Abstract

Some species of macroalgae continue to live for extended periods of time after detachment and may even maintain reproductive structures, yet very little is known about this process. Here, we describe the presence of sporophylls (with sporogenous tis- sues) on floating kelp rafts of Macrocystis spp. along the coast of Chile. Surveys were conducted at nine sites (18–501 S) during austral summer 2002, and floating kelp rafts were seen and collected at seven of these nine sites (between 22 and 501 S). Fifteen (26.8%) of the 56 samples had sporophylls, indicat- ing maintenance of sporophylls after detachment. Some of the kelp sporophytes with reproductive blades showed signs of having been afloat for long periods (indicated by the large size of attached stalk- ed barnacles). Additionally, experiments showed that floating kelps released viable zoospores. To un- derstand the reproductive dynamics of floating kelps, we compared these results with information from attached populations of Macrocystis spp. at nearby coastal sites. In general, attached kelp had higher proportions of sporophylls than floating rafts, suggesting that detachment may negatively affect reproductive status. Nevertheless, floating kelps remained functionally reproductive, suggest- ing that zoospores may be dispersed via floating rafts. Published reports on other macroalgae indi- cate that some species (Lessoniaceae, Fucaceae, and Sargassaceae) are fertile and probably release zoo- spores or zygotes while floating or drifting in ocean currents. Because dispersal distances achieved by spores of most macroalgae are relatively short, re- lease of spores from floating algae may be an alter- native mechanism of long-distance dispersal.