Farming the Ocean Desert

[mistermack]

You're talking about open systems though. If the system is closed, you could try adding ground limestone for example to replace compounds removed by shellfish in the shells. I was surprised that the stations producing oyster seed in the linked video didn't adjust the ph when they found that incoming water was acidified.

Weather might indeed be a problem, but presumably you would have some means of adjusting the depth of the plastic sheet so that it was not badly affected. Some weather could be helpful, in keeping the water agitated, and nutrients circulating.

[CharonY]

2 hours ago, mistermack said:

You don't seem to have even read the OP, or understood it. The open oceans are generally nutrient poor at the surface. So there's no point in having the system open. There's very little plankton, like there is in rich coastal waters, so what would be the point of an open system?

Because if you contain all the waste in a closed species you will have fouling. It is the basic reason why aquaculture are preferred over, say, aquariums. What you seem to propose is a semi-open system. I am talking about scale because it is one of the big limiting factors. Oceans are not static and there is a limit that you can control in a semi-closed system. If you want to pump up sediment (under the assumption that the area that you mix is actually rich in nutrients- that does not need to be the case as they can be transported ) or manipulate other things large-scale in a closed or even semi-closed environment things are going to be very difficult and massively expensive. This is one of the reason why folks actually use open system. The cost and difficulty generally do not become exponential higher with size. 

There are likely solutions for closed aquaculture farming, but I am not sure about cost, scalability etc.

Edited September 4, 2018 by CharonY

[mistermack]

There's no logic to that post at all. If costs became exponentially higher with size, (which I doubt) you would just expand by adding separate units of the ideal size. And you would obviously investigate the area before you started, so you would know if nutrients were available on the ocean floor.

The economics of pumping are an unknown. But from an energy point of view, it's friction in the pipe that is the main cost. The water is effectively nearly weightless, apart from a slight difference in density due to colder temperature deep down. So a wide pipe would be the most energy efficient. You could possibly use wind or solar to drive the pump, or even use the ocean current, if it was significant.

[CharonY]

I think I have been conflating size of the enclosures with scale of the operation. Let's take a step back. How do you envision to enclose a body of water with plastics in a way that prevents nutrient loss (if that is what you propose). How is the circulation with outside water to be managed (if at all)? How would those be different from existing closed containment devices? For the latter challenges have been well-described and can be used as starting point.

It should also be noted that one should make clear goals in terms of what one would like to achieve in the system. Phytoplankton in itself is not of sufficient commercial value. If one wants to have sufficient fish production, additional feed input is pretty much inevitable. Obviously, sediments in areas with poor nutrient input are not likely to yield high nutritional levels, for starters and establishing a self-sustainable ecosystem is a very ambitious goal.

If the main product is seaweed, IIRC a extremely large size needs to be used until the operation becomes commercially viable, which would make enclosed systems rather difficult. That all being said, folks are trying to exploit ocean for farming purposes. But the way I read it is that trivial solutions do not exist. The balance between ecological impact, economic feasibility and technical difficulty is still being investigated.

Edited September 4, 2018 by CharonY

[mistermack]

1 hour ago, CharonY said:

It should also be noted that one should make clear goals in terms of what one would like to achieve in the system. Phytoplankton in itself is not of sufficient commercial value. If one wants to have sufficient fish production, additional feed input is pretty much inevitable. Obviously, sediments in areas with poor nutrient input are not likely to yield high nutritional levels, for starters and establishing a self-sustainable ecosystem is a very ambitious goal.

That's not really in line with the upwellings info that I linked. These natural upwellings are not managed in any way, but produce 25 percent of the global fish catch, with no additional feed of any sort. Of course they are on a huge scale, but it does prove the concept works, if not the economics. Of course, these natural upwellings only temporarily add nutrient to the surface. It will gradually settle out, which was the point of the plastic sheet suggestion.

My own design for an experimental unit would be a circular 100m diameter sheet for the base, supported by floats and sunken with weights, with a vertical wall around it of similar plastic. You guess at a suitable depth to sink the floor to initially, and adjust by trial and error over time to get the best compromise. Then do something similar with the pumped sediment, and measure the resulting production of plankton. Like everything, the process would get better and more efficient over time.

I think adding feed would defeat the objective of producing food from the resources in situ. It would be less intensive than existing methods, but ideally covering a much bigger area.

This gif is interesting. It illustrates how surface wave action need not damage a sunken sheet :

Edited September 4, 2018 by mistermack

[rangerx]

2 hours ago, CharonY said:

There are likely solutions for closed aquaculture farming, but I am not sure about cost, scalability etc.

Unless you can gather spat fall naturally, artificial seawater is the viable option for hatcheries and growing food algae. It's not without it's problems, but it's otherwise easily contained and sterilized.

Then juveniles are relayed to a open setting on simple lines suspended from floats for final grow out.

 

1 hour ago, mistermack said:

This gif is interesting. It illustrates how surface wave action need not damage a sunken sheet :

Waves perhaps. Sticks, logs, kelp, grass, plastic will push it's breaking strength in currents. Although suggesting lesser nutrients at the surface, fouling organisms are their densest nearest the surface.

[CharonY]

On 9/4/2018 at 7:07 PM, rangerx said:

Waves perhaps. Sticks, logs, kelp, grass, plastic will push it's breaking strength in currents. Although suggesting lesser nutrients at the surface, fouling organisms are their densest nearest the surface.

I am also wondering how a sunken sheet would prevent nutrient dispersal.