New approaches to the study of temperate reefs: nighttime light pollution and the role of the microbiome

The last decade has witnessed a rapid and increasingly user-friendly technological development in data collection, capable of providing us with information on coastal systems at relatively large spatial and temporal scales (e.g. through unmanned airborne vehicles or drones, to the use of satellites), at very small spatial scales (such as increasingly low-cost sequencing techniques), or on little-studied aspects of coastal marine ecology (such as the role of natural and anthropogenic sound or light pollution). Despite a consequent increase in knowledge, many aspects remain poorly understood, such as the role of artificial light at night (ALAN) on temperate reefs, currently affecting over 22% of the world’s coastline. In particular, the paucity of studies on coastal marine primary producers is still evident, which is at odds with the role of seaweeds in supporting key ecosystem services, including carbon capture and biodiversity, especially in case of habitatforming macroalgae. In addition, evidence suggests that microorganisms play crucial roles in seaweeds’ health and functioning, posing questions on their importance in modulating ALAN impacts. To test for the potential role of microbiome in mediating ALAN effects on habitat-forming seaweeds, in summer 2024 we selected eight intertidal rockpools, along a sandstone shore in the northwestern Mediterranean Sea, dominated by canopy-forming macroalgae in the genus Cystoseira s.l.. Within each pool, macroalgal thalli were tagged and either treated with Betadine® to significantly disrupt the microbiome community or left intact as controls. Four randomly selected pools were then lit for four nights during a new moon period, by means of white LED lights to simulate coastal light pollution conditions. Maximum photosynthetic activity was monitored at the beginning and at the end of the experiment, to investigate the physiological response of macroalgal individuals. Thalli were then destructively sampled and data on richness and abundance of mobile invertebrates were collected to estimate effects on seaweeds’ vagile associated community. Results will shed light for the first time on the role of microbiome in mediating the effects of a still underestimated stressor, helping to define the best strategies for managing its impacts in urban environments.