Macroalgae species of the genus Cystoseira s.l. (Fucales, Phaeophyceae) are habitat-forming species from temperate areas characterised by their high productivity and associated diversity. These key species are clearly declining worldwide due to multiple anthropogenic and biotic pressures, such as habitat loss or climate change-related effects. These impacts are leading to local/regional extinctions of marine forests and increasing their populations' fragmentation and isolation. In the actual context of global climate change, discrete extreme temperature events in the ocean, known as marine heatwaves (MHWs), are rising as threats to marine boundaries in many areas of the planet. We analysed 74 years of daily sea surface temperature data on the occurrence of MHWs in the Cantabrian Sea (N Iberian Peninsula), finding a clear increase in their frequency, duration and intensity in the last 20 years. Also, we performed a 10-d mesocosm experiment to assess how MHWs affect synthetic fragmented and non-fragmented patches of Ericaria selaginoides. After this, those synthetic patches were deployed in a tidal rock pool during 10-d to detect effects on the recruitment of epifaunal assemblages. Mesocosm experiment results showed how E. selaginoides biomass, productivity and oxygen consumption significantly decreased as MHW intensity increased. Field deployment revealed that abundance, composition and structure of the epifaunal assemblages were significantly affected by the interaction of prior stress by MHWs and patch fragmentation. Overall, our results showed how a canopy-forming macroalga is affected by extreme temperature events and, consequently, having effects on the recruitment of epifauna according to the level of fragmentation of the microhabitat.

Primary Presenter: Alejandro Bernal-Ibáñez, MARE - Madeira (alejandro.bernal@mare-centre.pt)

Authors:

Ignacio Gestoso, University of Cádiz  (ignacio.gestoso@uca.es)

Eva Cacabelos, Hydrosphere S.L.  (evacacabelos@yahoo.es)