Thursday, August 09, 2007

'Inoculate' coral to save the tough ones?

Commenting on Regional Decline of Coral Cover in the Indo-Pacific (noted on Coral Bones here), Andrew Baker says:
This is an important study that shows that reefs in the Pacific have surprisingly similar levels of coral cover despite being very different in terms of their environment, physical oceanography and level of human impact. It also reveals considerable variability in coral cover from year to year, while also making the case that Indo-Pacific reefs were considerably impacted by the 1970s.

I find it interesting that the impacts of mass bleaching events (such as the 1997-98 El Nino) are quite difficult to detect given the dramatic year-to-year variation in coral cover preceding these events. Instead of suffering dramatic and obvious reductions in coral cover as a result of bleaching, reefs affected by mass bleaching appear to lose their year-to-year variability instead, as if they are being inexorably squashed towards some future minimum level. Instead of the usual, exuberant, boom-and-bust cycles of coral cover you might expect on healthy reefs, we are instead witnessing the whittling away of reefs to their most tenacious component species.

The fact that year-to-year variability in coral cover seems to have disappeared over the last decade might indicate that we are losing the more susceptible coral species from reefs, and we are instead being left with more resistant, hardy species that are able to withstand the relatively poor environmental conditions we are leaving them with. These surviving corals are likely to include varieties that are more resistant to coral bleaching (as documented by Baker et al., Nature 2004).

We should do more to try and understand what makes corals resistant to bleaching, and explore whether there are any actions we can take to boost the natural adaptive capacity of corals to survive environmental changes. This might include attempts to inoculate the largest and oldest colonies on reefs with reserves of heat tolerant symbiotic algae (that are usually lost from corals during bleaching events) that might help them survive bleaching events, and so help perpetuate the essential framework upon which reefs depend.

However, one has to wonder at what point does one draw the line in this decline and ask "When is a reef not a reef"? That is an unanswered question that I fear will become a research focus in coming years.

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