acute, and the deep sea diversity in the Alboran Sea is especially low in relation to
the adjacent Atlantic Ocean (Coll et al. 2010). By contrast, the infralittoral biota,
which refers to the area which is permanently submerged up to the depth with
presence of photophilic marine algae and seagrass (normally, and depending on
the quality of the waters, down to 20 or 30 metres deep, sometimes more than 60 m)
is highly diverse. The community of fish inhabiting the infralittoral area is very
important, as well as the variety of ecosystems or biocenoses found in it, particularly
the seagrass communities of the genera Zostera, Cymodocea, and Posidonia. Studies
carried out since 1980 (Reina Hervás et al. 1982; Reina Hervás and Nuñez 1985;
Reina-Hervás 1987; Reina Hervás 1989; Reina Hervás and Serrano 1987a, b; Reina
Hervás and Serrano 1993) on the infralittoral ichthyofauna (0–20 m deep) of the
coast of Málaga reported a total of 248 species of fish that are considered frequent in
this zone, belonging to 65 families, being Bleniidae with 22 species, Labridae with
21, Gobiidae with 20, and Sparidae with 19 species the most frequently represented.
Below the infralittoral zone, the Spanish Institute of Oceanography conducted
several fishing surveys, both in Spanish and in Moroccan waters (Gil de Sola 1994;
Gil de Sola et al. 2017). The MEDITS demersal fishing survey was the most
extensively studied. Several studies of this faunistic database analyzed specifically
the demersal ichthyofauna of the Alboran Sea (Lloris et al. 2000; Gaertner et al.
2013; García-Ruiz et al. 2015; Gil de Sola et al. 2017). A total of 186 species were
inventoried in the Alboran Sea (27% of the total of those mentioned for the
Mediterranean), encompassed in 3 classes, 24 orders, and 69 families. The values
of total abundance were higher in the continental shelf than in the slope, decreasing
sharply from it. The interval between 301 and 500 m. appeared as a transition zone
where certain species, more abundant in the shelf, disappeared, and those that are
typical of the slope showed up, with the exception of eight species considered as
eurybathic (Conger conger, Helicolenus dactylopterus, Lepidopus caudatus,
Lophius budegassa, Merluccius merluccius smiridus, Pagellus acarne, Pagellus
bogaraveo, and Symphurus nigrescens), which were distributed throughout the
bathymetric range studied.
On the contrary, due to the short latitudinal and longitudinal variation
encompassed by the Alboran Sea, the species richness gradients associated to their
respective geographical ranges are moderate. Latitudinal variations are observed in
the Alboran Sea, although not very frequently. For example, the Scombridae
Orcynopsis unicolor is frequently found in the landings at Moroccan Alboran
ports, but it is rare in ports of the Spanish Alboran coast (UNEP-MAP-RAC/SPA
2015). Longitudinal distribution gradients in species richness also exist (Fig. 11.5),
normally due to extinction-recolonization processes associated to the distance to the
Strait of Gibraltar of the kind that have been used to explain the longitudinal gradient
of chondrichthyes species richness in the Mediterranean Sea (Meléndez et al. 2017).
There is also a longitudinal pattern of westward gradual substitution of the Mediterranean flora and fauna that makes them increasingly more similar to the Atlantic
ones. The Atlantic character of the fish fauna of the Mediterranean is particularly
high in the area of influence of the Atlantic, i.e. between Gibraltar and Malaga in the
north and along the northern coast of Morocco in the south (especially between
11 Biogeographical and Macroecological Context of the Alboran Sea
445
the adjacent Atlantic Ocean (Coll et al. 2010). By contrast, the infralittoral biota,
which refers to the area which is permanently submerged up to the depth with
presence of photophilic marine algae and seagrass (normally, and depending on
the quality of the waters, down to 20 or 30 metres deep, sometimes more than 60 m)
is highly diverse. The community of fish inhabiting the infralittoral area is very
important, as well as the variety of ecosystems or biocenoses found in it, particularly
the seagrass communities of the genera Zostera, Cymodocea, and Posidonia. Studies
carried out since 1980 (Reina Hervás et al. 1982; Reina Hervás and Nuñez 1985;
Reina-Hervás 1987; Reina Hervás 1989; Reina Hervás and Serrano 1987a, b; Reina
Hervás and Serrano 1993) on the infralittoral ichthyofauna (0–20 m deep) of the
coast of Málaga reported a total of 248 species of fish that are considered frequent in
this zone, belonging to 65 families, being Bleniidae with 22 species, Labridae with
21, Gobiidae with 20, and Sparidae with 19 species the most frequently represented.
Below the infralittoral zone, the Spanish Institute of Oceanography conducted
several fishing surveys, both in Spanish and in Moroccan waters (Gil de Sola 1994;
Gil de Sola et al. 2017). The MEDITS demersal fishing survey was the most
extensively studied. Several studies of this faunistic database analyzed specifically
the demersal ichthyofauna of the Alboran Sea (Lloris et al. 2000; Gaertner et al.
2013; García-Ruiz et al. 2015; Gil de Sola et al. 2017). A total of 186 species were
inventoried in the Alboran Sea (27% of the total of those mentioned for the
Mediterranean), encompassed in 3 classes, 24 orders, and 69 families. The values
of total abundance were higher in the continental shelf than in the slope, decreasing
sharply from it. The interval between 301 and 500 m. appeared as a transition zone
where certain species, more abundant in the shelf, disappeared, and those that are
typical of the slope showed up, with the exception of eight species considered as
eurybathic (Conger conger, Helicolenus dactylopterus, Lepidopus caudatus,
Lophius budegassa, Merluccius merluccius smiridus, Pagellus acarne, Pagellus
bogaraveo, and Symphurus nigrescens), which were distributed throughout the
bathymetric range studied.
On the contrary, due to the short latitudinal and longitudinal variation
encompassed by the Alboran Sea, the species richness gradients associated to their
respective geographical ranges are moderate. Latitudinal variations are observed in
the Alboran Sea, although not very frequently. For example, the Scombridae
Orcynopsis unicolor is frequently found in the landings at Moroccan Alboran
ports, but it is rare in ports of the Spanish Alboran coast (UNEP-MAP-RAC/SPA
2015). Longitudinal distribution gradients in species richness also exist (Fig. 11.5),
normally due to extinction-recolonization processes associated to the distance to the
Strait of Gibraltar of the kind that have been used to explain the longitudinal gradient
of chondrichthyes species richness in the Mediterranean Sea (Meléndez et al. 2017).
There is also a longitudinal pattern of westward gradual substitution of the Mediterranean flora and fauna that makes them increasingly more similar to the Atlantic
ones. The Atlantic character of the fish fauna of the Mediterranean is particularly
high in the area of influence of the Atlantic, i.e. between Gibraltar and Malaga in the
north and along the northern coast of Morocco in the south (especially between
11 Biogeographical and Macroecological Context of the Alboran Sea
445