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Topic

Spatiotemporal Distribution, Abundance, and Persistence of Kelp Forests in the Broughton Archipelago, British Columbia, Canada

Department of Geography

Date & location

• Friday, December 13, 2024

• 12:00 P.M.

• Clearihue Building, Room B017

• and Virtual Defence

Reviewers

Supervisory Committee

• Dr. Maycira Costa, Department of Geography, University of Victoria (Supervisor)

• Dr. Amanda Bates, Department of Biology, UVic (Member) 

External Examiner

• Dr. Kylee Pawluk, Department of Aquaculture, Government of British Columbia 

Chair of Oral Examination

• Dr. Darcy Mathews, School of Environmental Studies, UVic

   

Abstract

Kelp forests are highly productive coastal ecosystems on 25% of the world’s coastlines, providing key biogenic habitats in nearshore ecosystems. These ecosystems are experiencing variable changes worldwide, ranging from detrimental impacts from climate change and pollution to trophic collapses. Still, in British Columbia (BC), Canada, the kelp distribution and drivers of kelp change remain largely unknown in many locations. Thus, local-scale studies are needed to understand kelp dynamics to inform marine spatial planning decisions for coastal practitioners. In particular, the Broughton Archipelago, BC, located in Kwakwakaʼwakw territories, supports floating kelp forests of various species compositions and sizes in a spatially explicit environmental gradient across an outer archipelago subregion and an inner fjord subregion. The Mamalilikulla First Nation, ‘'Namgis First Nation, and the Kwikwasut’inuxw/Haxwa’mis First Nation, who formed the Broughton Aquaculture Transition Initiative (BATI), are interested in the status and trends of kelp forests due to their utility as juvenile salmon habitat. This research investigates kelp forests' spatiotemporal distribution, abundance, and persistence in the Broughton Archipelago. We first identify environmental and biotic variables that drive spatial differences in kelp forest distribution and abundance. We achieved this by mapping floating kelp abundance (giant kelp: Macrocystis pyrifera, bull kelp: Nereocystis luetkeana) at 31 focal sites across the environmental gradient using unmanned aerial vehicle and high-resolution satellite imagery, compiling environmental data from in-situ sources and environmental models, and characterizing grazer (sea urchins, Strongylocentrus spp.) and predator (sunflower sea stars, Pycnopodia helianthoides) abundances from remotely operated vehicle footage. Second, we investigate the spatiotemporal persistence and resilience of kelp forests in the face of climate change. This was achieved by creating long-term (1984 to 2023) and short-term (2016 to 2023) time series of floating kelp areas in association with environmental drivers of change using medium- (30 m) to high- (3 m) resolution satellite imagery, and spatially combining yearly kelp areas to identify spatial patterns of kelp persistence. Overall, we found that the lower sea-surface temperatures, flatter bottom slopes, and higher tidal current speeds typical of the archipelago subregion were positively associated with kelp abundance; whereas the warmer sea-surface temperatures, steeper bottom slopes, and lower tidal current speeds found in the fjord subregion were negatively associated with kelp abundance, reinforcing the known spatial patterns of kelp distribution and abundance found in other studies across the BC coast. Biotically, sea urchin and Pycnopodia abundances did not significantly affect kelp abundance. Kelp forests were temporally persistent, with most kelp areas displaying increases or no change in kelp areas, and kelps were more persistent in their centers than the edges of each kelp bed. These findings provide a baseline understanding of kelp distribution, abundance, persistence, and their associated environmental and biotic drivers in the Broughton Archipelago. Ultimately, this can contribute to the conservation and management of kelp forest ecosystems by local communities and First Nations and inform a broader regional understanding of the spatiotemporal patterns of kelp forests in the Northeast Pacific Ocean.