地中海寡營養鹽地區， nano級 (2~20μm)微細鞭毛蟲攝食自營性和異營性 pico級 (0.2~2μm)浮游生物

Reporter: Wang ciou-jyu

Objective

• Vertical and spatial distribution of the autotrophic and heterotrophic prokaryotes

• assess the relative importance of nanoflagellate grazing on their population in the Mediterranean.

Introduction

0.2~2μm

• Heterotrophic bacteria

• Synechococcus

• Prochlorococcus

2~20μm

1. Heterotrophic nanoflagellates

2. pigment

nanoflagellates

20~200μm

Ex: ciliate

1983 年 Azam microbial loop

• 地中海是一個高度貧營養地區，所以此地區的生產率和攝食率均偏低• 地中海有一個明顯的貧營養階層• Nutrient depletion ： 遞增• productivity : 遞減• Chlorophyll concentration : 遞減

西 東

• Concerning consumption of cyanobacteria by nanoflagellates, the few existing field studies are based on community approaches such as size fractionation , dilution , specific inhibitors , disappearance rates of prey analogues (Landry et al.,1984;Kudoh et al., 1990; Caron et al., 1991; Liu et al., 1995; Reckermann and Veldhuis,1997)

• A single study exists based on direct estimates from food vacuole content analysis of nature marine heterotrophic nanoflagellate populations (Dolan and Simek,1999).

Method

採樣時間 : 1999 年 6/4 ~7/2

採樣深度 : 0-200m

• Nanoplankton ， picoplankton population and biomass estimates

1. 螢光顯微鏡

Bac Syn(FDC) 記數NF

2.Flow cytometry

分 HF , PF

Syn , Prochlorococcus 流式細胞儀進行分析

3.Conversion to biomass

( NF 分三種大小 : ＜ 3μm , 3-5μm, 5-10μm )

• Heterotrophic bacterial productionBacterial production 3H-labell leucine

•Heterotrophic bacterial grazing measurementStation: 2 (120m) 、 4(75m) 、 6(75m) 、 8(75m) 、 9 (60m)

Bac. growth rate in situ ＝BP

BB

Maximum fluorescence depth

a. Analysis of ingested FLB in food vacuoes

20ml

<20μm 4h

b. Disappearance rate of FLB in long-term incubations(42h)

<20μm <100μm <0.8μm

42h 各取 10ml 算 bac , FLB

各取 30ml 算 HF

FLB ingestion

rate

Bac. Ingestion rate

FLB disappearance

rate

c. Changes in bacteria in 0.8μm and <20μm(HF present) screened sea water (42h)

d. The consumption of bacterial by HFClearance rate ＝ 105× body volume h-1 (Fenchel, 1982b)

ml

f h×

bac

ml＝

bac

f h

no predator predator

Ingestion rate (g)

μnet= K μnet= K - g

Synchoccus consumption by HNF

• 使用螢光顯微鏡觀察 SYN in food vacuoles

• 由於表層的 SYN 色素微弱，所以看深度 50-120m

• Ingestion rate

Results & discussion

60m

120m

葉綠素最大值︰東邊到西邊 由深到淺 (Turley et al.,2000)

>105

102~104

Pnf : 7000 cells/ml 75m 1500 cells/ml

HF: 3200 cells/ml 1300 cells/ml

▲75~100m

50~75m

Small protist (<3μm) dominated the bacterivore assemblage

75

13

現場細菌成長率較快

Oligotrophic area:

Pico- and nanoplankton abundance and biomass

dominance of heterotrophs

(Gasol et al.,1997; Sanders et al.,2000)

heterotrophs ＞ autotrophs

1. Consumption of heterotrophic bacteria

2 倍

∵ 有 30% 的 HF(>3μm) 會攝食比細菌大的生物

1. 45-87%

Clearance rate ＝ 105× body volume h-1

PN 沒有攝食 FLB

similar result: other marine (Caron et al.,1991); freshwater system (Simek et al.,1997)

所以不排除此研究的 PN 有可能拒絕攝食 P.diminuta FLB

FLB decrease <20μm

16-30%

<100 μm

18-34%

90% of bacterial consumption was due to grazers <20μm

90% of bac -> HNF

2. Consumption of cyanobacteria

•Few clearance rates of HF on natural synechococcus population are reported in the literature.

•HN : 0.01~0.15 cells HN-1(mean ± SD, 0.06 ± 0.04)

0.5-45%

( 平均 13%)

FDC : 2.6 ~ 40%St1:33%, St2:33%, St3:22%Other stations:7~17%

HF seem to select against FDC

Some other types of predators probably select for FDC, keeping the population under control.

Other potential SYN sources of mortality :

ciliates, phagotrophic phytoplagellates, viruses.

NF grazing rates on syn.

: =10-100 倍

(Pitta et al.,2001) 地中海Ciliate grazing rate

s on syn.

But ciliate abundance (low): 4-350cells/l

Moderate consumption

• 5%of PN ingesting SYN

• 地中海 (Christaki et al.,1999b; Dolan and Simek, 1999):

Few ingested synechococcus among PN, suggesting a minor role of phagotrophic phytoflagellates, in synechococcus consumption in this region.

• Prochlorococcus cells are ingested according to their standing stock.(Reckermann and Veldhuis,1997)

• HN were unable to consume their cell production.

100 倍

Clearance rate ×ml

餌料= Ingestion rate

27%

Conclusion

bacteria

HNF

90%

Synechococcus Prochlorococcus

27% carbon

PNF5%