The tolerance of a keystone ecosystem engineer to extreme heat stress is hampered by microplastic leachates

Plastic pollution and ongoing climatic changes exert considerable pressure on coastal ecosystems. Unraveling the combined effects of these two threats is essential to management and conservation actions to reduce the overall environmental risks. We assessed the capacity of a coastal ecosystem engineer, the blue mussel Mytilus edulis, to cope with various levels of aerial heat stress (20, 25, 30, and 35°C) after exposure to substances leached from beached and virgin low-density polyethylene pellets. Our results revealed a significant interaction between temperature and plastic leachates on mussel survival rates. Specifically, microplastic leachates had no effect on mussel survival at 20, 25 and 30°C. In turn, mussel survival rates significantly decreased at 35°C, and this decrease was even more significant following exposure to leachates from beached pellets; these pellets had a higher concentration of additives compared to the virgin ones, potentially causing a bioenergetic imbalanc..., , , # The tolerance of a keystone ecosystem engineer to extreme heat stress is hampered by microplastic leachates

This file contains the data required to reproduce analyses and figures reported in the associated manuscript.

## File Description

### **S7\_Temperature\_Plastic\_data.xlsx:**

This Excel file contains a dataset that results from 72h immersion-emersion experiments at 20°C with the second emersion where the mussels were exposed to the control temperature (20°C) or a low (25°C), moderate (30°C) or high (35°C) aerial heat stress event. It includes data for Control, virgin, and beached microplastic leachate (respectively, V-MPL and B-MPL) solutions. This file is used to produce the statistical analyses and figures in the manuscript and Supporting Information.

Note that the experiment was designed to mimic the typical tidal cycle at the sampling site (i.e., 6 hours immersion/emersion). For each experimental treatment (temperature × solution), 20 mussels were used in triplicates.

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