The theory of island biogeography (TIB) predicts that species richness in isolated areas is determined by the processes of colonization and extinction, and, in turn, governed by island size and isolation. Metacommunity models extend the TIB, predicting that both habitat and species interactions are important drivers of community vital rates and structure, and that marine metacommunities will exhibit higher extinction/colonization rates relative to terrestrial ecosystems. Here we demonstrate that oceanic banks can be considered islands, and document how application of these theories advanced our understanding of the dynamics of these submarine islands following the fishery-induced collapse of predatory groundfish populations. We employed a 48 yr dataset of fish communities on 10 offshore banks of the Scotian Shelf, Northwest Atlantic Ocean to examine colonization and extinction rates before and after the collapse. Bank-specific colonization, extinction and turnover rates were quantified using the island R package to correct for imperfect detectability, inherent to all sampling of natural systems. Colonization and extinction events were briefly unbalanced following the predator collapse, and reflected in increases in species richness and turnover, most notably on the largest banks. However, over the longer term, a dynamic equilibrium of colonization and extinction events prevailed on 8 of the 10 banks. This resulted in a generally time-invariant species richness, and a negative relationship between species turnover and bank area, as predicted by theory. Our study provides support for the relevance of island biogeography and metacommunity theories in guiding exploration and understanding of the mechanisms governing marine community vital rates and structure.