Corals already have the genes to survive another 250 years of climate change

A new paper finds that there is already enough genetic variety spread across the Great Barrier Reef to adapt to the imagined “unprecedented” warming coming in the next two centuries. We don’t need to rely on random mutations or consider fantasy solutions of man-made oceanic sunscreens, mass sunshades, or giant reef fans. Corals already have a major immigration program running pretty effectively to juggle 200 million years of genetic material and then spread the successes far and wide. Meddling humans can help things (maybe) by moving a few bits of coral around. That’s it. Cancel the scare please.

Skeptics have been saying this for years — who needs a computer model to predict that the Barrier Reef will adapt? How bad could global warming be? The global oceans span a 32C range and corals prefer the hottest five degrees of that. Indeed, there is a five degree temperature range from one end of the Great Barrier Reef to the other, and corals are clearly, obviously pretty happy about it. Meanwhile, the atmosphere is warming at a mere tenth of a degree per decade. Then there is the well known phenomenon that corals spawn in vast clouds that are so big they can be seen from space and there is a whole new generation of corals every five years. You don’t need to be Nostradamus to figure out that survivors from some parts of the reef will reseed other parts, as they have done for eons. Half of the coral genera around today have been around since the Oligocene (23-34 million years ago).

Corals also adapt to heatwaves by chucking out the algal symbionts that don’t thrive in higher temperatures. So on top of their own genetic adaptability, they can “gear up” in different ways too. In the unlikely event that IPCC climate models are right for the first time in history, corals will cope.

h/t to GWPF which has a library of coral reef science news.

Climate change just shifts this large range slightly south. So what?

If the water gets warmer to the South, Great Barrier Reef corals will probably spread further.

Keppel Island at the far south end has quite a different population:

(A) Locations of sampled populations where mean midsummer month sea surface temperature differed by up to ~3°C. (B) Principal component analysis of water quality and temperature parameters at the sampled locations. Winter.T—10% quantile of winter temperature, Summer.T– 90% quantile of summer temperature, Daily.T– 90% quantile of daily temperature range, Phos–total dissolved phosphorus, Chl–chlorophyll, NO3 –nitrate, Secchi–Secchi depth (water clarity). Locations are colored according to summer temperature as in panel A. (C) Principal component analysis of genome-wide genetic variation (inset–Acropora millepora). Centroid labels are initial letters of population names as in panel A. (D) ADMIXTURE plot of ancestry proportions with K = 2 (the lowest cross-validation error was observed with K = 1). Analyses on panels C and D were based on 11,426 SNPs spaced at least 2.5 kb apart and not including F ST outliers.

Note the paper does not suggest we need to set up a carbon trading scheme to improve coral genetic fitness. We might consider picking up a few bits of coral and spreading them around:

Implications for Reef Management

We found that genetic diversity of Acropora millepora was not yet strongly affected by climate change and that the migration patterns were well positioned to facilitate persistence of the GBR metapopulation for a century or more. Our results underscore the pivotal role of standing genetic variation and migrant exchange in the future metapopulation persistence, suggesting management interventions such as assisted gene flow [41] by moving adult reproductively active colonies or by outplanting lab-reared offspring produced by crossing corals from different populations. With the estimated natural migration rates on the order of 0.1–1% (10–100) migrants per generation, human-assisted genotype exchange could appreciably contribute to the genetic rescue without risking disruption of the natural local adaptation patterns [42]

The authors stress that they underestimated the adaptability of the coral populations in most of their estimates. The only bad news part of their model analysis was that populations might become more sensitive to random heatwaves. Given that this relies on IPCC model forecasts of ocean temperatures, I remain unconcerned.

Despite this capacity for adaptation, our model predicts that coral populations would become increasingly sensitive to random thermal fluctuations such as ENSO cycles or heat waves, which corresponds well with the recent increase in frequency of catastrophic coral bleaching events.

What recent increase in “catastrophic” coral bleaching events? We have no long term good data on historic bleaching events, the extent of bleaching is hotly contested, and corals are already recovering. If there was mass coral bleaching in 1066, and corals didn’t recover til 1086, how would we know?

The Background of Reef Survival

…

Author summary

Coral reefs worldwide are suffering high mortality from severe thermal stress episodes induced by acute ocean warming events. Under the current rate of warming, will corals be gone before the end of this century? Here we combine population genomics with biophysical and evolutionary modeling to investigate adaptive potential of a common reef-building coral from the Great Barrier Reef. To approach this task, we have developed a predictive model of polygenic adaptation in a system of multiple inter-connected populations that exist in a heterogeneous and changing environment. Applying this model to our coral species, we find that populations successfully adapt to diverse local temperatures along the range of the Great Barrier Reef despite high migrant exchange and should collectively harbor enough adaptive genetic variants to fuel region-wide thermal adaptation for another century and perhaps longer. In the same time, the model predicts that random thermal fluctuations will induce increasingly severe coral mortality episodes, which aligns well with observations over the last few decades.

REFERENCES

Matz MV, Treml EA, Aglyamova GV, Bay LK (2018) Potential and limits for rapid genetic adaptation to warming in a Great Barrier Reef coral. PLoS Genet 14(4): e1007220. https://doi.org/10.1371/journal.pgen.1007220

Image: Wikimedia, author Wise Hok Wai Lum: Flynn Reef 2014.

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