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Date: Dec 21 1999 16:06:40 EST
From: "Reef Ball's Interested List" <>
Subject: Reef Ball Update-Science Only Today

Message #134

For years, scientists have debated if artificial reefs attract fish or produce fish. Of course the answer is a little of both but we thought everyone might like this e-mail from Bill Alevizon, a renowned artificial reef researcher.

RDBG's Favorite quote from this e-mail, 'I believe that the available evidence overwhelmingly supports this view [Production], and that the "burden of proof" has shifted to those who still dogmatically maintain that ARs simply rearrange fish biomass within an area, and result in no real increase.'

Here's the e-mail:

An open letter from Bill Alevizon,
Research Associate in Coral Conservation
Osborn Laboratories of Marine Science

Regarding the issue of Attraction Vs. Production

The experiments upon which these (my) papers are based clearly demonstrate the capacity of artificial reefs to increase local population sizes of certain types of fishes under the "right" environmental conditions. The earlier experiments (circa 1982-1985) simply documented the accumulation of grunts and snappers around replicate sets of artificial reefs placed in different types of habitats on the Little Bahamas Bank. Because some of the reefs were almost a mile from the nearest sizeable recruitment sources ((extensive mangroves) it was not possible to establish that the recruitment sources suffered no long-term population decrease concomitant with the observed increases at the ARs.

This led to the second experiment in the Florida Keys (1989 ref), in which we actually experimentally demonstrated that upon deployment of an artificial reef, nearby recruitment sources at first suffered rapid population loss due to emigration, but soon recovered to pre-disturbance levels.

Now, of course we could not conclusively "prove" that the observed results did not ultimately result in fewer snappers or grunts in Trinidad or Bermuda, but the most parsimonious interpretation of these experiments is that, for shelter-limited species in shelter-poor coastal habitats (e.g., sand plains, grass beds), artificial reefs function by drawing recruits from nearby small shelter-spaces. These shelters in turn - because they are now "under-populated" in terms of available shelter - quickly re-recruit even smaller individuals from less-optimal shelters such as sponges, small shells, etc. - fishes that will not "make it" much longer without access to such larger shelter sites as they grow.

So, in a nutshell, here is my take on all of this. All my experience in observing Caribbean reef fishes at many locations and contexts over the last thirty years has convinced me that the kinds of fishes (snapper, grunts) most abundantly recruited to artificial reefs in this region have a pronounced innate drive to search out and establish residence on any available unoccupied or sparsely occupied shelter space that will support individuals of their size, which is of course continually increasing with age. We therefore have continually-mobile populations of younger fishes, searching out increasingly larger shelter spaces that will accommodate their increasing size.

This leads to the results so widely observed and reported -not just by my experiments but by many others. Artificial reefs in Caribbean waters are quickly and heavily occupied by such fishes. I am convinced (and my experiments have shown) that initial rapid population decreases incurred from habitats near the site of a recently deployed artificial reef are soon made up by recruitment from nearby, even less-optimal shelters, and so on, until we are left with the ultimate recruitment source - an overabundance of very many small individuals living amongst seagrass blades, etc., most of whom will eventually fall prey to larger fishes because there is simply not enough naturally available shelter space to accommodate all these individuals as they increase in size.

Relatively large artificial reefs, by providing shelter at the top end of this chain, have ripple effects all the way down, actually increasing the biomass of these fishes in the area of deployment without affecting biomass of these same species in adjacent waters; in other words in this context ARS do not "take" fish from other suitable habitat - rather, they function by increasing survivorship within a spectrum of sixe-classes within a population. I believe that the available evidence overwhelmingly supports this view, and that the "burden of proof" has shifted to those who still dogmatically maintain that ARs simply rearrange fish biomass within an area, and result in no real increase.

Of course, my comments are based on the particular species and environmental contexts specified - I have also seen that where natural reef is plentiful, ARs are of little value and have very different recruitment characteristics.

The bottom line is that ARs are a fishery management tool with the capacity to increase OR simply redistribute fish populations, depending upon the species and environmental context - there is no simple "either or" answer.

End of E-mail

At Reef Ball, we have observed similar trends in many varied worldwide habitats. One exception seems to be that extraordinarily large reefs (in comparison with natural reefs) seem to hold higher than natural populations of fish which might crash local resources which some suggest may reduce fecundity and growth rates in the fish assemblages in immediate proximity of these overpopulated reefs.

Thanks Bill for your candid yet insightful observations!

You can find more links and contact information to Bill's work on the Reef Ball researcher pages (

Have a great day.


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