南灣海域浮游植物群聚組成之時空變異研究

Abstract

本論文主要研究南灣海域浮游植物類群組成與時空變異，進而分析與探討環境因子對此浮游植物時空變異的可能影響。南灣為一半封閉的海灣，灣內長期紀錄到區域性的冷水湧升現象，一般而言季節或氣候改變形成的湧升流會將富含營養鹽的深層水抬升至表水層，此湧升現象可能影響浮游植物的生長與群聚組成。研究地點為南灣海域，樣水採集利用海研一號與海研三號進行，浮游植物群聚組成透過浮游植物的指紋色素鑑別，其它測量的環境因子包括：溫度、鹽度、營養鹽濃度 (NO3-、NO2-、PO43-、SiO42-)、顆粒性有機碳 (POC)、溶解態有機碳(DOC) 與異營性細菌生產力 (BP) 等。研究期間共計於2002/11 ~ 2003/6完成四個航次 (分別代表四季) 之採樣、測量與分析。結果顯示南灣海域中 (葉綠素甲除外) 主要浮游植物色素包括葉綠素乙(Chlorophyll b)、玉米黃質(Zezxanthin)、藻褐素(Fucoxanthin)與19’-hexanoyloxyfucoxanthin等四種，其相對應的浮游植物主要分別為綠藻 (Chlorophyceae)、藍綠藻 (Cyanophyta)、矽藻 (Bacillariophyta) 以及Prymnesiophytes。就季節變異而言，代表浮游植物總生物量的葉綠素甲濃度以冬季最高 (0.44 ± 0.04 mg Chla m-3)，其次為秋季 (0.30 ± 0.06 mg Chla m-3) 與夏季 (0.30 ± 0.08 mg Chla m-3)，春季最低 (0.19 ± 0.08 mg Chla m-3)。浮游植物種類組成方面，秋季四類浮游植物組成比例相近；冬季綠藻組成比例最高 (33%)，Prymnesiophyceae (27%) 和矽藻 (23%) 次之，藍綠藻最少 (16%)；春季浮游植物的種類組成比例以藍綠藻最高(58%)，綠藻、矽藻與Prymnesiophyceae的含量與比例均較前兩季低；夏季則是以綠藻 (39%) 和藍綠藻 (34%) 最多，Prymnesiophyceae次之 (19%)，矽藻含量與比例最低 (8%)。論文中亦探討影響浮游植物時空變化的可能環境因子，結果發現浮游植物的生長和季節間的種類組成變化可能與無機營養鹽和溫度有顯著相關。此外，浮游植物總量與POC和DOC間亦有顯著相關，由於異營細菌生長主要受控於有機碳濃度的多寡，此結果建議南灣海域中異營性細菌的生長可能間接受浮游植物生產力的影響。

The purpose of this thesis is to study the spatial and temporal variations of the phytoplanktonic composition and to understand the potential regulatory factors that effect on species composition of phytoplankton in the Nan-Wan Bay, Southern Taiwan. The Nan-Wan Bay, a semi-closed bay, has been recorded a local upwelling for a long time. In general, the seasonal or climatic upwelling lifts the deep-nutritional water to the surface layer of ocean; in addition, this upwelling is likely to change the growth and the composition of phytoplankton. Samples were collected on board R/V Ocean Research I and Ocean Research III during November 2002 to June 2003. Composition of phytoplankton was distinguished by using the pigments. Other measured variables including temperature, salinity, dissolved inorganic nutrients, particulate organic carbon (POC), dissolved organic carbon (DOC), as well as bacterial production (BP). Results showed that the major pigments of phytoplankton, except Chlorophyll a, in the Nan-Wan Bay are Chlorophyll b, Zeaxanthin, Fucoxanthin, and 19’-hexanoyloxyfucoxanthin, which stand for Chlorophyceae, Cyanophyta, Bacillariophyta, and Prymnesiophytes, respectively. Seasonally, concentration of Chl a was the highest in winter with mean ± sd values of 0.44 ± 0.04 mg Chla m-3, intermediate in autumn (0.30 ± 0.06 mg Chla m-3) and in summer (0.30 ± 0.08 mg Chla m-3), and the lowest values in spring (0.19 ± 0.08 mg Chla m-3). As for phytoplankton composition, previous four classes of phytoplankton almost contributed equally in biomass in autumn. The highest composition ratio of phytoplankton was found in Chlorophyceae (33%), intermediate in Prymnesiophyceae (27%) and in Baciliariophyta (23%), and the lowest ratio in Cyanophyta (16%). Cyanophyta, however, contributed more than 58% of phytoplankton composition in spring. In summer, the composition ratio of Chlorophyceae, Cyanophyta, Prymnesiophyceae, and Bacillariophyta was 39 %, 34%, 19%, and 8%, respectively. Further analyses suggested that growth and composition of phytoplankton might be affected by nutrients and temperature. Besides, significant relationships were observed between phytoplankton biomass versus POC and DOC. Since bacterial production was significantly related with organic carbon, it suggests that BP might be affected indirectly by phytoplankton in the Nan-Wan Bay.