[Coral-List] Atificial reefs
Eugene Shinn
eugeneshinn at mail.usf.edu
Mon Oct 21 13:21:40 EDT 2013
As co organizer of the first International Artificial Reef Symposium
(1973) in Houston, Texas, I have since had ample opportunity to follow
the subject of artificial reefs and categorize the various divergent
views they evoke. Basically there are two schools of thought that tend
to correlate with peoples socio/political views. In simple terms they
consist of, (1). Artificial reefs simply attract existing fish and
therefore do not increase the numbers of fish and at the same time
simply provide a convenient way to dispose of old boats, streetcars,
building materials, culverts, rubber tires, and oil platforms.(2).
Artificial reefs actually increase fish productivity if placed in the
right locations regardless of the materials used. Of course there is
truth in both sides of the argument.
I first entered this field while diving (spearfishing and photography)
under offshore oil platforms off Louisiana and Texas. At the time I was
a geologist working for Shell Oil Co.Later when I was promoted from
geology to the environmental affairs department understanding the
subject became part of my daily job. Yes, we had old offshore rigs that
needed disposal but recycling the steel was more costly than purchasing
new steel. If they could be left in place or moved to established
artificial reef sites there were valid reasons to investigate their
environmental functions.
What attracted my attention while diving under platforms was that those
in the northern Gulf were located on muddy bottom many miles from any
natural hard bottom. Surprisingly they were populated by an abundance of
tropical reef fish normally seen on Florida coral reefs.It became clear
they had arrived at the rigs as water borne larvae and encountered
suitable refuge and sources of food in the form of epiphytes, barnacles
and other attached organisms as well as an abundance of worms and shrimp
in the surrounding bottom sediment. Most of these fish larvae would
likely have succumbed in the hostile mud bottom environment of the
northern gulf had they not encountered these shelters. In addition there
were lobsters living among the cross beams well above the bottom. It
seems unlikely that they arrived as adults walking across many miles of
muddy bottom. The sea floor beneath these rigs consists of a thick layer
of drill cuttings, fingernail-size bits of rock, and yes, discarded
debris, that also provide habitat for fish and crustaceans. On the other
hand the Jacks, Barracuda, and most pelagic/migratory fish such as king
mackerel that swarm around and under the rigs, were likely attracted
both for shelter and to prey on the other fish that flourished there.
Those observations provide evidence for those who favor the other side
of the artificial reef discussion. Clearly some of both sides of the
discussion are true.
What was most striking about the platforms however, is the range of
habitats they provide that is not available on natural reefs. Different
habitats range from the surface to the bottom and Red snapper generally
occupy the rigs from bottom to the surface. I had never dived deep
enough to see a red snapper off the Florida Keys whereas they range all
the way to the surface under the rigs. Of course huge groupers of many
similar species may have arrived as post larval adults and simply took
up permanent residence. There is food/prey and shelter beneath the rigs
regardless how they got there.
That rigs are good places to fish is well known to fishermen and divers
in the Gulf of Mexico. However, there are non-fishermen citizens who
thoroughly dislike these artificial reefs because they make it easier to
catch the fish. That's a sociological side of the issue. And of course
there are those who seem to be born to hate oil companies and naturally
see no good in them.Off the east coast of Florida there is yet another
issue; conflict between divers and line fisherman. I never saw this as a
problem around the rigs but probably existed in some areas. To mediate
this conflict the Dade County artificial reef program sank some old
vessels and other objects, including surplus army tanks, in water to
deep for divers. They became the favorites among line fishermen. I
examined many of these "reefs" using a submersible to determine the
optimum depth to alleviate this conflict. The study found that it is
essential to place such artificial reefs well away from natural reef
bottom. The artificial reefs serve best when not in completion with
natural hard or coral reefs. On all of these artificial reefs we
examined there was no simple way to determine if they simply attracted
existing fish or served as primary producers. However, it was clear in
all cases that fish were feeding on algae and any crustaceans attached
to the objects. They do provide food and shelter.
These basic arguments, attraction versus production, will likely
continue well into the future as evidenced from range of opinions
evident from recent coral list postings. Gene
--
No Rocks, No Water, No Ecosystem (EAS)
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E. A. Shinn, Courtesy Professor
University of South Florida
College of Marine Science Room 221A
140 Seventh Avenue South
St. Petersburg, FL 33701
<eugeneshinn at mail.usf.edu>
Tel 727 553-1158
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