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Foodweb support for the threatened Delta smelt:
Phytoplankton production within the low salinity zone
Ulrika E.
1
Lidström ,
1 Romberg
Introduction
Anne M.
1
Slaughter ,
Edward J.
1
Carpenter
Tiburon Center for Environmental Studies, San Francisco State University, Tiburon, CA
2 Georgia Southern University, Statesboro, GA
Preliminary Results
This collaborative research
Preliminary Conclusions
San Francisco Bay and Delta
Phytoplankton Biomass
0
Sacramento
River
CA
northern San Francisco Estuary
Suisun
Bay
San Pablo
indicates Bay
that several species of estuarine
their copepod prey), may be
between their declines and
San Francisco
food limited, suggesting a link
•All salinities sampled follow similar trends of
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biomass fluctuations
4
sampling area
0.5-5 psu
Mar-Aug 2006
>5µm cells
San
Joaquin
River
Lower in summer; mostly dominated
by <5µm cells early, with a more
balanced mix of groups later
changes at lower trophic levels.
•Biomass peak in June, with max response at
Phytoplankton are considered major contributors of organic carbon to
the Delta foodweb, providing support for secondary consumers (e.g.
copepods, the major prey of Delta Smelt) and bacterial production.
upstream communities
0.5 psu
• Previous studies have found <5 µm cells never contribute a large
portion of the population (Cole et al. 1986). In contrast, our results indicate
2
Higher in early spring; dominated by
Carquinez
Strait
fish, including Delta Smelt (and
be due to increased rainfall causing greater transport of plankton from
8
<5 µm cells make up a large portion of the phytoplankton community in
0
Chlorophyll a (µg L-1)
low salinity zone (LSZ) of the
20
•The apparent dominance of >5 µm cells and high biomass in spring may
Total chl a
<5um cells
10
Kilometers
characterize the foodweb of the
Phytoplankton Biomass
Size fractionated Chlorophyll a
program is underway to
(SFE). Recent evidence
Risa A.
2
Cohen ,
the LSZ, particularly in the summer months. This supports previous
Tota chl al
<5um cells
10
findings of a shift in phytoplankton community structure (Lehman 2000)
8
2.0 psu
6
•The shift in composition to smaller (<5 µm) cells and lower biomass
during summer months could be due to grazing pressure. The Asian clam
(Corbula amurensis) is known as an inefficient grazer of <5 um cells
4
(Werner and Hollibaugh 1993) but could draw down overall biomass by
2
grazing on > 5um cells
0
2.0 psu, followed by 5.0 psu, but no peak at 0.5
10
psu
Picoplankton abundance
Total chl a
<5 um cells
•Abundance of picoplankton is similar throughout the LSZ. This may be
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expected considering it is mainly composed of cyanobacteria which are
These results are from the first year of a 2-year field sampling program
•A smaller second peak in August, again with
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that focused on establishing the species composition and biomass fluctuations
max response at 2.0 psu
4
salinities
2
•Slight temporal fluctuations in abundance are present, with peaks in the
of two size fractions of phytoplankton in the LSZ during spring and summer.
5.0 psu
known to exist in a wide range of habitats and can tolerate shifts in
summer months possibly due to release from predation pressure by
0
Mar-1 Apr-1 May-1 Jun-1 Jul-1 Aug-1
protists that normally stabilize picoplankton populations
(<5µm size fraction estimated by subtracting 5µm filtered chl a GF/F filtered ‘total’ chl a)
Literature cited
Cole, B.E., J.E. Cloern, A.E. Alpine. 1986 Biomass and productivity of three phytoplankton size classes in San Francisco Bay. Estuaries, 9(2): 117-126
Picoplankton abundance
Materials and methods
• weekly cruises March 14 to August 23, 2006 in northern SFE
• surface water collected at 0.5, 2.0 and 5.0 psu (nominal salinities)
Sample Processing & Analyses
Phytoplankton biomass (chlorophyll a, Smith et al. (1981) and Strickland and Parsons
(1972)) – 25-100mL water sample filtered onto 25mm GF/F and 5µm filters (n=3),
stored in dark freezer (-20°C), until analysis by fluorometer.
Picoplankton abundance – 10mL water sample filtered onto 25mm 0.6µm
polycarbonate filters, preserved (2% formalin), mounted on a slide and frozen (-20°C)
until analysis; cells counted on a Zeiss epifluoresence microscope under 1000x
magnification and green light excitation (causing autofluorescence of picoplankton
(~1 µm) cells).
Smith, R.C., K. S. Baker, and P. Dustan. 1981. Fluorometric Techniques for the Measurement of Oceanic Chlorophyll in the Support of Remote Sensing.
Scripps Institute of Oceanography: SIO Ref. 81-17.
Total Picoplankton Abundance
Abundance (cells mL-1)
Field Collection
0.5 psu
2.0psu
5.0psu
16,000
14,000
12,000
10,000
8,000
6,000
4,000
2,000
0
Lehman, P.W. 2000. Phytoplankton biomass, cell diameter, and species composition in the low salinity zone of northern San Francisco Bay Estuaries 23(2):
216-230
•Significant difference in abundance
between dates (ANOVA F20,40 = 3.02,
p < 0.05)
•Peak in abundance in June and July.
Strickland, J. D. H. and T. R. Parsons. 1972. Spectrophotometric determination of chlorophylls and total carotenoids, pp. 185-196, In A Practical Handbook
of Seawater Analysis, J. Strickland and T. Parsons (ed). Ottawa, Fisheries Research Board of Canada, Bulletin #167.
Werner, I and J.T. Hollibaugh. 1993. Potamocorbula amurensis: Comparison of clearance rates and assimilation efficiencies for phytoplankton and
bacterioplankton. Limnology and Oceanography 38: 949-964
Acknowledgments
The authors wish to thank Captain David Morgan and David Bell for their assistance aboard R/V
Questuary. Thanks also to Dr. Edward F. Connor for advice with statistical analyses. Funding for this
project was provided by CALFED Science Program Grant # SCI-05-C107.
•No significant difference in
abundance between salinities
Mar -1
Apr -1
May -1
Jun -1
Jul -1
Aug -1
(ANOVA F2,40 = 2.24, p >0.05)
Further information
Ulrika E. Lidström
[email protected]
Romberg Tiburon Center of Environmental Studies http://rtc.sfsu.edu/