Biodiversity influences invasion success of a facultative epiphytic seaweed in a marine forest
The biotic resistance hypothesis predicts that more diverse communities should have greater resistance to invasions than species-poor communities. However for facultative and obligate epiphytic invaders a high native species richness, abundance and community complexity might provide more resources for the invader to thrive to. We conducted surveys across space and time to test for the influence of native algal species abundance and richness on the abundance of the invasive facultative epiphytic filamentous alga Lophocladia lallemandii in a Mediterranean Cystoseira balearica seaweed forest. By removing different functional groups of algae, we also tested whether these relationships were dependent on the complexity and abundance of the native algal community. When invasion was first detected, Lophocladia abundance was positively related to species richness, but the correlation became negative after two years of invasion. Similarly, a negative relationship was also observed across sites. The removal experiment revealed that more complex native communities were more heavily invaded, where also a positive relationship was found between native algal richness and Lophocladia, independently of the native algal abundance. Our observational and experimental data show that, at early stages of invasion, species-rich seaweed forests are not more resistant to invasion than species-poor communities. Higher richness of native algal species may increase resource availability (i.e. substrate) for invader establishment, thus facilitating invasion. After the initial invasion stage, native species richness decreases with time since invasion, suggesting negative impacts of invasive species on native biodiversity.
KeywordsBenthic community Invasibility Cystoseira Epiphytic Functional groups Lophocladia Mediterranean marine community Removal experiment Seaweed
This project has received funding from the Spanish Ministry Projects (CGL2016-76341-R and CGL2015-65346-R) and Fundación Biodiversidad. This output reflects only the authors’ views and the European Union cannot be held responsible for any use that may be made of the information contained therein. Managers of ACNP are acknowledged for sampling permissions. This is a contribution to CoCoNET (FP7 Grant Agreement: 287844) and INTRAMURAL CSIC 201330E065. EBD receives financial support from the Spanish Ministerio de Economía y Competitividad, through the Severo Ochoa Program for Centres of Excellence in R + D + I (SEV-2012-0262). EC is a member of the Marine Conservation Research Group (www.medrecover.org) from the Generalitat de Catalunya.
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