Regime, although with no particular mention of threat. The causes of the demise of
Z. marina beds in the Alboran Sea are not precisely known, but illegal trawling or
dredging, global warming and disease may have contributed.
9.6.3 Bioclastic Sands and Gravels
This kind of habitat is found generally below 20 m depth, and the sediment is formed
by medium to coarse sand with abundant bioclasts and a higher content of mud and
organic matter than the well-sorted fine sand. Most of the sediment originates from
the degradation of shells or other skeletal remains (Pérès and Picard 1964; Pérès
1982). In the shallower settings, this is the so-called “détritique côtier” which
normally grades offshore to more muddy sediments. At greater depths, typically
below 95–100 m and down to the shelf edge, is found the “détritique du large” where
the bioclasts are commonly remnants of Quaternary thanatocenoses. When the mud
input is low, both may form a continuum. In fact, the term “détritique” is a misnomer
because, in geological vocabulary, it should refer to products of erosion of
pre-existing rocks, whereas here the elements result from bioconstruction and should
properly be referred to as bioclasts.
Coastal bioclastic sands and gravels are quite extensive in the Strait of Gibraltar
area, e.g. near Barbate (Manjón-Cabeza and García Raso 1998; Rueda et al. 2000;
García Raso and Manjón Cabeza 2002) and Punta Cires (Bazairi et al. 2016) in a
setting where strong currents winnow the finer sediment particles. They are also well
represented in some parts of the coast of Málaga (Urra et al. 2013a, b, c) and Granada
(Marina et al. 2015). The extension of this habitat along the Moroccan coast is not
precisely known, but taking into account the scarcity of sediment input from rivers, it
should be considerable.
Coastal bioclastic sands and gravels generally show high species richness and low
dominance values, thanks to the heterogeneity generated by the larger bioclasts.
Among the molluscs, the gastropods are dominant in number of species, but the
bivalves show, in general, higher abundances (Rueda et al. 2000; Rueda and Salas
2003; Urra et al. 2011). Characteristic species are the bivalves Digitaria digitaria,
Gouldia minima, Nucula hanleyi, Lembulus pella, Laevicardium crassum,
Parvicardium scabrum, Pitar rudis and Timoclea ovata. Among the gastropods,
Calyptraea chinensis, which lives inside large empty valves lying on the sediment, is
one of dominant species. Other characteristic gastropods are the carnivorous Euspira
nitida, Crassopleura maravignae, Fusinus pulchellus and Bolinus brandaris.
Among the crustaceans, the pagurids are dominant in the littoral of Málaga, mainly
Paguristes eremita and Anapagurus hyndmanni, but Diogenes pugilator,
Anapagurus alboranensis, Dardanus arrosor, Pagurus forbesii and
P. pseudosculptimanus are also abundant (García-Muñoz et al. 2008, 2014). Other
characteristic crustaceans of this bottom are Ebalia tumefacta, E. deshayesi, Pisidia
longicornis and Galathea intermedia. In the littoral of Granada, Anapagurus
alboranensis is also a dominant species in the assemblage (Marina et al. 2015).
9 Benthic Fauna of Littoral and Deep-Sea Habitats of the Alboran Sea: A. . .
327
Z. marina beds in the Alboran Sea are not precisely known, but illegal trawling or
dredging, global warming and disease may have contributed.
9.6.3 Bioclastic Sands and Gravels
This kind of habitat is found generally below 20 m depth, and the sediment is formed
by medium to coarse sand with abundant bioclasts and a higher content of mud and
organic matter than the well-sorted fine sand. Most of the sediment originates from
the degradation of shells or other skeletal remains (Pérès and Picard 1964; Pérès
1982). In the shallower settings, this is the so-called “détritique côtier” which
normally grades offshore to more muddy sediments. At greater depths, typically
below 95–100 m and down to the shelf edge, is found the “détritique du large” where
the bioclasts are commonly remnants of Quaternary thanatocenoses. When the mud
input is low, both may form a continuum. In fact, the term “détritique” is a misnomer
because, in geological vocabulary, it should refer to products of erosion of
pre-existing rocks, whereas here the elements result from bioconstruction and should
properly be referred to as bioclasts.
Coastal bioclastic sands and gravels are quite extensive in the Strait of Gibraltar
area, e.g. near Barbate (Manjón-Cabeza and García Raso 1998; Rueda et al. 2000;
García Raso and Manjón Cabeza 2002) and Punta Cires (Bazairi et al. 2016) in a
setting where strong currents winnow the finer sediment particles. They are also well
represented in some parts of the coast of Málaga (Urra et al. 2013a, b, c) and Granada
(Marina et al. 2015). The extension of this habitat along the Moroccan coast is not
precisely known, but taking into account the scarcity of sediment input from rivers, it
should be considerable.
Coastal bioclastic sands and gravels generally show high species richness and low
dominance values, thanks to the heterogeneity generated by the larger bioclasts.
Among the molluscs, the gastropods are dominant in number of species, but the
bivalves show, in general, higher abundances (Rueda et al. 2000; Rueda and Salas
2003; Urra et al. 2011). Characteristic species are the bivalves Digitaria digitaria,
Gouldia minima, Nucula hanleyi, Lembulus pella, Laevicardium crassum,
Parvicardium scabrum, Pitar rudis and Timoclea ovata. Among the gastropods,
Calyptraea chinensis, which lives inside large empty valves lying on the sediment, is
one of dominant species. Other characteristic gastropods are the carnivorous Euspira
nitida, Crassopleura maravignae, Fusinus pulchellus and Bolinus brandaris.
Among the crustaceans, the pagurids are dominant in the littoral of Málaga, mainly
Paguristes eremita and Anapagurus hyndmanni, but Diogenes pugilator,
Anapagurus alboranensis, Dardanus arrosor, Pagurus forbesii and
P. pseudosculptimanus are also abundant (García-Muñoz et al. 2008, 2014). Other
characteristic crustaceans of this bottom are Ebalia tumefacta, E. deshayesi, Pisidia
longicornis and Galathea intermedia. In the littoral of Granada, Anapagurus
alboranensis is also a dominant species in the assemblage (Marina et al. 2015).
9 Benthic Fauna of Littoral and Deep-Sea Habitats of the Alboran Sea: A. . .
327