2010-2012年間東海底棲性魚類群聚之時空變化

Abstract

本研究於2010-2012年間，藉由海研一號研究船以底拖網採集東海底棲魚類，並分析魚類群聚與環境因子之相關性。魚類群聚不論季節皆依近岸離岸而有明顯分別，且與深度和鹽度梯度相關，溫度在春秋兩季可能是影響群聚組成的主要環境因子。生物多樣性、物種豐富度和均勻度等生物指數皆與葉綠素濃度、表層營養鹽呈現負相關而與溶氧呈現正相關，近岸的缺氧區域主要優勢物種為小型鰕虎魚(Amblychaeturichthys hexanema)，顯示大多數魚種無法存活於缺氧環境。魚類群聚在季節上的變動於離岸區域相較穩定，近岸區域則在夏秋兩季有明顯差異，其物種組成的改變主要來自於鰕虎科之優勢物種A. hexanema的比例降低，而舌鰨科與石首魚科比例升高。特別是在2011年夏季低氧的區域，生物指標於秋季時略為上升且單一物種A. hexanema的優勢比例下降，顯示魚類群聚在低氧影響過後，物種組成逐漸趨向多樣化，但短暫恢復期對於整體底棲魚類資源的回復仍是不足。穩定碳氮同位素的分析顯示，在初級生產力較低的秋季，底棲魚類仍主要仰賴海洋表面的基礎生產力而非陸源的有機碎屑。魚體碳同位素值在近岸較離岸高，此結果反映了在夏秋兩季底棲魚類利用海洋表層的藻華。氮同位素值在空間上的變異較小而秋季略高於夏季，此結果可能顯示在夏季營養鹽供應充足，浮游植物同化作用過程中對於氮同位素的選擇性利用，而較低的氮同位素值再經由食物鏈反映至底棲魚類。本研究透過底棲魚類群聚與碳氮同位素值的分析，連結環境變動與魚類群聚的變化，可對於東海區域底棲魚類資源與環境變動之關係提供更多資訊。

In order to understand the demersal fish assemblages and its link to the environments, beam trawl surveys and hydrographic measurements were conducted across the East China Sea continental shelf in 2010 - 2012. The results suggested that the fish assemblages varied with the depth and salinity gradients with significant difference in composition between inshore and offshore areas. Water temperature might be an important factor in shaping the spatial pattern during spring and autumn periods. Bio-indices (e.g. diversity, richness and evenness) showed negative correlations with Chl. a concentrations and nutrients levels and positively correlated with dissolved oxygen. The eutrophication and subsequent hypoxia in the inshore area during summer periods favored the high dominance of opportunistic species (Amblychaeturichthys hexanema). These results suggested the negative impacts of eutrophication and hypoxia on the demersal fish assemblages. Seasonal changes of fish compositions were only found in the inshore area, which may attribute to the succession of dominant species. In addition, we found moderate recovery of fish communities after summer hypoxia but the short-periods of alleviation from stressful condition might not be adequate to compensate the simplified assemblages during hypoxia. Despite the variation of primary productions in different seasons, d13C value of fish muscle suggested that in situ primary production was the main food sources to the demersal fish rather than the terrestrial POM. d15N of demersal fish were higher in autumn than in summer, which might attribute to the preferential uptake of isotopic lighter N source or the shift in baseline rather than elongation of food chain. Our results provided further insights into the demersal fish assemblages in the ECS, and the influences of environmental parameters on fish compositions.