1. LSSF Experiment: Phytobenthic Colonization Michael D. Yard Dean W. Blinn US Geological Survey Grand Canyon Monitoring and Research Center Northern Arizona University

2. LSSF Experiment: Phytobenthic Colonization Michael D. Yard Dean W. Blinn US Geological Survey Grand Canyon Monitoring and Research Center Northern Arizona University

3. Is colonization an immediate response upon substrate submersion?

4. Or, is there a time-lag? And if so, is this dependent on the degree of prior cobble conditioning? When does this newly submerged area become biologically productive?When does this newly submerged area become biologically productive?

5. Study Objectives Determine if there were differential rates in phytobenthic colonization Determine most likely mode of propagation Determine accrual rates for algae and invertebrates

6. Sampling Approach Treatment Types –2 Previously Colonized Scrapped never desiccated Scrapped and desiccated 1 yr –1 Never Colonized (>100 yr) Sampling Period –Colonization period (105 d) –1 June 2000 to 12 September 2000 Sampling Trips - 11

7. Sampling Frequency –10 to 12 d sampling interval Random block design –Randomly assigned cobbles –Perpendicular Transects 11 transects/treatments (3) and control (1) 44 transects 20 cobbles/transect

8. Randomly Assigned –Sample point location Pre-assigned –Transect –Sample –Samples independent Sampling Template 4 cm dia.

9. Rapid Assessment Procedure (Blinn et al. 1998) Field sorted (n = 880) –14 Gross Categories »Algae »Macrophytes »Invertebrates

10. –Dry Weight Determination (g) AFSM Conversion (Shannon et al. 2000) Sampling Approach

11. Experimental Closure (105 d) Treatment 1, No previous colonization, exposed > 100 yrTreatment 2, Previously colonized, exposed for 1 yrTreatment 3, Scrapped not exposed to prolonged desiccationControl Cobble

12. Treatment 1 & 2, –Not significantly different –Conditioning Trend Response Time –50 to 60 days before it accrued any appreciable biomass Flood Effect –Not significant –Cobble displacement 5 % Mode of Propigation –Zoospores (80% Ulothrix/Zygnematales Cladophora –Fragmentation Fall Spike Treatment 1 & 2

13. Treatment 3 - Mode of Propigation –Significantly different –Basal holdfast structure Predominantly Cladophora Ulothrix/Zygnematales –Fragmentation Response Time –10 to 20 days before it accrued any appreciable biomass –Increased in biomass 50 to 60 g m -2 AFDM –Accrual Rate 1 g m -2 d -1 AFDM Asymptote –60 days Flood Effect –Cobble displacement 5 % Treatment 3

14. Invertebrate Composition –90 to 95% Snail biomass –Maximum biomass T1 5.8 g m -2 T2 11.2 g m -2 –Densities T1 26 x 10 3 m -2 T2 35.5 x 10 3 m -2 –Treatments 1 & 2 Significantly different Response Time –Initial invert biomass 0.95 g m -2 (SD 0.5) –50 to 60 days before it accrued any appreciable biomass –Significantly correlated to phytobenthic biomass Flood Effect –Significant reduction between days 93 & 105 Treatment 1 & 2

15. Flood Effect –T3 Invertebrate biomass did not significantly change –Invertebrate densities did not significantly change Treatment 3 Invertebrate Composition –90% Snail biomass Response Time –Immediate response (10 d) –Significantly correlated to phytobenthic biomass Snail biomass –Mean maximum biomass T3 38.1 g m -2 Snail Densities –Mean maximum Densities T3 108 x 10 3 m -2 Proportion of snail biomass to total biomass –Treat 1 = 82% (SD 0.16) –Treat 2 = 73% (SD 0.21) –Treat 3 = 47% (SD 0.20) Fall Spike

16. Sum of all Photosynthetic ComponentsPrimary Production Estimate (Assumes no loss) Fall Spike Flow

17. Treatment 3 CONTROL Cladophora 30 to 75% photosynthetic biomass

18. Snail biomass to high to be supported by algal biomass Attained >90 gC m -2 ; Densities >200 x 10 3 m -2

19. Algal Reduction by Snails (density dependent) –Hunter 1980 –Mulholland et al. 1983 –Jacoby 1985 –Steinman et al. 1987 –Lowe and Hunter 1988 –Osenberg 1989 –Underwood and Thomas 1990 –Bronmark et al. 1991 –Tuchman and Stevenson 1991 –Hill et al. 1991 –Steinman 1992 –Rosemond et al. 1993 Algal Biomass increase in response to grazing –Removal of senescent cells Lamberti and Resh 1983 Swamikannu and Hoagland 1989 –Nutrient cycling McCormick and Stevenson 1991 Stewart 1987 Mulholland et al. 1991 –Removal of epiphytes Dudley 1992 Sarnelle et al. 1993

20. Treatment 3 2.1 g/d Treatment 3 0.6 g /m 2 d 2.1 g/m 2 d

21. Net Primary Production Model Output, assumes that all net excess production is diverted toward biomass accrual (no loss in photosynthates, drift, grazing) Asymptote due to balance between net photosynthesis and respiration demands

22. So, under this model net primary production is self-limiting and constrained by size

23. 8.5 gC/m 2 d DOC Consumed by Inverts/Fish Drift Structure Cumulative production through time 4 gC/m 2 d ?? gC/m 2 d 0.25 gC/m 2 d

24. Conclusion Damaged or mechanically removed thallus structure will rapidly recover (Assuming ideal growing conditions) –If basal holdfast structure remains intact and viable Newly submerged substrate has a slower colonization response –No difference in response for cobbles exposed 1 yr or greater

25. Newly submerged substrate has a slower colonization response –Colonization appears to be predominantly by zoospores –Fragmentation does not appear to the major propagation mode –Recovery response may be more rapid if substrate is conditioned Microflora (organic material, bacteria, diatom assemblage)

26. We cannot be sure if colonization response would be different if grazing pressure was absent Stable flows may result in substantial amounts of production –Both primary and secondary –However, this may not be apparent by just measuring biomass –It may be difficult to separate out effects from flows

27. Acknowledgements Northern Arizona UniversityNorthern Arizona University –Aquatic Ecology Lab Allen Haden, Ally Martinez, Molly McCormick, Ian McKinnon, Joe ShannonAllen Haden, Ally Martinez, Molly McCormick, Ian McKinnon, Joe Shannon –Geology Department Matt Kaplinsky, & Mark ManoneMatt Kaplinsky, & Mark Manone –Faculty Michael Kearsley, George Koch, Peter Price, & Rod ParnellMichael Kearsley, George Koch, Peter Price, & Rod Parnell Grand Canyon Monitoring and Research CenterGrand Canyon Monitoring and Research Center Dave Baker, Carol Fritzinger, Barry Gold, Susan Hueftle, Barbara Ralston, & Jake TiegsDave Baker, Carol Fritzinger, Barry Gold, Susan Hueftle, Barbara Ralston, & Jake Tiegs Indispensable InsistenceIndispensable Insistence Helen YardHelen Yard