Diatom silicification changes in a high pCO2 environment: a mesocosm

experiment

Kiely ShuttUniversity of Washington

Friday Harbor LaboratoriesSpring 2013

Diatoms: A Brief Overview

•Major primary producers•Most common phytoplankton•Single celled, some are chain forming•Primary controllers of silica cycling in the ocean•Radial or bilateral symmetry•Diatoms have a silica requirement in order to build frustules

Silicification

Dissolved H4SiO4

Biogenic Silica SiO2

Upt

ake

MethodsBiogenic Silica Filtering

Rapid filter method by Paasche (1980)Prepped and ran on spectrometer using

Strickland and Parsons (1968)

Biogenic Silica/Diatom Cell CalculationBiogenic Silica

Liter

( Phytoplankton Cells

Liter

# Diatoms# Cells )

Research Questions

• Does biogenic silica differ between pCO2 treatments?

• What stressors affected biogenic silica and silica per diatom cell?– Micronutrient limitation? (Iron, Zinc)– Macronutrient limitation? (Nitrate, Silicate)– Microzooplankton grazing pressure?– Light limitation?

F(2,32)= 5.250, p=0.072

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 202

4

6

8

10

12

14Control

High

Dock

Drift

Time (Days)

Med

ian

Biog

enic

Sili

ca (µ

mol

L-1

)Biogenic silica through time

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200

5

10

15

20

25

0

5

10

15

20

25

Time (Days)

Med

ian

Nitr

ate

(µm

ol L-

1)

Med

ian

Biog

enic

Sili

ca (µ

mol

L-1)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200

5

10

15

20

25

0

5

10

15

20

25

Control Ni-trate

High Nitrate

Drift Nitrate

Dock Nitrate

Control BioS

High BioS

Drift BioS

Dock BioS

Time (Days)

Med

ian

Nitr

ate

(µm

ol L-

1)

Med

ian

Biog

enic

Sili

ca (µ

mol

L-1)

Statistically strong negative correlations for all treatment groups: ρ= -.923, -.913, -.884

Nitrate and biogenic silica through time

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200

5

10

15

20

25

30

35

40

45

50

0

5

10

15

20

25

30

35

40

45

50

Time (Days)

Med

ian

Silic

ate

(µm

ol L-

1)

Med

ian

Biog

enic

Sili

ca (µ

mol

L-1

)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200

5

10

15

20

25

30

35

40

45

50

0

5

10

15

20

25

30

35

40

45

50

Control BioS

High BioS

Drift BioS

Dock BioS

Control Sil-icate

High Silicate

Drift Silicate

Dock Silicate

Time (Days)

Med

ian

Silic

ate

(µm

ol L-

1)

Med

ian

Biog

enic

Sili

ca (µ

mol

L-1

)

Biogenic silica and dissolved silicate through time

Statistically strong negative correlations for all treatment groups: ρ= -.939, -.897, -.854

Grazing pressure

Treatment Spearman ρ

Control .382

High -.054

In order to show a significant association between silicification and grazing, our ρ value would need to be closer to -1 or 1.

Previous studies found increase in diatom silicification under grazing pressure (Pondaven et al 2007)

0 20 40 60 80 100 120 1400.5

1

1.5

2

2.5

3

3.5

4

4.5 Irradiance (inside mesocosms) µmol m-2 s-1

Dept

h (m

)

0 20 40 60 80 100 120 1400.5

1

1.5

2

2.5

3

3.5

4

4.5

T0 ControlT0 HighT0 DriftT11 ControlT11 HighT11 Drift

Irradiance (inside mesocosms) µmol m-2 s-1

Dept

h (m

)

PAR

(Eie

nste

ins m

-2 d

-1)

Adapted from (Martin-jézéquel et al 2000)

F(2,30)= 4.200, p=0.122

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 200

20

40

60

80

100

120

140

160

180ControlHighDrift

Time (Days)

Pico

mol

e Si

lica

Cell

-1Picomole Silica Per Cell Through Time

Research Questions - Revisited

• Does biogenic silica differ between pCO2 treatments? Nope!

• What stressors affected biogenic silica and silica per diatom cell?– Micronutrient limitation? (Iron, Zinc)– Macronutrient limitation? (Nitrate, Silicate)– Grazing pressure?– Light limitation? Could be!

Conclusions

• No significant differences between pCO2 treatments for biogenic silica or silicification in diatoms

• Macronutrient limitation and grazing pressure were not affecting silicification in diatoms

• Light limitation likely to be the reason why we see the trends in silicification data as well as other unmeasured variables within our mesocosm system

Acknowledgements• Jim Murray• Robin Kodner• Kelsey Gaessner • Evelyn Lessard• Mike Foy• Barbara Paul• Amanda Fay• Molly Roberts• Kitae Park• Peers: Phil Gravinese, Kelly Govenar, Jen

Apple, Andrew Turner, Daneil Newcomb, Natsuko Porcino, Amy Stephens

• University of Washington - Friday Harbor Labs

• Mary Gates Endowment• Henry and Holly Wednt Endowment• Educational Foundation of America• Herbs Tavern