Species, community, and ecosystem-level responses following the invasion of the red alga Dasysiphonia japonica to the western North Atlantic Ocean
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Species invasions have been increasing in frequency worldwide, yet critical gaps remain in our understanding of how invaders affect community structure and ecosystem functioning, particularly during the initial stages of invasion. Even less is known about changes in the invader that may take place immediately following an invasion. This study examined the recent invasion of the red macroalga Dasysiphonia (formerly, Heterosiphonia) japonica to the western North Atlantic Ocean with the aim of filling in gaps in our understanding of the impacts that invasive seaweeds have at the species, community and ecosystem levels immediately following their establishment. Within 5 years of invasion, community composition had changed and biodiversity had decreased to nearly half of pre-invasion levels. In addition, the relative proportion of Dasysiphonia decreased by 35% over our four-year study from initially high levels shortly after establishment. We found evidence that functional traits of this initially aggressive invader changed over time, as it ultimately became a less aggressive, co-inhabiting member of the local algal community, particularly with respect to nutrient uptake and relative abundances, although native diversity remained low relative to pre-invasion levels. Using these realistic changes in community structure, including decreases in biodiversity, we also showed that nutrient uptake of algal assemblages changed over time, suggesting changes in the functional characteristics of invaded communities, with implications for ecosystem-level processes such as nutrient fluxes. This study provides rare empirical evidence about the successional stages occurring at the individual, community, and ecosystem levels during the first 5 years of an invasion.
KeywordsInvasive species Biodiversity Ecosystem functioning Nutrient uptake Dasysiphonia japonica
We thank N. Low, V. Perini, I. Rosenfield, and V. Selesnick for diving and laboratory assistance. K. Benes provided additional laboratory assistance. We would also like to acknowledge Northeastern University’s Marine Science Center Diving Program and Diving Safety Officers: L. Bentley-Magee, S. Genovese and T. Lyman. Research described in this publication was supported by the Massachusetts Institute of Technology Sea Grant College Program, under National Oceanic and Atmospheric Administration Grant Number NA14OAR4170077, MIT SG Project Number 2014-R/RCM-37; the National Science Foundation (Award OCE-0963010); Woods Hole Sea Grant (Subaward A100923) to M.E.S.B and C. S. Thornber; and the Fonds québécois de la recherche sur la nature et les technologies (FQRNT). This is contribution number 346 from the Marine Science Center of Northeastern University.
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