'Inoculation: not a cure-all but worth trying'

This blog has hosted a short exchange about 'inoculation' as a way of trying to save coral reefs (posts 1 and 2 are here and here). Here is Andrew Baker's answer to critics:

As I wrote previously, I believe that attempts to boost the natural abundance of heat resistant symbionts by “inoculation” (for want of a better word, this is not a very good one as it comes with a lot of unintended meaning) would indeed be useful and worthwhile if we selectively target the oldest and largest colonies on selected reefs. In some circles this is indeed viewed as naïve, either because prospective algae won’t establish symbioses with these corals (Ove [Hoegh-Guldberg]’s view), or these symbionts will never propagate across reefs to make much of a difference (Charles [Shepard]s’ view). Both of these are valid concerns. I myself avoided this line of research for several years as it’s a bit of a “Go to Jail” card for those of us in the research community (“Do Not Pass Go, Do Not Collect £200”). Ove and Charles comments bear witness to that concern, and I am sure their viewpoints are not unique.

However, in my view, the main justifications for attempting inoculation are that: (1) some of the most important reef builders are already known to be able to host these symbionts (which addresses Ove’s worries regarding “evolutionary switching”); and (2) one doesn’t need to affect entire reefs to potentially make a detectable difference (Charles’ concern), especially if large and/or old colonies are targeted. If we lose these colonies it may take hundreds of years to replace them, so it stands to reason we might want to take extraordinary steps to keep them alive. This might not be a strategy that we can use to save the world’s coral reefs from climate change. However, it might help us keep more corals alive, and preserve reef function in the near-term, while we figure out what other options become available to us (I agree with Charles’ pragmatic view that we never know what the future holds in store).

In the Caribbean, for example, large colonies of the important reef-building star coral Montastraea faveolata are naturally capable of hosting (heat tolerant) Symbiodinium in clade D. The problem is that relatively few of them contain sufficient numbers of these symbionts to prevent mortality in the event of bleaching episode. I have suggested that large scale bleaching and mortality events result in shifts on reefs to favor more Symbiodinium D, and this ends up making these reefs more resistant to future bleaching events. Many mechanisms can account for these shifts in symbionts. However, the problem is that, regardless of mechanism, these shifts are only significant when the bleaching is severe enough to cause dramatic mortality.

These reefs seem to have to pass through the eye of a (hot) needle for their constituent corals to end up being more thermally resistant, and many of them simply don’t make it. I am suggesting that we should attempt to boost the natural abundance of heat tolerant symbionts so that these shifts can be made with less accompanying mortality. Ove and Charles are both correct in identifying problems that will prevent this action from being some kind of miraculous cure-all. It won’t be. However, we should not ignore the fact that an ability to improve the survivorship of corals during a bleaching event is nevertheless an improvement on where we stand now. Currently, we understand the basic cellular physiology of bleaching, but are still unable to make a difference when thermal anomalies pass through and cause widespread bleaching. This is not very satisfactory when all is said and done.

I believe that an attempt to boost the natural abundance of heat resistant symbionts to encourage species-by-species “survivorship networks” on reefs, although ambitious, controversial and high-risk, nevertheless has considerable value as a research activity. This is not just because it might actually work (and increase coral survivorship on critical reefs), but also because the need to demonstrate a willingness to act (to mitigate and alleviate the effects of climate change), as opposed to the need to observe (to predict and understand them) has never been greater. I agree with Ove that blind optimism is no recipe for success. However, reasonable scientific gambles that have half a dozen reasons why they might work are still work attempting, even if there are twice as many reasons they won’t work. It would be a sad state of affairs indeed if, faced with the greatest environmental challenge in history, we excluded activities that might improve survival trajectories because we decided they wouldn’t work in advance of actually trying them.

Thanks to all those who commented.