Molecular identification of green algae from the rafts based infrastructure of Porphyra yezoensis

► According to ITS and rbcL sequences, 84 samples fell into four clades. ► Four clades: LPP complex, Ulva flexuosa, Blidingia sp. and Urospora spp. ► Based on the 5S rDNA, only one of the 84 samples belonged to Ulva prolifera. ► U. prolifera bloom in Qingdao sea area might have more than one origin. ► Porphyra aquaculture rafts was only one of the possible causes.