Foodweb support for the threatened Delta Smelt:Foodweb support for the threatened Delta Smelt:Summary of program objectives and preliminary resultsSummary of program objectives and preliminary results

Anne SlaughterAnne Slaughter11 and The CALFED Foodweb Research Team and The CALFED Foodweb Research Team1,2,3,41,2,3,4

1 1 Romberg Tiburon Center, San Francisco State University Romberg Tiburon Center, San Francisco State University •• 22 U.S. Geological Survey, Menlo Park, CA U.S. Geological Survey, Menlo Park, CA 33 Department of Biology, Georgia Southern University Department of Biology, Georgia Southern University • • 4 4 Department of Marine Sciences, University of ConnecticutDepartment of Marine Sciences, University of Connecticut

Preliminary Results

This collaborative research program is underway to characterize the foodweb of the low salinity zone (LSZ) of the northern San Francisco Estuary (SFE). Recent evidence indicates that several species of estuarine fish, including Delta Smelt (and their copepod prey), may be food limited, suggesting a link between their declines and changes

Water and plankton net samples were collected weekly at three salinities (0.5, 2 and 5 psu) from March 14 to August 23, 2006.

The following data and samples were collected at each salinity:

- water column salinity, temperature and clarity profiles (CTD with attached PAR sensor, Secchi disk)

- surface water collection via bucket- plankton (ring) net tows

Funding for this project was providedby CALFED Science Program Grant #SCI-05-C107

Sampling Program

Introduction

Acknowledgment

Posters1 R.A. Cohen, A.M. Slaughter, E.J. Carpenter. The effects of salinity on phytoplankton and dissolved organic carbon availability.

2 V.E. Hogue, A.E. Parker, R. Dugdale, A. Marchi, F. Wilkerson. The role of excess ammonium in reducing phytoplankton in the San Francisco Estuary.

3 T.R. Ignoffo, A.Gould, W.J. Kimmerer. Growth and development of Limnoithona tetraspina, the most abundant copepod in the estuary.

4 U.E. Lidstrom, A.M. Slaughter, R.A. Cohen, E.J. Carpenter. Phytoplankton production within the Low Salinity Zone.

5 A.E. Parker, V.E. Hogue, F. Wilkerson, R. Dugdale. Evaluating the potential contribution of bacterial carbon for higher trophic levels.

6 J.K. Thompson, F. Parchaso. Grazing potential of Corbula amurensis on lower trophic levels.

7 J.K. York, B. Costas, G. McManus, A.M. Slaughter, T. Ignoffo, W. Kimmerer. Microzooplankton dynamics in the Low Salinity Zone of the San Francisco Estuary.

Oral PresentationW.J. Kimmerer.  Foodweb support for the threatened delta smelt:  Subtle interactions may be a cause of the pelagic organism decline.(Tuesday 1:10 PM, POD session)

The CALFED Foodweb Research Team

at lower trophic levels. Exogenous organic carbon likely provides important support to the LSZ foodweb. Our research examines the base of the foodweb, from phytoplankton and bacteria to copepods, in the LSZ. The data presented here resulted from the first year of a 2-year field sampling and experimental program that included weekly sampling cruises during two periods (spring and summer) when larval, juvenile and adult delta smelt are present. During this time, we focused on the potential influence of ammonium concentration on nitrate uptake (and therefore growth of phytoplankton), phytoplankton production and lysis (a potential source of DOC), bacterial production, microzooplankton and zooplankton grazing and production and abundance of and grazing impact by Corbula amurensis.

San Francisco Estuary

Suisun BaySan Pablo

Bay

Sacramento River

San Joaquin

RiverSa

n Fra

ncisco

0 20

Kilometers

CarquinezStrait

CA

sampling area0.5-5 psu

Mar-Aug 2006

Delta Smelt(and other fish)

0

20

40

60

80

0

2

4

6

8

10

Mar Apr May Jun Jul Aug

0.5 2 5 X2

Dis

tanc

e, k

m

Sal

inity

, psu

Benthic grazing effects6

0

5

10

15

20

25

30

35

86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06

Year

0

1

2

3

chlo

rop

hyl

l a (µ

g L

-1)

gra

zing

rate

(m3

m2 d

-1)

Phytoplankton biomass rarely exceeded 10 µg L-1 unless Corbula amurensis grazing was <0.3 m3 m-2 d-1

(Data based on analyses of DWR D7 bivalve samples and chl a values, shallow water of Grizzly Bay)

Surface salinity (top; horizontal lines represent nominal salinities) and position of each station (bottom), including X2 (calculated distance, from the Golden Gate, of the 2 psu bottom isohaline). X2 and surface salinity diverged in spring, primarily due to collection of surface measurements when salinity was strongly stratified; X2 is also not well-predicted when less than ~55 km. Later in the season, the 2 psu distance and X2 were in closer agreement.

2006 – an anomalously wet year

Red lines indicate field sampling period for this project. Green numbers indicate rank of each month (in terms of monthly outflow); e.g., April 2006 was the wettest April since 1980, May 2006 was the third wettest May since 1980, etc.

0

5

10

15

1980 1985 1990 1995 2000 20050

5

10

15

Jan Feb Mar Apr May Jun Jul Aug Sep

2

134

1

34 5 7 8

Year

Out

flow

,100

0 m

3 s-1

net D

elta

out

flow

(10

00 m

3 s-1)

Phytoplankton production4

0

2

4

6

8

10

12

1-Mar 31-Mar 30-Apr 30-May 29-Jun 29-Jul

chlo

roph

yll a

(ce

lls m

L-1)

0.5 psu2.0 psu5.0 psu

Mar Apr May Jun Jul Aug

Several peaks in total chlorophyll biomass were observed in spring and summer

9% to 84% of primary production passed to microzooplankton grazers

43%0.521.21Aug 22

71%1.121.59Aug 15

70%1.211.73Jul 18

84%1.661.97Jul 11

17%0.140.83May 09

20%0.180.92May 02

9%0.060.69Apr 18

38%0.190.51Apr 11

42%0.170.41Mar 21

21%0.040.19Mar 14

grazing/growth

Microzooplankton grazing rate

(day -1)

Phytoplankton growth rate

(day -1) 

Microzooplankton grazing7

0.0

0.1

0.2

0.3

Apr May Jun

Gro

wth

Rat

e, d

-1gr

owth

rat

e d-1

Copepod production3

Limnoithona tetraspina is the most abundant copepod in the LSZ and had a growth rate of ~10% d-1 (mean of all juvenile stages)

Effects of salinity on phytoplankton1

More saline phytoplankton lysed when exposed to lower salinities, potentially releasing DOC for bacterial production

Hours Hours

chlo

roph

yll (

µg

L-1)

10

15

20

25

30

0 2 4 6 8 10 12

y = -0.088x + 20.860y = -0.464x + 21.682y = -0.871x + 22.206

Skeletonema spp.Saline (5 psu) cells 0.5, 2,

5 psu

10

15

20

25

30

0 2 4 6 8 10 12

y = 0.690x + 17.309y = 0.340x + 20.919y = 0.076x + 22.216 5.0 psu

2.0 psu0.5 psu

Treatments

Scenedesmus spp.Fresh (0.5 psu) cells 0.5, 2, 5 psu

Nitrate concentrations decreased following phytoplankton peaks; nitrate concentrations were similar at all salinities

Nutrients2

Feb M ar M ay Jun Jul Aug

0

5

10

15

20

25

0

4

8

12

5.0 psu2.0 psu0.5 psu

chlorophyll (µg L

-1)

nitr

ate

(µM

)3/14 3/28 4/11 4/25 5/9 5/23 6/6 6/20 7/4 7/18 8/1

Leuc

ine

Inco

pora

tion

(pm

ol L

-1 h

-1)

0

100

200

300

400

500

600

0.5 psu2.0 psu5.0 psu

Bacterial production5

Free-living bacteria contributed 67-93% to bacterial production