Comparative Phenology of Sargassum muticum and Halidrys siliquosa (Phaeophyceae: Fucales) in Limfjorden, Denmark

Abstract

Sargassum muticum (Fucales: Sargassaceae) has been present in Scandinavia since 1984. In Limfjorden, a shallow Danish sound, it has invaded the habitat of the indigenous Halidrys siliquosa (Fucales: Cystoseiraceae). Studies have suggested a displacement of indigenous relatives by Sargassum muticum and that this could be due to differences in life history strategies. Our study is the first to document the phenology of S. muticum at the northern part of its European distribution range (Scandinavia) and the first to document the phenology of Halidrys siliquosa. Thallus height and weight, species cover and tissue carbon, nitrogen and phosphorus were measured. For Sargassum muticum a strong seasonality with midsummer maxima, similar to previously published results from other European sites, was found. Halidrys siliquosa only exhibited moderate seasonality, if any. Hence, the two species were found to be functionally different and have different life histories. Our results support the idea that the competitive success of Sargassum muticum is caused by its pseudo-perennial life history compared to the truly perennial life histories of many indigenous relatives. Conversion factors between commonly used biometric measures were derived from the phenological data.

Epibiota communities of the introduced and indigenous macroalgal relatives Sargassum muticum and Halidrys siliquosa in Limfjorden (Denmark)

“…There was also a highly significant difference in thallus biomass among species at different sampling times. These results agree closely with the observations of Wernberg et al (2001), and suggest that the canopy habitat of the sampled specimens conformed to the quantitative and qualitative patterns hypothesised to influence the epibiota communities.…”

“…no differences among invader and indigenous species). S. muticum has been a dominant component of the macroalgal flora at our study site for more than 10 years (Wernberg-Møller et al 1998a), and because of large differences in abundance of the two macroalgae (Wernberg et al 2001) it cannot be ruled out that the epibiota community structure radically changed with the invasion of S. muticum and that the contemporary epibiota community structure of H. siliquosa is, to a large degree, the result of a 'spill-over' effect. The observed quantitative differences in epibiota between S. muticum and H. siliquosa are, however, independent of this, and thus a real consequence of the introduction of S. muticum.…”

“…Algal FW was used as a proxy for canopy habitat. This was justified by tight correlations between algal height and biomass (Wernberg et al 2001) as well as height and canopy volume (sensu Hacker and Steneck 1990) for both macroalgal species (T. Wernberg, M.S. Thomsen and P.A.…”

“…S. muticum and H. siliquosa both have coarsely branched thalli that create a relatively large canopy which may be a suitable habitat for a wide variety of fauna and flora (Mukai 1971;Withers et al 1975;Haage 1976;Norton and Benson 1983;Aguilar-Rosas and Galindo 1990;Taylor and Cole 1994). During the course of a year, however, the habit of S. muticum is characterised by dramatic variation whereas the habit of H. siliquosa is much more constant (Wernberg et al 2001): in spring, S. muticum grows from a small (10-15 cm) perennial basal structure into a large (100-120 cm) erect canopy before it senesces back in autumn, whereas H. siliquosa retains an erect canopy of intermediate size (~35 cm) throughout the year. We proposed that these quantitative (host size) and qualitative (host phenology) differences in resource (canopy habitat) availability were important to the epibiota community, and therefore tested the hypothesis that S. muticum and H. siliquosa support different epibiota biomass and species composition.…”

Periodicity of propagule expulsion and settlement in the competing native and invasive brown seaweeds,Cystoseira humilisandSargassum muticum(Phaeophyta)

“…Algal species from the family Cystoseiraceae are common natives of the habitats invaded by S. muticum throughout Europe (Fletcher & Fletcher, 1975;Jephson & Gray, 1977;Gunnill, 1985;Arenas et al, 1995;Viejo, 1997;Andrew & Viejo, 1998;Wernberg et al, 2000). Members of the Cystoseiraceae and Sargassaceae are closely related (Rousseau & De Reviers, 1999), and some researchers have suggested that indigenous Cystoseiraceae are displaced by S. muticum (Fletcher & Fletcher, 1975a;Viejo, 1997;Staehr et al, 2000).…”