Halimeda's a genus of green macroalgae. The algal body (thallus)'s composed of calcified green segments. Calcium carbonate's deposited in its tissues, making it inedible to most herbivores. Halimeda's responsible for distinctive circular deposits in various parts of the Great Barrier Reef on the north-east coast of Queensland, Australia. Halimeda beds form in the western or lee side of outer shield reefs where flow of nutient-rich water from the open sea allows them to flourish, and are the mos… (More on Halimeda)