Dispersal distances for propagules of Sargassum spinuligerum (Sargassaceae, Phaeophyta) measured directly by vital staining and venturi suction sampling

Dispersal of propagules from fertile thalli of Sargassum spinuligerum was measured in situ using a novel technique. Propagules were stained with Toluidine Blue while still attached to parent thalli. After 24 h, the density of settled propagules was determined at different distances from the stained thalli with a venturi suction sampler Previous measurements of propagule or spore dispersal have not differentiated sources, measured only distances of dispersal outside existing stands of marine algae, and combined propagule dispersal and settlement patterns with post-settlement survival. However, the technique described here allows direct measurement of propagule dispersal in marine algae. Dispersal of propagules was highly localized. Numbers of recovered stained propagules differed between November and December 1990 and these differences are assumed to reflect different levels of release. The December study had a greater total number of recovered propagules (approximately 100000 versus 12 000 collected in November) and a more rapid decline in settlement density with distance (96 % of stained propagules were collected within 0.25 m of parent thalli). There was an exponential decline in the densities of stained propagules (m-) with distance 98 % were collected within 1 m of parent thalli. The localized dispersal pattern observed in this study fits previous descriptions of contagious patterns of recruitment in Sargassm and observed clumping of adults of other fucalean algae.