利用個體性狀評估八放珊瑚適應性策略

Abstract

在自然與人為干擾下，世界各地許多珊瑚礁發生由石珊瑚為主的群聚被其他底棲生物群聚取代。而八放珊瑚因具較高生理可塑性，在未來珊瑚中可能成為優勢物種。然而，並非所有八放珊瑚在面對干擾有相同反應，因此需要了解八放珊瑚物種的生理差異及對珊瑚群聚動態的影響。本研究提出一架構，利用個體生理性狀（trait）調查八放珊瑚種內變異性，並藉此推測適應性策略。本研究在北台灣不同季節採集九種常見且型態容易辨認的物種。個體性狀利用Gower distance產生表現性狀矩陣（performance trait matrix），並以PCoA視覺化為表現性狀空間（performance traits space）。表現性狀棲位（performance trait niche）是依照物種佔據性狀表現空間劃分，並比較物種的棲位大小。各物種表現性狀矩陣的中心點位置以及散布各別為外在與內在因子造成種內變異，分別利用PERMANOVA以及PERMDISP檢測季節間差異。最後利用k平均數叢聚（k-means clustering）將個體分為k個均值群，推測為適應環境的對策（tactic）。結果顯示軟珊瑚具最大表現性狀棲位，相對地柳珊瑚具最小表現性狀棲位。此外大部分種內變異能被外在因子解釋。k平均數叢聚支持127個個體中有五種對策存在。根據物種的不同對策組合，推測有五個策略（strategies），並且將兩個具最多及最少對策的策略，假設為廣適者（generalist）與狹適者（specialist）推測可能與適應能力有關。本篇研究進一步支持在面對各種環境時，相同物種的不同個體可能表現不同生理狀態。據我們所知，本研究為首次將種內變異性整合進八放珊瑚的適應性策略，此可能進一步改善在環境變動下珊瑚礁生態系統的預測。

Strangled by natural and human disturbances, scleractinians are substituted by alternative taxa in most of the reefs around the world. In these conditions, octocorallians could become more abundant in tomorrow’s reefs because of their higher physiological plasticity to environmental conditions. However, all octocorallians may be not equal for facing changes. Therefore, there is an urgent need to appreciate physiological differences among octocoral species and their possible consequences for reef community dynamics. Using a trait-based approach, this study proposes to set up a framework for delineating octocoral adaptive strategies on the basis of their intraspecific variability in key physiological parameters. Accordingly, we seasonally sampled 9 common and morphologically well-defined species in the benthic assemblages from the north of Taiwan, where colonies experience large variations in environmental conditions along the year. Individuals were compared using their trait similarity by Gower distance (i.e., performance trait matrix) and visualized into a performance traits space with a Principal Coordinates Analysis (PCoA). Performance trait niches were delineated by species occupation on performance traits space and the sizes were further examined across species. For each species trait performance matrices among seasons, the centroid positions and dispersions represented extrinsic and intrinsic causes of intraspecific variability respectively. These two causes were separately examined by permutational multivariate analysis of variance (PERMANOVA) and homogeneity of multivariate dispersions (PERMDISP). An unsupervised clustering algorithm, k-means clustering, was later used to identify k homogenous groups among individuals. The results show that the Alcyonarians have the largest performance trait niches and contrasts with the Gorgonian having the lowest ones. Most intraspecific variability could be explained by extrinsic factors affecting individual physiology. The k-mean algorithm supports the existence of five clusters that we suggest may depict a variety of tactics among the 1 individuals analyzed. According to their combination, five strategies were identified that vary between two extremes typifying ‘generalist’ and ‘specialist’ species. These findings further support strong difference in physiological performance among octocorals, as well as a variety of physiological status among the individual of the same species for facing contrasted environments. To our knowledge, this study is the first to consider intraspecific variability for a better understanding of octocoral adaptive strategies, which could further improve the predictions on reef ecosystems in a time of changes.