are multicellular, macroscopic, and generally benthic, marine algae
. As with all living organisms, they serve a purpose for the individual and a purpose for the whole. Their purpose for the individual is their own development, maintenance, and reproduction. Their purpose for the whole is to serve as a habitat and sometimes food for other sea creatures, as well as several valuable functions for human beings
, including used as a food, as fertilizer, a source of agar
, various biomedical uses, and so forth.