Abstract
Brown macroalgae within the genus Cystoseira are some of the most relevant “ecosystem-engineers” found throughout the Mediterranean and the adjacent Atlantic coasts. Cystoseira-dominated assemblages are sensitive to anthropogenic pressures, and historical declines have been reported from some regions. In particular, Cystoseira abies-marina, thriving on shallow rocky shores, is a key species for the ecosystems of the Canary Islands. In this work, we analyse changes in the distribution and extension of C. abies-marina in the last decades on the island of Gran Canaria. This alga dominated the shallow rocky shores of the entire island in the 1980s; a continuous belt extended along 120.5 km of the coastline and occupied 928 ha. In the first decade of the 21st century, fragmented populations were found along 52.2 km of the coastline and occupied 12.6 ha. Today, this species is found along 37.8 km of the coastline and occupies only 7.4 ha, mainly as scattered patches. This regression has been drastic around the whole island, even in areas with low anthropogenic pressure; the magnitude of the decline over time and the intensity of local human impacts have not shown a significant correlation. This study highlights a real need to implement conservation and restoration policies for C. abies-marina in this region.
Highlights
Coastal ecosystems are suffering severe impacts worldwide due to excessive human pressure
The Canary Islands are a “hot spot” of marine biodiversity in the North Atlantic (Sansón et al 2001), which is threatened by human impacts, e.g. pollution, overfishing, occupation of the coast and progressive tropicalization (Riera et al 2015)
During the 1980s (Fig. 2A), Cystoseira abies-marina dominated the rocky coasts of Gran Canaria, along 120.5 km of coastal perimeter, covering 928 ha
Summary
Coastal ecosystems are suffering severe impacts worldwide due to excessive human pressure. Along rocky shores of temperate and subtropical areas, large canopy-forming brown algae, in particular kelps (Laminariales, Phaeophyceae, Ochrophyta) and fucoids (Fucales, Phaeophyceae, Ochrophyta), are the dominant species in pristine environments (Schiel and Foster 2006). These large perennial macroalgae are considered as “engineering species” (Jones et al 1994), because their three-dimensional structure dramatically alters the physical, chemical and biological environment. The loss of these well-structured and diverse ecosystems facilitates the appearance of less complex habitats, such as filamentous algal turfs, ephemeral seaweed assemblages and barren grounds dominated by encrusting algae and sea urchins (Benedetti-Cecchi et al 2001, Ling et al 2015)
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