Spatial and temporal persistence of nearshore kelp beds on the west coast of British Columbia, Canada using satellite remote sensing

• Published in: Remote sensing in ecology and conservation Vol. 6; no. 3; pp. 327 - 343
• Main Authors: Schroeder, Sarah B., Boyer, Leanna, Juanes, Francis, Costa, Maycira, He, Kate, Lecours, Vincent
• Format: Journal Article
• Language: English
• Published: Oxford John Wiley & Sons, Inc 01.09.2020; Wiley
• Subjects: Bull kelp; change analysis; coastal regions; Coastal zone; Coasts; Ecosystem services; Ecosystems; Environmental changes; Environmental conditions; Food chains; Gravel; Habitats; Image classification; Kelp beds; Low currents; nearshore habitat; Nutrients; Regions; Reliability aspects; Remote sensing; Rivers; Salinity; satellite; Satellites; Shorelines; Substrates; Time series; Trends; Water quality; British Columbia Canada; Canada; Fraser River; Strait of Georgia; Salish Sea
• ISSN: 2056-3485; 2056-3485
• DOI: 10.1002/rse2.142

Bull kelp Nereocystis luetkeana is an important foundation species, providing structural habitat and nutrients to the nearshore ecosystems of temperate coastal regions in the Northeast Pacific. Sensitive to environmental conditions, this species thrives in cool, nutrient‐rich water. Reported declines in the extent and distribution of bull kelp may reflect changing oceanic conditions and result in breakdown of important food chains and ecosystem services. This study uses satellite remote sensing to map kelp bed extent from 2004 to 2017 in the Salish Sea on the West Coast of British Columbia, Canada and examines the relationship between trends in kelp persistence with local and global scale environmental conditions. In our study area, we found limited evidence of kelp decline. Local scale effects of current speed, temperature and substrate type may play a role in the spatial and temporal patterns of persistence. Kelp persistence was higher in sites with rocky substrate and lower in areas with low current and gravel or sand substrate. A decline in kelp was recorded from a high in 2015 to a low in 2017; however, a longer and more complete record is needed to distinguish declining trends from natural variability. This work highlights the importance of continued collection of long‐term data for use in time series of kelp abundance as multiple factors can influence the reliability of image interpretation and kelp classification. A time series of high‐resolution satellite imagery was used to detect floating kelp (Nereocystis luetkeana) in the nearshore region of coastal British Columbia. Kelp persistence over time was calculated and the spatial trends relating to environmental conditions of substrate, temperature and currents were examined. Areas with both high currents and rocky substrate had the highest kelp extent and greatest persistence, while those regions with either low currents or gravel substrate had higher variability and lower kelp presence. A decline in kelp extent was measured from a high in 2015 to a low in 2017.