Read more in The New York Times

Colemann Pat Dundass surveyed the rocky foreshore of the Kinnelly Islands, where the seaweed spread like a carpet.

To anyone else, it looked verdant. To Mr. Dundass, it wasn’t quite right. Someone had hacked it the wrong way years ago, he said, and it hadn’t grown back properly since.

Mr. Dundass, 78, has been harvesting seaweed for decades, like his father before him. Ashore, he plucked tangles of it from the rocks: the red moss, a homeopathic remedy steeped in tea; the long green strands, used as fertilizer for potatoes; bulbous green stalks, a salty snack edible right from the sea.

“Cutting seaweed up to now,” Mr. Dundass said, “it was very easy, nobody bothering you.”