Phytoplankton seasonal dynamics in a Mediterranean coastal lagoon: emphasis on the picoeukaryote community

JOURNAL OF PLANKTON RESEARCH VOLUME 27, NUMBER 9, PAGES 881–894, 2005

報告學生 : 王榮

指導教授 : 蔣國平 博士

118 119 120 121 122 123 124 125 126 127 128 129 130 Longitude (

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Y a n g t z e R i v e r

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已完成航次 : 2007 年 7 月

細菌 (bacteria) 與藍綠細菌 (Synechococcus)在東海陸棚海域 成長與被攝食速率的時空分布

INTRODUCTION

Picophytoplankton (class size: 0.2–2 μm)

Synechococcus and Prochlorococcus

picoeukaryotic algae

irradiance and water temperature (Kuosa,1991; Agawin et al., 1998, Vaquer et al., 1996).

Due to its small cell size, picophytoplankton has a competitive advantageto acquire nutrients in resource-limited environments (Raven, 1998),

In contrast, under high nutrient levels, is dominated by large phytoplankton (mainly diatoms)

The smallest photosynthetic picoeukaryote Ostreococcus tauri (Chre´tiennot-Dinet et al., 1995,Courties et al., 1994).

diatoms, cryptophyceae, dinophyceae and small phytoflagellates (Vaquer et al., 1996,Gangnery et al., 2003). picophytoplankton escapes grazing by filter-feeding bivalves because of their small size (Dupuy et al., 2000).

(i) seasonal variations in the abundances of picoeukaryotes and cyanobacteria,

(ii) the relative contribution of picophytoplankton to Chl a biomass and primary production by means of size-fr

actionation (2 μm) (iii) maximum growth rates of phytoplankton and its mortality r

ates due to microzooplankton grazing.

METHOD

Water samples were collected at 8:30 AM inside oyster farming zones (Fig. 1) by immersing two 20-L polycarbonate (PC) jars to a depth of 0.1 m and were immediately brought to the shore laboratory.

Chl a concentration

Phytoplankton primary production was estimated using the standard 14C technique (Steemann Nielsen, 1952).

The biomass-specific primary productivity [P/B, mg C (mg Chl a) -1 h-1] was calculated as the carbon fixation (P) per unit of Chl a biomass (B).

Phytoplankton abundances were estimated by flowcytometry

Dilution protocols

100% 80% 60% 40% 20%

<1000μm <0.2μm

Assumption ：1.Specific growth rate of prey is not density dependent

2.Predation is a direct linear function of prey abundance

y = -0.12x + 0.15R2 = 0.95

0

0.04

0.08

0.12

0.16

0 0.2 0.4 0.6 0.8 1 1.2

Treatment

Net

GR

(1/d

)

μ= k- g X

μ

X

k

K Trace Metal Solution:

NaNa22EDTA·2HEDTA·2H

22OO 41.6 g41.6 g

FeClFeCl33·6H·6H

22OO 3.15 g3.15 g

NaNa22MoOMoO

44·2H·2H22O (6.3 g/L dHO (6.3 g/L dH

22O)O) 1.0 ml1.0 ml

ZnSOZnSO44·7H·7H

22O (22.0 g/L dHO (22.0 g/L dH22O)O) 1.0 ml1.0 ml

CoClCoCl22·6H·6H

22O (10.0 g/L dHO (10.0 g/L dH22O)O) 1.0 ml1.0 ml

MnClMnCl22·4H·4H

22O (180.0 g/L dHO (180.0 g/L dH22O)O) 1.0 ml1.0 ml

CuSOCuSO44·5H·5H

22O (9.8 g/L dHO (9.8 g/L dH22O)O) 0.5 ml0.5 ml

Distilled waterDistilled water 1.0 L1.0 L

(μ0 = k0 + g).

The ratio μ0 /μmax is used to assess the impact of inorganic nutrient enrichmenton algal growth and estimate the nutrientsufficiency for phytoplankton growth (Landry et al., 1998).

淨成長率 = 原始成長率 - 攝食率。稀釋比

μ = k - g X Enriched

g

μMax

Unenriched

g0

k0

Variations of physical and chemical parameters

the annual mean contribution of picophytoplankton (29%) (Courties et al., 1994;Chre´tiennot-Dinet et al., 1995; Vaquer et al., 1996),

In warm and productive waters, the decreased contribution of picophytoplanktonhas been hypothesized to result from increased loss rates, such as strong grazing pressure (Agawin et al., 2000).

Autotrophic picoeukaryotes numerically dominated the phytoplankton community, and represented between 55 and 99.7% ofthe picoplanktonic cell density.

diatom bloom.

Maximum growth and mortality rates based on Chl a

μMax: -0.23~2.63

g: -0.28~1.13

total chlorophyll a (Chl a)

> 2 μm Chl a fraction

< 2 μm Chl a fraction

(Chaetoceros sp. and Skeletonema costatum, respectively).

indicating that grazing pressure on larger algae was negligible in bottle incubations.

Maximum growth and microzooplankton grazing rates based on flow cytometry

PEUK GROWTH RATE: 0.31~2.44

CYAN GROWTH RATE: 0.42~1.64

PEUK GRAZING RATE: -0.09~1.66

CYAN GRAZING RATE: 0.25~1.17

Nutrient enrichment impact

since nano- and micro-phytoplankton (in particular diatoms) in the Thau lagoon are mainly controlled top-down by bivalve suspension feeders (Dupuy et al.,2000), which were excluded from incubations.

Phytoplankton carbon assimilation

Factors controlling seasonal variations in phytoplankton growth

the annual variations in growth rates displayed a strong seasonality which could be related to seawater temperature and/or irradiance.

THE END