Predators on Community Structure and Dynamics Levi S. Lewis Scripps - PowerPoint PPT Presentation

Predation in Seagrass Beds: The Effects of Predators on Community Structure and Dynamics Levi S. Lewis Scripps Institution of Oceanography and Todd W. Anderson San Diego State University

Seagrasses 2006 2009

Seagrasses • Importance Uptake Nutrients • Trophic Ecology Stabilize Sequester Sediments Carbon

Seagrasses • Importance • Trophic Ecology

Seagrasses • Importance • Trophic Ecology

Seagrasses • Importance • Trophic Ecology

Seagrasses • Importance • Trophic Ecology

Seagrasses • Importance • Trophic Ecology

Seagrasses • Importance • Trophic Ecology

Seagrasses • Importance • Trophic Ecology

Research Question Do manipulations of small predators result in cascading effects that ultimately impact eelgrass performance in San Diego Bay?

Study Site: San Diego Bay Shelter Island

Experimental Design Treatments : P redator N o P redator O pen C ontrol

Experimental Design Treatments : P NP O C

Cage Design 1.5 m 1 m

Cage Design Predator Enclosures 4 X Micrometris minimus 1.5 m 2 X Paralabrax clathratus 1 m

Experimental Array June - August, 2007 Block 6 Block 5 Block 4 Block 3 Block 2 Block 1

Visual Observations – 17 Scuba observations – Predator abundance & biomass

Parameters & Sampling June - July - Aug – Invertebrates • biomass – Epiphytic Loads • mass, chlorophyll – Eelgrass • leaf production

Parameters & Sampling June - July - Aug – Invertebrates • biomass – Epiphytic Loads • mass, chlorophyll – Eelgrass • leaf production

Parameters & Sampling June - July - Aug – Invertebrates • biomass – Epiphytic Loads • mass, chlorophyll growth 2 weeks – Eelgrass hole • leaf production punch

Fish Observations 80 4.3 1.0 1.3 1.7 B Fish Biomass (g m -2 ) 60 40 20 0 P NP O C

Invertebrates 80 E Inv. Biomass (mg g -1 ) b 60 40 a a a 20 0 P NP O C

Fouling on Eelgrass Leaves 0.6 B NS 0.5 Total Chl (  g cm -2 ) 0.4 0.3 0.2 0.1 0.0 P NP O C

Fouling on Eelgrass Leaves 0.6 2.0 A B Epiphytic Load (mg cm -2 ) NS 0.5 Total Chl (  g cm -2 ) 1.5 0.4 b 0.3 1.0 0.2 0.5 a a a 0.1 0.0 0.0 P NP O C P NP O C

Eelgrass Growth 14 E Leaf Production (mg d -1 ) a a a 12 a a a 10 8 b b 6 4 2 0 P NP O C

Summary 80 E b Inv. Biomass (mg g -1 ) 60 a 40 a a • Treatments were effective 20 0 • Predators had consistent effects P NP O C ≈ ≈ 2.0 • A Epiphytic Load (mg cm -2 ) No cage artifacts b 1.5 1.0 • Exclosures were sig. different 0.5 a a a (+) invert. biomass 0.0 (+) epiphytic load P NP O C 14 (-) eelgrass growth a a a E Leaf Production (mg d -1 ) 12 10 b 8 6 4 2 0 P NP O C

Summary 80 E b Inv. Biomass (mg g -1 ) 60 a 40 a a • Treatments effective 20 0 • Predator effects all comparable P NP O C ≈ ≈ 2.0 • A Epiphytic Load (mg cm -2 ) No cage artifacts b 1.5 1.0 • Exclosures sig. different 0.5 a a a (+) invert. biomass 0.0 (+) epiphytic load P NP O C 14 (-) eelgrass growth a a a E Leaf Production (mg d -1 ) 12 10 b 8 6 Why? 4 2 0 P NP O C

Epifauna Effects Iscyrocerid SG FOULING 25 Amphipod A. Ischyroceridae 20 Mass (mg g -1 ) 15 10 5 Chapman 2007 0 Sewell 1995 P NP O C

Epifauna Effects Iscyrocerid SG FOULING 25 Amphipod A. Ischyroceridae 20 Mass (mg g -1 ) 15 10 5 Chapman 2007 0 Sewell 1995 P NP O C Seagrass Limpet SG GRAZING 10 B. Acmaeidae 8 Mass (mg g -1 ) 6 4 2 Zimmerman et al. 1996 0 Jorgenson et al. 2007 P NP O C

Conclusions • Fishes affected invertebrate communities • Grazing & fouling inverts reduced eelgrass growth • Fishes had positive indirect effects on eelgrass growth

Final Conclusions Humans Williams & Heck 2001 Pauly et al. 1998 Jackson et al. 2001 - Indirect Effect Piscivores ??? Fishes ??? Grazers Williams & Ruckelhaus 1993 Neckles et al. 1993 Algae Jernakoff et al. 1996 Seagrass

Final Conclusions Humans Williams & Heck 2001 Pauly et al. 1998 Jackson et al. 2001 - Indirect Effect Piscivores ??? Fishes Lewis and Anderson 2010 Grazers Williams & Ruckelhaus 1993 Neckles et al. 1993 Algae Jernakoff et al. 1996 Seagrass

Final Conclusions Humans Piscivores Fishes Lewis and Anderson 2010 SG Foulers SG Grazers Algae Grazers Algae Seagrass

Experiment # 2: Spring 2008 Is these patterns consistent across seasons? • Similar effects of fishes on limpets and seagrass grazing. • Complex effects on algal production and seagrass growth. • May indicate seasonal differences in dynamics.

Functional Diversity and Trophic Structure within the Amphipoda of Seagrass Beds Farlin, JP 1 , Lewis, LS 2 , Anderson, TW 1 , Lai, CT 1 1 San Diego State University, 2 Scripps Institution of Oceanography

Results Prim. Production

Conclusions  Significant Functional Diversity (Carbon Isotopes)  Significant Trophic Structure (Nitrogen Isotopes)  Amphipods exhibited significant trophic diversity and should not be considered as functionally redundant.

Funding

Funding

Project Summary (1) Support for: 1 M.S. Thesis, Levi Lewis (completed summer 2009) 1 Undergrad. Honors Thesis, James Farlin (completed fall 2009) > 12 undergraduate research assistants and volunteers (2) Presentations and Awards: - 2009. President’s Award . James Farlin. SDSU Res. Symposium - 2009. First Place . James Farlin. CSU State-wide Research Symposium - 2008. Deans Award. Levi Lewis. SDSU Research Symposium - 2008. Best Poster . Levi Lewis. Western Society of Naturalists - 2008. Levi Lewis. Southern California Academy of Sciences - 2007. Levi Lewis. Western Society of Naturalists (3) Manuscripts: - Lewis and Anderson. In prep. Effects of Predators in Seagrass Foodwebs - Farlin et al. In review. Functional Diversity of Amphipods in Seagrass Beds

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