Unusual distribution of floating seaweeds in the East China Sea in the early spring of 2012

Abstract

Floating seaweeds play important ecological roles in offshore waters. Recently, large amounts of rafting seaweed have been observed in the East China Sea. In early spring, juveniles of commercially important fish such as yellowtail accompany these seaweed rafts. Because the spatial distributions of seaweed rafts in the spring are poorly understood, research cruises were undertaken to investigate them in 2010, 2011, and 2012. Floating seaweed samples collected from the East China Sea during the three surveys contained only Sargassum horneri. In 2010 and 2011, seaweed rafts were distributed only in the continental shelf and the Kuroshio Front because they had become trapped in the convergence zone of the Kuroshio Front. However, in 2012, seaweed was also distributed in the Kuroshio Current and its outer waters, and massive strandings of seaweed rafts were observed on the northern coast of Taiwan and on Tarama Island in the Ryukyu Archipelago. Environmental data (wind, currents, and sea surface height) were compared among the surveys of 2010, 2011, and 2012. Two factors are speculated to have caused the unusual distribution in 2012. First, a continuous strong north wind produced an Ekman drift current that transported seaweed southwestward to the continental shelf and eventually stranded seaweed rafts on the coast of Taiwan. Second, an anticyclonic eddy covering northeast Taiwan and the Kuroshio Current west of Taiwan generated a geostrophic current that crossed the Kuroshio Current and transported the rafts to the Kuroshio Current and its outer waters. Such unusual seaweed distributions may influence the distribution of fauna accompanying the rafts.

Oceanic currents drove population genetic connectivity of the brown alga Sargassum thunbergii in the north‐west Pacific

“…The species can be used for alginate production and development of pharmaceuticals (Park et al ., ) as well as a food source for holothurian or abalone aquaculture (Seo et al ., ). Recent research cruises reported that Sargassum beds could be transported to fringe areas of the continental shelf and waters influenced by the KC after they become detached off Zhejiang Province, China (Komatsu et al ., ; Mizuno et al ., ). Phylogeographical studies of the brown algae S. hemiphyllum , S. horneri and S. fusiforme , which comprise the main component of floating Sargassum patches, showed that historical events (e.g.…”

Knowledge of Climate Change and the Perception of Nigeria’s Coastal Communities on the Occurrence of Sargassum natans and Sargassum fluitans

“…That could be explained by all those disturbances in the ocean environment such as increase in sea temperature, changes in global water cycle, changes in salinity which affect sea currents and marine life. Wind also affects currents which influence the transport and distribution of floating seaweeds according to [30]. These oceanic parameters are linked in such a way that any disturbance to one induces immediate imbalance in the others.…”

Attachment strength of the subtidal seaweed Sargassum horneri (Turner) C. Agardh varies among development stages and depths

“…Thalli mature in spring. Dense forests develop on hard substrata, such as bedrock or boulders, surviving from depths of 1–3 m (Umezaki 1984; Komatsu et al 2014). Populations grow down from the surface layer into the subtidal zone, reaching depths >7 m. On the Sanriku coasts of Japan, S. horneri forms stands of thalli that are attached to the bottom to a depth of 7 m and float upward, forming canopies on the sea surface (Komatsu et al 2015).…”

“…The thalli have many gas-filled vesicles that provide buoyancy for the floating canopy. Detached thalli float on the surface and often form rafts of tangled seaweed (Komatsu et al 2006). A large number of floating S. horneri rafts occurred in the southern Yellow Sea drifting from south to north (Cai et al 2014), and they were shown by genetic markers to be from Zhejiang province, China and Jiangling, Korea (Chen et al 2016).…”

“…In the spring–early summer period, most of the floating rafts on Japanese coastlines contain detached thalli of S. horneri (Yoshida 1963; Ikehara 2004), and in the East China Sea, the floating rafts contain only S. horneri fronds (Komatsu et al 2007, 2009, 2014; Mizuno et al 2014), on which commercially important pelagic fish lay their eggs. These fish species include flying fish, Pacific saury (C ololabis saira ), and Japanese halfbeak ( Hyporhamphus sajori ), which spawn egg-bearing filaments that attach to the floating seaweed rafts (Komatsu et al 2009).…”