Ricardo Augusto Scrosati

In intertidal environments, temperature fluctuations at hourly temporal scales are ecologically relevant because of the physiological stress that organisms must endure as a result. Tides constitute the main source of such changes, as low tides periodically expose intertidal habitats to aerial conditions, which can exhibit unusually high and low temperatures in summer and winter, respectively. The present study identifies another source of strong hourly thermal variation, one that acts only upon seawater (not air) temperature. Shortly after the arrival of cyclone Dorian to the Atlantic Canadian coast in September 2019, in-situ loggers revealed that sea surface temperature (SST) decreased in a matter of hours by 10-12 °C in intertidal environments. Data from online environmental services indicated that neither tidal amplitude nor air temperature were likely responsible for this marked SST drop. Conversely, data on wind speed support the notion that shear-induced vertical mixing of the water column caused by this cyclone was the main reason for the pronounced intertidal cooling. This is in line with previous studies that found offshore SST drops with tropical hurricanes. It remains to be seen how the observed decrease in SST may have affected intertidal organisms, as they were acclimated to summer conditions when Dorian hit the coast. As the frequency and intensity of cyclones in temperate latitudes is predicted to increase with climate change, cyclone-related intertidal thermal ecology might deserve further attention.