The first species is the sole zooxanthellate scleractinian reef-builder of the Mediterranean and has been affected by bleaching events in the last years due to seawater
warming (Kersting et al. 2013). Gambi et al. (2010) reported local mass mortality
events of the thermophilic azooxanthellate orange coral Astroides calycularis also
related to high water surface temperatures. Both species support a high biodiversity
(Pitacco et al. 2017; Terrón-Sigler et al. 2014).
Among molluscs, the better known cases of mass mortalities are the recurrent
events suffered by the bivalve Spondylus gaederopus since the 1980s and the more
recent mortality that have severely affected Pinna nobilis populations in the western
Mediterranean. The European thorny oyster (S. gaederopus), which lives attached
by the lower (right) valve to more or less vertical rock walls and other hard substrates, suffered the first known case of mass mortality in 1981 in France for causes
yet unknown (Meinesz and Mercier 1983). Similar mortality events were observed
in this species in the Alboran Sea since 1990, and subsequently there have been
mortalities in 2005 and later years, detected in the Granada coast (personal observations) and, particularly, in the Chafarinas Islands (Sánchez-Tocino et al. 2009).
Mass mortalities of S. gaederopus are easy to detect since this species loses the flat
upper (left) valve when it die and the white inside of the convex lower valve that
remains attached to the rock can be seen by divers from a distance of several meters
(Fig. 10.19). Observed mortalities of S. gaederopus often coincide with a number
higher than usual of empty shells of other bivalves that live attached with the byssus
to rocky bottoms, such as Arca noae and Barbatia barbata (personal observations).
For the former species, a massive mortality has been recently reported in the Strait of
Messina (Bottari et al. 2017). Currently, Spondylus gaederopus is still present in
many localities in the Alboran Sea, but it is uncommon, and its abundance has never
been the same since the recorded mortalities (Moreno et al. 2008b).
Nevertheless, the most drastic and surprising mass mortality event that has
affected any invertebrate species in the Alboran Sea and the whole Mediterranean
is that first detected in October 2016 in southeastern Spain (Fig. 10.19) affecting the
Mediterranean endemic and threatened fan mussel Pinna nobilis, one of the world’s
largest bivalves, which lives associated to seagrass meadows. By the end of 2016,
between 70% and 90% of the specimens died, and in the spring of 2017, practically
100% of the population died in most of the southern Spanish coasts including the
Alboran Sea. Vázquez-Luis et al. (2017) found in the Spanish Mediterranean Sea
mortality values of 100% in the North part of the Alboran Sea and of 90–99% in the
Chafarinas Islands. These authors and Darriba (2017) pointed out a haplosporidianlike parasite detected in dying individuals as the very likely cause of this mortality.
The parasite associated to this mortality (the protist Haplosporidium pinnae) was
subsequently described in 2018 (Catanese et al. 2018) and infects the vital organs of
the bivalve causing its death. It seems to be a very specific pathogen because it does
not affect the closely related species Pinna rudis, somewhat smaller and that prefers
rocky substrates, although it is also found in Posidonia meadows. By 2019, the
mortality of Pinna nobilis affects populations of other Mediterranean countries
(France, Italy, Malta, Greece, Croatia, Turkey, Cyprus, Tunisia and Morocco),
according to IUCN (2019). According to Cabanellas-Reboredo et al. (2019), the
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J. Templado et al.
warming (Kersting et al. 2013). Gambi et al. (2010) reported local mass mortality
events of the thermophilic azooxanthellate orange coral Astroides calycularis also
related to high water surface temperatures. Both species support a high biodiversity
(Pitacco et al. 2017; Terrón-Sigler et al. 2014).
Among molluscs, the better known cases of mass mortalities are the recurrent
events suffered by the bivalve Spondylus gaederopus since the 1980s and the more
recent mortality that have severely affected Pinna nobilis populations in the western
Mediterranean. The European thorny oyster (S. gaederopus), which lives attached
by the lower (right) valve to more or less vertical rock walls and other hard substrates, suffered the first known case of mass mortality in 1981 in France for causes
yet unknown (Meinesz and Mercier 1983). Similar mortality events were observed
in this species in the Alboran Sea since 1990, and subsequently there have been
mortalities in 2005 and later years, detected in the Granada coast (personal observations) and, particularly, in the Chafarinas Islands (Sánchez-Tocino et al. 2009).
Mass mortalities of S. gaederopus are easy to detect since this species loses the flat
upper (left) valve when it die and the white inside of the convex lower valve that
remains attached to the rock can be seen by divers from a distance of several meters
(Fig. 10.19). Observed mortalities of S. gaederopus often coincide with a number
higher than usual of empty shells of other bivalves that live attached with the byssus
to rocky bottoms, such as Arca noae and Barbatia barbata (personal observations).
For the former species, a massive mortality has been recently reported in the Strait of
Messina (Bottari et al. 2017). Currently, Spondylus gaederopus is still present in
many localities in the Alboran Sea, but it is uncommon, and its abundance has never
been the same since the recorded mortalities (Moreno et al. 2008b).
Nevertheless, the most drastic and surprising mass mortality event that has
affected any invertebrate species in the Alboran Sea and the whole Mediterranean
is that first detected in October 2016 in southeastern Spain (Fig. 10.19) affecting the
Mediterranean endemic and threatened fan mussel Pinna nobilis, one of the world’s
largest bivalves, which lives associated to seagrass meadows. By the end of 2016,
between 70% and 90% of the specimens died, and in the spring of 2017, practically
100% of the population died in most of the southern Spanish coasts including the
Alboran Sea. Vázquez-Luis et al. (2017) found in the Spanish Mediterranean Sea
mortality values of 100% in the North part of the Alboran Sea and of 90–99% in the
Chafarinas Islands. These authors and Darriba (2017) pointed out a haplosporidianlike parasite detected in dying individuals as the very likely cause of this mortality.
The parasite associated to this mortality (the protist Haplosporidium pinnae) was
subsequently described in 2018 (Catanese et al. 2018) and infects the vital organs of
the bivalve causing its death. It seems to be a very specific pathogen because it does
not affect the closely related species Pinna rudis, somewhat smaller and that prefers
rocky substrates, although it is also found in Posidonia meadows. By 2019, the
mortality of Pinna nobilis affects populations of other Mediterranean countries
(France, Italy, Malta, Greece, Croatia, Turkey, Cyprus, Tunisia and Morocco),
according to IUCN (2019). According to Cabanellas-Reboredo et al. (2019), the
414
J. Templado et al.