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Marine Ecology Progress Series

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MEPS 733:1-26 (2024)  -  DOI:

Local and regional variation in kelp loss and stability across coastal British Columbia

Samuel Starko1,2,3,*, Brian Timmer1,3, Luba Reshitnyk4, Matthew Csordas1,3, Jennifer McHenry1, Sarah Schroeder5, Margot Hessing-Lewis4, Maycira Costa5, Amanda Zielinksi6, Rob Zielinksi6, Sarah Cook7, Rob Underhill8, Leanna Boyer8,9, Christopher Fretwell8, Jennifer Yakimishyn10, William A. Heath11, Christine Gruman12, Dipti Hingmire13, Julia K. Baum1,3,#, Christopher J. Neufeld3,14,#

1Department of Biology, University of Victoria, 3800 Finnerty Rd., Victoria, British Columbia V8P 5C2, Canada
2School of Biological Sciences, University of Western Australia, Crawley 6009, WA, Australia
3The Kelp Rescue Initiative, Bamfield Marine Sciences Centre, 100 Pachena Rd., Bamfield, British Columbia V0R 1B0, Canada
4Hakai Institute, Heriot Bay, British Columbia V0P 1H0, Canada
5Department of Geography, University of Victoria, 3800 Finnerty Road, Victoria, British Columbia V8P 5C2, Canada
6Hornby Island Diving Ltd., 10795 Central Road, Hornby Island, British Columbia V0R 1Z0, Canada
7Coastal and Ocean Resources, 759A Vanalman Ave, Victoria, British Columbia V8Z 3B8, Canada
8Mayne Island Conservancy, 455-A Dixon Road, Mayne Island, British Columbia V0N 2J2, Canada
9Stqeeye’ Learning Society, PO Box 407, Salt Spring Island, British Columbia V8K 2W1, Canada
10Pacific Rim National Park Reserve, Parks Canada Agency, 2040 Pacific Rim Hwy, Ucluelet, British Columbia V0R 3A0, Canada
11Project Watershed Society, 2536a Rosewall Crescent, Coutenay, British Columbia V9N 5N3, Canada
12Huu-ay-aht First Nations, 170 Nookemus Road, Anacla, British Columbia V0R 1B0, Canada
13School of Earth and Ocean Sciences, University of Victoria, 3800 Finnerty Road, Victoria, British Columbia V8P 5C2, Canada
14University of British Columbia Okanagan, 1177 Research Road, Kelowna, British Columbia V1V 1V7, Canada
*Corresponding author: #These authors contributed equally to this work as co-senior authors

ABSTRACT: Kelp forests are among the most abundant coastal marine habitats but are vulnerable to climate change. The Northeast Pacific has experienced recent large-scale changes in kelp abundance and distribution, but little is known about changes north of the British Columbia (BC)-Washington border. Here, we assessed whether and how floating canopy kelp (Macrocystis pyrifera, Nereocystis luetkeana) distributions have changed in recent decades along the extensive coast of BC. We assembled and analysed available kelp distributional data, comparing snapshots of kelp linear extent from 1.5-3 decades ago (1994-2007) to recently collected data (2017-2021) across 11 different subregions spanning the province. We then leveraged timeseries, where available (n = 7 data sets), to contextualise patterns of change. In aggregate, the data suggest that kelp forests have declined considerably in some parts of the province, but with variable patterns of change across BC. In the warmest areas (southern BC), kelp persistence was negatively correlated with mean summer sea surface temperatures, which at times exceeded known thermal tolerances. In contrast, in northern subregions, top-down control by sea urchins and otters appeared to modulate kelp dynamics, with declines occurring in 2 subregions despite cool ocean temperatures. Timeseries data suggest that many declines occurred around the 2014-2016 marine heatwave, an event associated with sustained warming and altered trophic dynamics. Our results suggest that the extent of BC’s kelp forests has declined in some places in recent decades, but that regional and local-scale factors influence their responses to environmental change.

KEY WORDS: Climate change · Extirpation · Kelp forest · Marine heatwaves · Sea star wasting disease · Trophic cascade · Macrocystis · Nereocystis

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Cite this article as: Starko S, Timmer B, Reshitnyk L, Csordas M and others (2024) Local and regional variation in kelp loss and stability across coastal British Columbia. Mar Ecol Prog Ser 733:1-26.

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