Seasonal changes in plankton biomass, production and community structure

in southern Japan*

TORU KOBARIFaculty of Fisheries, Kagoshima University

* Partly supported by grants fromthe Japan Society for the Promotion of Science and the Fisheries Agency of Japan

CCCC REX Workshop on PICES 13th Annual MeetingOctober 14th, 2004

Hawaii Convention Center

Contents

1. Background

2. Sampling and experimental methods

3. Results

4. Summary

Seasonal patternsVertical distributionBiomassProductionCommunity structureGrowth rateMortality rate

Carbon budget

MammalsFishes

Copepod, Euphausiid

Ciliate

Bacteria, Cyanobacteria

GrazingGrazingFood WebFood Web

MicrobialMicrobialFood WebFood Web

Heterotrophic Nano-Flagellate

Diatom

0.2-2µ

2-20µ

20-200µ

>200µ

Epipelagic Marine EcosystemEpipelagic Marine Ecosystem

Pico

Nano

Micro

Meso

Early studiesEarly studies

Zooplankton grazing activity

Standing stock of phyto- and zooplankton

Seasonal variation

Satellite image of sea surface chlorophyll a

ALOHA

Station PaPa

EQPAC

Site H

Little knowledge of plankton food webin the oligotrophic waters

NOPACCS

ObjectiveObjective

Seasonal changes in biomass, production and community structure

of phyto- and zooplankton in the Kuroshio

Carbon budget within phyto- and zooplankton

Structure of plankton food web

SamplingSampling

Sampling station

Oceanographic observations

Kuroshio

200m

1000m

Sampling period

30˚N, 131˚E (Kuroshio)

June 2002 - October 2003(Monthly to Bimonthly)

Temperature, Salinity (CTD)Pico- to Micro-plankton (Niskin bottles)

0,10,20,30,50,75,100 mMeso-plankton (Plankton net)

0-100 m

Station A

Microscopic AnalysisMicroscopic AnalysisPico-plankton (<2µm)

BacteriaCyanobacteriaOther pico-phytoplankton

Autotrophic Nano-Flagellate (ANF)Heterotrophic Nano-Flagellate (HNF)

Nano-plankton (2-20µm)

Centric or Pannae DiatomAutotrophic Micro-flagellate (AMF)Heterotrophic Micro-flagellate (HMF)Naked CiliateTintinnid CiliateNauplii

Micro-plankton (20-200µm)

Meso-plankton (>200µm)CopepodGelatinous zooplanktonOther zooplankton

Conversion FactorsConversion Factors

Picoplankton: cell numbers were directly converted to carbonBacteriaCyanobacteriaOther picophytoplankton

12.8 fgC/cell250 fgC/cell220 fgC/cell

Autotrophic Nano-Flagellate (ANF)Heterotrophic Nano-Flagellate (HNF)Centric or Pannae DiatomAutotrophyic Micro-Flagellate (AMF)Heterotrophic Micro-Flagellate (HMF)Naked CiliateTintinnid CiliateNaupliiGelatinous mesoplanktonOther mesoplankton

Log10C=0.863Log10V×-0.3630.12 pgC/um3

Log10C=0.758Log10V×-0.422C=0.216V0.939

C=0.216V0.939

0.19 pgC/um3

C=444.5+0.053LV0.05 pgC/um3

0.003 pgC/um3

0.06 pgC/um3

Nano- to Meso-plankton: carbon contents were estimated from biovolume

C: Carbon (µgC), V: Volume (µm3), LV: Lorica volume (µm3)

Dilution ExperimentsDilution Experiments

Following by Following by LandryLandry & & HassettHassett (1982), (1982), Landry Landry et al. (1995)et al. (1995)

Incubating sea watersIncubating sea waters

Diluted seriesDiluted series

Enriched nutrientsEnriched nutrients

Enriched bottles: 30, 50, 75, 100%Enriched bottles: 30, 50, 75, 100%UnenrichedUnenriched bottles: 100%bottles: 100%

(to examine nutrient(to examine nutrient--limited growth)limited growth)

NONO3 3 : NH: NH44: PO: PO44 : Fe = 7.5: Fe = 7.5µµM : 0.5M : 0.5µµM : 0.5M : 0.5µµM : 1nMM : 1nM

MesoplanktonMesoplankton--FreeFree SW SW ＋＋ ParticleParticle--Free SWFree SW

ExperimentsExperimentsFebruary to October 2003 (monthly) February to October 2003 (monthly)

Vertical Distribution of Vertical Distribution of PhytoPhyto-- and Zooplankton Biomassand Zooplankton Biomass

* No data

0 20 40

0

10

20

30

50

75

100 Jun. Aug. Oct. Nov. Feb. Mar. Apr. May Jul. Aug. Sep. Oct.

0 20 40Biomass (mgC m-3)

0

10

20

30

50

75

100

MicroNanoPico

*

*

*

*

*

*

**

*

*

*

*

Phytoplankton Biomass and Community StructurePhytoplankton Biomass and Community Structure

*sea surface only

Bio

mas

s (m

gC m

-2)

Mic

ro-c

ompo

sitio

n (%

)P

ico-

com

posi

tion

(%)

0

500

1000

1500

Micro

Nano (ANF)

Pico

0

25

50

75

100

OtherPico

Cyano

0

25

50

75

100

J J A S O N D J F M A M J J A S OMonth

Pannae

Centric

Thecate MF

Naked MF

*

Zooplankton Biomass and Community StructureZooplankton Biomass and Community Structure

Bio

mas

s (m

gC m

-2)

Mic

ro-c

ompo

sitio

n (%

)M

eso-

com

posi

tion

(%)

*sea surface only

0

500

1000

1500

2000

Meso

Micro

Nano (HNF)

Pico

0

25

50

75

100

Nauplii

Tintinnid

Naked Ciliate

Thecate MF

Naked MF

0

25

50

75

100

J J A S O N D J F M A M J J A S OMonth

Others

Copepoda

Gelatinous

*

2106.7

Growth rateGrowth rate

0

0.5

1

1.5

2

Feb. Mar. Apr. May Jul. Aug. Sep. Oct.

Month

Micro-phyto

Nano-phyto

Other pico-phyto

Cyanobacteria

Bacteria

Max

imum

gro

wth

rate

(day

-1)

Nutrient effects on growth rateNutrient effects on growth rateU

nenr

iche

d gr

owth

rate

(day

-1)

Micro-phytoNano-phyto

Nano & MicroPico

-3 -2 -1 0 1 2

Enriched growth rate (day-1)

-3

-2

-1

0

1

2

-3 -2 -1 0 1 2

Enriched growth rate (day-1)

Other PicoBacteria

Cyano

Vertical Profiles of Temperature and SalinityVertical Profiles of Temperature and Salinity

Dep

th (m

)D

epth

(m)

100

80

60

40

20

0

100

80

60

40

20

0

Month

Temperature (ÞC)

Salinity (PSU)

20

2224

26

28

18

20

22

24

26

28

34.834.6

34.4

34.2

34.6

34.4

34.2

34.8

<34.0 <34.0

>29

J J A S O N D J F M A J JM A S O

sampling date

Relationship between Growth and MortalityRelationship between Growth and Mortality

0

1

2

3

0 1 2 3

Maximum growth rate (day -1)

Other picoCyano

Bacteria

0 1 2 3

Maximum growth rate (day -1)

Micro-phytoNano-phyto

Mor

talit

y ra

te (d

ay-1

)Nano & MicroPico

Carbon Budget in Plankton Food WebCarbon Budget in Plankton Food Web

PicoPico--phytophyto125.6125.6

BacBac172.6172.6

ANFANF212.6212.6

HNFHNF299.9299.9

MicroMicro--phytophyto140.5140.5

MicroMicro--zoozoo38.838.8

MesoMeso--zoozoo46.746.7

Mixing period (February-May)

749.8749.8

110.8110.8

321.8321.8

PicoPico--phytophyto470.0470.0

BacBac1483.91483.9

ANFANF0.00.0

HNFHNF1091.51091.5

MicroMicro--phytophyto27.427.4

MicroMicro--zoozoo74.074.0

MesoMeso--zoozoo93.993.9

2728.72728.7

211.3211.3

167.2167.2

Stratified period (July-October)

Production: mgC m-2

Respiratory requirement : mgC m-2

SummerySummerySeasonal pattern of phytoplanktonSeasonal pattern of phytoplankton

•• Autotrophic nanoAutotrophic nano--flagellatesflagellates and and cyanobacteriacyanobacteria contributed contributed to phytoplankton biomass.to phytoplankton biomass.

•• No seasonal patternNo seasonal pattern was observed for phytoplankton was observed for phytoplankton biomass.biomass.

•• Seasonal phytoplankton dynamics might be affected by Seasonal phytoplankton dynamics might be affected by nutrients from the neighboring watersnutrients from the neighboring waters..

Seasonal pattern of zooplanktonSeasonal pattern of zooplankton•• BacteriaBacteria and and copepods copepods dominated zooplankton biomass. dominated zooplankton biomass. •• Zooplankton biomass Zooplankton biomass increased during the stratified periodincreased during the stratified period..•• Seasonal patterns of biomass might be resulted from Seasonal patterns of biomass might be resulted from

temperaturetemperature--dependent growthdependent growth..Plankton food webPlankton food web

•• Grazing food web was functional Grazing food web was functional along microbial food web along microbial food web during the mixing period.during the mixing period.

•• During the stratified period, During the stratified period, microbial food webmicrobial food web was was predominated predominated and and carbon flow seems to be complicatedcarbon flow seems to be complicated..