That's very believable. Puritan protestants banned all kinds of things that produce "pleasure". How do you think westerners got so prudish about intercourse?

> but then I'd expect to see more seaweed etc in the South.

Warmer waters carry less oxygen(I think that's the gist of it), so less seaweed grows.

Just think about a perfect beach, with clear blue waters and seeing all the way down to the sand on the seafloor... you know it's somewhere very warm and there's no seaweed.