The upper Northwestern Gulf basin is characterized by a relatively shallow but well developed continental shelf with an extensive system of mid‐ and outer shelf hard banks formed on unique tectonically created salt diapirs of varying origin and composition. Collections made by our laboratory from ∼30 m depth by SCUBA while participating in monitoring cruises to the National Marine Sanctuaries of the East and West Flower Garden Banks (Texas), Stetson Banks (Texas) and Sonnier Banks (Louisiana), and while dredging off Louisiana at ∼45–90 m depth, reveal a surprisingly different floristic composition among the sites. Several range extensions, new macroalgal records for the Gulf of Mexico, and the establishment of new species for the region indicate that the NW Gulf encompasses complex macroalgal biota. Our ongoing project includes the development of a modern taxonomic, phylogenetic, morphological and genetic database essential to informed management for preservation of biological diversity. It also provides a framework for seasonal algal composition against which long‐term trends and anomalies in algal distribution and health of the Gulf of Mexico can be assessed at future dates.