南中國海及台灣東北海域深海底棲性生物的多樣性及食物網分析

Abstract

台灣四周環海，周邊海域的海底地形多變化，在淺水域的生物研究非常廣泛，但深海域的生物研究相對缺乏。深海海域廣大，維持著高度的生物多樣性，在早期的研究中指出，深度在1000-2000米的深水域是生物多樣性最高的區域。深海區域的底棲生態系，食物來源多為海洋表層所沉降下來的有機碎屑，這些有機碎屑大多是表層的浮游生物及少部分的生物排遺、屍體；但到達海洋底部的有機物質其實不到表層生產力的10%，因此本研究嘗試探討在極度缺乏食物的深海底棲生態系統的運作機制。本研究使用底拖網於2008、2009年夏季分別於南中國海及台灣東北海域採樣了不同深度的6個測站，藉此比較深海區域與淺海區域的生物多樣性，並藉由測定生物組織中的穩定性碳氮同位素，來架構生物間的食物階層及食物來源。生物多樣性指數在深度1000~2000米的測站為最高，而淺海域的透光區比微光區域高；深海底棲生態系可分為5個食物階層、淺海則為3個食物階層；底棲生態系的食物來源多為大洋性沉降的有機物質，只有台灣宜蘭近海（St.5）因靠近淡水輸入處，食物來源為陸源性的有機物質。在先前的研究表示，有機物質在沉降的過程中，會被附著於其上的微生物持續利用，造成深度越深，有機物質的δ15N值會越高，我們也發現懸浮濾食者、捕食者/食腐者、魚類、蟹類分群的生物，其δ15N值與深度為正相關；在底泥撿食碎屑者、蝦類、所有底棲生物分群中的δ15N值與深度沒有顯著的關係。底棲生態系的有機物質來源不一定只侷限於大洋表層所沉降的有機物質；缺乏食物的深海底棲生物藉由有機質不斷循環利用來維持穩定的生態系；深度造成有機物質有較高的δ15N值，表示沉降性有機質是底棲性生物的重要氮源。

The seas around Taiwan are characterized by various marine habitats. But very few benthic communities were surveyed in the deep-sea areas. The deep-sea areas are inhabited by diversified organisms with highest biodiversity between the depths of 1000-2000 meter. Most deep-sea ecosystems rely on the organic particles, such as planktonic and mammal carcasses or bodys, sinking from the euphotic and mesopelagic zones to the seafloors. However, only 1–10% of the material produced in the euphotic zones can reach to the deep-sea floors. Therefore, this study aim to evaluate the biodiversities between deep-sea areas and shallow areas by sampling 6 stations with bottom trawling at different depths from South China Sea and eastern coast of Taiwan in summer 2008 and 2009.. Another aim is to understand the food source and the food web structure of demersal organism by stable isotopic anaylsis. The highest biodiversities were found at the depth between 1000 to 2000 meters, and the biodiversities in the euphotic zone were higher than the twilight zone. Five trophic levels were identified in the deep-sea benthic ecosystem, and only 3 trophic levels were found in shallow benthic ecosystem. Organic materials produced in the euphotic zone were the main food for the benthic ecosystem except the St.5 in I-Lan coast, which received mostly land-derived organic matter. Previous studies showed that organic matter during the sinking process will be repeatedly catabolized by micro-organisms and enrich the δ15N of the organic matter. We also found that δ15N of suspension feeders, predator/scavengers, fishes and crabs was positively correlated with the depth. The δ15N of deposit feeder, shrimp, and all benthic organisms had no significant relationship with depth. Food sources of benthic ecosystem are not necessarily confined to the ocean surface. In the deep-sea benthic communities, the organic matter was continuously recycled to maintain a stable ecosystem. Higher δ15N for the organisms in the deeper zone indicated that organic matters sinking from the euphotic zone were the important nitrogen source to deep-sea benthic communities.