Marine wood-borers and burrowers can substantially alter habitats and human-created structures in the marine environment. While many marine borers and burrowers occur only in a few substrata, burrowing sphaeromatid isopods can damage a variety of substrata. On the Pacific coast of North America, burrowing by the non-native isopod, Sphaeroma quoianum, accelerates shoreline erosion and damages marine structures. We conducted a lab experiment to quantify the per capita burrowing effect of S. quoianum on four common estuarine substrata. After two months, isopods created longer and more voluminous burrows and removed the most material (per capita) in marsh banks and Styrofoam followed by sandstone and non-decayed wood. We also examined the burrow morphology (length, diameter, volume) of burrows of S. quoianum from those four substrata collected in the field. We observed longer and more voluminous burrows in marsh bank and Styrofoam substrata, although we only detected a significant difference in length between substrata. Based on our lab results, we estimate a population of 100 000 adult isopods burrowing for two months could remove approximately 176 liters of marsh bank, 103 1 of Styrofoam, 72 1 of sandstone, or 29 1 of non-decayed wood. While the per capita bioerosion effects are lower than some bioeroders, e.g., the shipworm Bankia setacea, the pholad Penitella penita, high densities and wide distributions of S. quoianum suggest it is a substantial bioeroder within the intertidal and shallow subtidal in temperate Coos Bay, Oregon, and perhaps the other estuaries it has invaded.