Distribution ofSargassum natans and some of its epibionts in the Sargasso Sea

Sargassum was collected during the Sargasso Sea Eel Expedition in Spring 1979. On average, the morphological form typeSargassum natans (I) made up 85 % of the total wet weight of the samples. South of the thermal front, larger amounts of weeds were observed. Here, the bladder size ofS. natans (I) was significantly smaller (surface 47±7 mm²) than in the northern part (surface: 64±15 mm²), while phylloids showed no differences. The composition and density of some epibionts were examined.Membranipora tuberculata (Bryozoa),Clytia noliformis (Hydrozoa) and the calcarious algae Melobesia sp. (Rhodophyta) were studied quantitatively according to different features at 17 stations.M. tuberculata was the most abundant epibiont followed byC. noliformis. Compared with these species, "Melobesia sp." occurred in considerably lower quantities.M. tuberculata showed a preference for bladders rather than phylloids;C. noliformis was found more frequently on phylloids than on bladders. "Melobesia sp." did not show any preference. Frequency and abundance of these epibionts were higher north of the thermal front than south of this front. North of the frontS. natans (I) was less abundant but bladders were larger.