Phytomyxid infection in the non-native seagrass Halophila stipulacea in St Eustatius, Caribbean Netherlands.
Phytomyxids are a monophyletic group of biotrophs/parasites of a variety of organisms including seagrasses with a wide distribution range that includes the Caribbean. The seagrass Halophila stipulacea, native to the Indo-Pacific and Red Sea, is a known host for phytomyxids in the Mediterranean. However, to date phytomyxid infection has not been reported for H. stipulacea in the Caribbean. Infection in H. stipulacea is characterized by swelling of the leaf petioles due to gall formation, and coloration of these galls varies depending on the stage of maturity. H. stipulacea fragments with an apparent phytomyxid infection as well as uninfected fragments were collected in St Eustatius, north-eastern Caribbean, for comparative biometric analysis. Measurements of leaf length, leaf width, internode and root length were taken. Infected H. stipulacea fragments were significantly smaller than uninfected fragments across all biometrics measured, and exhibited similar gall colorations and swelling of the leaf petioles previously described for H. stipulacea in the Mediterranean. Based on our observations, the apparent infection in H. stipulacea fragments on St. Eustatius is likely caused by a phytomyxid parasite and is the first record of phytomyxid infection of this seagrass species in the Caribbean.