institutions (Universidad Autónoma de Madrid and universities of Málaga, Cádiz,
Granada, Seville; Museo de Ciencias Naturales de Madrid-CSIC and the Environment Agency of the Junta de Andalucía). The community associated with the
P. oceanica meadows has been intensively studied, both in the northwestern and
northeastern Alboran Sea, although attention was biased to certain faunistic groups
(e.g. polychaetes, molluscs, decapods, echinoderms or fish) (San Martín et al. 1990,
García Raso 1990, García Raso et al. 1992, 2010; Luque and Templado 2004; Urra
et al. 2013b; Mateo-Ramírez et al. 2015). The community associated with Posidonia
is more complex and diverse than those associated with Z. marina or C. nodosa due
to the simpler structure of the leaf and rhizome strata and usually shallower occurrence of those small seagrasses associated with soft bottoms (Luque and Templado
2004). As an example of this structural complexity, more than 800 species have been
identified in the Posidonia meadows of the Almería coast (García Raso et al. 1992).
The polychaetes stand out for their high species richness (240 species, San Martín
et al. 1990; Luque and Templado 2004; Torres Gávila 2008) together with molluscs
(over 200 species, García Raso et al. 1992; Luque and Templado 2004; Urra et al.
2013b), amphipods (over 70 species, Luque and Templado 2004), decapods (over
50 species, García Raso 1990; García Raso et al. 1992; Luque and Templado 2004;
Mateo-Ramírez et al. 2015) and echinoderms (25 species, Luque and Templado
2004). Studies on other groups (e.g. foraminiferans, nemerteans, turbelarians)
inhabiting the Posidonia meadows of the Alboran Sea are very scarce.
Posidonia leaves, which can reach more than 1 m in length in the eastern part of
the Alboran Sea, including Chafarinas Islands, Cabo de Gata and other places in the
Almería province, constitute a very particular habitat. It is a dense, permanently
moving stratum, with illuminated and shaded areas (upper and lower surface of the
leaves) which considerably increases the available surface of colonizable substrate.
The most common epiphytic organisms in this substrate are calcareous algae, which
dominate especially in the illuminated area of the leaves, followed by encrusting
bryozoans (Electra posidoniae, Patinella radiata), hydroids (Sertularia,
Campanularia and Aglaophenia), colonial tunicates, serpulid polychaetes
(Spirorbis) and sea anemones (Parastephanauge paxi, better known under the
incorrect name Paractinia striata) (Junta de Andalucía 2008–2019). Among the
mobile fauna, the most abundant are gastropods (such as Tricolia speciosa,
Jujubinus spp., Gibbula ardens, Steromphala umbilicaris, juveniles of Crepidula
unguiformis, several rissoids such as Rissoa auriscalpium and R. ventricosa and the
emerald neritid Smaragdia viridis. Among the crustaceans, there are characteristic
isopods such as Synischia hectica, numerous amphipods and some characteristic
decapods, such as Hippolyte inermis. The planarian Planocera graffi and the echinoderm Asterina phylactica (previously identified as Asterina pancerii in Andalusian coasts and reconsidered by López-Márquez et al. 2018) are also recorded, at
least in the eastern part around Cabo de Gata. Some species of very small and cryptic
fish, such as Opeatogenys gracilis and Apletodon incognitus, occur among the
Posidonia leaves. In the westernmost part of the Alboran Sea, the “fundamental
stock” of molluscan species described by Russo et al. (1984) as associated to the leaf
stratum of Posidonia is either missing (e.g. Tricolia speciosa, Rissoa ventricosa,
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J. L. Rueda et al.
Granada, Seville; Museo de Ciencias Naturales de Madrid-CSIC and the Environment Agency of the Junta de Andalucía). The community associated with the
P. oceanica meadows has been intensively studied, both in the northwestern and
northeastern Alboran Sea, although attention was biased to certain faunistic groups
(e.g. polychaetes, molluscs, decapods, echinoderms or fish) (San Martín et al. 1990,
García Raso 1990, García Raso et al. 1992, 2010; Luque and Templado 2004; Urra
et al. 2013b; Mateo-Ramírez et al. 2015). The community associated with Posidonia
is more complex and diverse than those associated with Z. marina or C. nodosa due
to the simpler structure of the leaf and rhizome strata and usually shallower occurrence of those small seagrasses associated with soft bottoms (Luque and Templado
2004). As an example of this structural complexity, more than 800 species have been
identified in the Posidonia meadows of the Almería coast (García Raso et al. 1992).
The polychaetes stand out for their high species richness (240 species, San Martín
et al. 1990; Luque and Templado 2004; Torres Gávila 2008) together with molluscs
(over 200 species, García Raso et al. 1992; Luque and Templado 2004; Urra et al.
2013b), amphipods (over 70 species, Luque and Templado 2004), decapods (over
50 species, García Raso 1990; García Raso et al. 1992; Luque and Templado 2004;
Mateo-Ramírez et al. 2015) and echinoderms (25 species, Luque and Templado
2004). Studies on other groups (e.g. foraminiferans, nemerteans, turbelarians)
inhabiting the Posidonia meadows of the Alboran Sea are very scarce.
Posidonia leaves, which can reach more than 1 m in length in the eastern part of
the Alboran Sea, including Chafarinas Islands, Cabo de Gata and other places in the
Almería province, constitute a very particular habitat. It is a dense, permanently
moving stratum, with illuminated and shaded areas (upper and lower surface of the
leaves) which considerably increases the available surface of colonizable substrate.
The most common epiphytic organisms in this substrate are calcareous algae, which
dominate especially in the illuminated area of the leaves, followed by encrusting
bryozoans (Electra posidoniae, Patinella radiata), hydroids (Sertularia,
Campanularia and Aglaophenia), colonial tunicates, serpulid polychaetes
(Spirorbis) and sea anemones (Parastephanauge paxi, better known under the
incorrect name Paractinia striata) (Junta de Andalucía 2008–2019). Among the
mobile fauna, the most abundant are gastropods (such as Tricolia speciosa,
Jujubinus spp., Gibbula ardens, Steromphala umbilicaris, juveniles of Crepidula
unguiformis, several rissoids such as Rissoa auriscalpium and R. ventricosa and the
emerald neritid Smaragdia viridis. Among the crustaceans, there are characteristic
isopods such as Synischia hectica, numerous amphipods and some characteristic
decapods, such as Hippolyte inermis. The planarian Planocera graffi and the echinoderm Asterina phylactica (previously identified as Asterina pancerii in Andalusian coasts and reconsidered by López-Márquez et al. 2018) are also recorded, at
least in the eastern part around Cabo de Gata. Some species of very small and cryptic
fish, such as Opeatogenys gracilis and Apletodon incognitus, occur among the
Posidonia leaves. In the westernmost part of the Alboran Sea, the “fundamental
stock” of molluscan species described by Russo et al. (1984) as associated to the leaf
stratum of Posidonia is either missing (e.g. Tricolia speciosa, Rissoa ventricosa,
306
J. L. Rueda et al.