Thanks to @k8thegr8 for sharing this with us. My "Encyclopedia of Texas Seashells" (Tunnell et al., 2010) has this information: "Known to live in Port Isabel and Port Aransas in inlet-influenced areas. On aerial roots of Avicennia germinans [= Black Mangrove]".
This appears to be the northernmost record on the Texas coast so far on iNat! And there are several iNat records of Black Mangrove in/near Port O'Connor:
https://www.inaturalist.org/observations?place_id=1766&subview=map&taxon_id=62865