Effect of a Marine Heatwave on Intertidal Kelp Percent Cover at Wizard Islet, BC

Abstract

Intertidal species are threatened by warming air and ocean temperatures, as they live near their thermal tolerance. In order to determine how intertidal kelp species respond to a marine heatwave, which brings warmer than average temperatures to an area, a long term monitoring dataset from Wizard Islet, British Columbia was examined. The percent cover of Alaria marginata, Hedophyllum sessile, Egregia menziesii, and Laminaria setchelli at varying tidal heights were compared before and after the heatwave. There were significant declines in percent cover for all species after the heatwave in 2017 with total kelp cover dropping from 43% to 13.6%. In 2020, the percent cover for all kelp increased to 26.5%, but this trend is not significant. This indicates there is no significant recovery in kelp from 2017 to 2020. There is large variation in species response in 2020 and highlights the importance of examining individual species trends in order to best protect the rich biodiversity of the rocky intertidal.