[Coral-List] Artificial reefs

[Michael Risk]

Hello John, colleagues.

I should start by saying that I am in sympathy with your points. Many
artificial reefs have been badly-situated, and some have seemed more of
an exercise in terrestrial garbage-removal than in reef rehab (pedicabs
in Jakarta Bay and the like). The answer isn't providing more fish
habitat, it's looking after the habitat that was there to start with.

On the other hand-your posting was fairly piscicentric, and I took
another approach 30 years ago. I figured, why should all the carbon in
those vast marine grassbeds go into the sediments, when it could be
converted into fish/lobster/snail protein? In addition to accessing
hitherto-unused carbon sources, there might also be value in providing
hard substrate. Suspended particulate matter (SPM)is a maximum at the
sediment-water interface, and declines upwards. Jorge Cortes and I had
just shown that coral spat would not settle on the bottom of an
environment subjected to heavy sedimentation stress, but that they
would settle on any available hard substrate elevated off the bottom.

In 1973, I built three small artificial reefs in Discovery Bay, east
side, in an eelgrass bed. They were at least a half-km from the nearest
extent of healthy reef. Each reef was 2-3m long, 1-2 wide, 1 high.
(This is all extracted from the paper, Risk Atoll Res Bull 255: 1981.)
Organised Reef was an array of concrete blocks, spaces so as to
maximise the holes. Rock Reef was-a pile of rocks. Veneer Reef was a
pile of rocks with blocks veneered on top.

Spiny lobsters were on the reefs within weeks, and the local fishers
began potting the reefs within 6 months. (Lobsters must be an exception
to your comments, given their migratory habits.)

After a year, all three reefs had corals growing on them-a half-dozen
species, colonies up to 20 cm in length. Plus the usual other
associates-algae, oysters, bioeroders...

After a couple of years, Organised Reef had bigger fish, but fewer
nocturnal species (both likely due to the large holes)-Veneer Reef had
larger total numbers of fish.

All three survived Hurricanes Allen, Georges, etc etc. When I last saw
them (late 90's) they were slowly settling into the sediment, being
undermined by Callianassa-but they were covered with coral.

And here I stop rambling and get to the point: all three (long-lived,
effective) reefs were built from locally-available material, in one
diver-day, for a total cost (in 1973) of $20 Canadian. Two cases of
beer.

I agree with you that a case has to be made for any artificial reef.
Will it serve a purpose other than increasing fishing pressure? Have
the land-based sources been evaluated? etc etc. BUT if the case can be
made, we should be quite clear that no expensive interventions are
necessary. Local people can build these themselves for a few bucks. 

If you like "piscicentric" I will make up some more words for you.

Mike