2008年夏季東海底棲性魚類多樣性及海洋生物與環境之相關性

Abstract

東海擁有廣泛的大陸棚區域，並且由於長江輸入大量營養鹽，東海也具備了高營養鹽、高初級生產力以及豐富漁業資源的特性。然而，統計數據指出，從1960年代開始，從長江輸入東海的營養鹽含量已經增加了10倍以上，並且經常造成優養化及水體缺氧的情況發生。另一方面，長江三峽大壩的興建及運作已被證實了會大幅減少營養鹽排放入東海的量。然而，在此兩個反向的作用下，目前東海的營養鹽狀態對底棲生物群聚的影響仍是未知且值得關注的。由於過去數十年的營養鹽過量輸入，我們能夠推測目前東海的營養鹽狀態仍是過盛的，並且很可能會對造成底棲生物群聚造成負面的影響。 為探討此一問題，本研究於2008年夏季7月份利用底拖網在東海海域進行了從近岸至離岸的穿越線調查。總共採集了3935隻底棲性魚類，分屬於71種，41科。在物種組成方面，有明顯的南北以及離岸遠近的差異。生物多樣性指數則是以離岸較遠的測站有較高值，而又以靠近長江河口及杭州灣的測站A1和B1有著最低的生物多樣性。生物與環境間的相關分析結果顯示，各測站間物種組成的差異和緯度、深度、溶氧、磷酸鹽類及亞硝酸鹽類有較密切的相關性。此外，生物多樣性指標和底部溶氧呈現顯著正相關，且和營養鹽及葉綠素濃度呈顯著負相關。 以上結果顯示了東海的底棲魚類物種組成不僅受魚類的生物地理學偏好所影響，同時也會因物種間對營養鹽濃度梯度及缺氧的情形的耐受性不同而有所差異。總結來說，目前東海的營養鹽狀態仍是過盛的，且其後續的效應，如：有機物質堆積以及底部缺氧皆會對底棲生物群聚造成危害。

The East China Sea (ECS) was characterized by nutrient-rich condition, high primary productivity and high fishery yield, due to the massive input of nutrient from Changjiang (CJ). However, the anthropogenic nutrient load from CJ has increased over 10-fold since 1960’s, and caused frequent eutrophication and hypoxia events. In addition, construction of Three Gorges Dam has been proved to reduce the nutrients discharge. The effects of present nutrient status on the benthos assemblage were still obscure. Nevertheless, we presume that the nutrient status in the ECS is still excessive, and may injure the benthos communities in the ECS. To verify our assumption, oceanographic survey was conducted across the inshore-offshore transects. Totally 3935 dermal fish including 71 species were collected by the beam trawl. Fish species composition varied greatly between northern and southern sites as well as between inshore and offshore sites. Higher diversity appeared at offshore sites and lowest diversity occurred at the inshore site close to Changjiang Estuary. The fish community structure among each site was related to depth, latitude, dissolved oxygen, PO4 and NO2. Besides, the fish species diversity is significantly positive correlated to dissolved oxygen and negative to concentrations of various nutrients and chlorophyll a. This result implied that the fish communities were not only determined by specific biogeographic distribution, but also by the nutrients and hypoxia conditions. In conclusion, the nutrient status in the ECS is still redundant, and its follow up consequences, including organic matters accumulation and benthic hypoxia have negatively impacted the community of demersal fish.