Can this particular weed be eaten as-is, by human or animal, or is it known to e.g. be toxic or full of waste? Because it seems to me rather beneficial that the ocean washes it up on the shoreline ready for pick-up.
This is a losing battle if all they do is shovel or fish it faster. The conditions in the environment are such that they favor the seaweed. Treat the cause not the effect, or else they’ll have to employ some very fancy genetic engineering to halt it.
Find a way to lower salt & arsenic content, and it could be an excellent fertilizer.
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