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

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 advantage to 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- fractionation (2 μm) (iii) maximum growth rates of phytoplankton and its mortality rates 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 14 C 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 μ= k- g X μ X k

K Trace Metal Solution: Na 2 EDTA·2H 2 O 41.6 g FeCl 3 ·6H 2 O 3.15 g Na 2 MoO 4 ·2H 2 O (6.3 g/L dH 2 O) 1.0 ml ZnSO 4 ·7H 2 O (22.0 g/L dH 2 O) 1.0 ml CoCl 2 ·6H 2 O (10.0 g/L dH 2 O) 1.0 ml MnCl 2 ·4H 2 O (180.0 g/L dH 2 O) 1.0 ml CuSO 4 ·5H 2 O (9.8 g/L dH 2 O) 0.5 ml Distilled water 1.0 L (μ 0 = k 0 + g). The ratio μ 0 /μ max is used to assess the impact of inorganic nutrient enrichment on algal growth and estimate the nutrient sufficiency 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 μ Max Unenriched g0g0 k0k0

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 picophytoplankton has 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% of the picoplanktonic cell density. diatom bloom.

Maximum growth and mortality rates based on Chl a μ Max : -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