Large (up to 31-meter high) coral banks (or bioherms) occur on the con
tinental shelf off mid-Norway at water depths between 220 and 310 mete
rs. They are built up by the cold-water, ahermatypic, scleractinian co
ral Lophelia pertusa (L.). A 3-km-wide and 200-km-long traverse was ma
pped geophysically across a large part of the mid-Norway shelf: A tota
l of 57 suspected individual banks were found. Although they occur in
local clusters of up to 9 banks per Km(2), the mean density along the
whole transect is only 0.09 suspected banks per Km(2), with the highes
t regional density (1.2 banks per km(2)) occurring above subcropping p
resumed Paleocene bedrock. A detailed investigation employing an ROV (
remotely operated vehicle) was conducted of a cluster consisting of 9
individual banks. Based on geophysical, visual, geochemical, radiocarb
on, and other analyses, we conclude that at least some of the coral ba
nks have been forming at the same locality for over 8,000 years, and t
hat there is a strong correlation between coral-bank occurrence and re
latively high values of light hydrocarbons (methane, ethane, propane,
and n-butane) in near-surface sediments. To explain, the structure and
distribution of these coral banks, we propose a model where they form
as a consequence of local fertilization that results from focused hyd
rocarbon micro-seepage of deep thermogenic hydrocarbons migrating to t
he surface along inclined, permeable sedimentary strata. A direct coro
llary of this model is that if and when the source of local fertilizat
ion is shut off; the bioherms die out. This possibly could be the reas
on why extinct bioherms are more common, than live ones in some areas
of the ocean.