Kam W. Tang Kam W. Tang Amy R. Shields Amy R. Shields Walker O. Smith, Jr. Walker O. Smith, Jr.

Virginia Institute of Marine ScienceVirginia Institute of Marine ScienceGloucester Point, Virginia, USAGloucester Point, Virginia, USA

Dark and cold survival ofDark and cold survival ofPhaeocystis antarcticaPhaeocystis antarctica

David Elliott Maureen Lynch Jennifer GaydosDavid Elliott Maureen Lynch Jennifer GaydosBritt Anderson Eva Bailey Heidi GeiszBritt Anderson Eva Bailey Heidi GeiszAdriana Veloza Emily YamAdriana Veloza Emily Yam

ESCAPESCAPEcology of Solitary and Colonial Antarctic Ecology of Solitary and Colonial Antarctic PhaeocystisPhaeocystis

Acknowledgements:Acknowledgements:U.S. NSF ANT-0440478U.S. NSF ANT-0440478RPSC, McMurdo Station, Crary LabRPSC, McMurdo Station, Crary Lab

Rousseau et al. (1994)

P. globosaP. globosaP. pouchetiiP. pouchetiiP. antarcticaP. antarctica

ESCAP – Ecology of Solitary and Colonial Antarctic ESCAP – Ecology of Solitary and Colonial Antarctic PhaeocystisPhaeocystis

- Survival of grazing- Survival of grazing

- Survival of freezing and darkness in winter- Survival of freezing and darkness in winter

Chlorophyll-size-fraction-specific grazing by microzooplankton in McMurdo Sound as determined by dilution technique (Preliminary results)

Grazing coefficient (d-1) Date 0.7 m fraction 5 m fraction 20 m fraction

01-03-06 NS 0.14 NS

01-09-06 0.05 NS NS

01-16-06 NS NS NS

01-24-06 0.14 0.24 0.12 01-30-06 NS NS NS

02-06-06 0.17 0.10 NS

Chlorophyll-size-fraction-specific grazing by microzooplankton in McMurdo Sound as determined by dilution technique

> >>

Zo

op

lan

kto

n D

MS

P (

nm

ol in

d-1 )

0

5

10

15

20

25McMurdo Sound 2005-2006 Long Island Sound

Limac

ina

Clione

Calanu

s acu

tus

Oithon

a

Micr

ocala

nus

Calano

ides

Parae

ucha

eta

Copep

od n

aupli

i

Steph

os

Polych

aete

larv

ae

Cteno

phor

e

P. antarctica single cells and small colonies are consumed by (small) grazers, which subsequently support the higher trophic levels.

P. antarctica

Grazers + Food

Dialysis bag

Does grazing affect colony formation?(sensu Jakobsen & Tang 2002)

Grazing Signal experiment S-1numbers represent geometric mean

underlined numbers indicate significant difference betweengrazing treatment and control; Rank-sum Test; p<0.05

Day

0 5 10 15

Co

lon

y d

iam

eter

( m

)

0

200

400

600

Day

0 5 10 15

Co

lon

y d

iam

eter

( m

)

0

200

400

600

105.8 111.8

93.1

105.8 44.446.4

Grazing

Control

137.0

68.8

Consistent with previous studies on P. globosa (Jakobsen & Tang 2002; Tang 2003)

Grazer

No grazer

P. antarctica exposed to “grazing signal” had significantly larger colonies

* * *

Can P. antarctica survive austral winter?

• Physiological response to long period of darkness.

• Physiological response to freeze-thaw treatment.

Light treatmentLight treatment

Dark treatmentDark treatment

Dark-treatment

0 5 10 15 20

0.7

m fr

actio

n ch

loro

phyl

l

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 5 10 15 20

5 m

frac

tion

chlo

roph

yll

0.2

0.3

0.4

0.5

0.6

0.7

Day

0 5 10 15 20

20

m fr

actio

n ch

loro

phyl

l

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

p< 0.001

p< 0.05

>0.7 m “Single cells + Colonies”

>5 m “Small+ Large colonies”

>20 m “Large colonies”

Ch

loro

phy

ll (

g l-1

)Significant decrease

Significant increase

Day

0 5 10 15 20

Sin

gle

ce

lls m

l-1 (

me

an

±sd

)

0

500

1000

1500

2000

2500

3000

Col 1 vs Col 4

Day

0 5 10 15 20

Co

lon

ies

ml-1 (

me

an

±sd

)

0

20

40

60

80

100

Day

0 5 10 15 20

Colo

ny d

iam

ete

r (m

m)

0.00

0.02

0.04

0.06

0.08

0.10

Pbmax in culture: 0.19 - 4.10 (Schoemann et al. 2005)

Irradiance (mol photons m-2 s-1)

0 100 200 300 400 500

Pb

(m

gC

mg

Ch

la-1

h-1

) fo

r >

0.7

m

siz

e f

ract

ion

0.0

0.1

0.2

0.3

0.4

0.5

LightDark

Pbmax = 0.4 mgC mgChla-1 h-1

Pbmax = 0.26 mgC mgChla-1 h-1

Freeze for 15 daysFreeze for 15 days

Recovery for up to 21 daysRecovery for up to 21 days

Freeze-Thaw experiment FT-1(freeze-15-day)

Day

-15 0 7 14 21

Co

lon

y d

iam

ete

r (

m)

0

50

100

150

200

250

300

116.8

85.8

110.9

60.2 70.3

Freeze-Thaw experiment FT-1(freeze-15-day)

Day

-15 0 7 14 21

Cel

ls o

r co

loni

es m

l-1

10

100

1000

10000Single cellsColonies

Day

-15 0 7 14 21

Chl

orop

hyll

(g

l-1)

0

5

10

15

20

25

>0.7 m >20 m

Freeze-Thaw experiment FT-1(freeze-15-day)

Day

-15 0 7 14 21

Cel

ls o

r co

loni

es m

l-1

10

100

1000

10000Single cellsColonies

Day

-15 0 7 14 21

Chl

orop

hyll

(g

l-1)

0

5

10

15

20

25

>0.7 m >20 m

Freeze-Thaw expt FT-1freeze-15-day

Day

-15 0 7 14 21

Fv/F

m (

me

an

+s

d)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Irradiance

0 200 400 600 800 1000 1200

ET

R

0

10

20

30

40

50 Before freezingDay 0 recoveryDay 7 recoveryDay 14 recoveryDay 21 recovery

Grazing signal led to larger colonies --- potential defense mechanism against small grazers

P. antarctica may survive long darkness and freezing in ice during austral winter, and subsequently seed the water column population in the spring.