Dr Christopher Harley1, Fiona Beaty1, Graham Brownlee1, Carter Burtlake1, Lara Calvo1, Sandra Emry1, Dr. Alyssa Gehman1, Rebecca Hansen1, Dr. Amelia Hesketh1, Jessica Kennedy1, Jessica Li1, Natalie Rivlin1
1University Of British Columbia, Vancouver, Canada
The 2021 Western North American Heatwave brought unprecedented temperatures to the northwestern United States and western Canada, shattering the all-time Canadian high temperature record by over 4°C. These extreme temperatures coincided with very low tides, resulting in severe thermal stress in intertidal ecosystems. Mass-mortalities of intertidal invertebrates were documented over five degrees of latitude and many thousands of kilometers of shoreline. We documented the patterns of this mortality among species and across spatial scales on rocky shores. Bay mussels (Mytilus trossulus) and acorn barnacles (Balanus glandula) were especially heavily impacted, although extensive mortality was also found for oysters (Magallana gigas), rockweed (Fucus distichus), dogwhelks (Nucella lamellosa), and other taxa. At regional scales, mortality was low on the wave exposed shores of the outer coast where low tides occurred in the morning, higher in wave-protected inlets, and very high in the Salish Sea where low tides occurred in the mid-afternoon when air and sea surface temperatures were highest. Mortality was also strongly determined by local-scale factors that influence solar insolation. South-facing surfaces had much higher mortality that north-facing surfaces, and sessile animals protected by a seaweed canopy suffered less mortality than those without one. Very rough estimates suggest that many billions of intertidal animals died during the event. Ecological recovery is underway one year later, but the increased frequency and magnitude of extreme thermal events is likely to shift the system away from cold-water native species towards species that have been introduced from warmer parts of the world.
Presentation Slides – Chris Harley
Biography:
Chris Harley has been studying coastal marine ecosystems along the west coast and around the world for over 25 years. He completed his PhD at the University of Washington in 2001, and spent several years as a postdoctoral fellow at Stanford University and the University of California, Davis. He joined the faculty at the University of British Columbia in 2005, and he is currently joint-appointed in the Department of Zoology and the Institute for Oceans and Fisheries. He and his students are interested in how marine ecosystems are changing and why, with emphases on climate change, species interactions, and biodiversity.
