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 enrichment factorsenrichment 3.4/0.8 3.4/0.8 Didymo Low/No Didymo High – C/N
Proportion ProportionProportion Proportion POMBIO 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 SPOM POMBIO , Amphipods,Simulids, Planarians and showedthetrends same SPOM Ephemerella CELL CELL FILBIO STALK FILBIO STALK FILMAC Proportions 5 group: by Source Source Proportions 1 group: by MACRO FILMAC MACRO LEAF LEAF CPOM STICK CPOM STICK
Proportion Proportion POMBIO 0.0 0.2 0.4 0.6 0.8 1.0 0.0 0.2 0.4 0.6 0.8 1.0 SPOM POMBIO SPOM CELL Chironomid CELL FILBIO STALK FILBIO STALK FILMAC Source Proportions 1 group: by Proportions 3 group: by Source MACRO FILMAC MACRO LEAF LEAF CPOM STICK CPOM STICK
Proportion Proportion
0.0 0.2 0.4 0.6 0.8 1.0 POMBIO 0.0 0.2 0.4 0.6 0.8 1.0 SPOM POMBIO SPOM CELL Oligocheate CELL FILBIO STALK FILBIO STALK FILMAC Source Proportions 6 group: by Source Proportions 4 group: by MACRO FILMAC MACRO LEAF LEAF CPOM STICK CPOM STICK 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 )
179-356 mm Breakpoint at 2005 Pre 2005 slope = 0.51 Post 2005 slope -1.14
Brown Trout Relative Weight ( Wr Weight Relative Trout Brown 357-778 mm Breakpoint at 2004 Pre 2004 slope = 0.18 Post 2004 slope -0.70
Year Trout Stable Isotopes ProportionProportion of Diet Watauga River
0.0 0.2 0.4 0.6 0.8 1.0 PLAN PLA Brown Trout MUSCLE AMP AMP – CELL High Didymo High Source CELL Proportions 3 group: by STALK STALK NOT DIDYMO NOTDIDYMO ProportionProportion of Diet
0.0 0.2 0.4 0.6 0.8 1.0 South HolstonSouth River CPOM CPOM MAC Brown TroutMUSCLE STALK STALK AMP AMP Source Proportions 3 group: by PLAN - PLA Low Didymo BIO/POM/CELL/FIL SIM SIM CHI/EPH CHIEPH 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