Sargassum muticum (Fucales, Phaeophyta): regrowth and interaction with Rhodomela larix (Ceramiales, Rhodophyta)

Invasion of Sargassum muticum in Limfjorden (Denmark) and its possible impact on the indigenous macroalgal community

“…Clearing experiments (Deysher & Norton 1982, de Wreede 1983, Viejo 1997) have shown, however, that S. muticum can benefit from catastrophic events whereby hard substrates are cleared of other algae by physical disturbance, because it can regenerate fast from its basal part and because its recruits seem to be superior competitors compared to recruits of most other species. S. muticum may, therefore, be able to affect the reestablishment of other species after future disturbances (de Wreede 1983, Critchley et al 1987) and thus increase its abundance further. Grown Sargassum muticum populations cannot be sustained for prolonged periods at salinities below 15 ‰, since reproduction becomes impaired (Kjeldsen & Pinney 1972, Steen 1992.…”

“…Deysher & Norton (1982) found that dense populations of naturally occurring algae prevented settlement and development of S. muticum, thus indicating that juvenile S. muticum is a poor competitor relative to grown specimens of other algae. On the other hand, Ambrose & Nelson (1982) and de Wreede (1983) found that dense populations of adult S. muticum could restrict settlement and early development of leathery and filamentous algae such as Macrocystis pyrifera and Rhodomela larix, respectively, indicating that, as competitors, grown specimens of S. muticum are superior to juveniles of many other algae. We also found a weak decline in the cover of foliose and filamentous algae between 1992 and 1997, indicating competitive interference between S. muticum and these groups.…”

“…Experiments have indicated that successful settlement and initial development of germlings depend on the availability of cleared substrate with low or no competition from other algae (Deysher & Norton 1982, de Wreede 1983, Critchley et al 1987, Andrew & Viejo 1998). When first established, however, S. muticum may efficiently prevent settling and development of other algae due to high recruit densities and fast growth (Ambrose & Nelson 1982, De Wreede 1983, Critchley et al 1990). Critchley et al showed that the irradiance was reduced by 95% within the uppermost 5 cm of a dense S. muticum surface canopy, thus preventing understory algae to develop and thrive.…”

“…Although several authors have suggested that the invasion of S. muticum may have had a significant impact on the structure of indigenous algal communities through competitive displacement and/or exclusion (e.g. Fletcher & Fletcher 1975, Rueness 1989, Walker & Kendrick 1998, observational and experimental evidence is still rather scarce (see however, Ambrose & Nelson 1982, de Wreede 1983, Critchley et al 1987, Viejo 1997.…”

Grazer-controlled recruitment of the introduced Sargassum muticum (Phaeophyceae, Fucales) in northern Europe

“…Several studies suggest that Sargassum spp. are susceptible to grazing by sea urchins (De Wreede 1983), herbivorous fish (McCook 1996), amphipods and gastropods (Norton & Benson 1983). Grazing is probably the most important factor in reducing survival of juvenile fucoid algae (Vadas et al 1992, Chapman 1995.…”