[Coral-List] Artificial Reefs

[Dennis Hubbard]

I think there are two extremes to this discussion. First, if you put ANY
topographic structure on an open bottom, it will attract fish (they don't
care - look at all the fish around those deep-water nuclear disposal
sites). Also, corals will grow on it. However, the other side of the coin
is that any structure you place into the environment will have some impact.
Some of that will respond to the laws of physics (diffraction, diversion of
flow, etc.) but much of it will respond to factors we largely do not
understand. So the question is whether we should take the time to learn
those factors so we can engineer the environment.

About two decades ago, we placed ca. 100 rocks (5-7,000 lbs each) onto a
terrace that had been the site of a flourishing *Acropora palmata* reef in
the 60s (we didn't know this when we started the project). It had been
killed not by disease but by dredge pipes that were raked across the reef
to move sediment from the bay to cover the municipal dump for this island
of St. Thomas (it was being decommissioned). Ironically, the owner of the
dump who wanted to sell the land for development purposes was also the
first director of the newly created Department of Conservation and Cultural
Affairs (talk about irony.... and I can't lay out the half of it here).
When we were called in, a huge hotel complex had just been built  and
someone suddenly realized, "We have no beach!" This reflects a common
development perception that the natural system can be engineered so all
they have to do is throw money at a consultant like they do for financial
issues.

In this case, historical research revealed that this site had always had a
wide beach and we could identify no realistic reason for it to not be there
today. Further research into DPNR records revealed the bizarre situation I
just laid out.... the reef had been mechanically destroyed and the loss of
protection caused a wholesale exit of beach sand back into the hole).  We
ultimately decided that, while we could not replace the biological
function, we might replace the physical function by very carefully placing
these large stones in a way that allowed wave energy to pas through (i.e.,
it was not an impermeable structure but rather large boulders that broke up
incoming waves and partially protected the shore). We also set it up so
that strong unidirectional flow persisted behind the ridge (all that water
coming in between the blocks had to exit - creatinf strong shore-parallel
flow. The net result was that the new artificial beach persisted even after
Hurricane Marilyn) and water quality remained acceptable behind the loosely
scattered rocks. Our ultimate decisions on rock placement were based on
climbing up on the hotel roof and looking at how the 10 rocks we'd placed
each day affected wave refraction and diffraction patterns (very
empirical). To keep them in place, e had 3-inch holes pre-drilled in the
rocks and then pinned them to the bottom by drilling into the underlying
substrate and inserting steel rods and marine cement into the rocks and the
underlying substrate).

When I visited the site years later, corals (even *Acropora palmata*) had
colonized on the rocks - and the fish had moved in. The corals we had
transplanted to the fron of thi area were still doing better than the
natural ones nearby. This had become a reasonably popular snorkeling spot
due to the easy access from the adjacent beach.

Having set up this rosy scenario, I do not advocate the sense that physical
structures are anything more than last-minute reactions to poor decisions
in the past. While our structure created protection and made the hotel more
viable, this was not a substitute for even a mediocre natural structure
and, while the history of the area is amusing, it is also pathetic.I have
always wondered how much these kinds of minor "successes" just feed the
perceptions of developers that they can rely on the engineering/ecological
community to come in and move things around a bit to cover their
shortsightedness. I consider our project as one that was doomed to failure
from the start even though the financial picture was improved and the
ecological side was at least made no worse. I vowed to never do one of
these projects again and can happily report that the slate is still clean.

Dennis


On Tue, Oct 1, 2013 at 3:54 PM, Rachel D'Silva <rachdsilva at yahoo.com> wrote:

> Hey Coral List,
> I'm looking for articles/papers with design and engineering options for
> major functioning breakwaters (shallow) combined with reef restoration. I
> like the idea of sections of the breakwater having a design component that
> can be head started with coral fragments as well as functioning as a
> potential dive/snorkel site. The standard designs and structures will
> function as FADs...but in over fished waters.. this really isnt enough.
>
> I really appreciate any ideas/info you might have.
>
>
> Rachel
> 'Unless someone like you cares a whole awful lot, nothing is going to get
> better. It's not'.- The Lorax
>
>
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-- 
Dennis Hubbard
Chair, Dept of Geology-Oberlin College Oberlin OH 44074
(440) 775-8346

* "When you get on the wrong train.... every stop is the wrong stop"*
 Benjamin Stein: "*Ludes, A Ballad of the Drug and the Dream*"