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

Abstract

Sargassum muticum (Phaeophyceae, Fucales) has recently been introduced to Limfjorden (Denmark) where its closest relative is the indigenous Halidrys siliquosa. Previous studies have demonstrated large quantitative (canopy biomass) and qualitative (canopy persistence) differences in the habitat available to epibiota within the canopies of these two macroalgae. We therefore hypothesised that these algae would support different epibiota communities and tested this by sampling the epibiota of S. muticum and H. siliquosa on seven occasions throughout 1997 by enclosing entire thalli in mesh bags. We found 53 epibiota taxa and, with only one exception, they were all recorded on both host species. Species richness and abundance of epibiota exhibited clear seasonal variation on both host species, although epibiota biomass was seasonally constant on H. siliquosa but not on S. muticum. These patterns were consistent with the different life histories of the host species. There was a weakly negative correlation between thallus size and epibiota biomass for both host species. When taking species-specific seasonal variation in thallus size into consideration, S. muticum and H. siliquosa were found to support significantly different epibiota biomasses. Multivariate analyses showed that epibiota community structure was different, although highly overlapping, between the two species, whereas there was an almost parallel temporal development in epibiota community structure. We conclude that it is unlikely that the introduction of S. muticum to Limfjorden has caused major changes in local epibiota community structure. However, the standing stock of epibiota is likely to have increased.

How an introduced seaweed can affect epibiota diversity in different coastal systems

“…The likeness of the two epibiotic assemblages on Helgoland also indicates that most of the associated species are non-selective and have a non-specific relationship with their host plant, an observation confirmed by other studies investigating epibiota on morphologically similar algae (e.g. Taylor and Cole 1994;Viejo 1999;Wernberg et al 2004). Wernberg et al (2004) argue that this general pattern (lack of host specificity) may resemble an adaptation of epibiota to the fluctuating environment of temperate regions, because the seasonality of many epibiota species tracks that of the algae.…”

“…Therefore, it can be considered primarily as an addition to the native macroalgal pool, providing additional habitat space and consequently facilitating epibiota abundances. This was also observed on other European coasts (Withers et al 1975;Viejo 1999;Wernberg et al 2004). Wernberg et al (2004) point out, however, that, in the absence of pre-invasion data, this conclusion warrants caution, as it is equally possible that the epibiota community of native algae undergoes radical change following the invasion of an exotic species.…”

“…1), when associated organisms are most abundant on all investigated algal species (Viejo 1999;Rindi and Guiry 2004;Wernberg et al 2004) and potential differences between epibiota communities are expected to be most pronounced. At both study sites, sampling was performed during tidal submergence and at the same tidal elevation, i.e.…”

“…Taylor and Cole 1994;Viejo 1999;Wernberg et al 2004). Wernberg et al (2004) argue that this general pattern (lack of host specificity) may resemble an adaptation of epibiota to the fluctuating environment of temperate regions, because the seasonality of many epibiota species tracks that of the algae.…”

“…We expected a neutral effect of S. muticum for Helgoland's rocky shore, because the introduced and the native seaweed hosts have very similar morphologies and occur in overlapping habitats (Wernberg et al 2004). In contrast, an increase in epibiota diversity was expected for Sylt.…”