Man-made reefs and ecosystems

[Spratman]

I have a question or two that I've been mulling over and I'd like some feedback on.

First of all, I'm a new diver and have little knowledge on the subject so please don't beat me...

Having watched both "Spring Break Shark Attack" (lame) and "Beast" 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).

Therefore, the results would be the same.

So, is there any evidence from research that would indicate that the proliferation and/or the lack of marine life will attract larger predators, and thereby, start affecting diving and swimming in those areas? Logic would seem to dictate that...

Thanks for your consideration.

Jack

 

[Stirling]

... Having watched both "Spring Break Shark Attack" (lame) and "Beast" 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).

Therefore, the results would be the same.

So, is there any evidence from research that would indicate that the proliferation and/or the lack of marine life will attract larger predators, and thereby, start affecting diving and swimming in those areas? Logic would seem to dictate that...

I don't know, but I can think of a couple of points that would affect the end result.

First, man-made structures like artificial reefs should create opportunities for new growth, habitat, etc., which (we hope and expect) will have a beneficial effect for the fish, etc. that thrive in those environments. However,

Second, in the big scheme of things, I cannot imagine that the localized beneficial effects of creating artificial reefs and the like will amount to much more than a drop in the bucket compared to the damage being done by overfishing and pollution. I think they're a good thing for divers, and a good thing for the fishies, too, but it's not like artificial reefs in only those parts of the ocean that are accessible and attractive to divers are going to make a very big impact overall. You're not going to restore the populations of cod and whales and the like with these kinds of structures. So,

Third, I don't think the overall result is "the same."

Fourth, if a pelagic predator can't find enough food out in the deep water, will it come into the areas occupied by divers and their artificial reefs, etc. to find food? I suppose so, although once more I doubt the "big picture" effect would be very great. Fish that are adapted to eating food in one environment or part of the food chain may not be able to adapt to finding sufficient food to support them if they move into a different environment.

I don't know for sure, but I think I would expect a big decline in the pelagic species' numbers more than I would expect a lot of them to start showing up in shallow water artificial reefs. Some of them might try to make it in a different environment, but I doubt that is a good long-term survival strategy for most big fish that are not already adapted to the kind of environment created by an artificial reef.

On edit: Will the types of predators that already live in shallow water reef environments (like black tip sharks, etc.) be attracted to artificial reefs that are also occupied by divers? Sure they will, if the artificial reef is a success, and speaking for myself at any rate, I certainly hope they will show up.

 

[archman]

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

This is far from ascertained. A lot of the fish survey folks are under the belief that all these structures do is concentrate existing fish populations into areas that humans can more easily monitor. Jury's still out on whether or not we're getting much in the way of additional fish out of the deal. Some man-made structures are believed to offer far greater success with this (i.e. reef balls) than others (wrecks).

 

[paolov]

just checked out a new artificial project this weekend. the artificial reef is made up of cement structures whose sides are of course sand debris.

what i can say is that i saw a lot of juvenile fish. newly hatched fingelings 1mm to 2mm in size. so i can say is that they take refuge in them artificial structures. and i have to say that this year the fish activity in the area has improved greatly from the time there were no structures.

the structures were placed at around 80ft sand. reef edge would be some 40 ft. away.


paolo

This is far from ascertained. A lot of the fish survey folks are under the belief that all these structures do is concentrate existing fish populations into areas that humans can more easily monitor. Jury's still out on whether or not we're getting much in the way of additional fish out of the deal. Some man-made structures are believed to offer far greater success with this (i.e. reef balls) than others (wrecks).

 

[archman]

what i can say is that i saw a lot of juvenile fish. newly hatched fingelings 1mm to 2mm in size. so i can say is that they take refuge in them artificial structures. and i have to say that this year the fish activity in the area has improved greatly from the time there were no structures.

The real question is, are those fingerlings net gains to the regional ecology, or would they have been simply born and developed somewhere else that divers don't frequent so much? Is the gain in fish activity at the artifical reef site coming at the loss of fish activity somewhere else? That's what happens in freshwater fishing lakes in the U.S.. Fishermen plop down structures to attract their target fish. You don't really get any extra fish into the lake, rather you concentrate the existing ones into areas that the fishermen can exploit. It only seems like there are more fish.

But so long as artifical reef structures aren't used to exploit the fishes paolov, I don't see them doing any harm in your neck of the woods. Kudos.

 

[paolov]

They are new and this season is after breeding season. and there are lots of juvenile fishes , around the 1mm size around the area. The fishes are growing in numbers from two years ago. and what's best is that it is an occurence in most of the diving spots around the area. So the awareness and efforts of protecting some areas from fishing is indeed benefiting the local area for now. i just hope the rehabilitation of the area is sustained.

Though the 1meter grouper (at Groupies rock , 100ft) is no longer there. i have noticed a number of other fishes , like sea bass, growing in numbers around the area. like juvenile yellow tail barracudas which where no where to be found three years ago.

So i may say from my observation that the area is having an increase in fish numbers. and there is a distinct difference from those areas around the area where no protection is being offered (where fishing is not regulated). And i think them fishes know the area where it would be relatively safe for them while still young.

If i may add. inside the artificial reefs, we place some wine bottles, and it has been our observation that these bottles serve to be homes to several small fishes. they take on to them quickly.

paolo

The real question is, are those fingerlings net gains to the regional ecology, or would they have been simply born and developed somewhere else that divers don't frequent so much? Is the gain in fish activity at the artifical reef site coming at the loss of fish activity somewhere else? That's what happens in freshwater fishing lakes in the U.S.. Fishermen plop down structures to attract their target fish. You don't really get any extra fish into the lake, rather you concentrate the existing ones into areas that the fishermen can exploit. It only seems like there are more fish.

But so long as artifical reef structures aren't used to exploit the fishes paolov, I don't see them doing any harm in your neck of the woods. Kudos.

 

[Spratman]

Thanks for the response. I hadn't considered lack of prey in the food chain. Extinction is a definite result alright. I don't believe that most species are very adaptable to new environments.

I understand that Florida is considering a moratorium on sport fishing.

I suspect as far as pollution goes, the coasts along some of the Carribean countries is still horrendous. My daughter was in Belize two years ago and said you cannot swim in the water there because sewage flows out into the sea from the rivers. You have to go several miles off the mainland to swim, dive, etc.

I appreciate your insight and comments along with Palao and Archman. I'll be quiet now and read other responses.


Jack

I don't know, but I can think of a couple of points that would affect the end result.

First, man-made structures like artificial reefs should create opportunities for new growth, habitat, etc., which (we hope and expect) will have a beneficial effect for the fish, etc. that thrive in those environments. However,

Second, in the big scheme of things, I cannot imagine that the localized beneficial effects of creating artificial reefs and the like will amount to much more than a drop in the bucket compared to the damage being done by overfishing and pollution. I think they're a good thing for divers, and a good thing for the fishies, too, but it's not like artificial reefs in only those parts of the ocean that are accessible and attractive to divers are going to make a very big impact overall. You're not going to restore the populations of cod and whales and the like with these kinds of structures. So,

Third, I don't think the overall result is "the same."

Fourth, if a pelagic predator can't find enough food out in the deep water, will it come into the areas occupied by divers and their artificial reefs, etc. to find food? I suppose so, although once more I doubt the "big picture" effect would be very great. Fish that are adapted to eating food in one environment or part of the food chain may not be able to adapt to finding sufficient food to support them if they move into a different environment.

I don't know for sure, but I think I would expect a big decline in the pelagic species' numbers more than I would expect a lot of them to start showing up in shallow water artificial reefs. Some of them might try to make it in a different environment, but I doubt that is a good long-term survival strategy for most big fish that are not already adapted to the kind of environment created by an artificial reef.

On edit: Will the types of predators that already live in shallow water reef environments (like black tip sharks, etc.) be attracted to artificial reefs that are also occupied by divers? Sure they will, if the artificial reef is a success, and speaking for myself at any rate, I certainly hope they will show up.

 

[Spratman]

Sorry Paolo, Got the name wrong....Geez. Great observations regarding reef life and the new arrivals.

 

[FredT]

A few basic observations from watching this for 30+ years.

1. The bottom end of the fish food chain are almost all plankton grazers.
2. There is a plehera of plankton near most shorelines with quantities variable by light and runoff nutrients. In any case what food is available on any artificial structure is also available over mud bottom 1/2 mile away. It's the presence ofof the cover taht allows the fish to survive there
3. The "cover" the structure provides will generally allow fry and fingerlings to develop to a larger size before significant predaton kicks in.
4. Where open ocean bait species can find "cover" and suitable breeding habitat the amount of fry that survives to breed will increase, increasing the next year's crop.
5. Predators that are on the 'human harvest" prey list will tend to go down in size and up in numbers around published habitat near inlets. Unpublished habitat and habitat farther from the inlet than a 5 gal can of gas will get a small boat will continue to have a good mix of predator sizes.


Archman,

The problem with the freshwater model is that the habitat for the adults is NOT what is needed for the fry. To get an increase in numbers fry friendly habitat (grass beds, neutral or positively buoyant rope mats, etc.) need to be placed in conjunction with adult friendly habitat. In Salt water the habitat is most effective for the fry of the bottom end of the food chain, thus boosting the net productivity of the bottom area.

FT

 

[archman]

The problem with the freshwater model is that the habitat for the adults is NOT what is needed for the fry. To get an increase in numbers fry friendly habitat (grass beds, neutral or positively buoyant rope mats, etc.) need to be placed in conjunction with adult friendly habitat.

Well, the freshwater "model" IS designed strictly to catch more fish. The sportsfishermen could care less whether or no they're enhancing the habitat for fingerling-size-classes.

The problem with reef fishes is, their pelagic larvae tend to get highly dispersed all over the place, usually along prevailing surface currents. So babies spawned at artifical reef X very likely drop out of the water column somewhere else entirely. In line with this, baby fishes hanging out at artifical reef X probably were spawned somewhere else too. Constructing artifical reefs that complement the transition from juvenile to adult have far more success in enhancing stocks than one that merely attracts adult fishes, true enough. But the reef fish recruitment system isn't compartmentalized around specific reef sites, not unless you get something like circular surface currents or something functionally similar.

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...