Seafoam avoidance is driven by both chemosensory and contact cues and points towards the presence of soft-surface thigmotaxis in the intertidal gastropod Littorina littorea

Seafoam accumulation in coastal waters has long been acknowledged as ecologically, socially and economically relevant. However, its putative effects on the intertidal biota have been alarmingly under-researched despite the ubiquitous nature of onshore foam formation. This study examines the behavioural responses of the common periwinkle, Littorina littorea , exposed to two types of seafoam: a fresh seafoam (freshly formed) and an aged seafoam (collected after three hours of exposure in the field), using experimental assays carried out under controlled laboratory conditions. L. littorea consistently avoid seafoam, and exhibit a stronger aversion for fresh seafoam. They avoid crossing both seafoam, suggesting that contact cues play a crucial role in this avoidance behaviour. In this context, we introduce the concept of soft-surface thigmotaxis, by which L. littorea is able to follow soft physical discontinuities. Snails exhibited more tortuous movements and reduced speed before actually getting into physical contact with the fresh seafoam, suggesting that chemosensory influence foam avoidance, probably due to repellent volatile compounds requiring further identification. Observations suggest that snails show differential responses potentially influenced by variations in foam properties, such as phytoplankton content and the physical properties of the seafoam. Seafoam avoidance by L. littorea could have wider ecological implications by disrupting the snails' ability to find refuges, increasing their vulnerability to other environmental stresses. Investigating surfactants and pollutants in seafoam is crucial due to their toxicity to aquatic life. The study highlights the need for interdisciplinary research to fully understand and mitigate seafoam's effects on intertidal organism. • Marine foams are ubiquitous in the intertidal zone. • Littorina littorea actively avoid foam, with a stronger aversion for fresh one. • L. littorea respond to both chemosensory and contact cues. • Littorinids follows soft physical discontinuities like seafoam. • Seafoam accumulation can cause additional stress to rocky intertidal species.