Man-made reefs and ecosystems

[Diver0001]

two diametrically opposing points

a) Man-made structures will increase the sea-life and strengthen the ecosystem.

b) Overfishing and pollutants will destroy the sea-life and ecosystem. (I've read all of Benchley's books).

Why are these opposing points in your mind? To me they're two unrelated variables in a massive balancing act.

I know something about the first point, though. Wrecks and other man made objects on the bottom are like nesting grounds for certain species and they offer cover to many others. Where I live, the North Sea is basically a featureless mostly lifeless sandy expanse except for the numerous wrecks which have huge concentrations of life on them. Cod do particularly well on wrecks and if we are serious about increasing Cod stocks then sinking ten thousand fishing boats in strategic locations would help a lot on two fronts.....

R..

 

[archman]

Where I live, the North Sea is basically a featureless mostly lifeless sandy expanse except for the numerous wrecks which have huge concentrations of life on them. Cod do particularly well on wrecks and if we are serious about increasing Cod stocks then sinking ten thousand fishing boats in strategic locations would help a lot on two fronts.....

I doubt NMFS would subscribe to this without scrutinizing the details. That's what fred was calling my "bass fishing model". Dumping a pile of wrecks in a soft sediment area merely converts one habitat type into another. There has to be valid arguments showing that the cod stocks are increasing overall as a result, not merely concentrating their existing numbers into smaller areas. What is it about the wrecks that the cod find attractive? There has to be a discernible benefit that'll increase growth rate, reproductive rate, reproductive intensity, or survival of juveniles/larvae.

Ten THOUSAND fishing boats? Sure you're not just an overzelaous wreck diver, Diver0001?

 

[Diver0001]

I doubt NMFS would subscribe to this without scrutinizing the details. That's what fred was calling my "bass fishing model". Dumping a pile of wrecks in a soft sediment area merely converts one habitat type into another. There has to be valid arguments showing that the cod stocks are increasing overall as a result, not merely concentrating their existing numbers into smaller areas. What is it about the wrecks that the cod find attractive? There has to be a discernible benefit that'll increase growth rate, reproductive rate, reproductive intensity, or survival of juveniles/larvae.

Ten THOUSAND fishing boats? Sure you're not just an overzelaous wreck diver, Diver0001?

I don't know what the cod like but I konw what I see. I see Cod from 6 inches to 6 feet on the wrecks I dive. They nest there and there would appear to be generations of Cod living on the wrecks.

If I had to guess I would guess that they can avoid getting fished up on the wrecks. The large Cod live inside the wrecks while the juveniles swim about with the Pouting on the outside. And since Pouting isn't a supermarket species I guess that offers some protection.

To save the oceans I think we would need to get more than 10k boats out of action. I worry about this because massive overfishing is going to bite back and the little people will pay the price in hunger as the politicians play the blame games and the power games. If fish stocks were like credit-limits we would have been sent to jail for fraud already......

R..

 

[Diver0001]

I doubt NMFS would subscribe to this without scrutinizing the details. That's what fred was calling my "bass fishing model". Dumping a pile of wrecks in a soft sediment area merely converts one habitat type into another. There has to be valid arguments showing that the cod stocks are increasing overall as a result, not merely concentrating their existing numbers into smaller areas. What is it about the wrecks that the cod find attractive? There has to be a discernible benefit that'll increase growth rate, reproductive rate, reproductive intensity, or survival of juveniles/larvae.

Ten THOUSAND fishing boats? Sure you're not just an overzelaous wreck diver, Diver0001?

Oh and the NMFS people should just go diving. They're probably the same scientists who will bicker until the Sahara covers 1/2 the planet about whether or not global warming is real..... Environmental scientists have a serious case of "analysis paralysis". When what we really need is action and for people to draw conclusions and show some vision what we're getting is a huge wimp factor while the politicians run roughshod over the people who know what's going on....

R..

 

[paolov]

oh i have to add to my post earlier,

Visibility is poor this season due to high plankton growth !!! this is good, this means the Month of MAY would be Such a blast in activity !!!!!

I wish you guys could be here and see for yourself. and the best part is water temp is 24 to 27 centigrade. NO need for thick wetsuits !!! :yelclap:

 

[FredT]

This is why its better to build a bunch of artificial reefs that daisy-chain along with larval dispersal patterns, rather than a bunch of reefs clustered together, or one big reef.

Wonder if anyone's designed an artificial mangrove yet...

Agreed that more is better. 5000 rigs make a good chain of habitat. The mothball fleet would make a pretty good start on a system too. Now if we can just "get over" the drive to demand all the expensive "cleaning" necessary to sink a ship and just get on with it. You'd think a few environmental studies of WWII era wrecks would handle that, but truth doesn't seem to work with the emotional ecofreaks.

Perhaps a few good category 5 storms will push the condo commandos inland enough to let the mangroves regrow, while the wreckage will provide cover for the fry until they do.

FT

 

[archman]

The mothball fleet would make a pretty good start on a system too. Now if we can just "get over" the drive to demand all the expensive "cleaning" necessary to sink a ship and just get on with it. You'd think a few environmental studies of WWII era wrecks would handle that, but truth doesn't seem to work with the emotional ecofreaks.
FT

Speaking for myself and several of my NOAA diving pals, we'll take concrete reefs over sunken ships or oil rigs anytime. We have this nagging doubt regarding how long such metal structures would hold together... anybody got any crude predictors? I haven't heard one that exceeded 150 years, personally. That's an ecologically weenie-sized timescale for a reef-type community, and wouldn't fulfill the Habitat Heterogeneity Hypothesis that coral reef environs adhere to. Need some "reefs" that'll persist long enough for biological overgrowth to take over.

'Course if the oil companies or Navy pony up the bill and effort to plop down some significant steel on a silted-over reef or hard bank, that's fine by me. I don't understand why the steel isn't recycled back at the factories, though. I thought steel recycling had been perfected to an art form in the U.S.... a marine engineer I know is always blabbing to me how "glorious" the process is. You'd think the guy was Conan the Barbarian. :viking:

 

[FredT]

Speaking for myself and several of my NOAA diving pals, we'll take concrete reefs over sunken ships or oil rigs anytime. We have this nagging doubt regarding how long such metal structures would hold together... anybody got any crude predictors? I haven't heard one that exceeded 150 years, personally. That's an ecologically weenie-sized timescale for a reef-type community, and wouldn't fulfill the Habitat Heterogeneity Hypothesis that coral reef environs adhere to. Need some "reefs" that'll persist long enough for biological overgrowth to take over.

'Course if the oil companies or Navy pony up the bill and effort to plop down some significant steel on a silted-over reef or hard bank, that's fine by me. I don't understand why the steel isn't recycled back at the factories, though. I thought steel recycling had been perfected to an art form in the U.S.... a marine engineer I know is always blabbing to me how "glorious" the process is. You'd think the guy was Conan the Barbarian. :viking:

Steel and stainless steel corrodes in seawater at a rate of about .008" per year. Armor plate is a bit less as it wll tend to be protected by the rest of the hull until it dissolves. A warship with 24" of armor plate will last quite a while. Many merchant ship hulls are made of 1" to 1.5" plate. Of course if dropped in reef building areas the accretion will work as a 'seed reef' once the metal dissolves. Considering that modern steel ship construction is considerably less than 150 years old it doesn't surprise me that there aren't any older "modern" shipwrecks to be studied. Riveted construction wrecks are much more fragile than the all welded hulls now being scheduled for disposition.

As for recycling the steel in ships see the EPA and OSHA rules on shipbreaking for why it isn't done much anymore. Since the middle 70's there isn't enough money in the steel to pay for the dismantling cost, even with the premium price paid for the armor plate. Shipbreaking a warship costs over three times what skinking one does, over and above the money recieved from the sale of the steel. This is true even with the truly insane cleaning rules now in effect.

FT

 

[RickI]

The exact manner and forms of resource enhancement of artificial reefs has been under evaluation and consideration for several decades. Take the case of surface or midwater reefs. You can have the recruitment of thousands of fish in less than a day, hence the use of the name "fish aggregating devices" or FADs. Ship moorings can sometimes show similar influences again in fairly rapid fashion.

In the case of benthic or bottom based artificial reefs, recruitment typically takes substantially longer. Given that benthic species may be less prone to wide migration as opposed to midwater species that may be attracted by FADs, residency time and life cycle phases present may widely differ between benthic and suspended artificial reefs.

Benthic reefs may provide alternative hard bottom habitat for marine life permanently or temporarily recruited from natural hard bottom communities. More viable room across benthic community niches in theory should expand net quantity of marine life.

Do artificial reefs unduly increase stocks of higher order preditors, i.e. sharks potentially creating a constructive nuisance to coastal areas? I doubt it. One example could be Ft. Lauderdale, FL which has had a incredible increase in the quantity of artificial reefs (mainly ships) over the last 30 years. I am not aware of an unusual increase in the presence of sharks in the area over this time period. Annual fish migrations seem to be a more significant cause of increased sightings of sharks for a very long time as opposed to new substrates.

What may work in Hollywood, may not have much hope in nature.

 

[Spratman]

Sorry, my original premise was the basis for the story lines. One stated if the natural food chain is destroyed by pollution and overfishing, then something else will become the replacement in the food chain. The second was man messing with the environment i.e. artificial reefs, and it draws unintentioned results.

So my actual question was, dealing with both scenarios, wouldn't the end result be possible, where humans are more involved as replacements in the food chain.

All the responses have been from differing points of view and very informational for me. I'm the type that gathers as much information as possible and then sorts through it. I think that it helps me be a better diver if I have as much knowledge as possible before making the practical application.

Why are these opposing points in your mind? To me they're two unrelated variables in a massive balancing act.

I know something about the first point, though. Wrecks and other man made objects on the bottom are like nesting grounds for certain species and they offer cover to many others. Where I live, the North Sea is basically a featureless mostly lifeless sandy expanse except for the numerous wrecks which have huge concentrations of life on them. Cod do particularly well on wrecks and if we are serious about increasing Cod stocks then sinking ten thousand fishing boats in strategic locations would help a lot on two fronts.....

R..