Abstract
Sensitive molecular analyses show that most corals host a complement of Symbiodinium genotypes that includes thermo-tolerant types in low abundance. While tolerant symbiont types are hypothesized to facilitate tolerance to temperature and recovery from bleaching, empirical data on their distribution and relative abundance in corals under ambient and stress conditions are still rare. We quantified visual bleaching and mortality of coral hosts, along with relative abundance of C- and D-type Symbiodinium cells in 82 Acropora millepora colonies from three locations on the Great Barrier Reef transplanted to a central inshore site over a 13 month period. Our analyses reveal dynamic change in symbiont associations within colonies and among populations over time. Coral bleaching and declines in C- but not D-type symbionts were observed in transplanted corals. Survival and recovery of 25% of corals from one population was associated with either initial D-dominance or an increase in D-type symbionts that could be predicted by a minimum pre-stress D : C ratio of 0.003. One-third of corals from this population became D dominated at the bleached stage despite no initial detection of this symbiont type, but failed to recover and died in mid to late summer. These results provide a predictive threshold minimum density of background D-type symbionts in A. millepora, above which survival following extreme thermal stress is increased.
Highlights
Coral cover is declining on reefs around the world through the effects of global and local stressors associated with human activities [1,2,3]
Significant variation exists in associations between coral host and Symbiodinium types [12,13] and may correlate with environmental variation suggesting the potential for local adaptation in coral–symbiont associations
We add new insights to this emerging literature with a field experiment that demonstrates the dynamic nature of coral–Symbiodinium associations
Summary
Coral cover is declining on reefs around the world through the effects of global and local stressors (mostly) associated with human activities [1,2,3]. A major source of variation in coral physiology and stress tolerance results from their symbiosis with photosynthetic microalgae (Symbiodinium spp.). Differences in function and performance by Symbiodinium [7] can affect the growth [8], disease susceptibility [9,10] and thermal tolerance [5,6,11] of coral hosts. Significant variation exists in associations between coral host and Symbiodinium types [12,13] and may correlate with environmental variation suggesting the potential for local adaptation in coral–symbiont associations. As our understanding of the distribution of Symbiodinium within coral species and among geographical locations increases, questions regarding their relative abundance during ambient and stressful conditions, and the effects on coral hosts’ physiology and bleaching susceptibility can be addressed [3]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
