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發育垂直遷徙

Abstract

早期生活史為深海底棲魚類重要的發育階段，透過族群分布的研究發現多數物種會進行發育垂直遷徙(ontogenetic vertical migration)，藉由改變棲息深度以利發育及生存。魚類耳石由碳酸鈣沉積形成，其微細結構可以用來判斷魚類的年齡與生活史階段，而耳石的穩定性氧與碳同位素資訊(δ18O, δ13C)則記錄個體經歷的環境與生理資訊。本研究所使用的材料包含由研究船採集自台灣東北部及西南部、南海北部及東部海域的魚類樣本(深度> 500 m)，以及大溪漁港採集的樣本(深度< 500 m)，分析了共8科17種深海底棲魚類的耳石微細結構與穩定性同位素組成，以個體角度探討各物種發育垂直遷徙之生活史。 研究結果顯示耳石δ13C與δ18O分別反映代謝與環境溫度的變化，並且能夠證實個體具有發育垂直遷徙的行為，並推算早期生活史之深度。早期生活史是否採取發育垂直遷徙與生殖策略有關：例如唯有產沉性大卵的黑頭魚科(Alepocephalidae)早期生活史因孵化體型大，而沒有發育垂直遷徙。在底棲時期多數物種具有發育垂直遷徙的行為，藉由耳石δ13C與δ18O相關性研判，應與能量的權衡有關，且不因其生殖策略而有所差異，顯示發育垂直遷徙是深海底棲性魚類中普遍採取的一種生活史策略。另外，成體棲息深度會影響到具有發育垂直遷徙物種的遷徙程度與模式：例如鼬鳚科中較深海的物種，遷徙模式以稚魚階段行漂浮性方式下降為主，沉降後深度變化不大，普遍而言，棲息在越深的物種其遷徙程度越大。 本研究顯示了不同分類群、生殖策略、棲息深度的深海底棲魚類採取不同的生活史模式，而各生活史階段在垂直深度上的多樣變化，暗示發育垂直遷徙為適應深海環境之重要策略以及深海魚類之多樣性。

Early life history stage of deep sea demersal fishes is crucial to population survival. Population and community studies had reported that deep sea demersal species ususally have ontogenetic vertical migration (OVM) which they change their inhabiting depth in order to survive and develop. Fish otolith microstructure has been used to determine the ages of fish and life history stage. And stable isotope composition of oxygen and carbon (δ13C, δ18O) within calcium carbonates can record the environmental signals and physiological status of fish. Fish samples were collected in northeastern and southwestern Taiwan, north and east continental slope of South China Sea by research vessel (depth > 500 m), and from fish collected at DaiShi harbor (depth< 500 m). In this study, we investigate the ontogenetic vertical life histories of 17 species within 8 families of deep sea demersal fishes in autecological perspective, by analyzing otolith microstructure and stable isotope composition. The results suggest that δ13C and δ18O reflect metabolism and environmental temperature respectively, prove individual to have OVM, and provide the habiting depth of early life stage of species. Whether early life history takes OVM or not is determined by reproductive tactics. (e.g., slickheads with large demersal egg with sufficient nutrient and development will not take OVM.) In settlement stage, most of the species take OVM unrelated to reproductive tactics and this is correlated to energy trade-off by the judge of δ13C-δ18O correlation, which suggests that OVM is a common life strategy in deep sea demersal fishes. Adult’s habitat depth may affect the distance and patterns of OVM. (e.g. deeper cusk eels migrate more and depend most of the migration on pelagic juvenile.) Generally, OVM distance increases with increasing habiting depth. Life history patterns of deep sea demersal fishes varied among taxonomy, reproductive tactics and habitat depth, displaying different adaptations or diverse life strategies to the deep sea environment, indicating the importance of OVM.