Shallow-water coral communities in Taiwan and the systematics of deep-sea precious corals
Chang-Feng Dai 教授（Institute of Oceanography, National Taiwan University）
2015年11月25日（水）16:00～17:00
Hexacorals and octocorals are widely distributed in the waters surrounding Taiwan. The distribution of shallow-water reef-building corals show a clear latitudinal gradient from southern (ca. 300 species) to northern (ca. 110 species) Taiwan in a distance of approximately 350 km and this pattern is consistent with those of sea surface temperature distributions. However, the decrease of scleractinian species along latitude is not homogeneous among families. Active reef-builders such as Acroporidae, Pocilloporidae and Poritidae decrease rapidly, while other families such as Faviidae, Agariciidae and Lobophylliidae remain similar. This pattern suggests that the limits of physiological adaptation of different corals may be the main factor controlling their latitudinal distribution. On local scale, soft corals dominate certain reef areas in Nanwan Bay, Green Island, and Dongsha atoll. The soft coral communities in Nanwan Bay and Dongsha atoll are mainly composed of Alcyoniidae, while that in Green Island is composed of Xeniidae. The life history traits of Xeniidae indicate they are fugitive species, while Alcyoniidae species can tolerate storm disturbances and show great persistence. The difference of life history traits may explain their dominance in certain reef areas. On temporal scale, long-term dynamics of coral communities in northern and southern Taiwan showed that the species composition changed and coral coverage decreased remarkably during the past 20-30 years. Drastic changes were mainly induced by natural disturbances (typhoons or mass bleaching), while gradual changes were driven by anthropogenic factors.
The deep-sea precious corals (Octocorallia: Coralliidae) have been harvested as jewelry for hundreds of years. Due to resource depletion, their conservation has become a critical issue and the species delineation have been increasingly studied using molecular-based approaches. We used 110 specimens collected from major museums worldwide and newly collected specimens to study the systematics of Corallidae. Eight mitochondrial genes and one nuclear gene were applied as molecular markers to construct their phylogenetic relationship. The phylogenetic trees of Coralliidae showed that there are two monophyletic clades with distinct mitochondrial gene orders, and Clade I could be further divided to two subclades (IA and IB). Detailed morphological studies revealed that species in Clades IA, IB, and II could be defined by unique morphological features corresponding to those of Corallium Cuvier 1797, Hemicorallium Gray 1867, and Pleurocorallium Gray 1867, respectively. Therefore, we proposed to resurrect the 3-genera taxonomy of Coralliidae by Gray (1867) to replace the 2-genera system defined by Bayer and Cairns (2003). According to the revised taxonomic system, there are 7, 15 and 12 species in Corallium, Hemicorallium, and Pleurocorallium, respectively. This system based on the coherence of phylogenetic relationships and morphological features can be applied to the assessment of population status of Corallidae.