熱帶與亞熱帶珊瑚礁魚類能量流動模式差異

Abstract

生態功能意指系統內的能量流動（生物量變化），反映生態系統的健康度。而珊瑚礁魚類在珊瑚礁生態系的生態過程 (ecological process) 中扮演重要角色，且受海洋環境中的生物與非生物因子所影響，為評估珊瑚礁健康度的重要指標。臺灣差異性極大的沿岸環境造就多樣的底棲生物群集，連帶塑造不同的魚類組成，使得台灣成為探究珊瑚礁魚種組成改變及其能量流動變異的理想地點。本研究選定五個區域（墾丁、綠島、蘭嶼、東部和北部區域）橫跨熱帶與亞熱帶。魚類與底棲生物群集分別使用水下立體影像系統及樣框沿著穿越線進行調查。魚類能量流動 (energy flow) 使用三個指標：生物量 (standing biomass) 、生產力 (productivity) 和轉換率 (turnover) 作為代表。底棲生物利用珊瑚網 (CoralNet) 將其分類為不同的形態功能群 (morpho-functional group) 。結構複雜度、底質類型、初級生產量和海面溫度的數據來自底棲調查以及衛星資料。利用廣義線性混合模型分析魚類能量流動的內在（生物性，形態功能群）及外在（非生物性，環境及人為因素）的影響因子。本研究發現魚類的能量流動模式呈現區域性的差異，亞熱帶區域的能量流動具有較高的異質性，而食浮游生物的雀鯛為主要的貢獻者；熱帶及過渡區域的能量流動主要貢獻者為鸚哥魚及刺尾鯛，此外在墾丁和東部的低能量流動指出該區域的珊瑚礁健康度已經下降且所實施保育成效可能有限。珊瑚礁生態系中的五個內在（殼狀珊瑚藻、表覆形石珊瑚、柱形石珊瑚、指形八放珊瑚和大型皮質藻類）及四個外在因子（穩固底質、海水表面溫度、基礎生產力和大尺度側面曲度）被發現會影響魚類能量流動，在維持生態功能中扮演重要的角色。本研究提供台灣五個區域中珊瑚礁魚類能量流動的基線資訊，並奠定未來探討珊瑚礁生態功能變化等相關研究重要的基礎。

Energy flows (change of biomass) reflect the status of ecosystem functioning, which are associated with reef health. Reef fishes are involved in important ecological processes that promote ecosystem functioning and respond rapidly to biotic and abiotic changes, making them ideal indicators for assessing coral reef health. Taiwan, with its diverse benthic communities that thrive in contrasting environments, is an ideal location for studying variations in energy flows associated with changes in fish composition. Fish and benthic communities were surveyed by stereo-video and photo-quadrat transects in five regions spanning tropical and subtropical latitudes (Kenting, Orchid Island, Green Island, East and North Taiwan). Fish assemblages were characterized using three energy flow metrics (standing biomass, productivity, and turnover), which were further compared between regions, fish family, and dietary groups. Benthic communities were assessed for their composition in morpho-functional groups using automatic identification from CoralNET trained on a local dataset. Structural complexity, substrate type, primary production, and sea surface temperature were obtained from benthic surveys at study sites and satellite database. Generalized Linear Mixed Models were used to identify intrinsic (biotic, i.e., morpho-functional groups) and extrinsic (abiotic, i.e., environmental and anthropogenic factors) drivers of fish energy flows. Our results show regional specificities in the patterns of fish energy flows. The subtropical region, where planktivorous damselfish have a major influence, has greater heterogeneity in energy flows. Parrotfishes and surgeonfishes are important contributors to energy flows in the tropical and transitional regions. The unusual weak energy flows observed in Kenting and East Taiwan reveal a deterioration of coral reef health and raise concerns about the effectiveness of marine conservation in these regions. Five intrinsic (crustose coralline algae, corticated macrophyte algae, columnar hard coral, encrusting hard coral, and digitate octocoral) and four extrinsic drivers (stable substrate, rough scale profile curvature, sea surface temperature, and primary production) were associated with fish energy flows, which may provide leverages for maintaining ecosystem functioning. Overall, our study provides baseline information of fish energy flows among coral reefs in Taiwan, which is important to evaluate changes experienced by coral reefs through the Anthropocene.