8.4.2 Eulittoral Zone
This zone extends between the tidal limits, which in the Alboran Sea oscillate around
30–50 cm. Desiccation during periods of emersion (low tide) and hydrodynamism
are the main factors that affect the development of plant communities in this zone.
The main adaptations involve the shape of thalli, the most frequent biotypes being
crusts, elastic thalli, and thalli with incrustations of calcium carbonate. In this zone,
two subsidiary zones can be differentiated (Fig. 8.4a). The upper zone generally
appears less populated, whereas in the lower zone, the longer immersion time favors
more stable environmental conditions and the presence of species with welldeveloped thalli. Although the environmental conditions are not optimal for their
development, the eulittoral communities constitute the first belt of macroscopic algae
that we can observe on the coast.
In the upper zone, red algae are the main and most striking floristic component
due to the elastic nature of their thalli. In this first belt of algae, there are species such
as Rissoella verruculosa (Fig. 8.4b) forming striking bands. This species was
considered a Mediterranean endemic, but it is now known in the Canary Islands
(Haroun et al. 2003). It develops preferentially on siliceous and dolomitic substrates,
so it is absent at Alboran Island (Templado et al. 2006) and in other large areas of the
Alboran Sea. Other species characteristics of this community are Nemalion
helminthoides (Fig. 8.4b), Rivularia bullata, R. atra, Ralfsia verrucosa, Mesospora
macrocarpa, and several ephemeral and seasonal species such as Bangia
atropurpurea and Pyropia leucosticta. At this level, in areas such as harbors or
breakwaters with more unfavorable conditions generally linked to eutrophication, an
uncompacted dark brown and very dense belt of Huismaniella nigrescens is developed, associated with other opportunistic species such as Cladophora laetevirens or
Ulva spp.
The eulittoral communities of the lower zone present a long list of species with a
very characteristic morphology, clearly different from that of the upper zone: a
colorful, soft, very compact turf of small algae (Fig. 8.4c). Calcareous algae form
the base of this vegetation, sometimes standing out above the rest of the species,
depending on the greater or less hydrodynamism. In sheltered environments, a very
dense cespitose biotype community develops, where it is difficult to distinguish all
the constituents at first sight. Among the most frequent and easily recognizable
species are Huismaniella nigrescens, Gelidium latifolium, G. pusillum,
Chondracanthus acicularis, Caulacanthus ustulatus, Osmundea pinnatifida,
Hypnea musciformis, Ellisolandia elongata, Colpomenia sinuosa, Champia
parvula, Cladophora pellucida, Chaetomorpha linum, Ulva lactuca, and
U. rigida, as well as various species of Polysiphonia and Ceramium. As the intensity
of the hydrodynamism increases, they begin to dominate rather than the calcareous
algae, while the cespitose vegetation is masked or even disappears on the highly
exposed vertical surfaces, where E. elongata clearly dominates. In addition to these
species, Lithophyllum incrustans and Mesophyllum alternans frequently occur. At
the westernmost extent of the coast of the Iberian Peninsula and on the African coast,
8 Seaweeds and Seagrasses: The Marine Forests from the Alboran Sea
255
This zone extends between the tidal limits, which in the Alboran Sea oscillate around
30–50 cm. Desiccation during periods of emersion (low tide) and hydrodynamism
are the main factors that affect the development of plant communities in this zone.
The main adaptations involve the shape of thalli, the most frequent biotypes being
crusts, elastic thalli, and thalli with incrustations of calcium carbonate. In this zone,
two subsidiary zones can be differentiated (Fig. 8.4a). The upper zone generally
appears less populated, whereas in the lower zone, the longer immersion time favors
more stable environmental conditions and the presence of species with welldeveloped thalli. Although the environmental conditions are not optimal for their
development, the eulittoral communities constitute the first belt of macroscopic algae
that we can observe on the coast.
In the upper zone, red algae are the main and most striking floristic component
due to the elastic nature of their thalli. In this first belt of algae, there are species such
as Rissoella verruculosa (Fig. 8.4b) forming striking bands. This species was
considered a Mediterranean endemic, but it is now known in the Canary Islands
(Haroun et al. 2003). It develops preferentially on siliceous and dolomitic substrates,
so it is absent at Alboran Island (Templado et al. 2006) and in other large areas of the
Alboran Sea. Other species characteristics of this community are Nemalion
helminthoides (Fig. 8.4b), Rivularia bullata, R. atra, Ralfsia verrucosa, Mesospora
macrocarpa, and several ephemeral and seasonal species such as Bangia
atropurpurea and Pyropia leucosticta. At this level, in areas such as harbors or
breakwaters with more unfavorable conditions generally linked to eutrophication, an
uncompacted dark brown and very dense belt of Huismaniella nigrescens is developed, associated with other opportunistic species such as Cladophora laetevirens or
Ulva spp.
The eulittoral communities of the lower zone present a long list of species with a
very characteristic morphology, clearly different from that of the upper zone: a
colorful, soft, very compact turf of small algae (Fig. 8.4c). Calcareous algae form
the base of this vegetation, sometimes standing out above the rest of the species,
depending on the greater or less hydrodynamism. In sheltered environments, a very
dense cespitose biotype community develops, where it is difficult to distinguish all
the constituents at first sight. Among the most frequent and easily recognizable
species are Huismaniella nigrescens, Gelidium latifolium, G. pusillum,
Chondracanthus acicularis, Caulacanthus ustulatus, Osmundea pinnatifida,
Hypnea musciformis, Ellisolandia elongata, Colpomenia sinuosa, Champia
parvula, Cladophora pellucida, Chaetomorpha linum, Ulva lactuca, and
U. rigida, as well as various species of Polysiphonia and Ceramium. As the intensity
of the hydrodynamism increases, they begin to dominate rather than the calcareous
algae, while the cespitose vegetation is masked or even disappears on the highly
exposed vertical surfaces, where E. elongata clearly dominates. In addition to these
species, Lithophyllum incrustans and Mesophyllum alternans frequently occur. At
the westernmost extent of the coast of the Iberian Peninsula and on the African coast,
8 Seaweeds and Seagrasses: The Marine Forests from the Alboran Sea
255