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A regime shift in intertidal assemblages triggered by loss of algal canopies: A multidecadal survey

Álvarez-Losada, Óscar, Arrontes, Julio, Martínez, Brezo, Fernández, Consolación, Viejo, Rosa M.
Marine environmental research 2020 v.160 pp. 104981
Fucus serratus, canopy, climate change, coasts, dieback, food webs, littoral zone, macroalgae, surveys, Spain
Canopy-forming macroalgae recently experienced a worldwide decline. This is relevant, because canopies sustain complex food webs in temperate coasts. We assessed the die-back of the canopy-forming alga Fucus serratus in N Spain, at its warm distributional range boundary, and its effects on associated assemblages. We combined long-term descriptive surveys with canopy-removal experiments. Results showed that rapid shifts to turf-forming communities were mostly the direct consequence of the canopy loss, rather than a concurrent process directly triggered by climate change. The switch alters the whole food web, as the prominent role of F.serratus and other cold-temperate intertidal fucoids is not being replaced by functionally equivalent species. Canopy loss caused a rapid biotic homogenization at regional scale which is spreading towards the west, from the edge to the central part of the former distributional range of F.serratus in N Spain. The most obvious effect is the ecological and functional impoverishment of the coastal system.