Abstract We organized environmental observations (Sea Surface Temperature, chlorophyll concentration, and primary productivity) and biological diversity indices based on reconstructed fisheries landings obtained from the Sea Around Us project to address two objectives: 1) to understand whether adjacent Large Marine Ecosystems (LMEs) of the Americas form megaregions for assemblages of commercially-valuable fish; and 2) to assess changes in the diversity of fisheries landings in LMEs of the Americas over time (1982 to 2010). To test for similarities between LMEs, we used the seascape approach of unsupervised clustering of annual mean environmental observations and fisheries-derived diversity indices. Beta-diversity estimates based on fisheries landings were used to evaluate the degree to which species spanned LMEs. Temporal trends were computed for each dataset by linear least-squares. Three megaregions emerged when considering similarities in species composition of fisheries landings, fisheries-derived diversity indices, and characteristic environmental conditions among LMEs. These include (A) the South Brazil Shelf, East Brazil Shelf, and North Brazil Shelf LMEs, (B) the Gulf of Mexico and Southeast U.S. Continental Shelf LMEs, and (C) the Northeast U.S. Continental Shelf, Scotian Shelf, and Newfoundland-Labrador Shelf LMEs. No megaregions emerged for the Pacific Ocean. While there were some shared species assemblages between the California Current and the Gulf of Alaska, the Gulf of California, and the Pacific Central-American Coastal LMEs, these showed different average environmental conditions and fishery-derived diversity indices, so they did not cluster as a megaregion. In the Pacific Ocean, the high dissimilarity in the fisheries is in part related to different top-down pressures and strong regional differences in oceanographic properties, including upwelling and impacts of El-Nino Southern Oscillation events. Overall, between 1982 and 2010, seven LMEs diversified their fisheries (Pacific Central-America Coastal, Patagonian Shelf, South Brazil Shelf, East Brazil Shelf, North Brazil Shelf, Southeast U.S. Continental Shelf, and Newfoundland-Labrador Shelf). This may be due to a number of reasons including decreasing fishing pressure but expansion of target stocks due to management quotas, changes in regional markets, competition, effort, or a decrease in particular target stocks. Three LMEs showed increasingly less diversified fisheries, namely the California Current, the Northeast U.S. Continental Shelf, and the Caribbean Sea LMEs. While in some cases this may be related to historical overfishing, such as in the Northeast U.S. Continental Shelf LME, the California Current LME has been subjected to strong and conservative management practices. The Caribbean Sea LME was likely subjected to heavy fishing at a time of rapid environmental change.