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The ecological role of invading Undaria pinnatifida: an experimental test of the driver–passenger models

South, Paul M., Thomsen, Mads S.
Marine biology 2016 v.163 no.8 pp. 175
Fucales, Undaria pinnatifida, adverse effects, colonizing ability, littoral zone, macroalgae, macroinvertebrates, models
There have been dramatic increases in the frequency of invasions and distributions of invaders worldwide, yet the ecological roles of invasive macroalgae are poorly understood. Here, hypotheses about (1) the mechanisms and (2) the impact of invasion in stands of native canopy-forming algae were tested. First, native canopies were removed to possibly facilitate an invasion by Undaria pinnatifida. Then, invading U. pinnatifida was removed from half of the disturbed plots to test for its impact on early succession and recovery of the recipient assemblage. Recruitment success of the invader, per cent cover of sessile species, counts of mobile macroinvertebrates and recruitment of canopy-forming species were contrasted among disturbed and non-disturbed plots characterized by either native canopies or established U. pinnatifida stands. The removal of native canopies resulted in strong recruitment of U. pinnatifida, whereas only low abundance was found in plots dominated by native canopy-formers. There were few effects of invading U. pinnatifida on native sub-canopy species or the recruitment of fucoid algae. The only significant invasion effect within the disturbed plots was a negative effect on the alga, Colpomenia sinuosa that was also facilitated by disturbance. Together these results suggest that U. pinnatifida was a “passenger”, not “driver”, of ecological change. This study supports the notion that invasion success can be decoupled from invasion impact, particularly for invaders that only dominate in limited temporal windows. U. pinnatifida is a highly successful cosmopolitan invader, but its direct impacts on local intertidal communities appear limited and specific to species that have similar traits.