A recently published article in Nature Communications uses a land-use modeling exercise to address how future deforestation interacts with climate change to affect sedimentation rates on coastal reefs in Madagascar. In summary they find that while climate change is likely to have negative impact on river discharge (which is good for corals if those discharges are sediment laden), the sedimentation on local reefs is still likely to increase due to increasing sediment loads caused by decreasing forest cover. Basically, because deforestation in Madagascar is so extreme in rate and extent, even with reduced precipitation, sediment loads will increase without vegetation holding the soil together. More below…
This was sort of an interesting paper for me. While there are some limitations that might affect the accuracy of their projections, I do think it is a worthy exercise. Coral reefs face a litany of challenges in the future decades. Some of these challenges are global, as in climate change. Others are local (e.g., overfishing, coral harvesting, eutrophication, sedimentation). This is the first paper I have seen that attempts to link coral fate using both of these scales, with some interesting results. Now to some limitations: first, climate change is predicted to have myriad effects on oceanic systems, namely acidification. This paper seems to omit these changes and just models the effects of climate change restricted to the watershed and it’s discharge of sediments. That’s fine, and of course a very, very important part of understanding the various interacting changes coming, but we just have to remember that this paper is about sedimentation only. How sediments and acidification interact would be a cool project as well. Anyone know of one?
Another important aspect of this paper is how conservation and restoration of uplands can have important implications for coastal ecosystems. It seems that we all to often forget how integrated these ecosystems are. By restoring forests in Madagascar the authors estimate that sedimentation could be reduced by 20-80%. Marine systems are projected to face increasingly adverse conditions, restoring the uplands would not only help protect the terrestrial systems, but the marine ones as well. I wonder if the reverse is true.
As always, remember I am not a coral scientist, modeler, or climate change specialist. If you have anything to add that might increase the accuracy or otherwise clarify my interpretation, please do so!
Maina, J., de Moel, H., Zinke, J., Madin, J., McClanahan, T., & Vermaat J.E. 2013. Human deforestation outweighs future climate change impacts of sedimentation on coral reefs. Nature Communications. 4:1968. DOI: 10.1038/ncomms2986