Ships, planes, and other vessels that come to rest on the seafloor introduce metals to the marine environment. Underwater cultural heritage (UCH) sites become important habitats for sessile invertebrates, but the materials they are made from can impact the composition of species living on them. We collected and analyzed images from three sites in Palau (two shipwrecks and one plane wreck from WWII) along with directly adjacent (1-5 m away) naturally occurring coral reefs. Community composition on UCH after similar to 80 years of submergence was significantly different from adjacent coral reefs, but summary metrics (i.e., richness, diversity, and evenness) were not. Differences in community composition were driven by which taxa-not how many-were present. Sponges were more common on UCH than coral reefs, reflecting their elevated metal tolerance and competitive dominance over corals. Coral taxa that dominated UCH habitats were characterized as "weedy" or "stress tolerant" in a previous study based on their life-history traits. However, stress-tolerant Porites corals were less common on UCH than coral reefs, potentially reflecting their sensitivity to bleaching in the presence of elevated iron. Coral juveniles on UCH were significantly different from adults on UCH and coral reefs, although their diversity was not sufficiently captured by our study. Overall, this study highlights differences in community composition between UCH habitats and adjacent natural reefs and raises questions for further investigation to understand the driving mechanisms.
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