Macroalgae are among the most important and diverse primary producers in coastal ecosystems, ranging in form from >30m high giant kelp to mm-scale filamentous turfs, and shape coastal ecosystems worldwide.  The diversity of macroalgae has hampered a general understanding of the processes structuring these communities. Functional groups based on morphology have been erected to alleviate this issue, and have had some success in interpreting ecological patterns, but quantitative tests of their predictions have often failed and much information is lost in broad groupings. We propose to take a quantitative approach to trait-based ecology of macroalgae, building on the success of work on phytoplankton.  Our project combines basic field and laboratory research to measure macroagal traits with rigorous trait-based modeling and quantitative field surveys to validate models. The result will be a framework for general understanding of macroalgal communities. This project will be strengthened by the presence of a long-term ecological research program in the study area: the Santa Barbara Coastal LTER (SBC-LTER) that focuses on kelp forest ecosystems.  SBC LTER monitors biomass and productivity of common species of macroalgae and benthic community structure at several reefs in the Santa Barbara Channel, including some of our proposed study sites. This project will be done near or on the UCSB campus, on small boats or in the laboratory, and will involve undergraduate and graduate students, including underrepresented groups, in field and laboratory work and independent research projects.