ANEMOBS

Marine heatwaves are becoming increasingly frequent and intense in the Mediterranean Sea, with particularly strong effects in shallow coastal habitats. Symbiotic cnidarians are especially vulnerable because thermal stress can disrupt the association between the animal host and its photosynthetic dinoflagellate endosymbionts, leading to bleaching and potentially affecting organismal performance, survival and ecological interactions.

Unlike tropical corals, however, the responses of Mediterranean symbiotic cnidarians remain relatively little monitored in the field. The snakelocks anemone Anemonia viridis is abundant in very shallow rocky habitats and displays conspicuous variation in colour, from strongly pigmented green–brown individuals to partially or extensively bleached phenotypes during summer heatwaves. Because these populations are accessible from the shore and by snorkelling, they provide a unique opportunity to study the impacts of marine heatwaves on iconic Mediterranean organisms via repeated monitoring and observations at broad spatial and temporal scales.

Since summer 2025, AnemObs has monitored natural populations along the Côte Vermeille, in the South of France. Initial surveys combined colour measurements with observations of associated fauna; since 2026, this monitoring has been expanded to physiological measurements including symbiont density, chlorophyll content, energetic reserves and pollutant bioaccumulation. Standardised underwater photographs acquired with colour references provide the basis for linking visible phenotypes to biological condition.

AnemObs examines the biological responses of A. viridis populations to marine heatwaves and investigates whether the visible colour of snakelocks anemones can reveal their physiological and ecological responses to environmental stress, ultimately providing a simple indicator for large-scale monitoring of coastal ecosystem health.