The green hitchhikers: epiphytic filamentous algae and a green algal weed associated with eucheumatoids cultivated in an outdoor land-based nursery

Abstract Epiphytic algae threaten the productivity of cultivated carrageenophytes, particularly Kappaphycus spp. and Eucheuma denticulatum, yet their diversity remains poorly documented. Using DNA barcoding (ITS and tuf A) integrated with culture-based observations, we identified Ulva torta, U. ohnoi, U. tentaculosa, U. intestinalis, Cladophora sp., and Bryopsis sp. as filamentous epiphytes, while Chaetomorpha linum occurred as an unattached algal weed. ITS phylogeny recovered two distinct C. linum lineages, highlighting the need for authenticated type or topotype sequences. These findings underscore the need for molecularly validated inventories to detect overlooked epiphyte diversity and strengthen biosecurity surveillance and early warning in cultivated eucheumatoids.