Sometimes I just leave my browser open to some source, like NYTimes.com or Salon.com, and through the day go back and click around. For some reason today it is NewScientist.com, which is an okay science publication but not one that I spend as much time on as it might seem today.
Anyway, there's an article about how coral reefs make dimethyl suflide (DMS), which can act as a cloud condensation nucleus... a nucleation site for water for those of you who prefer. So basically the coral makes a mucous with a ton of DMS, which mixes around in the shallow water where coral live. Then the wind blows (a common assumption in atmosci!), and sea spray is whipped up into the atmosphere. Inside the sea spray is lots of DMS, which apparently was puzzling in the 1970s (I don't know why they "didn't know about DMS in the 1970s"). The DMS might then help make clouds around the reefs.
There has been a Gaia hypothesis floating around for quite a long time by which the Earth system acts as an organism, reacting to changes to maintain itself. I think it dates back to Lovelace in the 1970s, but I'll have to check. One example used DMS, but not from coral. It went something like: (1) assume some kind of global warming, (2) low clouds are reduced because the boundary layer warms and dries (questionable), (3) more sun gets to the sea surface, (4) phytoplankton go crazy with biological activity, (5) they DMS produced by the phytoplankton gets into the atmosphere to act as cloud condensation nuclei (CCN), (6) the increased cloudiness acts to decrease the sunlight at the surface and reflects it back to space (cooling the atmosphere). Of course, that effect has never been quantified, but it is possible in some sense.
The coral reefs can now be considered in the same way, I guess. However, from the coral reefs that I know about, they tend to grow in places that are more sunny more often. Like the tropics instead of the subtropics. So increasing the CCN there might lead to more clouds, but they'd probably be small cumulus, not big thick layers of stratocumulus, so that probably wouldn't be much of a feedback. There might be a possibility of a local precipitation feedback, but the importance of such an effect on climate is questionable. It deserves some study, but it won't save humanity... or the coral reefs.