AbstractCoral reefs accommodate a myriad of species, many of which live in association with a host organism. Decapod crustaceans make up a large part of this associated fauna on coral reefs. Among these, cryptochirid crabs are obligately associated with scleractinian corals, in which they create dwellings where they permanently reside. These gall crabs show various levels of host specificity, with the majority of cryptochirids inhabiting a specific coral genus or species. Here, we report the first records of gall crabs living in association with two differentPoritesspecies in the Red Sea. Crescent‐shaped dwellings were observed inPorites rusand aPoritessp. in situ, and colonies with crabs were collected for further study in the laboratory. Using a combination of morphology and DNA barcoding, the crabs were identified as belonging toOpecarcinus, a genus only known to inhabit Agariciidae corals. The coral skeleton was bleached and studied under a stereo microscope, which revealed that thePoritescorals overgrew adjoining agariciidPavonacolonies. We hypothesize that the gall crab originally settled onPavona, its primary host of choice. Due to coral interspecific competition thePoritescolony overgrew the adjacentPavonacolonies, resulting in a secondary and never before reported association ofOpecarcinuswithPorites. These findings suggest that cryptochirid crabs can adapt to the new microenvironment provided by a different coral host and survive competition for space on coral reefs.