Effects of TBT dosing on common species of macroinvertebrates associated with Thalassia testudinum were documented, and compared with measured tracer burdens of different species. Species with the strongest response, some showing virtual population lethality after 3 to 5 weeks of dosing at the highest dosing rate, included polychaetes (Pista quadrilobata and Nereis pelagica), an amphipod (Cymadusa compta), and molluscs (Crepidula maculosa and Cumingia tellinoides). Tissue tracer concentration at a given dose level varied over about an order of magnitude across 18 affected and unaffected species. Accumulated burden of TBT was, in part, inversely related to the size of an organism, but the variability suggested that diet/ecological role of species may be a significant aspect to consider in dose-burden models.