By comparing censuses of living, shallow marine molluscan communities with their associated time-averaged dead remains, we gain an understanding of compositional changes that have taken place through time. Our ability to diagnose anthropogenic or natural environmental changes based on dissimilarities between life and death assemblages, however, is contingent on the existence of a time lag between changes in the life assemblage and their manifestations in the time-averaged death assemblage (taphonomic inertia). Here, we utilized a unique set of multiyear census records of live and dead marine mollusks from Smuggler's Cove, St. Croix, U.S. Virgin Islands to determine the magnitude of taphonomic inertia in this setting. We found that over a more than three-decade interval from 1980 to 2012, both the life and death assemblage composition varied significantly. Most of this variation was driven by shifting rank orders of several key species, including: Cerithium litteratum, Modulus modulus, and lucinid bivalves. Decadal-scale variations in the life assemblage for the most abundant species, C. litteratum, are mirrored in death assemblages collected throughout the entire study interval, suggesting that the upper limit of taphonomic inertia is a decade or less. On the other hand, notable differences in composition between life assemblages, but not death assemblages, among samples collected 1.5 years apart suggest a minimum degree of inertia that is greater than seasonal. Precipitation and temperature, investigated as possible environmental drivers of change, vary significantly over the period in question, and likely play some role in regulating the abundances of these key species, although this remains speculative.