Volume 17, Number 37: 10 September 2014
In a jaw-dropping paper published in Marine Biology, Roff et al. (2014) remind us of the great devastation caused by the 1997/1998 El Niņo Southern Oscillation (ENSO), which resulted in the loss of approximately 16% of the world's coral reefs and was, in their words, "particularly severe in French Polynesia, where unprecedented mortality of massive Porites was observed in lagoonal sites of Rangiroa Atoll." And in a study designed to learn what happened subsequently, they returned 15 years later to the site of greatest devastation to resurvey the size structure and extent of what coral yet remained alive. And what did they find?
The six scientists report that their survey "revealed an abundance of massive Porites colonies rising from the shallow lagoonal floor," where "the relative cover of recently dead skeleton within quadrats declined from 42.8% in 1998 to zero in 2013." And at the colony level, they found that "the proportion of Porites dominated by living tissue increased from 34.9% in 1998 to 73.9% in 2013, indicating rapid recovery of recent dead skeleton to living tissue rather than transitioning to old dead skeleton."
In discussing these amazing results, the six scientists - hailing from Australia, France and the United States - say that "such rapid post-bleaching recovery is unprecedented in massive Porites and resulted from remarkable self-regeneration termed the 'Phoenix effect,' whereby remnant cryptic patches of tissue that survived the 1997/1998 ENSO event regenerated and rapidly overgrew adjacent dead skeleton." And thus the question arises: How did the coral do it?
One possibility suggested by Roff et al. is that bleaching acts as a selective cause of mortality on susceptible genotypes within colonies, citing van Oppen et al. (2011). And if so, in their words, "it may be possible that the surviving patches of tissue that survived the 1998 bleaching event represent mutant genotypes that are better adapted to thermal stress, rather than remnant existing genotypes," for "if this were the case," as they continue, "then the Phoenix-like recovery of these newly evolved genotypes would confer rapid thermal tolerance in massive Porites at a colony scale over short timescales (i.e., 15 years)."
In any event, as Roff et al. write in the concluding sentence of their paper, "our observations of remarkable regenerative capacity and the 'Phoenix effect' in massive Porites following mass coral bleaching-related mortality provides an optimistic scope for resilience in an otherwise gloomy future for the world's coral reefs."
Sherwood, Keith and Craig Idso
References
Roff, G., Bejarano, S., Bozec, Y.-M., Nugues, M., Steneck, R.S. and Mumby, P.J. 2014. Porites and the Phoenix effect: unprecedented recovery after a mass coral bleaching event at Rangiroa Atoll, French Polynesia. Marine Biology 161: 1385-1393.
van Oppen, M.J.H., Souter, P., Howells, E.J., Heyward, A. and Berkelmans, R. 2011. Novel genetic diversity through somatic mutations: fuel for adaptation of reef corals? Diversity 3: 405-423.