within the Alboran Sea must be considered as a management unit different from
those outside the Mediterranean (Sacco et al. 2017).
On the other hand, the hydrographic front between Oran and Almeria has been
effective in maintaining a low presence of endemic Mediterranean species in the
Alboran Sea, even though the Mediterranean as a whole house a large number of
endemic species. For example, only 10 of the 248 infralittoral fish species reported in
the Alboran Sea (Reina Hervás et al. 1982; Reina-Hervás 1987; Reina Hervás 1989;
Reina Hervás and Serrano 1987a, b; Reina Hervás and Serrano 1993) are exclusive
to the Mediterranean. Examples of endemic Mediterranean fish that are absent from
the Alboran Sea are Coelorinchus mediterraneus, Gouania willdenowi, Paralepis
speciosa, Pegusa nasuta, Syngnathus tenuirostris, and Nansenia iberica an Iberian
mesopelagic endemism (500–800 m depth) that lives around the Balearic Islands and
the Iberian Peninsula but not in the Alboran Sea. There are also Mediterranean
endemics that avoid the Alboran sea or hardly penetrate there (e.g. the gastropod
Tricolia speciosa in addition to the already mentioned Homalopoma sanguineum, or
the bivalves Cardites antiquatus and Glans trapezia). Probably also due to the
ecological characteristics of the Alboran basin, such as the scarce flow of the rivers,
the fish endemic species Aphanius iberus, which have freshwater preferences but
also inhabits marine habitats (e.g. estuaries and the Mar Menor) is also absent from
Alboran (Crivelli 2006).
Consequently, the historical, geographical, and hydrographic characteristics of
the Alboran Sea have affected both the internal composition of its biota and the
relationship with that of the surrounding waters, which warrants the consideration of
the Alboran Sea as a valid biogeographical entity. This has been particularly well
established for certain groups of species, such as sponges (Maldonado and Uriz
1995). The biogeographical identity of the area is also recognized in the classification by Spalding et al. (2007) as an ecoregion independent of the rest of the
Mediterranean.
Several internal biogeographical regionalizations have been also proposed for the
Alboran Sea. Using checklists of macrophytes from Cádiz (Spain) to Italy on the
European coast, and from Tangier to Tunis on the African coast, Conde (1989)
identified two subsectors in the Alboran Sea, divided by an imaginary line that joins
Calaburras (Málaga) with the border area between Morocco and Algeria, passing
along Alboran Island. He pointed to several species as evidence of the presence of
these subsectors, with Posidonia oceanica and Rissoella verruculosa occurring only
in the oriental sector, and Fucus guiryi and some Laminariales in the Atlantic sector,
and considered that the incoming Atlantic water was the main driver of the benthic
macroalgae biogeography in the Alboran Sea.
In more recent studies, focused only on macrophytes of the littoral and upper
sublittoral areas of the north coast of the Alboran Sea, three oceanographic and three
biogeographic subregions were identified, exhibiting a “very good” or “excellent”
correspondence between them (Bermejo et al. 2015, 2016). Biogeographic subregions were characterized by landscape and species composition. The western
subregion spans from the Strait of Gibraltar to Calaburras, and is characterized by
a flora with elements of very different affinities, but rich in Atlantic species, which
11 Biogeographical and Macroecological Context of the Alboran Sea
439
those outside the Mediterranean (Sacco et al. 2017).
On the other hand, the hydrographic front between Oran and Almeria has been
effective in maintaining a low presence of endemic Mediterranean species in the
Alboran Sea, even though the Mediterranean as a whole house a large number of
endemic species. For example, only 10 of the 248 infralittoral fish species reported in
the Alboran Sea (Reina Hervás et al. 1982; Reina-Hervás 1987; Reina Hervás 1989;
Reina Hervás and Serrano 1987a, b; Reina Hervás and Serrano 1993) are exclusive
to the Mediterranean. Examples of endemic Mediterranean fish that are absent from
the Alboran Sea are Coelorinchus mediterraneus, Gouania willdenowi, Paralepis
speciosa, Pegusa nasuta, Syngnathus tenuirostris, and Nansenia iberica an Iberian
mesopelagic endemism (500–800 m depth) that lives around the Balearic Islands and
the Iberian Peninsula but not in the Alboran Sea. There are also Mediterranean
endemics that avoid the Alboran sea or hardly penetrate there (e.g. the gastropod
Tricolia speciosa in addition to the already mentioned Homalopoma sanguineum, or
the bivalves Cardites antiquatus and Glans trapezia). Probably also due to the
ecological characteristics of the Alboran basin, such as the scarce flow of the rivers,
the fish endemic species Aphanius iberus, which have freshwater preferences but
also inhabits marine habitats (e.g. estuaries and the Mar Menor) is also absent from
Alboran (Crivelli 2006).
Consequently, the historical, geographical, and hydrographic characteristics of
the Alboran Sea have affected both the internal composition of its biota and the
relationship with that of the surrounding waters, which warrants the consideration of
the Alboran Sea as a valid biogeographical entity. This has been particularly well
established for certain groups of species, such as sponges (Maldonado and Uriz
1995). The biogeographical identity of the area is also recognized in the classification by Spalding et al. (2007) as an ecoregion independent of the rest of the
Mediterranean.
Several internal biogeographical regionalizations have been also proposed for the
Alboran Sea. Using checklists of macrophytes from Cádiz (Spain) to Italy on the
European coast, and from Tangier to Tunis on the African coast, Conde (1989)
identified two subsectors in the Alboran Sea, divided by an imaginary line that joins
Calaburras (Málaga) with the border area between Morocco and Algeria, passing
along Alboran Island. He pointed to several species as evidence of the presence of
these subsectors, with Posidonia oceanica and Rissoella verruculosa occurring only
in the oriental sector, and Fucus guiryi and some Laminariales in the Atlantic sector,
and considered that the incoming Atlantic water was the main driver of the benthic
macroalgae biogeography in the Alboran Sea.
In more recent studies, focused only on macrophytes of the littoral and upper
sublittoral areas of the north coast of the Alboran Sea, three oceanographic and three
biogeographic subregions were identified, exhibiting a “very good” or “excellent”
correspondence between them (Bermejo et al. 2015, 2016). Biogeographic subregions were characterized by landscape and species composition. The western
subregion spans from the Strait of Gibraltar to Calaburras, and is characterized by
a flora with elements of very different affinities, but rich in Atlantic species, which
11 Biogeographical and Macroecological Context of the Alboran Sea
439