Didymosphenia geminata mat impacts vary across trophic levels of Southern Appalachian stream food webs Justin N. Murdock, Natalie E. Knorp, Lucas A. Hix, and Andrea N. Engle Tennessee Tech University

100  m

South Holston River, TN Changes physical habitat – Homogenizes habitat – Changes near-bed velocities (Larned et al. 2011) – Changes macroinvertebrate structure (Kilroy et al. 2006, Larned et al 2007, Gillis and Chalifour 2010, and many more) – Fish impacts (James and Chips 2016) Mechanisms for changes? – Increases overall organic matter (Reid and Torres 2014) – Epiphytes (Spaulding 2007)

Does Didymo alter food web structure and/or food resource use?

Current Tennessee Regional Distribution Tennessee North Carolina KentuckyVirginia

Didymo ( ) Mat coverage (%) Clinch South Holston Watauga

Study design Benthic community and food resources 3 rivers (tailwaters), varying mat coverage 3 rivers (tailwaters), varying mat coverage 3 sites per river; macroinvertebrate composition, habitat and water quality (spring, summer, fall) 3 sites per river; macroinvertebrate composition, habitat and water quality (spring, summer, fall) 2 sites per river for food web stable isotope, lipids, gut contents (summer) 2 sites per river for food web stable isotope, lipids, gut contents (summer) 2 years ( ) 2 years ( ) Fish (Brown and Rainbow trout) Yearly abundance and condition data at each river ( , TWRA) Yearly abundance and condition data at each river ( , TWRA) Isotopes, lipids, and gut contents (2015, USGS) Isotopes, lipids, and gut contents (2015, USGS)

Macroinvertebrate Abundance Spring 2014 Total Macroinvertebrates / m 2 0% 5% 51%1% 50%18%6%

Macroinvertebrate Abundance Summer 2014 Total Macroinvertebrates / m 2

South HolstonWataugaClinch High Didymo (upstream) Low/No Didymo (downstream) Chironomid Amphipoda Chironomid Amphipoda Chironomid Ephemerella Oligocheate Ephemerella Planaria Ephemerella Chironomid Oligocheate Isopoda Hydracarina Chironomid Amphipoda Elmidae 0% 5% >1% 51% 50% 18% Macroinvertebrate Composition: Spring 2014

High Didymo (upstream) Low/No Didymo (downstream) Spring South Holston River Temporal Trends Summer Fall Chironomid Oligocheate Ephemerella

Spring 2014 CCA

Variance Partitioning: Spring 2014 Didymo Cells Mat cover Habitat Chl a Macrophytes Discharge Substrate type Water Quality Total N Conductivity DO Temperature

Variance Partitioning: Summer 2014 Didymo Cells Mat cover Habitat Chl a Macrophytes Discharge Substrate type Water Quality DO Temperature

Variance Partitioning: Fall 2014 Didymo Cells Mat cover Habitat Chl a Macrophytes Discharge Substrate type Water Quality Total N pH

Resource Use Change: South Holston River - Stable isotopes: Spring 2014 No DidymoHigh Didymo

POMBIO CELL STALK FILMAC LEAF STICK POMBIO CELL STALK FILMAC LEAF STICK POMBIO CELL STALK FILMAC LEAF STICK Proportion Low/No Didymo SPOM FILBIO MACRO CPOM SPOM FILBIO MACRO CPOM SPOM FILBIO MACRO CPOM Proportion Ephemerella Chironomid Oligocheate Simulids, Amphipods, and Planarians showed the same trends 3.4/0.8 – C/N enrichment factors

Increase in the 18:2ω6/18:3ω3 ratio in the presence of Didymo suggests a shift food source from biofilms to vascular plants, like macrophytes.

There is a reduced reliance on diatoms for consumers following introduction of didymo. % Diatom FA markers

Habera et al Region IV trout fisheries report: Tennessee Wildlife Resources Agency. Fish: (Brown trout)

No breakpoint Linear Slope = 0.24 Breakpoint at 2005 Pre 2005 slope = 0.51 Post 2005 slope Breakpoint at 2004 Pre 2004 slope = 0.18 Post 2004 slope Brown Trout Relative Weight (Wr) Year < 178 mm mm mm

Watauga River Trout – High Didymo Not Didymo: Biofilm Filamentous algae Macrophytes SPOM FBOM

Brown Trout FINBrown Trout MUSCLEBrown Trout LIVER PLANCELL STALK NOTDIDY AMP PLANCELL STALK NOTDIDY AMP PLANCELL STALK NOTDIDY AMP Proportion of Diet Watauga River– High Didymo

Brown Trout MUSCLE Proportion of Diet PLAN BIO/POM/CELL/FIL STALK CHI/EPH AMP CPOM SIM MAC South Holston River- Low Didymo

Conclusions Macroinvertebrates (Year 1) Seasonal impact Increases biomass, shifts to more chironomids / oligocheates Decreases diversity Shifts food from biofilms to macrophytes Stalk epiphytes?

Trout Small trout: Didymo good? – Fitness not impacted despite increasing density. Larger trout: Didymo not good? – Decreased abundance and fitness, but still a great fishery. Trout eating Didymo and may be assimilating stalks? – We are missing parts of brown trout food webs and lipid data to come. Threshold mat coverage to have an impact? Conclusions

Acknowledgements Funding: USFWS NPS – Great Smoky Mountains National Park Trout Unlimited Data collection and analyses: Jon O’Brien, Canisius College Many undergraduate and graduate students Tennessee Wildlife Resources Agency Tennessee Tech USGS Fisheries Cooperative Unit