Spatial distribution mechanism of Sargassum horneri around Gouqi Island, Shengsi,China*.

This research surveys distribution and growing states of S.horneri under different habitat by using underwater quadrat sampling method, and also studies the relationship, in both large and small scales (among sites and inside site), between the spatial distribution of S.horneri and influenced factors, thus provides references to protect and recover seaweed field. It has been found that in among sites , much of S.horneri grows in sheltered bay, where plant distribution density and plant length are obviously higher than those in stations of wave exposure (P<0.05), while water motion and turbidity in sites of wave exposure are inversely more remarkable than those in sheltered sites (P<0.05), which suggests that water motion become a limiting factor on the horizontal distribution and growing of S.horneri. Within site, the vertical distribution of S.horneri has distinctive characteristics. Distribution density and plant length of S.horneri at the bottom of intertidal zone are obviously higher than those in subtidal zone (P<0.05).Study result also shows that, in small scale, the distribution density and plant length of S.horneri have some degree of correlation with the roughness, slope gradient and slope aspect of attachment substances. However, correlation analysis manifests that water depth has the highest correlation with the distribution density and plant length of S.horneri (r=-0.337,p=0.001), and roughness has a second highest correlation (r=0.175,p=0.092), while slope gradient and slope aspect merely have small correlation.So,it indicates that light condition maybe become the other limiting factor on the vertical distribution and grow of S.horneri.Study finally finds that physical characters of attachment substances are not the vital factors in affecting the distribution of S.horneri. We can infer that sediment is the key factor in affecting spatial distribution pattern of S.horneri,as a result of water motion arise resuspention of sediment to influence the light condition which S.horneri need.