Fw: Julian Sprung's Email

Bruce Carlson carlson at soest.hawaii.edu
Fri Aug 25 20:05:09 EDT 2000


Let me add a comment to your message (below).  Objects in shallow water
exposed to strong sunlight can and do get warmer than the surrounding water.
I can detect that all the time in our outdoor coral tanks (but I haven't
taken the actual temperatures of the corals to know how much warmer).  But
interestingly (and I'm sure others will corroborate this), during the 1998
bleaching event in Palau, corals in very shallow water survived much better
than those just a few feet deeper.  You'd think these shallow corals would
get extremely hot and of course there is no water flow when exposed to air.
Presumably corals on these these shallow water reefs are acclimated/adapted
(?) to extreme heat and sun due to exposure during low spring tides, and
therefore better able to survive a warm water anomaly (FYI, I'm thinking of
shallow patch reefs near German Channel).

>From what I've seen in Fiji and Palau, there are four reef environments
where corals have a better chance of survival during a warm water anomaly:

1.  Reefs that are exposed at low spring tide
2.  Reefs close to shore especially near rivers
3.  Reefs with strong water flow during changing tides
4.  Reefs below about 30 meters depth

I'm sure a lot will be said at the Bali conference about the variability of
coral survival during the 1998 event and recent 2000 event in the
south-central Pacific region.


> Bruce,
> If you have ever laid out in the sun to get a tan on a real calm day did
> notice how hot your skin got. Did you notice how just a little breeze
> you off.
> My hypothesis is that during El Nino years there are more days where the
> waters are exceptionally calm with little water see-sawing over coral
> This gives rise to rapid heating of the coral tissue. It is no surprise to
> me that coral bathed by moving water would be able to survive better. The
> flow of water cools the coral tissue.
> I contend that extended periods of calm/still water is a significant
> coupled with higher sea surface temperature that affects coral bleaching.
>    ...   Bill Mahood, PhD

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