artificial reefs vs. coral reefs

[Craig Lilyestrom]

Recently, someone commented to me on the enormous quantity of fish
biomass present around some artificial reef units (concrete
structures designed by a well-known company) in Puerto Rico.  He did
not estimate the biomass, but rather described having to almost push
the fish out of the way with his hands, in order to swim forwards.
The units were installed several years ago.  The precise location of
these units is not public knowledge, and hence fishing effort on them
is minimal or non-existent.

My question is whether it is reasonable to assume that coral reefs
are potentially capable of sustaining similar quantities of fish
biomass, or whether this phenomenon is attributable to the particular
attractive feature of artificial reefs.  Coral reefs in Puerto Rico
are considered quite overfished, and the density of fish described on
the artificial reefs is never seen.

I'd appreciate any enlightenment.

--Craig
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