Abstract
Marine forests ecosystems are typical of temperate rocky benthic areas. These systems are formed by canopy-forming macroalgae (Laminariales, Tilopteridales, and Fucales) of high ecological value that provide numerous ecosystem services. These key species are also indicators of good environmental status. In recent decades, marine forests have been threatened by different impacts of local and global origin, putting their stability and survival in question. On a global scale, in many temperate areas of the planet, marine forests have been replaced by “sea-urchins barrens.” We present a general overview of sea-urchins’ population status in the archipelagos of Azores, Webbnesia (Madeira, Selvagens, and Canary Islands) and Cabo Verde, focusing on their role in the maintenance of the so-called “alternate stable state.” After an in-depth evaluation of the different anthropogenic and environmental pressures, we conclude that sea-urchins population explosion has been facilitated in the benthic habitats of Madeira and Canary Islands, preventing the recovery of canopy-forming macroalgae assemblages and being one of the main drivers in maintaining a stable barren state.Diadema africanumis the main barrens-forming species in Webbnesia, where it reaches high densities and strongly impacts macroalgal assemblages. On the other hand, in the most pristine areas, such as the Selvagens Islands and other Marine Protected Areas from the Canary Islands, the density ofD. africanumis up to 65% lower than in the nearby Madeira Island, and macroalgal communities are preserved in good status. This information is critical for marine environmental management, highlighting the urgent need for implementation of appropriate control mechanisms and restoration actions headed to the conservation of marine forests in Macaronesian archipelagos.
Highlights
Canopy-forming algae (Laminariales, Tilopteridales, and Fucales) have been widely recognized as the underwater forests of temperate rocky systems (Dayton, 1985)
It is a consequence of the high variability on the conditions and the interplay of multiple environmental factors of the areas that modulate the sea-urchin population dynamics (Figure 4)
Regulation of fisheries can lead the recovery of macroalgal forests by cascade effects, promoting the conservation of predatory fishes to maximize predation across the size spectrum of D. africanum (Clemente et al, 2010)
Summary
Canopy-forming algae (Laminariales, Tilopteridales, and Fucales) have been widely recognized as the underwater forests of temperate rocky systems (Dayton, 1985). Sea-urchin population explosions have been detected over the last decades, with the consequent loss of macroalgal covers from the Sargassaceae family as dominant habitat-forming species of the region (Tuya et al, 2004a,b). Sea-urchin species known to occur in Madeira archipelago include P. lividus, A. lixula, S. granularis, D. africanum, with lower abundances of A. elegans and C. longispinus (Wirtz, 1995).
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