[Coral-List] Atificial reefs

[Eugene Shinn]

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

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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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