Abstract
The coral symbiont Symbiodinium plays important roles in the adaptation of coral to environmental changes. However, coral-Symbiodinium symbiotic associations are not well-understood in the South China Sea (SCS) whilst considering environmental factors and host taxa. In this study, next-generation sequencing of the internal transcribed spacer region 2 (ITS2) marker gene was used to explore the symbiotic associations between Symbiodinium and five typical coral species across tropical and subtropical reef regions of the SCS. The results showed that Acropora sp., Galaxea fascicularis, Platygyra lamellina, and Sarcophyton glaucum exhibited distinct Symbiodinium compositions between tropical and subtropical reef regions, whereas Porites lutea had stable Symbiodinium compositions. More heterogeneous Symbiodinium compositions among different coral species were observed in the tropical region, but there were no statistically significant differences in Symbiodinium compositions among different coral species in subtropical reef regions. There was a correlation between the Symbiodinium compositions and environmental factors, except for the composition of P. lutea. Symbiodinium subclades D1, D2, C71, C71a, C21, C3b, and C161 were primarily explained by the seawater temperature, nitrate, ammonia, and phosphate. Several host-specific Symbiodinium subclades (e.g., C15, C15.6, and C91) were observed in P. lutea as well. The findings of this study demonstrate the relationship of Symbiodinium diversity with coral hosts and the environment are helpful for elucidating the adaptation of corals to global climate change and anthropogenic disturbance.
Highlights
Coral symbiont Symbiodinium, a photosynthetic algae that is a dinoflagellate, plays a central role in the adaptation of corals and the maintenance of coral reefs (Kemp et al, 2014)
Symbiodinium subclade compositions among different coral species were more heterogeneous in the Sanya Bay (SY) reef region, but there were no notable differences in Symbiodinium subclade compositions among the explored coral species in the XW and Daya Bay (DY) reef regions
The Symbiodinium subclade C3 was dominant in most explored corals, the subclade D1 was mainly detected in corals in the SY reef region, and the subclade C161 was mainly associated with corals in the XW and DY reef regions
Summary
Coral symbiont Symbiodinium, a photosynthetic algae that is a dinoflagellate, plays a central role in the adaptation of corals and the maintenance of coral reefs (Kemp et al, 2014). Monitoring Symbiodinium compositions and their mutually symbiotic associations with different coral hosts under different environmental stresses is essential to further project the fate of corals and to develop coral reef conservation strategies. Previous studies have revealed that the environment could influence Symbiodinium compositions, as well as their mutually symbiotic associations with corals, and the breakdown of Symbiodinium-coral associations because of the effects of climate change and anthropogenic disturbance that would contribute to dramatic declines in coral reef cover worldwide (Hughes et al, 2003, 2017; Hoegh-Guldberg et al, 2007). Certain coral species still maintain highly stable coral-Symbiodinium symbiotic associations over broad geographical ranges and temperature gradients, as well as through bleaching events or after transplantation (LaJeunesse et al, 2004a,b; Stat et al, 2009; Thomas et al, 2014). Most corals can adapt to environmental changes by changing their symbiont communities, but some corals (most notably the genus Porites) remain common on devastated reefs, even though they fail to change their symbiont communities
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