Abstract
The distribution and ecology of the invasive brown alga Fucus serratus along the 500 km Atlantic coast of Nova Scotia, Canada, has been poorly explored. We observed significant intertidal penetration at four sites in the southwestern part of the province, and then examined numerous sites along the Atlantic coast of Nova Scotia. Surveys of attached algae in intertidal and shallow subtidal zones and wrack show that F. serratus has become a dominant plant in the low to mid-intertidal zone and can be expected on headlands along the South Shore of Nova Scotia where it can occupy up to 40% of the intertidal zone with cover >75% and mean densities of up to 10 kg m−1. In this zone, F. serratus has replaced Chondrus crispus as the major canopy species, although C. crispus and Corallina officinalis remain primary understory species. At slightly higher elevations, F. serratus was common as an understory beneath Ascophyllum nodosum and Fucus vesiculosus. While geographic spread along the Atlantic coast might reflect the natural dispersal capacity of F. serratus, we hypothesize that the ecological extension into the intertidal zone may be facilitated by harvesting of A. nodosum and by climate change in an ocean-warming hotspot.
Funding source: Natural Sciences and Engineering Research Council of Canada http://dx.doi.org/10.13039/501100000038
Award Identifier / Grant number: 24304
About the authors

David J. Garbary is Professor of Biology and Co-ordinator of Interdisciplinary Studies in Aquatic Resources at St. Francis Xavier University. He has degrees from Acadia University (BSc, MSc) the University of Liverpool (PhD), and was a research associate at the University of British Columbia. His primary research in Nova Scotia has been the biology of Ascophyllum nodosum, cell biology of red and brown algae, and the evolution of land plants. From 2015 to 2020 he was the Editor-in-Chief of Phycologia.

Megan P. Fass is a MSc student at Saint Francis Xavier University, supervised by Prof. David J. Garbary. Their research focuses on the impacts of the commercial rockweed harvest on the macroalgae communities of Nova Scotia, and incomporates remote sensing techniques into their work. Megan completed their undergraduate degree at the University of British Columbia, where they studied the impacts of wave exposure on intertidal macroalgal community change over time.

Herb Vandermeulen studied with Prof. R.E. DeWreede (Ph.D. in Botany in 1984). After a post-doc in Israel, he returned to Canada and developed whole lake remediation methods, was Chair of the National Marine Indicators Working Group, and National Coordinator of Marine Environmental Quality. At the Bedford Institute of Oceanography he explored nearshore habitat mapping techniques and provided science advice on the commercial harvest of seaweeds. In retirement, he teaches Diversity of Algae at Dalhousie University with his partner Beverly Hymes.
Acknowledgments
We thank Carolyn Bird and Beverly Hymes for assistance with field work.
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Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.
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Research funding: MPF was supported by a postgraduate fellowship from the Natural Sciences and Engineering Research Council of Canada (NSERC). This work was supported by NSERC Discovery grants to DG.
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Conflict of interest statement: The authors declare no conflicts of interest regarding this article.
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