利用耳石元素指紋圖研究仔稚魚在河口間的擴散模式—以鰕虎與鯛科為例

Use of otolith elemental signature to study the dispersal patterns of fish larvae among estuaries – a case study of Gobioidei and Sparidae

張美瑜(MEI-YU CHANG)

指導教授 ： 曾萬年

國立臺灣大學/生命科學院/漁業科學研究所/博士(2008年)

https://doi.org/10.6342/NTU.2008.00461

摘要

為了了解仔稚魚在河口域哺育場之間的擴散行為，本研究以臺灣西部沿岸兩棲洄游性鰕虎魚類以及河口依賴型的海洋性鯛科魚類的仔稚魚為目標魚種，藉由其耳石日週輪及元素組成之分析，來了解這些魚類的仔稚魚在不同河口之間的關連性。採用的標本包括1997年於公司田溪（GST）採集到的10種鰕虎仔稚魚，1998年於臺灣西部沿岸的公司田溪、大肚溪（TT）和東港溪（TK）採得的極樂吻鰕虎仔稚魚，1997、1998和2005年在同樣的三個河口採得的黑鯛仔稚魚，以及1998與2005年於公司田溪和大肚溪採得的黃鰭鯛仔稚魚。這些仔稚魚為每月大潮期間以待袋網在漲潮時採集的。利用溶液進樣系統的感應耦合電漿質譜儀（ICPMS）分析全耳石以及水樣的元素組成；水樣是2005年仔稚魚採集期間，於漲、退潮時所採集，並同時測定水溫及鹽度。耳石元素組成分析結果以判別函數解析不同河口之間的仔稚魚之擴散及交流情形。結果如下：
（1）公司田溪河口的10種鰕虎仔稚魚耳石的元素組成有顯著的種間差異。從PCA的分群結果來看，仔稚魚的分群與成魚洄游型態的分群不盡相同，顯示成魚的洄游型態雖有不同，其仔稚魚的微棲地環境卻相似。而仔稚魚在進入孵育場的過程中，有些個體出現偏離正常者棲地的現象，印證了流浪者假說（member-vagrant hypothesis）。
（2）仔稚魚的平均體長、日齡以及成長率，除了東港溪的黑鯛仔稚魚體長明顯小於公司田溪與大肚溪的仔魚之外（p < 0.001），其餘的部分不論是極樂吻鰕虎、黑鯛或是黃鰭鯛，其體長、日齡以及平均成長率都無河口間之差異性存在（p > 0.05）。
（3）耳石元素組成經判別函數分析結果，極樂吻鰕虎仔魚來自原採樣的河口域與月份的判別成功率分別為TT05：93.75%，TK03：94.12%，而GST08、TT08和TK05的判別成功率則均高達100%。顯示不同河口域的極樂吻鰕虎仔魚，大多數留在原採樣河口域，河口域間只有少量或是沒有互相交流的現象。
（4）黑鯛有87.5 ~ 100 %的判別成功率（除了1998年的大肚溪以外，僅20%的判別成功率），黃鰭鯛仔魚有90 ~ 100 %的判別成功率。這些結果顯示北部的公司田溪與南部的東港溪河口中的黑鯛可能是分別獨立的族群，而大肚溪河口中的黑鯛則可能是來自於南、北族群的混合群。但是公司田溪與大肚溪的黃鰭鯛仔稚魚則可能為各自獨立的族群。
（5）水體中共測得Mn、Fe、Co、Ni、Cu、Zn、Cd、Pb、Ca、Sr和Ba等11種元素，AMOVA檢定結果發現不同河口的水體有不同的元素組成，而且這些組成也隨著漲、退潮而改變。顯示不同的河川有各自特有的元素指紋圖，但這些指紋圖會隨著時間改變。
綜合以上結果，可以推論耳石上元素組成的河口間差異，可能是反映了水體環境的變化，因此耳石元素組成可以用來做為追蹤、回推仔稚魚河川起源以及散佈模式的自然標記。經由耳石元素指紋圖的判別函數分析可以探討仔稚魚孵育場的起源河川以及不同河口間子族群的關連性，提供棲地保育及漁業管理單位劃定之參考。

關鍵字

仔稚魚 ； 耳石 ； 元素指紋圖 ； 河川起源 ； 蝦虎 ； 鯛科

並列摘要

In order to understand the dispersal of the fish larvae among estuaries in the coastal waters of western Taiwan, the daily growth increments and elemental composition in otoliths of both river-origin amphidromous goby and estuarine-dependent marine sparids were analyzed. Including 10 species of larval gobies in Gongshytyan Creek (GST) in 1997, larval Rhinogobius giurinus in the estuaries of Gongshytyan Creek, Tatu River (TT), and Tongkang Creek (TK) of western Taiwan, larval black porgies Acanthopagrus schlegi in the same three estuaries in 1997, 1998, and 2005, and larval yellowfin seabream A. latus in GST and TT in 1998 and 2005 were collected by Fyke net set against flood tide during night-time spring tide. The water temperature, salinity, and water samples were also measured and collected in both flood and ebb tide during sampling in 2005. The elemental composition in both otoliths of the larvae and water samples were analyzed by a solution-based inductively coupled plasma mass spectrometer (ICP-MS). Jackknife classification analysis was used to clarify the dispersal and connectance of the metapopulations among estuaries. The results of the findings were listed as follows:
(1) The otolith elemental compositions were significantly different among 10 species of larval gobies. According to the result of PCA, the grouping of the larvae was different from the migratory type of the adults. This indicated that the larvae used similar microhabitat as nursery area, irrespective of different migratory type of the adults. It was also found that some individuals dispersed away from the common habitat. Some vagrant individuals might have drifted away from the population's normal migratory circuit.
(2) The mean total length, daily age, and growth rate of the larvae including larval R. giurinus, A. schlegi, and A. latus were all not significantly different among estuaries (p > 0.05) except the total length of larval A. schlegi in TK which was shorter than that in GST and TT (p < 0.001).
(3) The discriminant function analysis of otolith elemental composition indicated that 93.75-100% of larval R. giurinus could be successfully assigned to their original estuary and birth month. These indicate that R. giurnus is a self-sustained population with minimum connection among estuaries of Taiwan.
(4) Similarly, 87.5-100 % of the larvae of black porgy and yellowfin seabream could be also successfully assigned to their original estuaries. However, only 20% of the black porgy collected in TT in 1998 could be successfully assigned to TT, the rest 80% were from both GST and TK. The low assignment might be due to the mixing by tidal current because the flood tide came from both TK in the south and GST in the north and then merged in the coast of central Taiwan nearby TT.
(5) Eleven elements (Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb, Ca, Sr, and Ba) in the water samples were detected. The elemental composition of the water samples was significantly different between GST and TT, and between flood and ebb tides, indicating that the water elemental signature is river-dependent and changes with time.
In conclusion, the differences in elemental signature in otolith of the larvae among estuaries may reflect the water chemistry of the estuaries and thus the otolith signature can be used as tracer to track their estuarine origin and dispersal among estuaries. Through the analysis of otolith elemental composition by Jackknife classification of discriminant function analysis, the larvae can be successfully assigned to their estuarine origin. This can help us to delineate the habitat conservation and fisheries management unit of the fish in the coastal waters of Taiwan.

並列關鍵字

fish larvae ； otolith ； elemental fingerprints ； estuarine origin ； goby ； sparidae

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