User:Tillman/Mastocarpus papillatus

Mastocarpus papillatus, commonly known as "Turkish washcloth" or (in its other lifestage) "tar spot" or Petrocelis, is an interesting marine alga  species with two distinct lifecycle phases.

The crusts are generally more resistant to grazing then the frond phase, so the relative abundance of crust vs. frond will reflect the grazing pressure at a given locality.