or number of individuals face a high risk of extinction, because of demographic
fluctuations or reproductive failure due to different impacts (Vermeij and Grosberg
2018). Nevertheless, rarity may also hold the key to survival during crises (e.g.,
Bianchi et al. 2014), and many species persist chronically rare.
Most communities are composed of a few dominant species and a high number of
rare species. Indeed, the bulk of biodiversity at species level consists of a host of
small, inconspicuous and little-known species. Nevertheless, rare species are the
neglected component of biodiversity, and they are often considered as “noise” and
ignored in ecological studies (Piraino et al. 2002). Likewise, biodiversity conservation focuses mainly on a few charismatic species (generally either vertebrates or
large and conspicuous invertebrates) and disregards what represents the most of the
biodiversity. Conversely, the importance of rare species could be crucial as a
reservoir of potential diversity and provide information for the possible future
composition of a community after changes in environmental conditions. Highly
distinct combinations of traits are supported predominantly by rare species. It is
thus not only the quantity but also the quality of biodiversity that matters (Mouillot
et al. 2013).
A broad array of species may allow ecosystems to maintain their functioning, and
a high number of species serves as a buffer against the effects of environmental
impacts and enhances the recovery potential of communities. Therefore, rare species
are particularly important from the point of view of conservation, ecology and
evolutionary biology (Lim et al. 2012). Furthermore, since rare species are
represented by only a few individuals or small populations often restricted to
particular habitats, they are vulnerable to being lost. To summarize, although still
incomplete, there is growing scientific evidence that many rare or little-known
species may play key ecological roles in the function, structure and composition of
some ecological communities and could be important as a genetic reservoir and for
long-term evolutionary potential. Nevertheless, rare or little-known species are, by
their nature of being scarce, often not explicitly included in conservation and natural
resource planning (Raphael and Molina 2007).
We consider here as rare species those that are very restricted in number of
individuals or spatial occurrence but also those of unusual morphological or biological characteristics. Sometimes the supposed rare species are not so much but belong
to groups of tiny animals very poorly studied. Indeed, the number of rare species in
the Alboran Sea is very high, and here we will mention only a few of them as
examples.
10.2.1 Porifera
The bottoms of the Alboran Sea are characterized by a high richness and diversity of
sponges. Among this fauna, there are a significant number of Mediterranean endemisms and rare species, along with numerous “Atlantic” species found in this
westernmost Mediterranean area where may reach notable abundances (Sitjà and
366
J. Templado et al.
fluctuations or reproductive failure due to different impacts (Vermeij and Grosberg
2018). Nevertheless, rarity may also hold the key to survival during crises (e.g.,
Bianchi et al. 2014), and many species persist chronically rare.
Most communities are composed of a few dominant species and a high number of
rare species. Indeed, the bulk of biodiversity at species level consists of a host of
small, inconspicuous and little-known species. Nevertheless, rare species are the
neglected component of biodiversity, and they are often considered as “noise” and
ignored in ecological studies (Piraino et al. 2002). Likewise, biodiversity conservation focuses mainly on a few charismatic species (generally either vertebrates or
large and conspicuous invertebrates) and disregards what represents the most of the
biodiversity. Conversely, the importance of rare species could be crucial as a
reservoir of potential diversity and provide information for the possible future
composition of a community after changes in environmental conditions. Highly
distinct combinations of traits are supported predominantly by rare species. It is
thus not only the quantity but also the quality of biodiversity that matters (Mouillot
et al. 2013).
A broad array of species may allow ecosystems to maintain their functioning, and
a high number of species serves as a buffer against the effects of environmental
impacts and enhances the recovery potential of communities. Therefore, rare species
are particularly important from the point of view of conservation, ecology and
evolutionary biology (Lim et al. 2012). Furthermore, since rare species are
represented by only a few individuals or small populations often restricted to
particular habitats, they are vulnerable to being lost. To summarize, although still
incomplete, there is growing scientific evidence that many rare or little-known
species may play key ecological roles in the function, structure and composition of
some ecological communities and could be important as a genetic reservoir and for
long-term evolutionary potential. Nevertheless, rare or little-known species are, by
their nature of being scarce, often not explicitly included in conservation and natural
resource planning (Raphael and Molina 2007).
We consider here as rare species those that are very restricted in number of
individuals or spatial occurrence but also those of unusual morphological or biological characteristics. Sometimes the supposed rare species are not so much but belong
to groups of tiny animals very poorly studied. Indeed, the number of rare species in
the Alboran Sea is very high, and here we will mention only a few of them as
examples.
10.2.1 Porifera
The bottoms of the Alboran Sea are characterized by a high richness and diversity of
sponges. Among this fauna, there are a significant number of Mediterranean endemisms and rare species, along with numerous “Atlantic” species found in this
westernmost Mediterranean area where may reach notable abundances (Sitjà and
366
J. Templado et al.