海洋沿岸底棲生物群聚之特性、角色及驅動因子

Abstract

沿岸的底棲群聚受到環境影響，並隨著時空的差異而改變。在某些群聚裡，基本物種與其他物種間的生物交互關係可以調控生態動態及生態系功能，這些基本物種因而被視為關鍵生物。然而，人為及氣候的壓力因子正在改變這些交互關係，但目前對於這些底棲群聚的改變趨勢仍不確定，可能源於尚未釐清群聚原本的組成結構所致。底棲群聚的異質性經常在大空間尺度下被探討，此異質性可能造成這些群聚在不同的生物地理區間有不同的動態；小空間尺度的底棲群聚變異對解釋群聚重組和有效的保育政策擬定相當的重要，但卻較少被討論。臺灣地處珊瑚大三角的北邊，同時也是熱帶及亞熱帶的交接處，這樣的地理位置使臺灣成為一個適合探討此異質性的天然實驗室，除了可以認識多樣化的底棲群聚，也可以調查這些群聚在全球氣候變遷下分別扮演的角色，還能找出造成底棲群聚變異可能的非生物因子。本論文以臺灣為例，在研究架構上，先描繪多個不同組成及分佈的群聚。並假設在面對氣候變遷時，這些群聚會有完全不同的反應，所以在其他礁區物種面對氣候變遷時，這些群聚也會扮演不一樣的角色。有鑑於此，此論文接著探究這些底棲群聚在礁區魚類因暖化而往極區擴張分布時可能扮演的角色，最後找出有哪些非生物因子會使底棲群聚產生空間上的變異。研究結果顯示，臺灣有著相當高的底棲異質性，迥然不同的海洋環境造就了多樣的底棲群聚，同時證實了這些底棲群聚在礁區魚類的分佈往極區擴張的過程中扮演著極為重要的角色。除此之外，本論文也證明人為活動的影響使得台灣周邊海域底棲群聚受到干擾並產生相變，這可能會使底棲群聚在氣候變遷下無法維持原本的群聚組成，也顯示臺灣現行的保育政策無法解決造成底棲群聚衰退的根本問題。總體來說，此研究因考量到本地底棲群聚的獨特性及限制性，將可為台灣海洋保育管理提供有效的方針。

Coastal benthic communities vary in space and time influenced by environmental conditions. In some communities, foundation species emerge as key organisms upon which biotic interactions are important by regulating ecological processes and undermining ecosystem functioning. Human and climatic stressors are modifying interactions in place, yet the trajectory of a given community remains uncertain as it will often depend on its initial configuration. Benthic heterogeneity is commonly recognized at large spatial scales and causes contrasting benthic dynamics across biogeographic provinces. Yet, the small-scale variations in communities are rarely considered despite being equally crucial in interpreting benthic reconfiguration and supporting efficient conservation strategies. The location of Taiwan, directly to the north of the Coral Triangle and at a transition area between tropical and subtropical realms, makes the country an exciting location to this heterogeneity. Indeed, the island constitutes a natural laboratory to recognize benthic communities, examine differential roles associated with these communities under climate change, and identify abiotic drivers causing the differences. In this thesis, I first delineated communities with distinctive composition and distribution, hypothesizing they may bear contrasting responses and roles under climate change. I then explored the possible roles of both tropical and subtropical benthic habitats in the poleward migration of reef fishes. Finally, I scrutinized the abiotic drivers causing spatial heterogeneity in the benthic assemblage in Taiwan. My results showed that benthic assemblages in Taiwan are highly heterogenous and that divergent communities emerged in contrasting environmental conditions. Those communities were further demonstrated to be critically important for some reef fishes considering their poleward migration under global warming. However, benthic communities were proven to be under the influence of human activities that contribute, country-wide, to the omnipresence of a degraded community. Anthropogenic disturbances may hinder the long-term persistence of communities under climate change and expose that the current conservation effort in Taiwan has failed to address the root causes of degradation. Overall, this work opens an opportunity for the development of tailor-made management of the benthic communities (and associated services), taking into consideration local specificities and constraints.