以耳石微細結構與穩定性同位素組成探討深海底棲魚類之生活史

Abstract

耳石為魚類自然生物礦化沉積形成的碳酸鈣結構，其微細結構可以用來判讀魚類的年齡以及生活史階段，而沉積於其中的化學訊號則記錄下魚類經歷過的環境資訊。本研究共分析7科16種深海底棲魚類耳石上的微細結構、穩定性碳氧同位素以及化學組成，用以探討其生活史，這些魚類分別採樣自台灣東北部海域與南海北部。以氧同位素所推算的溫度變化顯示在本次研究的物種中，可分為有發育性垂直遷移(ontogenetic vertical migration)的種類以及具底棲性仔稚魚的種類。具有發育性垂直遷移的魚類可依不同的分類群和棲地深度有不同的生活史模式，例如有柳葉幼生(leptocephalus)的通鰓鰻科(Synaphobranchidae)和海蜥魚科(Halosauridae)、產下浮性卵和浮游仔稚魚的鼠尾鱈科(Macrouridae)和鼬魚科(Ophidiidae)以及胎生的棕斑盲鼬鳚(Barathronus maculates)等，不同的魚種有不同的仔稚魚棲息深度與沉降時的發育階段。另外，黑頭魚科和黑首燧鯛(Hoplostethus melanopterus)則是在仔稚魚時期即在與成體棲息深度類似的深海底棲環境生活。碳同位素顯示了有垂直遷移習性的魚類，其幼齡時有較高的代謝率而在遷至深處時則明顯變低，無垂直遷移或遷移距離較短的魚類則是隨著個體發育無明顯的代謝率改變。 本研究結果顯示了不同分類群和不同棲息深度的深海底棲魚類有不同的生活史模式並且由耳石所建立出的生活史和前人的研究相符。此多樣化的生活史暗示了深海生物不同的適應策略以及深海生物多樣性。

Otolith is a metabolically inert calcium carbonate that has been used to study the life history of fish. In this study, we investigate the life histories of 16 species of deep-sea demersal fishes, which were collected in the Pacific off north-eastern Taiwan and northern South China Sea by examining otolith microstructures, stable isotopic and chemical compositions. Otolith δ18O profiles suggested two major life history patterns; some species had ontogenetic vertical migration and some species were non-migrators. Vertical migrations were found in oviparous Synaphobranchidae, Halosauridae, Macrouridae, Ophidiidae and viviparous Barathronus maculates but with different migratory distances and timing, although they all had pelagic larvae. On the other hand, with demersal larvae, Alepocephalidae and Hoplostethus mwlanopterus spent most of their time on similar depths from larvae to adults. Otolith δ13C profiles suggested that fishes with longer vertical migration distance had higher metabolic rate in their early life-history stages than the later stages. However, the metabolic rate did not varied for the fishes living in the certain depth from larvae to adults. Life history patterns of deep-sea demersal fishes varied among different taxonomic groups and habitat depths. The results were comparable to previous studies. Different life histories indicated different adaptations or life strategies to the deep-sea environment.