Effect of intertidal terrain surface aspect on Mytilus Species Complex distribution after the 2021 Pacific Northwest heat dome (PNWHD)

Abstract

In June 2021, the Pacific Northwest heat dome (PNWHD) impacted British Columbia
(BC), leading to unprecedented heat-induced mass mortality of blue mussels (Mytilus spp.).
The invasive species, Mytilus galloprovincialis (Mg) and Mytilus edulis (Me), may threaten
the native species, Mytilus trossulus (Mt) because Mt has a lower heat tolerance - resulting in
a shift in BC’s marine ecosystem dynamics. In this observational study, we examined four
cardinal aspects (north, south, east, and west) of Pasley Island, B.C., to understand the
distribution of Mytilus species’ post-disturbance recruitment, as each aspect reflects different
solar radiation levels. We expect to see Mt being the worst competitor of the species complex
at the south and west aspects, where mussel beds were more exposed to solar radiation at
daylight low tides during the PNWHD. We collected 40 mussels (10 from each aspect) from
Pasley Island. To identify the Mytilus species, DNA isolation, Polymerase Chain Reaction
(PCR), and gel-electrophoresis were performed. Our observational data showed higher counts
of non-native mussels (Mg and Me) than native juvenile mussels (Mt) in all aspects, with
higher differences in the south and west aspects. Me was found only in south and west
sample locations. Our findings suggest that Mg has the highest tolerance to direct solar
radiation relative to Me and Mt.