of the water that affects the vegetation communities, as well as sedimentation of
particles that results in burying benthic species in the affected areas. Seagrasses are
especially sensitive to increases in sedimentation rates.
The generalized eutrophication suffered throughout the Mediterranean is felt in a
special way in the Alboran Sea. Numerous uncontrolled spills of various kinds,
poorly treated wastewater, and discharges from activities related to agriculture result
in the entry into the sea of a significant amount of nutrients and chemicals that result
in a significant loss of biodiversity and deterioration of marine biocenoses. The
eulittoral zone is the first to suffer these consequences, with increasingly frequent
opportunistic algae populations growing rapidly, occupying a large part of the rocky
substrates to the detriment of the species typical of these environments in pristine
conditions.
An increase in surface water temperature is the most obvious manifestation of
climate change, and although it has not yet been demonstrated that this has a direct
effect on the marine plant communities of the Alboran Sea, it may have a close
relationship with a series of phenomena that are causing the loss of biological
diversity and homogenization of these communities, as supported by ample evidence
in other regions (Thibaut et al. 2005; Wernberg et al. 2011, 2013; Araujo et al. 2016;
Krumhansl et al. 2016; Casado et al. 2019). Algae are organisms whose basic
biological processes are thermo-dependent, especially reproductive processes,
which are constrained to very narrow temperature ranges and on which the maintenance of populations depends (Breeman 1988; Lüning 1990). The distribution of
many species of the Alboran Sea can therefore be constrained by both episodic and
prolonged increases in sea temperature. Particularly sensitive to this threat are
species in their native range of distribution, such as many species of Cystoseira,
the red alga Rissoella verruculosa, or the marine phanerogam Posidonia oceanica.
Meanwhile the increase in temperature, while negatively affecting native species,
may be favoring the establishment and dispersion of allochthonous species from
more temperate waters, which can occupy the niches left by native species and so act
as invasive species. The number of allochthonous species introduced into the
Alboran Sea is unknown, but it is known with certainty that in the last 20 years,
this region has suffered the invasion of four species of invasive macroalgae of IndoPacific origin, the four currently homogenizing important extensions of its coastline.
In order of chronological appearance, these four species are the red algae
Asparagopsis armata (Seoane 1965) and Asparagopsis taxiformis (Altamirano
1999; Altamirano et al. 2008a; Zanolla et al. 2018), the green alga Caulerpa
cylindracea (Altamirano et al. 2014), and, since 2016, the brown alga Rugulopteryx
okamurae (Altamirano et al. 2016, 2017; García-Gómez et al. 2019).
This cascade of invasions reveals an invasional meltdown phenomenon in the
waters of the Alboran Sea, which is leading to an alarming loss of biological
diversity in many coastal areas, especially in the Strait of Gibraltar. Thus, the recent
introduction of R. okamurae has led to the disappearance of important forests of
Fucales in Ceuta and Laminariales on the Mediterranean coast of Cadiz, as well as
other smaller photophilic algae species, such as prairies of Halopteris spp. and
Dictyota spp. (García-Gómez et al. 2019). The north bay of Ceuta has suffered an
8 Seaweeds and Seagrasses: The Marine Forests from the Alboran Sea
277
particles that results in burying benthic species in the affected areas. Seagrasses are
especially sensitive to increases in sedimentation rates.
The generalized eutrophication suffered throughout the Mediterranean is felt in a
special way in the Alboran Sea. Numerous uncontrolled spills of various kinds,
poorly treated wastewater, and discharges from activities related to agriculture result
in the entry into the sea of a significant amount of nutrients and chemicals that result
in a significant loss of biodiversity and deterioration of marine biocenoses. The
eulittoral zone is the first to suffer these consequences, with increasingly frequent
opportunistic algae populations growing rapidly, occupying a large part of the rocky
substrates to the detriment of the species typical of these environments in pristine
conditions.
An increase in surface water temperature is the most obvious manifestation of
climate change, and although it has not yet been demonstrated that this has a direct
effect on the marine plant communities of the Alboran Sea, it may have a close
relationship with a series of phenomena that are causing the loss of biological
diversity and homogenization of these communities, as supported by ample evidence
in other regions (Thibaut et al. 2005; Wernberg et al. 2011, 2013; Araujo et al. 2016;
Krumhansl et al. 2016; Casado et al. 2019). Algae are organisms whose basic
biological processes are thermo-dependent, especially reproductive processes,
which are constrained to very narrow temperature ranges and on which the maintenance of populations depends (Breeman 1988; Lüning 1990). The distribution of
many species of the Alboran Sea can therefore be constrained by both episodic and
prolonged increases in sea temperature. Particularly sensitive to this threat are
species in their native range of distribution, such as many species of Cystoseira,
the red alga Rissoella verruculosa, or the marine phanerogam Posidonia oceanica.
Meanwhile the increase in temperature, while negatively affecting native species,
may be favoring the establishment and dispersion of allochthonous species from
more temperate waters, which can occupy the niches left by native species and so act
as invasive species. The number of allochthonous species introduced into the
Alboran Sea is unknown, but it is known with certainty that in the last 20 years,
this region has suffered the invasion of four species of invasive macroalgae of IndoPacific origin, the four currently homogenizing important extensions of its coastline.
In order of chronological appearance, these four species are the red algae
Asparagopsis armata (Seoane 1965) and Asparagopsis taxiformis (Altamirano
1999; Altamirano et al. 2008a; Zanolla et al. 2018), the green alga Caulerpa
cylindracea (Altamirano et al. 2014), and, since 2016, the brown alga Rugulopteryx
okamurae (Altamirano et al. 2016, 2017; García-Gómez et al. 2019).
This cascade of invasions reveals an invasional meltdown phenomenon in the
waters of the Alboran Sea, which is leading to an alarming loss of biological
diversity in many coastal areas, especially in the Strait of Gibraltar. Thus, the recent
introduction of R. okamurae has led to the disappearance of important forests of
Fucales in Ceuta and Laminariales on the Mediterranean coast of Cadiz, as well as
other smaller photophilic algae species, such as prairies of Halopteris spp. and
Dictyota spp. (García-Gómez et al. 2019). The north bay of Ceuta has suffered an
8 Seaweeds and Seagrasses: The Marine Forests from the Alboran Sea
277