The area around the Canary Islands includes a set of islands and seamounts influenced by magma-driven processes over tens of millions of years over the Canary hotspot. This subtropical region is located 100 km off the northwestern coast of Africa. Due to its proximity to Africa and the Sahara Desert, the archipelago is influenced by coastal upwelling that produces complex mesoscale variation in temperature and organic matter (Arístegui et al., 2009). The archipelago comprises seven major islands, a group of islets in the northeast andthree seamounts fields: one in the northeast of the archipelago, one in the southwest and another between the emerged islands. Some of these seamounts (Concepción Bank, El Banquete and Amanay) have been intensively studied over the years and even as a Site of Community Interest (SCI).

In total, the Canary Islands archipelago includes 39 marine Special Areas of Conservation, two Sites of Community Importance and three marine reserves; one of them, in the northeast of Lanzarote, is the largest marine reserve in Europe and covers 706.34 km². Wave exposure also varies within the islands according to shoreline orientation. The northern and northeastern coasts of the islands are the most exposed to wave action due to dominant winds from the northeast and fetch (a measure of coastal exposure to wind and waves that corresponds to the length of water over which a given wind blows). Western–southwestern shores are more sheltered in comparison. The volcanic origin of the Canary Islands and associated geological processes mean the islands stand on narrow platforms, in between which the waters reaches depths of up to 3000 m. The shallow seabed immediately surrounding the islands is characterized by a seascape of rocky platforms, large stones, pebbles and sandy patches. Erosion has generated a higher proportion of sandy or mixed substrates on the northern and eastern shores, especially around the two oldest islands of the archipelago, Lanzarote and Fuerteventura. By contrast, La Palma and El Hierro, the western islands, have narrower platforms and are dominated by rocky bottoms.

The geographic location of the Canary Islands archipelago and its lack of a continental shelf likely contribute to its dissimilarity compared to other Spanish marine areas. Moreover, this area is rich and diverse due to the effect of the Canary Current Large Marine Ecosystem (Arístegui et al., 2009; Hernández-Guerra et al., 2017), its location, the great environmental heterogeneity of the archipelago, and the high diversity of habitats (Brito et al., 2001; Falcón, 2015).

The Canary Islands archipelago belongs to the Northeastern Atlantic Warm Temperate Region, the biogeographic region with the highest seaweed richness on eastern side of the Atlantic (Hoek, 1984; Lüning, 1990). Flora and fauna around the Canary Islands consists of an ensemble of species from both warm temperate and tropical regions (Sansón et al., 2001; Brito and Ocaña, 2004; Sangil et al., 2011). In recent years there have been many changes in the composition and richness of the habitats and marine communities of the region. The oceanographic conditions of the area (subtropical region with presence of upwelling) create unique conditions for the development of species with both tropical and temperate affinity. Studies currently being carried out in deep areas will expand the information on the different roles that the seamount and oceanic island play in the colonization and development of benthic species and communities.

The seamounts, located in flat abyssal areas, pose topographic obstacles that modify the circulation and lead to complex vortices and Taylor columns (Roden, 1986), whereby a rotating body of water is retained over the summit of a seamount. These effects promote blooms of primary production, with increases in zooplankton and suprabenthos, which lead to increases in the availability of food for wildlife (White et al., 2007). Taylor columns can also trap advected organisms and zooplankton with vertical migration. All these conditions translate into an external contribution of food for the seamount communities. In addition, the currents and steep slopes expose the rock and favour, together with the increase in production, the presence of sessile-gorgonian suspension feeders, corals, sponges, etc., and therefore the development of vulnerable habitats. The increase of food and the increase of the environmental complexity that these sessile benthic communities contribute favour the aggregations of demersal and benthopelagic fish and, consequently, the increase in the presence of migrant species such as pelagic sharks, tunas, cetaceans, turtles and seabirds. Finally, the particular conditions of isolation and high diversity of environments favour the appearance of a large number of endemic species (Almón et al., 2014b).

The existence of anchialine caves (volcanic tubes flooded by the sea) on islands such as Lanzarote, where there are conditions of isolation and specific environmental variables, propitiates the existence of endemic species such as Munidopsis polymorpha (Koelbel, 1892), and others under study, such as several species of polychaetes.

The area includes 13 Important Bird and Biodiversity Areas (IBAs, BirdLife International 2019). Key species breeding in the Canary archipelago and using the area to forage, rest or commute are the Cory's shearwater (Calonectris diomedea), band-rumped storm-petrel (Hydrobates castro), white-faced storm-petrel (Pelagodroma marina), Audubon’s shearwater (Puffinus lherminieri), Bulwer's petrel (Bulweria bulwerii), roseate tern (Sterna dougallii) and common tern (Sterna hirundo) (BirdLIfe International 2019). All these species occur in regionally or globally significant numbers that meet the criteria to classify the IBAs in the region (BirdLife International 2019; Donald et al. 2018).

The area is located in and around the Canary Islands, between the parallels 24º60’N and 32º27’N and meridians 20º96’W and 30º33’W. It includes volcanic edifices (e.g., emerged islands, seamounts and banks) and has a maximum depth of 3000 m.

        Variety of benthic habitats that are considered hotspots of biodiversity

The Canary Islands is one of five archipelagos of Macaronesia, a biogeographic region of the North Atlantic, that share similar characteristics, such as vulcanological origin or the high number of endemic species. The area includes a great variety of benthic habitats, from typically infralittoral to bathyal depths (Aguilar et al., 2009; Brito, 2004), as well as seamounts or banks located on the northern and central areas of the islands (Almón et al., 2014a, 2014b). Research on seamounts located to the south of the islands has also been done in the framework of the Drago0511 oceanographic campaign, which yielded biological information that is yet to be analysed and published.

The study area has a wide variety of communities due to the occurrence of a great bathymetric variation, coupled with different types of substrates. Several communities are included under the Habitats Directive habitat type 1170 "Reefs". Regarding the infralittoral and circalittoral areas, there are different species of erect algae (mainly fucoids and red macroalgae), black corals (Antipathella wollastoni), Stichopathes spp. on the rocky slopes and gorgonians (Leptogorgia spp) in mixed substrates (Martín-García et al, 2016).

In the bathyal zone, we highlight the presence of rocky bottoms with corals (antipataria) and large hexactinellid sponges (Asconema), frequently observed on different substrates (rocky, soft and mixed sediments) of bathyal zones. Other important habitats and communities are gorgonian forests comprising Callogorgia verticillata and Narella bellissima species and accompanied by high densities of Bebryce mollis and Eunicella verrucose, as well as Pheronema carpenteri and Paramuricea biscaya on rocky bottoms between 500 and 1500 m, or those formed by lithistid sponges (Leiodermatium-Neophryssospongia). At the same depth range, siliceous sponges occur on rocky substrates covered by sediments. The anthozoan Viminella flagellum is also present mixed with these sponges. Corallium niobe and Corallium tricolor are found on rocky substrate between 500 and 1600m depth. It should be noted that habitats included in the 1170 habitat type relate to the group of white cold-water corals (Scleractinia), such as Dendrophyllia cornigera and Phakellia ventilabrum, which usually appear in the rocky reefs of the lower part of the continental shelf and upper area of the slope, and the deep coral reefs of Lophelia pertusa and / or Madrepora oculata, and the habitat defined by a white coral of cold waters Solenosmilia variabilis, the main framework building coral of reefs in deeper areas between 1300 and 1700 m.

In soft bottoms, considered the “1110” habitat type under the Habitats Directive, we have found important communities at shallow depths, such as seagrass meadows of Cymodocea nodosa and Halophila decipiens sometimes mixed with the green algae Caulerpa prolifera, or the large populations of garden eels (Heteronger longissimus). The coral Flabellum, which lives on sandy bottoms, together with sea urchins, and the habitat defined by dead coral or rubble are all present in the bathyal and muddy seabed (Martín-Sosa et al, 2013).

Three species of seagrass meadows have been found in the Canary Islands: Cymodocea nodosa, Halophila decipiens and Zostera noltii. However, C. nodosa is the seagrass that forms the largest meadows throughout the Canary Islands, and it is of greater importance in marine ecosystems (Reyes et al. 1995, Barquín-Diez et al., 2005). Seagrass meadows play a crucial role in coastal areas because of their high primary production and their support to the increasing biodiversity (Mazzella et al., 1993) and food web complexity (Mazzella et al., 1992; Buia et al.,2000). But seagrass meadows are undergoing a world-wide decline, with global loss rates estimated at 2-5 per cent per year, compared to 0.5 per cent per year for tropical forests (Duarte & Gattuso, 2008). In the Canaries, Cymodocea meadows are considered a habitat in decline throughout the coastal areas; hence Cymodocea nodosa has been legislated as an endangered species.

Seaweed assemblages, dominated by the brown algae (Cystoseira abies-marina and Lobophora variegate), red algae (Gelidium spp.) or mixed species (Dyctiota, Lobophora and filamentous red algae) cover a high proportion of the hard substrate with good conservation status in the infralittoral zone (Martín-García et al. 2016). These communities have high biological productivity and represent refuge habitat for fish and juveniles of many species. In deeper bottoms (from 30 m depth) but in the infralittoral areas, there are vast areas of maërl (Lithothamniun corallioides, Lithophyllum, Mesophyllum y Peyssonnelia rosa-marina) around the islands (Afonso-Carrillo & Gil-Rodríguez, 1982), most of them understudied.  Maërl beds can harbour high densities of broodstock bivalves and act as nursery areas for the juvenile stages of commercial species (Barberá et al., 2003).

The Canary Islands are considered a biodiversity hotspot.  The most recent revision on fishes in Spanish waters recorded a total of 1075 species, the Canary Islands being the most diverse, with 795 species, and also having the greatest species richness (see Table 1 from Báez et al., 2019).

Taking into account only the littoral zone (from shore to a depth of 200 m), a marine multi-taxon study of the Macaronesian ecoregion (Freitas et al. in press) shows that the Canary Islands are by far the most diverse archipelago for five of the six groups studied (85 echinoderms, 811 gastropods, 120 brachyurans (Crustacea:Decapoda), 465 polychaetes, 689 macroalgae), and they have a similar number of coastal fish (299) as Cape Verde (303), despite the latter’s location in the tropical region. This same study highlights the importance of the Canary Islands in relation to the high number of species restricted to two or more of the Macaronesian archipelagos (130 of a total of 144 shared endemic species).

        Important area for cetaceans

The Canary Islands archipelago is one of the most important areas for cetaceans, with a high diversity of species, since the distributions of tropical and warm water species in this oceanic region overlap with those of large oceanic migrants (López, 2017).

Around 30 species of cetaceans have been documented in the Canary Islands, making it one of the world’s marine mammal hotspots. The Canary Islands archipelago shows the highest diversity of cetaceans in Macaronesia and harbours five resident species. Due to the islands’ location, they also harbour as many tropical marine mammal species as those in colder latitudes. Moreover, due to the steep slopes and canyons surrounding the islands, deep-diving species are well represented, including two resident species of beaked whales: Blainville´s beaked whale  (Mesoplodon densirostris) and Cuvier´s beaked whale (Ziphius cavirostris) with an estimate of 103 (87-130) and 87 (78-106) off El Hierro island, respectively (Aparicio, 2008; Arranz, 2011; Reyes, 2017). In the Canary Islands, we can also find one the few resident populations of short-finned pilot whales (Globicephala macrorhynchus) of the world, with a population estimate of 391 (325-470) off Tenerife (Marrero et al. 2016).

In summary, the following species are common in the archipelago:

Physeter macrocephalus                       Grampus griseus                      Globicephala macrorhynchus

Delphinus delphis                                 Steno bradanensis                     Stenella coeruleoalba

Stenella frontalis                                  Tursiops truncatus                    Balaenoptera acutorostrata

Balaenoptera physalus                          Balaenoptera edeni                   Ziphius cavirostris

Mesoplodon europaeus

Other species are occasional visitors or have been observed anecdotally:

Balaenoptera musculus                         Eubalaena glacialis                  Megaptera novaeangliae

Kogia sima                                           Kogia breviceps                         Lagenorhynchus acutus

Lagenodelphis hosei                             Lagenorhynchus albirostris       Stenella attenuata

Stenella longirostris                              Pseudorca crassidens               Feresa attenuata

Balaenoptera borealis                          Mesoplodon densirostris           Hyperoodon ampullatus

Mesoplodon bidens                               Mesoplodon mirus

        Habitats for endangered, threatened and declining species

Listed below are some examples of species registered in the area that need special attention:

IUCN Red List of threatened species

Physeter macrocephalus                       Balaenoptera physalus              Caretta caretta

Dermochelys coriacea                          Squatina squatina                     Sardinella maderensis

Megalops atlanticus                              Trachurus trachurus                 Kajikia albida 

Makaira nigricans                                Bodianus scrofa                        Pomatomus saltatrix    

Thunnus obesus                                    Thunnus thynnus                      Epinephelus itajara     

Epinephelus marginatus                        Mycteroperca fusca                  Dentex dentex 

Balistes capriscus                                 Mola mola                               Carcharhinus falciformis

Carcharhinus obscurus                         Sphyrna lewini                         Sphyrna zygaena         

Galeorhinus galeus                               Mustelus mustelus                    Alopias superciliosus   

Alopias vulpinus                                   Carcharodon carcharias           Isurus oxyrinchus        

Gymnura altavela                                 Manta birostris                        Mobula mobular          

Mobula tarapacana                              Rhincodon typus                       Pristis pristis               

Dipturus batis                                      Leucoraja circularis                 Raja maderensis          

Rostroraja alba                                    Rhinobatos rhinobatos              Centrophorus granulosus

Centrophorus squamosus                      Dalatias licha                          Centroscymnus owstoni

Squatina squatina                                 Eunicella verrucosa

Most of key threats to the marine environment and biodiversity around the Canary Islands are no different from those affecting coastal marine flora and fauna across the globe, but these have different local importance and a different degree of ecological concern along the depth range. The main threats are described and summarised by Riera et al. (2014):

• Climate change. Climate change arguably poses the greatest threat to the marine ecosystem around the Canary Islands, particularly the western islands (e.g., El Hierro, La Gomera and La Palma), which are less affected by the Saharan upwelling off the African coast (Barton et al., 1998). A progressive tropicalization of coastal ecosystems of the Canary archipelago has been observed in recent decades, and 78 per cent of the fish species newly recorded in recent years are considered to have tropical origins (Brito et al., 2005). Ocean warming has promoted the arrival of tropical species. There are several cases occurring at present in coastal waters of the Canaries related to invasive algal species, including the green alga Caulerpa racemosa aff. Cylindracea, the cyanobacteria Lyngbya majuscula (Martín-García et al. 2014), or the proliferation of the green alga Penicillus capitatus (Sangil et al., 2010).

• Fishing activities. Coastal fisheries have been massively overexploited in the Canary Islands due to pressure from artisanal fisheries and recreational fishers (Falcon et al., 1996). The target species are demersal species of the central Atlantic. The shallowest seamounts have a higher level of richness of target species and are the most suscentible to fishing activity. In addition, the shallowest seamounts commonly host the most sensitive habitats formed by hard corals and gorgonians (IEO 2012).

• Coastal development pressure on coastal ecosystems in the Canaries is driven by high human population density and continues to increase rapidly. About 9 per cent of the Canarian coast has been heavily transformed by the construction of rockwalls and other artificial structures on the shoreline. Highest concentrations of coastal structures (e.g., groins, dykes, breakwaters) and beach infrastructure (e.g., boardwalks) are located in tourist areas on the south coast of Tenerife and Gran Canaria, to protect and encourage use of artificial beaches. Likewise, a consistent increase in the number of harbours and marina facilities has occurred along the coast, without significant effort to understand the impacts of these coastal structures on marine biodiversity. Besides, impacts of land-based facilities and transport infrastructure associated with harbours would add additional impacts and pollution sources at different levels upon mesolittoral and sublittoral habitats.

• Water pollution. The waters surrounding the Canary Islands are oligotrophic, lacking the seasonal phytoplankton blooms that typify warm temperate seas elsewhere (Barton et al., 1998; Basterretxea and Arístegui, 2000). The archipelago also lacks permanent rivers, so nutrients and inorganic pollutants tend to enter the sea via smaller, isolated point sources like pipelines, sea-cage aquaculture (mainly for seabass Dicentrarchus labrax and seabream Sparus aurata) or desalination plants. Organic and inorganic pollutants from intensive farming (mainly banana and tomato) along the coast also have an impact on marine waters but their effects are not well understood. Fortunately, the presence of continuous coastal currents around the Canary Islands facilitates the dispersion of pollutants. Thus, while impacts may be acute near highly concentrated point sources, broader impacts of pollution along coastlines have not been identified.

• Shipping and maritime traffic. Chronic pollution derived from ship traffic is another potentially large but understudied threat to the marine environment of the islands. On average, 30,000 commercial vessels per year entered and exited local harbours (mostly in Gran Canaria and Tenerife) between 1998 and 2012 (ISTAC 2013). Aside from pollutant emissions from moving and docked ships, the impact for cetaceans posed by collisions and other disturbances (noise and vibration, human presence) is far from negligible. African hind (Cephalopholis taeniops) and the butterflyfish (Chaetodon sanctaehelenae) are two examples of fish species believed to have arrived at the Canaries in ballast water (Brito et al., 2005, 2010).

• Proliferation of the sea urchin Diadema africanum. This species has been responsible for an acute impoverishment of coastal rocky substrates in all the islands of the archipelago, with the exception of El Hierro, where fishing pressure has been lower and more strictly regulated in recent decades (Tuya et al., 2004). Effects of ocean warming on recruitment and growth, topographic complexity, and release from predation due to overfishing of predators (sensu Ling et al., 2009) are all likely to have played a role in the explosion of D. africanum populations in the Canaries (Hereu et al., 2004; Clemente et al., 2007), with the latter mechanism appearing most important (Tuya et al., 2004).

Extraction of construction materials from the seabed, and fuel prospecting and extraction, are two further disturbance sources for the marine biota of the Canary Islands, with unknown impacts.

In general, most of the impact occurs in the coastal and infralittoral zones. At present, there are many studies that different research entities are carrying out to better understand the impact of both climate change and invasive species on the shallowest waters of the archipelago. On the other hand, the human impacts and threats in deep waters, including seamounts, are insufficiently studied. The Spanish Institute of Oceanography (IEO) is currently working on the effects of fishing activities in some seamounts included in Special Areas of Conservation of the Canary Islands. There are more specific studies of biodiversity and oceanography of all seamounts of the region, but these are isolated and scarce.