|Abstract: ||本研究於2006年6月至2011年10月間，利用海研一號及二號共計9個航次之採樣。其樣本以主成分及典型相關分析法探討東海仔稚魚豐度、組成多樣性及優勢物種分布結構與水文因子間之關係。以及利用群集分析法探討群聚組成變動與水團分布之關係，並說明優勢物種日本鯷(Engraulis japonicas)及七星底燈魚(Benthosema pterotum)在東海陸棚的分布情形。在水文部分共計有287個測站資料，經檢定不同季節之表層溫度顯著不同，另外，於夏季航次則發現鹽度結構亦有顯著差異，顯示東海環境隨著季節推移海域環境亦有變化。東海海域為黑潮水、臺灣海峽水及黃海水所匯集之處，其環境變化因海流勢力消長而有所影響。黑潮水擁有高溫、高鹽、高密度且低葉綠素的特性，臺灣海峽水則擁有溫暖且高鹽的特性，黃海水顯示特徵為低溫及低鹽，研究結果證實於夏季探測期間，黑潮與臺灣海峽水一同流入東海陸棚，反之，於冬季探測期間大陸沿岸水夾帶黃海冷水南下影響東海海域，夏季航次也顯示長江沖淡水影響範圍與幅度變動劇烈。 生物採集部分共計有174個測站，共採集仔稚魚59,340尾，鑑定出仔稚魚139科183屬401種，總豐度為176,862 ind./1000m3，豐度比例大1%之優勢種分別為E. japonicus (70.61%)、B. pterotum (7.91%)、Sillago japonica (4.59%)、Bregmaceros arabicus (1.49%)、Setipinna tenuifilis (1.40%)、Sigmops gracilis (1.32%)、Saurida elongata (1.29%)、Diaphus B group (1.15%)及Vinciguerria nimbaria (1.03%)，且海域內仔稚魚日夜間之豐度並無顯著差異，但季節間豐度與物種組成差異明顯。以前10優勢物種來說，所有夏季航次的優勢物種以E. japonicas及B. pterotum重複出現，另外，春夏季出現之優勢物種有E. japonicas (2.82~68.18%)及B. pterotum (2.30~3.14%)，秋冬季則有S. gracilis (4.40~10.43%)、Diaphus A (3.14~6.31%)及B (4.94~11.93%) group，且春夏季豐度較高，其平均約在738~2,716 ind./1000m3間變動，而秋冬季較低，約在150~753 ind./1000m3間變動。除秋季外，仔稚魚豐度變動亦與環境因子有關，夏季時，其變動方向與溫度趨勢相同，並有與鹽度趨勢相反之情形，春季時，仔稚魚豐度則明顯受到葉綠素濃度趨勢的影響，冬季仔稚魚豐度則與底層溶氧量多寡較為一致。在仔稚魚種類數上，其變動隨環境鹽度與表層溫度遞增，但隨表層溶氧量及浮游動物豐度遞減，均勻度與底層溫度則呈現正相關且與葉綠素呈現負相關。另外，仔稚魚豐度與長江沖淡水流量有明顯正相關，而浮游動物豐度與長江沖淡水流量呈現負相關，且在長江沖淡水範圍內物種豐富度較低，顯示在長江沖淡水範圍內有極優勢物種大量出現，導致物種豐富度低，此結果也反映仔稚魚歧異度隨環境鹽度增加而增大。 在水團及仔稚魚群聚分析上，隨季節與水文環境之推移，仔稚魚群聚可概分為: 沿岸水群、沿岸混合水群、臺灣海峽水群、臺灣海峽混合水群、黑潮水群、黃海水群等6類。物種方面，黑潮物種主要為鑽光魚(gonostomatid)、光器魚(phosichthyid)及燈籠魚科(myctophid)魚種，Auxis spp.、B. pterotum及Bregmaceros spp.常見於夏季臺灣海峽水及其混合水中，而Moolgarda spp.、scorpaenid spp. 則於冬季臺灣海峽水及其混合水中，其中，scorpaenid物種亦於黃海水中出現。此外前兩項優勢物種E. japonicas與B. pterotum豐度分布與環境關係顯示，前者豐度與葉綠素濃度呈現正相關，但與表層鹽度呈現負相關，其豐度集中也受到長江沖淡水量與月齡之影響。後者之豐度影響因子則依其發育階段不同而有所改變，於發育階段初期與表層溶氧和浮游動物豐度呈現明顯的負相關，隨著成長到發育階段後期則與葉綠素濃度多寡有關。|
In this study, nine cruises that stationed 287 times were conducted from June 2006 to October 2011 onboard Ocean Research I and II to investigate how ichthyoplankton assemblages are affected by the hydrological environment in the East China Sea. Principal components and canonical correlation analysis were used to illustrate the relationships between the abundance, composition, diversity, and dominant species of larval fish and the hydrological environment. Cluster analysis was implemented to examine the variation of ichthyoplankton assemblages and composition structure in the East China Sea. The spatial distribution of Engraulis japonicas and Benthosema pterotum, the two dominant species among the samples, are described in this study. Regarding hydrographic conditions, various structures in surface temperature were observed among the seasons, and significantly distinct salinity structures were observed during summers as caused by a runoff of diluted water from the Yangtze River (<31), indicating that hydrographic environments varied seasonally. Water from the Kuroshio Current, the Taiwan Strait, and the Yellow Sea was observed to seasonally meet in the East China Sea. The results indicated that water from the Kuroshio current and Taiwan Strait flowed into the continental shelf of the East China Sea during the summer, and that cold water flowed along the coast of Mainland China because of the southward flow of China’s coastal current with water from the Yellow Sea during the winter. In addition, during the summer, diluted water from the Yangtze River caused drastic changes. Regarding biological samples, 59,340 larval fish were collected from 174 stations. The larvae gathered comprised 401 taxa belonging to 139 families and 183 genera, yielding a total abundance of 176,862 ind./1,000 m3. The top nine dominant species of larval fish (>1%) included E. japonicus (70.61%), B. pterotum (7.91%), Sillago japonica (4.59%), Bregmaceros arabicus (1.49%), Setipinna tenuifilis (1.40%), Sigmops gracilis (1.32%), Saurida elongata (1.29%), Diaphus B group (1.15%), and Vinciguerria nimbaria (1.03%). The larval abundance exhibited a significant difference among seasons (Mann–Whitney U test, p < .05), but not between day and night in each cruise. In spring and summer, the two dominant species were E. japonicas (2.82–68.18%) and B. pterotum (2.30–3.14%), respectively, whereas the dominant species included S. gracilis (4.40–10.43%), and Diaphus A (3.14–6.31%) and B (4.94–11.93%) groups in autumn and winter. The average larval abundance range during spring and summer was between 738–2,716 ind./1,000 m3, which is higher than that during autumn and winter (150–753 ind./1,000 m3). Larval abundance was also associated with the environment except during autumn. It was significantly and positively correlated with temperature but negatively correlated with salinity in summer; moreover, it was positively correlated with chlorophyll in spring, and positively correlated with dissolved oxygen in winter. In addition, the abundance of fish larvae was significantly positively correlated with the runoff of the Yangtze River, which was the opposite effect on the abundance of zooplankton. The species richness of larval fish increased with salinity and surface temperature, but decreased with surface dissolved oxygen and zooplankton abundance. Evenness of larval fish was positively correlated with bottom temperature, but negatively correlated with chlorophyll a. Finally, six assemblages were recognized based on cluster analysis and water mass analysis. They were the coastal water group, Taiwan Strait water group, coastal mixed water group, Taiwan Strait mixed water group, Yellow Sea water group, and Kuroshio water group. The most dominant species of larvae in the Kuroshio group were the gonostomatid, phosichthyid, and myctophid species. During summer, the most dominant species in Taiwan Strait water were Auxis spp., B. pterotum, and Bregmaceros spp. In the same waters, the most dominant species in winter were Moolgarda spp. and scorpaenid; scorpaenid also appears in the Yellow Sea water group. In addition, we focused on the distribution of E. japonicas and B. pterotum, the two most dominant species in this survey. The former was positively correlated with chlorophyll a but negatively correlated with surface salinity. A substantial correlation was also observed between E. japonicas and the runoff of the Yangtze River; the distribution of this species was possibly influenced by the diluted water from the Yangtze River and the phases of the moon. The latter exhibited varied distribution depending on the development stage. In early development stages, a substantial and negative correlation was observed with surface dissolved oxygen and zooplankton abundance; in later development stages, a positive correlation was observed with chlorophyll a.