Abstract
Halophila stipulacea is an invasive seagrass in the Caribbean Sea that also harbors a phytomyxid endoparasite. Phytomyxean parasites are known to cause disease in agricultural crops and are documented to form galls in some seagrass species. Here we make the first report of phytomyxid infection of Halophila stipulacea in the Bahía de Jobos in Salinas, Puerto Rico. We found phytomyxid infected H. stipulacea at 3 of 5 sites examined; expanding the documented range of the Marinomyxa marina phytomyxid infection by almost 400 km from where it was first documented in 2018. Presence of the endoparasite has not impeded H. stipulacea dispersal and continued expansion of H. stipulacea will likely spread both the host seagrass and the endoparasite.