Distribution and diversity of the sympatric macroalgae of the pelagic Sargassum horneri in the Yellow and East China seas.

The massive pelagic Sargassum horneri (Turner) C. Agardh, 1820 has increasingly occurred in the Yellow Sea and East China Sea. Significant intrusion of floating S. horneri into the southwestern Yellow Sea, the major bloom region of the green tides, has aroused speculations on the blooming mechanism and confounded concurrent prevention practices of green tides. The floating S. horneri were surveyed and sampled throughout its distributional range to study the diversity and abundance of sympatric macroalgae, including the epiphytes and non-epiphytes. The study showed that both types of macroalgae commonly coexisted with the pelagic S. horneri and showed distinct distribution patterns. The non-epiphytic green macroalgae, primarily Ulva prolifera , were free floating with S. horneri. They were initiated from the nearshore water of Jiangsu in late April followed by a rapid accumulation and expansion as the green tide developed. The non-epiphytic green algae were mostly restricted in the western coast of southern YS with biomass decreasing evidently toward offshore. Four species in Phaeophyta were commonly detected epiphytic on the pelagic S. horneri in the survey region and Proselachista taeniiformis was dominant. Unlike the co-occurring green algae, the species composition and abundance of epiphytes have no significant variation in the distributional range of the pelagic S. horneri. High frequency (80%) and abundance (0.25 ± 0.17 g Epi /g Sar) of epiphytes indicated significant biological interactions with their hosts and ecological functions of this pelagic system, which deserves further investigation. • Epiphytic and co-occurring macroalgae of pelagic S. horneri in YS and ECS showed distinct distribution patterns. • U. prolifera was not attaching to pelagic S. horneri and restricted in the coasts of southwestern YS. • High frequency and abundance of algae in Phaeophyta was observed epiphytic on the pelagic S. horneri. • Proselachista taeniiformis was the dominant epiphyte of S. horneri in the survey region. [ABSTRACT FROM AUTHOR]