Symbiotic endolithic microbes reduce host vulnerability to an unprecedented heatwave.

Area of Science:

• Marine Biology
• Ecology
• Symbiosis Research

Background:

• Intertidal ecosystems face increasing threats from severe marine heatwaves.
• Mytilus edulis (blue mussels) are vulnerable to thermal stress due to high environmental variability.
• Endolithic microbes within shells can alter shell properties, potentially mitigating heat stress.

Purpose of the Study:

• To investigate the role of endolithic microbes in mitigating thermal stress in Mytilus edulis during the 2022 English Channel heatwave.
• To quantify the thermal buffering effect provided by the endolith-mussel symbiosis.
• To explore the ecological implications of this symbiosis for mussel populations and associated ecosystems.

Main Methods:

• Field observations during the 2022 heatwave in the English Channel.
• Deployment of biomimetic temperature loggers to measure mussel body temperatures.
• Comparison of survival rates and thermal profiles between mussels with and without endolithic symbionts.

Main Results:

• Microbial infestation significantly enhanced mussel survival, especially in higher, hotter shore zones.
• Endolithic symbionts provided a thermal buffer, with temperature differences up to 3.2°C observed compared to non-infested mussels.
• The protective effect was more pronounced under conditions of extreme heat stress.

Conclusions:

• The endolith-mussel symbiosis is a critical factor in mussel resilience to extreme heat events.
• This interaction influences mussel survival, reef-building capacity, and has cascading effects on biodiversity and ecosystem services.
• Abiotic factors dynamically shape the parasitic-mutualistic relationship between endolithic microbes and mussels.