The pools swell with thong weed, sea lettuce, bladderwrack and more.

The idea of using seaweed to make an anti-wrinkle cream may strike some people as just a load of bladderwrack.

Among them was the algae that many readers would know as bladderwrack, and which is also closely related to the islanders' blackweed.

They were rafts of unknown weed, great clots of mutant bladderwrack that moved suddenly away from the city under some motive power of their own.

Fields of kelp and edible bladderwracks grew on rafts suspended below the city, alongside mesh-cages full of crustaceans and food-fish.