Didymosphenia geminata effects on river food webs Justin N. Murdock, Natalie E. Knorp, Lucas A. Hix, and Andrea N. Engle Tennessee Tech University 100 µm Spaulding and Elwell 2007 • Changes physical habitat South Holston River, TN – 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 of macroinvertebrates and trout? Macrophytes FBOM Filamentous Algae Rock Biofilms Didymo Current Tennessee Regional Distribution Kentucky Virginia Tennessee North Carolina Monitoring for Didymosphenia geminata: An Environmental DNA Approach. Funded by GSMFC Aquatic Invasive Species Program Didymo Coverage (2014-2015) Mat coverage (%) coverage Mat Clinch South Holston Watauga Study design Benthic community and food resources • 3 rivers (tailwaters), varying mat coverage • 3 sites per river; macroinvertebrate composition, habitat and water quality (spring, summer, fall) • 2 sites per river for food web stable isotope and lipids (summer) • 2 years (2014 - 2015) Fish (Brown and Rainbow trout) • Yearly abundance and condition data at each river (1996-2015, TWRA) • Isotopes and lipids (2015, USGS Coop) Macroinvertebrate Abundance Spring 2014 2 50% 6% 18% 0% 5% 0% 51% 1% 1% Total Macroinvertebrates / m Macroinvertebrates Total Macroinvertebrate Composition: Spring 2014 South Holston Watauga Clinch 51% 50% 5% Amphipoda Amphipoda Chironomid High Didymo Planaria (upstream) Ephemerella Chironomid Chironomid Oligocheate Hydracarina Isopoda >1% 18% 0% Planaria Amphipoda Low/No Didymo Chironomid (downstream) Oligocheate Chironomid Elmidae Ephemerella Ephemerella South Holston River Temporal Trends Spring Summer Fall High Didymo Oligocheate Oligocheate (upstream) Chironomid Chironomid Ephemerella Chironomid Low/No Didymo (downstream) Spring 2014 CCA Variance Partitioning: Spring 2014 Didymo Habitat Chl a • Cells • Macrophytes • Mat cover • 0.28 0.06 • Discharge • Substrate type 0.14 0.06 Water Quality • Total N • Conductivity • DO • Temperature Resource Use Change: South Holston River - Stable isotopes: 2014 High Didymo No Didymo EphemerellaProportions by group: 1 ChironomidProportions by group: 3 OligocheateProportions by group: 4 1.0 1.0 1.0 0.8 0.8 0.8 0.6 0.6 High 0.6 Proportion Proportion Proportion Didymo 0.4 0.4 0.4 Proportion 0.2 0.2 0.2 0.0 0.0 0.0 POMBIO CELL STALK FILMAC LEAF STICK POMBIO STALK LEAF POMBIO CELL STALK FILMAC LEAF STICK POMBIO CELL STALK FILMAC LEAF STICK Source POMBIO STALK LEAF POMBIO STALK LEAF Source Source CELL FILMAC STICK CELL FILMAC STICK CELL FILMAC STICK Proportions by group: 5 Proportions by group: 1 Proportions by group: 6 1.0 1.0 1.0 0.8 0.8 0.8 0.6 0.6 Low/No 0.6 Proportion Proportion Proportion 0.4 0.4 Didymo 0.4 Proportion 0.2 0.2 0.2 0.0 0.0 0.0 SPOM FILBIO MACRO CPOM SPOM FILBIO MACRO CPOM SPOM FILBIO MACRO CPOM Source MACRO MACRO SPOM MACRO SPOM Source SPOM Source FILBIO CPOM FILBIO CPOM FILBIO CPOM 3.4/0.8 – C/N enrichment factors Simulids, Amphipods, and Planarians showed the same trends 7 6 FA 5 4 3 ratio 2 1 18:2ω6/18:3ω3 0 No Didymo Didymo 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. 30% 25% 20% 15% 10% 5% 0% % Diatom FA markers FA Diatom % No Didymo Didymo There is a reduced reliance on diatoms for consumers following introduction of Didymo. Fish: (Brown trout) Habera et al. 2014. Region IV trout fisheries report: 2014. Tennessee Wildlife Resources Agency. < 178 mm No breakpoint Linear Slope = 0.24 ) Wr 179-356 mm Breakpoint at 2005 Pre 2005 slope = 0.51 Post 2005 slope -1.14 Brown Trout Relative Weight ( Weight Relative Trout Brown 357-778 mm Breakpoint at 2004 Pre 2004 slope = 0.18 Post 2004 slope -0.70 Year Trout Stable Isotopes Watauga River– High Didymo Brown TroutProportions MUSCLE by group: 3 1.0 0.8 0.6 Proportion 0.4 Proportion Diet of Proportion 0.2 0.0 PLANPLA AMP CELLCELL STALK NOTNOTDIDYMO DIDYMO AMP Source STALK South Holston River- Low Didymo Brown TroutProportions MUSCLE by group: 3 1.0 0.8 0.6 Proportion 0.4 Proportion Diet of Proportion 0.2 0.0 CPOMCPOMMAC STALKSTALKAMPAMP PLANPLA SIMSIM CHI/EPHCHIEPH Source BIO/POM/CELL/FIL Trout Lipids 16 14 * 12 10 8 No Didymo 6Ratio ω Didymo 3: 6 ω 4 2 0 Rainbow Brown Conclusions Macroinvertebrates • Food resources switching with mat coverage >50%. Eating resources that did not get covered. - Biofilms to macrophytes. • Did not assimilate Didymo cells or stalks. • Lipids had same trend as isotopes. • Less reliance on diatoms in general. • Effects less severe in “Patches” than “Blankets”. Conclusions Trout • Browns and Rainbows primarily assimilating flatworms, amphipods, and Didymo stalk at high and low Didymo sites. • Stalk signature could be epiphytes? • Stalks increase chironomid midge and oligochaete worm abundance, but the strongest isotopic signatures came from turbellarians and amphipods, which are typically found outside of mats. Conclusions Trout • Still missing part of the trout food web. • Small trout: Didymo good? – Fitness not impacted despite increasing density. • Large trout: Didymo not good? – Decreased abundance and fitness, but still a great fishery. Acknowledgements • GCMFA and USFWS • Jon O’Brien, Canisius College • Many undergraduate and graduate students • Tennessee Tech USGS Fisheries Cooperative Unit .