Shaping physiological plasticity: the impact of thermal regimes on benthic organismsResistance, Resilience and Phase Shifts

Zhengquan Zhou¹, Rhian Evans¹, Deevesh A. Hemraj², Juan Diego Gaitán-Espitia¹, Bayden D. Russell¹

¹The University of Hong Kong, China - ²Aarhus University, Denmark

Understanding the resilience and vulnerability of subtidal organisms to elevated temperatures is essential for predicting the ecological impacts of climate change. Benthic macrofauna, as key ecosystem engineers, play a crucial role in maintaining ecosystem functioning, yet they are increasingly subjected to thermal stress due to dynamic tidal regimes and rising ocean temperatures. While temperature naturally fluctuate, climate change is intensifying the frequency and severity of marine heatwaves, resulting in unpredictable thermal variability. To gain a broader understanding of how thermal stress affects benthic organisms, we first conducted a meta-analysis of recent experimental studies, synthesizing the physiological plasticity induced by various thermal stress. Building on the results, we performed mesocosm experiments with the intertidal bivalve Cerastoderma edule and the subtidal sea urchin Heliocidaris crassispina, exposing both species to thermal regimes of varying duration and intensity to simulate sustained and intermittent heat stress scenarios. Our preliminary results reveal key findings: i) sustained (longer than 10 days) or stronger exposure to stressful temperatures led to consistent increases in respiration rates, indicating uniform metabolic adjustments across individuals; ii) intermittent or weaker temperature cycles resulted in greater variability in respiration rates, reflecting diverse physiological responses within populations; and iii) the sequence of thermal exposure influenced the magnitude of metabolic responses, with progressively increasing thermal durations inducing more pronounced changes compared to decreasing regimes. These results underscore the importance of thermal intensity and timing in shaping physiological plasticity, emphasizing the need to account for temporal dynamics when evaluating the resilience of marine benthic organisms to climate change.