mm) Did juvenile crayfish grow faster on food from previously dried wetlands? 11 N.S. 10 Growth Assay Small juvenile crayfish fed bulk periphyton for 3 weeks control dried Day

Macrocosm TRT Median Night of Mortality (S.D.) Large Fish catch rate in July (S.E.

16 Did juvenile crayfish experience less mortality risk in the dried wetlands? PREDATION ASSAY: survival of tethered crayfish Results from Survival Analysis Wetland Macrocosm TRT Median Night of Mortality (S.D.) Large Fish catch rate in July (S.E.) M1 Control 2.8 (0.6) 8.4 (1.3) M2 Control 2.6 (0.5) 9.2 (1.1) M3 Dried 3.8 (0.9) 4 (0.9) M4 Dried 4.7 (1.1) 0.8 (0)

17 C. Crayfish density and hydrologic variability in Everglades sloughs

18 Do crayfish respond numerically to hydrologic variation in the sloughs of the Everglades? Water Conservation Area 3A ( ) 8 sites (25 ha each) Seasons: July-Aug. and Jan. Throw Traps: 5/site Hydrologic Covariates: created with Everglades Depth Estimation Network

19 Model Selection Analysis Season Season, Hydro Season, Hydro, Season*Hydro Hydrologic covariate LD = Length (D) of the dry disturbance (water <1 cm) in the previous year. Avg360 = Average depth over past year (cm)

20 Model selection statistics Hydro Model AICc AICc W i Parameter Season, LD, Season*LD (January)* 0.0 (August) Season, Avg360, Season*Avg (January)* 0.0 (August) Model Fit Season, LD, Season*LD, Avg Season, Avg360, Season*Avg360, LD Season, LD, Season*LD, Avg360, Season*Avg Season, Avg <0.001 Season, LD <0.001 Intercept only <0.001 Season <0.001

21 Mean Crayfish Density (sqrt # m -2 ) Wet Season (July-August) Dry Season (January) (R 2 = 0.5) Length (D) of Dry Disturbance

22 Dry disturbances temporarily release crayfish from limitation by aquatic predators. Dry Disturbance - + Predatory Fish Populations - Crayfish Production A) Sunfish limited crayfish recruitment in wetland mesocosms. B) Drying and modest reductions of large fish abundances enhanced crayfish densities in LILA wetlands. C) Survival of juveniles was best in LILA wetlands with lower large fish abundances. D) Crayfish densities in Everglades sloughs are higher in the winters (i.e., January) following dry disturbances.

Boyle, J. Bransky, J. Johnson, C. Kellogg, N. Knorp, E. Peters and C.

23 Acknowledgments Eric Cline Mac Kobza Mark Cook South Florida Water Management District Fred Sklar, Tom Dreschel and Ryan Desliu FAU: R. Boyle, J. Bransky, J. Johnson, C. Kellogg, N. Knorp, E. Peters and C. van der Heiden. Numerous others from FAU, SFWMD and FIU who helped with the fish removal.

24 Questions?

25 Performance The Consumer Stress Model applied to Wetlands high v Large Fish (Predators) Crayfish (Prey) low low medium high Frequency or Intensity of Dry Disturbances v

26 Small Fish Density (no response to manipulation) Mean Small Fish Density (#/m 2 ) control dried Before Before Date After After 0 Mar-09 Sep-09 Mar-10 Sep-10 Mar-11

Habitat Use of Everglades Fishes in Relation to Seasonal Hydrology: Implications for Wading Bird Prey Availability

Habitat Use of Everglades Fishes in Relation to Seasonal Hydrology: Implications for Wading Bird Prey Availability Mark I. Cook Everglades Systems Assessment, SFWMD Jennifer S. Rehage, Greg Hill Earth