Timing is everything: the effect of tidal timing on biodiversity during heatwaves

Abstract

Tidepool communities are highly vulnerable to ecological disturbances and serve as indicators of ecosystem health. A comprehensive understanding of tidepool response and recovery is crucial for assessing the long-term impacts of heatwaves on biodiversity and how these ecosystems respond. In this study, we examined how eight tidepools at Friday Harbor Labs, San Juan Island, WA, were impacted by a four-day heating event, where air temperature increased 5-10 °C above the mean monthly max normal. We surveyed biodiversity within pools before, three days, and eight days after the heatwave that took place from May 12th to May 15th. Coinciding with this heating period, a neap tide occurred, resulting in most of the observed pools being protected from exposure. Consequently, pools that remained submerged did not experience the adverse effects of increased air temperature. As a result, biodiversity did not change significantly over time. The pool at the highest elevation indicated no significant change in biodiversity during the heating event either– despite being exposed during the heatwave–likely due to its inhabitants being adapted for these stresses. This research highlights the importance of considering exposure and elevation in anticipating the effects of stress events on tidal communities.