Abalone Mortality Associated With Hypoxia in Tidepools During a Summer Heatwave.

Marine heatwaves are increasing in frequency, duration, and intensity, posing a growing threat to coastal ecosystems and contributing to widespread mortality of marine organisms. Along the intertidal rocky platforms of south-western Western Australia, extreme low tides coinciding with heatwave conditions can expose habitats to elevated temperatures and prolonged periods of limited water exchange. The Roe's abalone (Haliotis roei), a species of commercial and recreational importance, occurs both on exposed platform surfaces and within intertidal tidepools. During a marine heatwave, substantial mortality of H. roei was observed within tidepools, whereas little to no mortality was recorded among individuals inhabiting adjacent platform surfaces. Measurements of seawater temperature indicated similar thermal conditions between tidepools and the platform edge. In contrast, dissolved oxygen concentrations were markedly reduced within tidepools, reaching severely hypoxic levels. These observations suggest that oxygen depletion, potentially acting in combination with heatwave conditions and restricted water exchange, may have contributed to the observed mortality of H. roei within tidepool habitats during the heatwave event.