Climatic anomalies may create a long-lasting ecological phase shift by altering the reproduction of a foundation species

The resilience of ecological communities is often defined by one or a few species that have disproportionately important roles influencing many other species in the community. This is true for some areas of the Mediterranean Sea that are characterized by large brown fucoid algae of the genus Cystoseira that form dense underwater forests structurally similar to the giant kelps of the Pacific. While shorter than the giant kelp, Cystoseira species form dense underwater stands, contributing to the three‐dimensional complexity of the seascape (Fig. 1). These canopy‐forming seaweeds play a crucial role in primary production and nutrient cycling of temperate coastal ecosystems from the Mediterranean Sea to the Atlantic Ocean (Mineur et al. 2015) and act as “ecosystem engineers,” providing food, nursery, and shelter for a rich associated biota. Interacting human pressures are causing the widespread disappearance of these complex and productive species (Strain et al. 2014). As they are being replaced by simpler assemblages, biodiversity declines and ecosystem functions are altered (Falace et al. 2010, Sales et al. 2011). The natural recovery of these populations is hampered by their very limited dispersal ability (Capdevila et al. 2018