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Comment by cmrdporcupine | Hacker News Reader

That is really interesting. Can we cultivate sea grass to make carbon capture ponds or forests?

"The research stated that if microorganisms consumed the sucrose stored by the roots of the seagrass, at least 1.54 million tons of carbon dioxide would be released into the atmosphere, which is equivalent to the carbon emissions from by 330,000 cars in one year."

Those number strongly suggest no. "A million tons" and "hundreds of thousands" may sound large but in this context they're tiny. And if we did try to farm these we'd have to displace other ecosystems for the farm land (under ocean).

>And if we did try to farm these we'd have to displace other ecosystems for the farm land (under ocean).

but that isn't necessarily a problem.

Famous last words.

There's a lot of work going into blue carbon efforts at the moment .. better understanding and utilising seagrasses and algaes, mangroves, etc. as carbon sinks.

That said, what I've never understood about the potential of seagrass as a carbon sink (and this sugar thing might go someway to explaining it), is how it works given how short lived individual plants are, and how fragile - and shallow - seagrass ecosystems are.

CO2 / methane (?) released by decaying biomass at depth may stay trapped in sediment, but how realistic is this at depths of 20-40m? Does anyone have any more info?

Isn't what's going on here in particular something to do with symbiotic bacteria capturing carbon into sugars?

Yeah absolutely. My previous understanding was that the main carbon capture potential was simply in what ended up as part of the plant, rather than the portion being excreted / fed on by symbionts. That is fascinating news.

My question is that, given that the "capture" component relies on that carbon not being re-released into the atmosphere, how does "seagrass sequestration" fare given that seagrass meadows mostly occur in shallow waters, where the seafloor tends to experience higher levels of dusturbance compared to the deep sea (tides, currents, predation -of plants and sugars-, human impacts).

Seagrasses are short lived compared to trees. Soil / biomass carbon sinks are potentially easily disturbed. Do seagrasses still have a genuine/reliable/outstanding role to play in the carbon game?

Sea grass already grows pretty much everywhere it can grow, so I don't think we can cultivate a lot more (at least not without disrupting other sensitive marine ecosystems). It's more important to prevent pollution that would kill existing sea grass.

What are the limiting factors for it's range? Is there a critical nutrient that can be introduced?

It is grass. It needs sunlight and a substrate on which to grow. That means shallow/clear water over a sandy bottom, not a common thing in the ocean.

Seems like sunlight and substrate is much more common than seagrass is. I found this paper [1] that talks about the difference.

It estimated the area of suitable sunlight and substrate to be 4,320,000 km2 but estimated seagrass coverage of 177,000 km2.

I think this big difference indicates that there are additional factors at play.

https://iopscience.iop.org/article/10.1088/1748-9326/ab7d06

Earth has something like 150 million square kilometers of ocean. 4mil is a tiny corner of that area. Depth/light remains by far the primary limitation for sea grass, preventing it from even attempting to colonize the vast majority of the worlds oceans. Compare other carbon sinks like plankton which can exist across the ocean irrespective of water depth.

Sure, but Im not asking why seagrass doesn't cover the entire ocean or entire planet.

I'm asking why it doesn't cover more area than it currently does it appears that light and substrate is an insufficient answer. 90% of the area with suitable light and substrate is not covered, so something additional is going on.

> What are the limiting factors for it's range?

Fishermen and recreational sports

Have you got a reference for that?

This article suggests that "92% of the UK’s seagrass has been lost in the past two centuries, with 39% disappearing just since the 1980s, thanks to pollution from industry, mining and farming, along with dredging, bottom trawling and coastal development."

https://www.theguardian.com/environment/2021/nov/05/seagrass...

That’s what https://www.runningtide.com/ is trying to do

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