High resilience of an invasive mussel to cumulative impacts of ocean warming and oil pollutionResistance, Resilience and Phase Shifts

Anton Kovalev^1,2, Mukaila Alhassan^1,2, Gil Rilov^2,1

¹University of Haifa, Israel - ²National Institute of Oceanography, Israel

Marine organisms are increasingly exposed to the combined impacts of global and local stressors, but the study of the impact of multiple stressors is still in its infancy. We have studied the combined impacts of oil pollution and ocean warming or marine heatwaves (MHW) on the survival and functioning the invasive tropical mussel Brachidontes pharaonis, that became highly dominant on the southeast Mediterranean rocky reefs but also suffered mass-mortality and was exposed to an oil spill off the coast of Israel in February 2021. To investigate this, we conducted microcosm and mesocosm experiments to assess the cumulative effects of temperature and heavy fuel oil on B. pharaonis. In the microcosm, mussels were exposed to short-term (5-day) heavy fuel oil exposure (90 ppm) under a range of temperatures to examine potential erosion of their thermal performance. In the mesocosm, we simulated oil spill scenarios (0, 100, and 500 ppm heavy fuel oil) for 14 days, followed by MHW conditions (control: 29°C; moderate MHW: 32°C; extreme MHW: 35°C) for 15 days. We measured metabolic performance (respiration), condition index, mortality rates, and byssus production traits, including attachment probability, byssus attachment force, and byssal plaque production intensity. Our results showed that oil exposure, even at high concentrations, did not affect the metabolic performance, mortality rates, or condition index. However, at control and moderate MHW temperatures, oil exposure stimulated byssus production. In contrast, under extreme MHW conditions, byssus production was suppressed. This suppression, despite unchanged metabolic performance, suggests a shift in energy allocation strategy, with critical implications for mussels’ ability to survive under combined thermal and pollution stress. These findings highlight the resilience of this key invasive habitat-forming species to the cumulative impacts of climate change and anthropogenic pollution, and emphasizes the need for further research into such interactions.