Blue Corals in the Maldives

[Patrick Mitchell-Jones]

Many thanks to you all for the responses to my query regarding 'Blue
Coral'. I have read all replies and would add the following: -

The most noticeable colour is indeed an iridescent pale blue which is
almost translucent up close. I suppose that it does look like the
colour in the polyps themselves rather than the usual opaque
coloration of the corals. I noticed the blue, a purple blue and some
pink colours as also seen by Jan Korrubel in Sodwana Bay. 

Craig Bingman writes that the loss of the symbiont population in
bleaching caused by stress can be as a result of high irradiance or
high temperature. I would surmise that, as the irradiation will
decrease with depth and the corals I noted were at various depths and
not particularly noticeable on the reef top but rather on the outside,
this would be a less likely cause than temperature. Indeed, with the
current relative turbidity of some areas this would also reduce the
irradiation. Certainly the temperature of the water was several
degrees higher than I noted in the same area in December. Bob Allison
asks for more details of the sites. Here goes Dive sites were as
follows....

Temperatures are subjective as my computer doesn't record them. Quoted
as between 28°c and 33°c

Kuramati House reef (Outside). Just to the west of the pier. Numerous
blue tinged staghorn with some blue/purple and occasional pink. These
were at variable depth. None seen on the inside. There were areas of
high temperature. I was told as high as 33°c

Rasdoo House Reef. Some visible here but the water seems slightly
cooler.

Maaya Thila. None seen. Water cooler and at a constant temperature

Fesdu House reef (outside). Some here. Temperature variable.

Veligandu North. Again, some evidence here but not as much as in the
shallower Kuramati area

Ukulas Thila. No evidence here.

The corals most affected with this type of colouration were the
Staghorns with the most intense colouration around the tips. The
Elkhorns (palmate type corals), which were generally a little deeper
than the Staghorns, seemed to present in a different manner. The
colouration did not seem to be a pale translucent type but an intense
royal blue. This occurred in patches and in one case the whole coral
was intense blue. I don't know if they are both caused by the same
thing but they certainly look different. Sorry if my terminology is
not correct, I am a microbiologist and not familiar with all the
scientific names of the corals.
Patrick Mitchell-Jones