New Lessons from an old Invader: The effects of an invasive mud snail on ecosystem function in northern California

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1 New Lessons from an old Invader: The effects of an invasive mud snail on ecosystem function in northern California Heidi Weiskel 1,5, Jeb Byers 2, Todd Huspeni 3, Chela Zabin 4, Basma Mohammad, Ted Grosholz 1 1 University of California, Davis 2 University of New Hampshire 3 University of Wisconsin, Stevens Point 4 Smithsonian Environmental Research Center 5 San Francisco Bay National Estuarine Research Reserve

2 Invasions are a concern Invasive species events are increasing in both terrestrial and aquatic ecosystems (Levine and d Antonio 2003) Suite of ecological, genetic, evolutionary impacts

3 Founder populations provide a unique opportunity Collect rare data on founder populations in marine systems Test predictions about distribution and rates of spread Investigate new impacts

4 Photo Credit: Mark Torchin Batillaria attramentaria Japanese mud snail

5 Invasion history Crassostrea gigas aquaculture around turn of century along west coast of the U.S. Batillaria shows up starting in 1930s (Byers 1999 and refs therein) Now...new populations in areas without oyster aquaculture in last ~ 5-10 years

6 Batillaria attramentaria invasion New populations (2000s) Original populations (1900s)

7 Batillaria impacts DOCUMENTED Competition with Cerithidea californica (Byers 1999, 2000) Introduction of novel trematode parasite (Torchin et al. 2005) showing up in native and invasive fishes loss of parasite diversity Invasion facilitation for both natives and invasives (Wonham et al. 2005)

8 Objectives for new CA populations 1) Characterize new Batillaria populations in comparison to established ones distribution parasite infection rate size frequency density genetic structure (snail and trematode) 2) Characterize effects of Batillaria on ecosystem function chlorophyll_a (proxy for standing biomass of benthic microalgae)

9 Population Surveys

10 Survey Methods Date Method May-06 Jul-06 Aug-06 Sep-06 Oct-06 Nov-06 May-07 Jul-07 Aug-07 Population Survey Pre-Removal Snail Sampling Habitat Characterization Sampling Removal (SFB only) SAN FRANCISCO BAY Determine extent invasion Sample distribution: 3 tidal heights every 30 meters fixed quadrats (143) Pick/sieve Monthly population sampling & habitat characterization Total mudflat area surveyed: 16,130 m 2 BODEGA HARBOR Determine extent invasion Sample distribution: transects across distribution area every 30 meters random and haphazard quadrats (124) Pick/sieve Total mudflat area surveyed: 7580 m 2 (after walking entire harbor)

11 Loch Lomond Marina San Francisco Bay 16,130 m 2 (539 m2)

12 Bodega Harbor, CA 7580 m 2 (2300 m 2 )

13 Rates of Infection by Cercaria batillariae San Francisco Bay: 1.41% overall * 0% in snails < 25mm * almost no snails > 25mm Bodega Harbor: 4.23 % overall * 0% in < 25mm * almost no snails > 25mm Tomales Bay: 41.89% overall * 10.53% in snails < 25mm * 93.75% in snails > 25mm

14 New v. Established Population Structure Size Frequency Distribution, San Francisco Bay 2006 Size Frequency Distribution San Francisco Bay Proportion Total Batillaria Proportion Total Batillaria < > 30 Size Class 0 < > 30 Size Class (mm) Size Frequency Bodega Harbor 2007 Size Frequency Distribution, Tomales Bay 2007 Proportion Total < > 30 Size Class (mm) Batillaria Proportion Total < > 30 Size Class (mm) Batillaria

15 Changes in SFB Size Distribution: effect of removal? July Number of snails Frequency > 30 Size class (mm) October 2006 Number of snails > 30 Frequency Size class (mm)

16 Densities are much higher in established populations , Density (snails/m2) Batillaria Tomales Bodega San Francisco 2006 Site San Francisco 2007

17 San Francisco Bay Habitat Characterization 16,130 m 2 (539 m2)

18 Chlorophyll_a: Batillaria area higher High Intertidal p = Chl_a(mg/cm2) NO SNAIL Site BATIILARIA Pre-Eradication Low Intertidal p = Chlorophyll_a (mg/cm2) NO SNAIL Site BATIILARIA Pre-Eradication

19 Chlorophyll_a: decreases after removal Chl_a (mg/cm2) NO SNAIL High Intertidal Site BATIILARIA P < Pre-Eradication Post-Erad Low Intertidal P < Chl_a(mg/cm2) NO SNAIL BATIILARIA Pre-Eradication Post-Erad Site

20 Carcinus maenas also affects primary production

21 2005 Bodega Harbor

22 Carcinus burrowing increases chlorophyll_a over time Chl_a mg/cm Day p < Avg_In Burrow Avg_Out Burrow

23 Conclusions SURVEYS Beachhead populations are young and contained Parasitism is low Disturbed populations may experience a recruitment explosion (removal) NOVEL IMPACT Benthic invaders may positively affect primary production if density or biomass of invader is high enough

24 Future Directions

25 Acknowledgements Advisor Ted Grosholz Funding UC Davis Bioinvasions IGERT (NSF) UC Davis Jastro-Shields Research Grant Bodega Marine Lab Travel Grant San Francisco Bay National Estuarine Research Reserve Graduate Research Fellowship National Park Service Lab Equipment Susan Williams & Al Carranza Volunteers & assistants Christy Bowles, Andy Chang, Shannon Waters, Betsy Wells, Eric Yoshizuka, Laura Rodriguez, Amanda Newsom, Chris Brown, Blu Forman, Brian Steves, Jelle Faber, Sarikka Attoe, Sarah Lewis, Ben Nilsen, Katie Faulkner, Gwen Santos