Mechanisms for persistence of Gracilariopsis andersonii in the Elkhorn Slough: links to sediments. Megan Wehrenberg Moss Landing Marine Labs

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1 Mechanisms for persistence of Gracilariopsis andersonii in the Elkhorn Slough: links to sediments Megan Wehrenberg Moss Landing Marine Labs

2 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

3 Study Sites Pigeon Point California Santa Cruz ~69 km apart Elkhorn Slough N Monterey

4 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

5 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

6 Study Site Mouth of Elkhorn Slough Estuary in Moss Landing Protected, soft-sediment beach Google Earth Van Dyke- CDFG

7 Survey Sampled Jan Jan 2009 Measured above- and belowground biomass Measured reproductive biomass

8 Monthly Biomass- Elkhorn Slough Average Biomass g/m² Above-ground Below-ground J F M A M J J A S O N D J -Highest above-ground biomass in Fall -Primarily below-ground during winters

9 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

10 Sexual Reproduction- Elkhorn Slough Average Biomass g/m² Vegetative Sexually reproductive 0 J F M A M J J A S O N D J -Only few reproductive fragments in August Sexual fertilization uncommon

11 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

12 Mouth of Elkhorn Slough CA DFG Tidal velocities can reach 1.25m/s (Broenkow and Breaker 2005)

13 Bathymetry of Main Channel and Beach Flat Hwy 1 Bridge Southern Sub-tidal Mud Bank (Israel and Watt 2005) Bridge Contours = 1m

14 Investigating Depositional History Mean Grain Size Large Small Standard Deviation of Grain Size (Sorting) WELL POOR

15 Particle movement Velocity (cm/sec) Particle Size (mm) modified Hjulström diagram

16 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

17 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

18 Questions 1. Was algal burial associated with seasonal sedimentary transport? 2. Did algae play a role in deposition (e.g. acting as sediment trap)?

19 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

20 Methods- Grain Size Analysis Cores extruded by gravity or with pressurized air Grain sizes analyzed using Coulter LS Laser Granulometer

21 Question 1. Was algal burial associated with seasonal sedimentary transport?

22 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

23 Question 2. Did algae play a role in deposition (e.g. acting as sediment trap)?

24 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

25 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

26 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

27 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

28 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

29 Results 1. Was algal burial associated with seasonal sedimentary transport?

30 Sediment Coring Months- Elkhorn Slough Average Biomass g/m² Above-ground Below-ground J F M A M J J A S O N D J

31 Results- Monthly surface sediments 5 Standard deviation (µm) July 08 October 08 January Mean diameter (µm)

32 Results- Monthly surface sediments 5 Better sorted Standard deviation (µm) July 08 October 08 January Mean diameter (µm) -Shift toward larger better sorted particles in Jan 09

33 Results- Monthly surface sediments 5 P= Average S.D (µm) SE July 08 n= 24 October 08 n= 24 January09 n= Average Mean (µm) SE

34 Nearby loss of beach sand Ivano Aiello, unpublished data

35 Minerals Smear slide of surface particles within site Identical mineral structure to sand found on surrounding beaches INT15 Ivano Aiello 500µm

36 Results 2. Did algae play a role in deposition (e.g. acting as sediment trap)?

37 Results- Core classifications in January 09 sediment 4 P > Average S.D. (µm) SE A N1 N2 N3 (n=19) (n=15) (n=9) (n=4) Average mean diameter (µm) SE

38 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

39 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

40 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

41 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)

42 Thank you!