The Role of Sea-Urchins in Marine Forests From Azores, Webbnesia, and Cabo Verde: Human Pressures, Climate-Change Effects and Restoration Opportunities

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 On a global scale, in many temperate areas of the planet, marine forests have been replaced by “sea-urchins barrens.”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 africanum is 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 of D. africanum is 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.

Surface Integrity Could Limit the Potential of Concrete as a Bio-Enhanced Material in the Marine Environment

“…Df: degrees of freedom; MS: mean sum of squares; bold: significant results (P (perm) <0.05). related to the decline of local ecosystems, such as native seaweed canopies (Cacabelos et al, 2016a;Bernal-Ibáñez et al, 2021), seagrass meadows (Tuya et al, 2014), and barnacle beds (Cacabelos et al, 2016b;Martins et al, 2016). Therefore, the impacts of coastal construction are highly relevant, regardless of the construction material used (Cacabelos et al, 2018;Sempere-Valverde et al, 2023b).…”

“…The shallow hard bottoms of Madeira are dominated by barren grounds of crustose coralline algae (CCA) resulting from urchins grazing activity (Bernal-Ibáñez et al, 2021;Monteiro et al, 2021). Calcifying epilithic organisms such as CCA can act as ecosystem engineers, as the superposition of calcareous biogenic layers cumulatively increases structural complexity (Steneck, 1986;this study).…”

Benthic community zonation from mesophotic to deep sea: Description of first deep-water kelp forest and coral gardens in the Madeira archipelago (central NE Atlantic)

“…Events of overgrazing can lead to severe reductions in plant biomass and in extreme cases to impoverished urchin barrens (Ling et al, 2015). The recovery of canopy-forming macroalgae assemblages in coastal areas of Madeira seems to have been inhibited by decades of sea-urchin barrens (Bernal-Ibañez et al, 2021). However, the community of the Madeira-Desertas Ridge appears quite fit with few urchins of A. lixula (90-112 m) and without signs of moderate to intense grazing on kelps.…”

Biodiversity Management in a Mediterranean National Park: The Long, Winding Path from a Species-Centred to an Ecosystem-Centred Approach

“…It is mainly controlled by predator fish [117][118][119][120]. Overfishing may result in the proliferation of sea urchins and the formation of barren grounds, where Fucales (e.g., Cystoseira, Ericaria and Gongolaria) forests are extirpated and the vegetation is reduced to a carpet of encrusting corallines and low algal turf [75,[121][122][123].…”