The structure of biogenic habitat and epibiotic assemblages associated with the global invasive kelp Undaria pinnatifida in comparison to native macroalgae

Abstract

Kelp forests dominate temperate and polar rocky coastlines and represent critical marine habitats because they support elevated rates of primary and secondary production and high biodiversity. A major threat to the stability of these ecosystems is the proliferation of nonnative species, such as the Japanese kelp Undaria pinnatifida ('Wakame'), which has recently colonised natural habitats in the UK. We quantified the abundance and biomass of U. pinnatifida on a natural rocky reef habitat over 10 months to make comparisons with three native canopy-forming brown algae (Laminaria ochroleuca, Saccharina latissima, and Saccorhiza polyschides). We also examined the biogenic habitat structure provided by, and epibiotic assemblages associated with, U. pinnatifida in comparison to native macroalgae. Surveys conducted within the Plymouth Sound Special Area of Conservation indicated that U. pinnatifida is now a dominant and conspicuous member of kelp-dominated communities on natural substrata. Crucially, U. pinnatifida supported a structurally dissimilar and less diverse epibiotic assemblage than the native perennial kelp species. However, U. pinnatifidaassociated assemblages were similar to those associated with Saccorhiza polyschides, which has a similar life history and growth strategy. Our results suggest that a shift towards U. pinnatifida dominated reefs could result in impoverished epibiotic assemblages and lower local biodiversity, although this could be offset, to some extent, by the climate-driven proliferation of L. ochroleuca at the poleward range edge, which provides complex biogenic habitat and harbours relatively high biodiversity. Clearly, greater understanding of the long-term dynamics and competitive interactions between these habitat-forming species is needed to accurately predict future biodiversity patterns.

Status, trends and drivers of kelp forests in Europe: an expert assessment

“…Aquaculture is also the primary vector of its introduction in Spain (Báez et al 2010). Local expansion has been documented in Brittany, as in UK and Ireland (Heiser et al 2014;Minchin and Nunn 2014;Arnold et al 2016), in the last two decades whereas Mediterranean populations decline, probably as a response to warm temperature and a predicted expansion was not confirmed by field data in Portugal (Veiga et al 2014). There is thus a qualitative invasive trend (i.e.…”

Undaria pinnatifida: A case study to highlight challenges in marine invasion ecology and management

“…Comparative studies have shown that Undaria harbors a distinct and reduced epifaunal and epifloral community when directly compared to native kelp species (Arnold, Teagle, Brown, & Smale, 2016;Raffo et al, 2009). However, as evidence suggests that Undaria is not able to displace native kelps, this does not indicate ecological impact in itself.…”

The role of kelp species as biogenic habitat formers in coastal marine ecosystems

“…Undaria pinnatifida supports impoverished assemblages compared with native habitat-forming 247 macroalgae (Arnold et al, 2016;Raffo et al, 2009). In Argentina, the larger holdfasts offered by M. 248 pyrifera support higher faunal richness and abundance than U. pinnatifida (Raffo et al, 2009).…”

“…In Argentina, the larger holdfasts offered by M. 248 pyrifera support higher faunal richness and abundance than U. pinnatifida (Raffo et al, 2009). In the 249 UK the longer-lived holdfasts offered by native perennial kelps support greater richness and biomass 250 of sessile fauna (Arnold et al, 2016). Both studies stated, however, that native kelp species may not 251 be negatively impacted by non-native U. pinnatifida, which may occupy a different niche both 252 spatially and temporally, and community-wide responses to invasion are likely to be complex and 253 context-specific.…”