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Yes, concrete in artificial reefs is a problem: it contains metals (such as zink) and it is toxic. Also, it may lure larger fish to a place where there is not the (necessary) food chain. Marine assemblages are very complex and, as somebody else observed, space may not be the limiting factor, in many cases. But we, divers, make up an environmental problem. In the Mediterranean, there have been several experiments both with artificial reefs and marine refugia. Reefs may enhance the abundance of some species __locally__ in combination with a limiting marine park or zone where fishing/diving is banned. Also, the presence of divers are a negative perturbation to fish assemblages. Some fish will get used to human presence but others will not and zones where scuba diving is banned hold both higher diversity and abundance relative to areas where diving is allowed. Cheers & thanks for replying to my RB and other questions. ---- aldo.solari@ho*.se* (fisheries biologist) Home page, www.ccbb.ulpgc.es/fish-ecology/solaris ---- mat.voss@t-*.de* MV> Michael, MV> thanks for your comments. MV> All this has been discussed here at the baltic shores in a very similar MV> way. There were multiple plans to create artificial reefs wit concrete MV> reefball, and laying fields of line to create habitats for mytilus MV> edilis. MV> There were mainly 2 arguments against : MV> a) concrete is not part of the natural environment and should not be MV> brought into the water. MV> Well, concrete has somewhat alkalic properties, as opposed to natural MV> minerals, but what minor part this play in the water ,i can only guess. MV> We have WW 2 remains here as artificial reefs which are abundant MV> habitats. MV> In fact, they help to extend the for some species well beyond there MV> common limits. MV> b) It was said by a Kiel Institute of Marine biology ( IFM) MV> biologist that artificial reefs would induce a deprivation of the MV> adjacent dandy areas in terms of diversity. MV> This is not neither true nor scientifically proven. MV> Thousands of dive hours of divers trained in environmental observation MV> stand against this hypothesis. MV> It is a side by side ralationship with no ill effects ( one could MV> imagine the reefs giving home to predators which would devastate the MV> surrounding communities. MV> Not the case. MV> The reefs are as well fish nurseries as places for seatrout, cod, eel , MV> cormoran, to name a few ( of which I know an english name ;-) to take MV> prey. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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