Mechanisms for persistence of Gracilariopsis andersonii in the Elkhorn Slough: links to sediments Megan Wehrenberg Moss Landing Marine Labs
Gracilariopsis andersonii in Central CA Intertidal Open Coast Attached to rocky shelves Direct impact of swells Bays and Estuaries Within soft sediment No direct swell energy
Study Sites Pigeon Point California Santa Cruz ~69 km apart Elkhorn Slough N Monterey
Gracilariopsis andersonii Cylindrical, erect, perennial red alga Grows up to 2 m long Attached by small discoid holdfast to rock or shell or unattached Can tolerate periodic inundation by sand
Gracilariopsis andersonii Can propagation through vegetative fragmentation Biomass loss stimulates branching and can therefore stimulate growth Gracilaroids are 3 rd most cultivated group of seaweeds worldwide; world s major source of agar
Study Site Mouth of Elkhorn Slough Estuary in Moss Landing Protected, soft-sediment beach Google Earth Van Dyke- CDFG
Survey Sampled Jan 2008 - Jan 2009 Measured above- and belowground biomass Measured reproductive biomass
Monthly Biomass- Elkhorn Slough Average Biomass g/m² 4000 3000 2000 1000 0-1000 Above-ground Below-ground -2000-3000 J F M A M J J A S O N D J -Highest above-ground biomass in Fall -Primarily below-ground during winters
Below-ground Biomass in Elkhorn Slough Up to 40 cm below surface Highly fragmented Pigmented Healthy Suggests that new growth can be a result of exposure of underground material
Sexual Reproduction- Elkhorn Slough Average Biomass g/m² 3000 2500 2000 1500 1000 500 Vegetative Sexually reproductive 0 J F M A M J J A S O N D J -Only few reproductive fragments in August 2008 -Sexual fertilization uncommon
Sedimentation in Elkhorn Slough Records of algal burial of this magnitude had not been reported Monthly algal biomass is greater or equal to the highest quantities reported in literature Sedimentation appears to play important role in the persistence of thriving bed
Mouth of Elkhorn Slough CA DFG Tidal velocities can reach 1.25m/s (Broenkow and Breaker 2005)
Bathymetry of Main Channel and Beach Flat Hwy 1 Bridge 10 8 4 2 0 Southern Sub-tidal Mud Bank (Israel and Watt 2005) Bridge Contours = 1m
Investigating Depositional History Mean Grain Size Large Small Standard Deviation of Grain Size (Sorting) WELL POOR
Particle movement Velocity (cm/sec) Particle Size (mm) modified Hjulström diagram
Estuarine Grain Size Domains Bivariate plots used to evaluate the energy of the environment and the degree of processing Estuarine domains: Tanner (1991) modified by Lario et al. (2000) Closed Basins Storm (high energy) Environments 10 More sorting Soritng 1 Closed Basin Closed Basin 1 10 Mean grain size
Aids to Sedimentation Biological material can aid in sediment stabilization as well as deposition Seagrasses have been shown to baffle currents Enhance smaller particle deposition Bryan Largay
Questions 1. Was algal burial associated with seasonal sedimentary transport? 2. Did algae play a role in deposition (e.g. acting as sediment trap)?
Methods- Grain Size Analysis 24 cores collected randomly: July 08, October 08, January 09 Cores: 1.5 x 1.5 and collecting ~1ft (30cm) of sediment
Methods- Grain Size Analysis Cores extruded by gravity or with pressurized air Grain sizes analyzed using Coulter LS 13 320 Laser Granulometer
Question 1. Was algal burial associated with seasonal sedimentary transport?
Methods- Monthly Surface Sediments I analyzed and compared grain sizes from the surface sediment (top 1cm of core) of all 24 cores collected in July 08, October 08, and January 09 Model I ANOVA (and Tukey post hoc) to test effect of month on sediment size 0-1cm for
Question 2. Did algae play a role in deposition (e.g. acting as sediment trap)?
Methods- Sediment Within Algae I analyzed and compared grain sizes from sediment within algae to sediment in locations without algae in January 09 cores only
Methods- Sediment Within Algae With Algae Without Algae 0cm 0cm 0cm 0cm 0cm 0cm 0cm 5cm 5cm 5cm 5cm 5cm 5cm 5cm 15cm 15cm 15cm 15cm 15cm 15cm 15cm 25cm 25cm 25cm 25cm 25cm 25cm 25cm 35cm 35cm 35cm 35cm 35cm 35cm 35cm
Methods- Sediment Within Algae With Algae A Without Algae 0cm 0cm 0cm 0cm 0cm 0cm 0cm 5cm 5cm 5cm 5cm 5cm 5cm 5cm 15cm 15cm 15cm 15cm 20cm 15cm 15cm 15cm 25cm 25cm 25cm 25cm 25cm 25cm 25cm 35cm 35cm 35cm 35cm 35cm 35cm 35cm
Methods- Sediment Within Algae With Algae A Without Algae N2 0cm 0cm 0cm 0cm 0cm 0cm 0cm 5cm 5cm 5cm 5cm 5cm 5cm 5cm 15cm 15cm 15cm 15cm 15cm 15cm 15cm 20cm 25cm 25cm 25cm 25cm 25cm 25cm 25cm 35cm 35cm 35cm 35cm 35cm 35cm 35cm N1 N3
Methods- Sediment Within Algae Compared grain sizes within core classifications A N1 N2 N3 with algae without algae Used Model I ANOVA (and Tukey post hoc) to test for effect of algae on sediment size composition
Results 1. Was algal burial associated with seasonal sedimentary transport?
Sediment Coring Months- Elkhorn Slough Average Biomass g/m² 4000 3000 2000 1000 0-1000 Above-ground Below-ground -2000-3000 J F M A M J J A S O N D J
Results- Monthly surface sediments 5 Standard deviation (µm) 4 3 2 July 08 October 08 January09 1 0 50 100 150 200 250 Mean diameter (µm)
Results- Monthly surface sediments 5 Better sorted Standard deviation (µm) 4 3 2 July 08 October 08 January09 1 0 50 100 150 200 250 Mean diameter (µm) -Shift toward larger better sorted particles in Jan 09
Results- Monthly surface sediments 5 P= 0.007 Average S.D (µm) SE 4 3 2 July 08 n= 24 October 08 n= 24 January09 n= 24 1 0 50 100 150 200 250 Average Mean (µm) SE
Nearby loss of beach sand Ivano Aiello, unpublished data
Minerals Smear slide of surface particles within site Identical mineral structure to sand found on surrounding beaches INT15 Ivano Aiello 500µm
Results 2. Did algae play a role in deposition (e.g. acting as sediment trap)?
Results- Core classifications in January 09 sediment 4 P > 0.001 Average S.D. (µm) SE 3 2 1 A N1 N2 N3 (n=19) (n=15) (n=9) (n=4) 0 0 50 100 150 200 250 Average mean diameter (µm) SE
Conclusion Algal burial coincided with: shift in surface sediment toward larger, better sorted particles Simultaneous increase in wave height and erosion of beach sand from closest beaches Suggests sediment coming from beaches outside of slough
Conclusion Algae contained sediment with smaller more poorly sorted particles Suggests a baffling of currents by the biological material, aiding in sedimentation The biology controls the geology and the geology controls the biology
Significance The unique sedimentation cycle in the lower slough is sustaining one of the most dense populations of Gracilariopsis andersonii in central CA In an tidal estuary which is readily eroding, a source of biological material which provides a mechanical aid to sediment stabilization can be a major asset
Acknowledgements FUNDING: PADI Foundation (Grant #69) Surfrider Foundation Graduate Scholarship Meyers Oceanographic Trust Packard Foundation Signe Lundstrom Memorial Fund PSA- Hoshaw Award THESIS COMMITTEE: Dr. Michael Graham (MLML) Dr. Ivano Aiello (MLML) Dr. Alejandro Buschmann (ULAGOS, Chile)
Thank you!