deepwater coral "reefs"?

[Don McAllister]

Helmut ZIBROWIUS wrote:
Surely, these are not reefs in the common established sense, and re-introducing
this term in the deep context forgets the efforts made by Teichmann and others to
make understood to geologists and paleontologists that not all ancient coral mass
occurrences are to be interpreted as reefs, in the sense of tropical and shallow.

Zibrowius poses a good question.  In my own papers on the topic of northern
deepwater corals I have preferentially used the term "groves" to reefs.

Part of my doubt has been due to the lack of information on whether the corals
occur in more or less isolated patches, or in relatively dense and large
groupings. The second part of my doubt is whether the deepwater corals have been
growing in situ for periods of say, centuries, and have built up a reef platform.
So my own personal presumption has been that reefs constitute fairly dense and
large clusters of colonies over periods measured in centuries and that the process
has resulted in the build-up of a reef platform.  I would be happy to be corrected
on this understanding and if someone would provide me with a concise widely
accepted definition of a 'coral reef.'  I would hope that, although our
understanding of coral assemblages has developed most strongly from tropical
experience, that the terminology could be adapted or could coin new terms which
would facilitate discussions of deep/cool coral assemblages.  Of course where
deep/cool coral assemblages do clearly differ from tropical ones is in the lack of
zooxanthellae in the colonies - to my knowledge (although zooxanthellae do occur
in northern sea anemonies).

The Norwegian and Irish instances show that deepwater corals do grow in masses,
many colonies in close approximation and measuring hundreds of metres long.  As
far as the building up of a platform, it looks like some sort of a platform occurs
in Norwegian coral assemblages.  In the case of Labrador scleractinian
assemblages, there is a base of fallen dead colonies that goes back about 10,000
years in age, with individual colonies more than a century or two old.  So the
latter certainly, aside from zooxanthellae, gives the closest approximation to
reef-like conditions.

Regards,
don
Don McAllister