[Coral-List] deep "coral oases"

Douglas Fenner douglasfennertassi at gmail.com
Tue Sep 15 22:12:31 UTC 2020

Deep beneath the high seas, researchers find rich coral oases


Notice the title says "coral oases" not "coral reefs" and does not say
"hard corals," but does say "rich."

There are a number of distinctions that some popular articles such as this
one tend to gloss over, and they tend to talk in ways that may lead people
to assume that these places are similar to shallow tropical coral reefs,
but that comparison is strained at best.  So, the original meaning of the
word "reef" is a structure that is near the water surface that a boat can
hit.  These are not reefs, they are in deep water.  Second, a coral reef
would be a reef built by coral.  There are deep sea structures built by
coral, some a few hundred feet tall and can be a mile or more long.  The
most famous of which are in the fjords of Norway, but others are scattered
around the world.  They are better termed "bioherms" since they are
constructed by organisms, but don't get close to the surface.  People
sometimes talk about their high diversity, but usually the construction is
built by only one species of coral, while many shallow tropical coral reefs
have hundreds of species of corals on them.  Plus, in the whole world,
there are only a few species of coral that can build deep water
constructions, maybe less than 10, and most or all are thin branching.  I
suspect, but don't know for a fact, that the diversity of other organisms
inhabiting them are also much lower than most shallow water tropical coral
reefs.  But much of what they are probably talking about here are "coral
communities" or ecosystems, as they are not constructional, there is no
geological structure built by them  The photograph for this article shows
many gorgonians, or octocorals, which can also be called soft corals, and
which do not build calcium structures (surprisingly, there are
non-gorgonian soft corals on shallow tropical coral reefs that add to the
geological structure, in a few places their contribution can actually be
greater to the construction than "hard corals" like Scleractinia).  Looks
like there is at least one that may be a black coral, a group which also
does not build coral reefs.  Among the hard corals, most are
"scleractinia".  On shallow water tropical coral reefs, most scleractinia
are zooxantellate, colonial and many large, and most contribute to building
the geological structure, which can be up to at least 1.6 km (one mile)
thick, depending on how long it has been building.  Scleractinian corals do
certainly live in deep and/or cold water, and there are about as many
species known that do that as on coral reefs.  They are all
azooxanthellate, most are solitary and small, and by far most of them do
not build any structures other than their own skeleton.  Often they are
scattered.  That doesn't mean that they aren't interesting or important,
just different.
     So deep water or cold water coral bioherms are interesting, part of
our world, as are deep water hard and soft coral communities.  They are
generally less studied because they are much more difficult and expensive
to access and study, and they are not restricted to warm, shallow water.
      I don't study them, I'm not an expert on them, so those that are,
please correct me if I'm wrong about this.
     Cheers, Doug

Douglas Fenner
Lynker Technologies, LLC, Contractor
NOAA Fisheries Service
Pacific Islands Regional Office
PO Box 7390
Pago Pago, American Samoa 96799  USA

The toxic effects of air pollution are so bad that moving from fossil fuels
to clean energy would pay for itself in health-care savings and
productivity gains
even if climate change didn’t exist.  In the US alone, decarbonization
would save 1.4 MILLION lives in the US alone.  And save $700 Billion a year.

"mitigating climate change is the critical wedge to set coral reefs on a
recovery trajectory"  Duarte et al 2020 Rebuilding marine life Nature

"Already, more people die  <http://www.nws.noaa.gov/om/hazstats.shtml>from
heat-related causes in the U.S. than from all other extreme weather events."


More information about the Coral-List mailing list