150
the few examples of such studies, is Song et al. (2016), who
used combined morphological and molecular approach to
investigate the collections of Chinese National Arctic
Research Expeditions in the Bering Sea. By means of 16S
rDNA sequences, a new species, Sertularia xuelongi, was
described and the potential biogeographic origin of this species discussed. By comparing 16 sequences of S. xuelongi
and of other congeneric species from the northwest of
France, Iceland, and the Chukchi Sea, they suggested that
these species are of Pacific origin, but may in fact constitute
a significant part of the deep-sea benthic fauna of the Arctic
(Song et al. 2016).
As mentioned earlier, important factors in shaping nowadays Arctic diversity were glaciation processes, during which
species were forced into refugia in order to survive, what
caused long-term isolation and thus differentiation of the species. After glaciation ceased, some of the expanding species
went in secondary contact, however, undergoing processes
were much more complicated (Maggs et al. 2008). One of the
interesting examples is blue mussel, Mytilus edulis, which
was gone for a long time from Svalbard waters, however
warming of the Arctic enabled its re-appearance (Berge et al.
2005). It has been proven that blue mussels can create hybrids
with other species, like Mytilus trossulus and Mytilus galloprovancialis in different Arctic regions, what leads to local
adaptations (Mathiesen et al. 2017). This topic has not been
investigated well yet, nonetheless it requires more insight as
Mytilus spp. are ecosystem engineers and global warming
opens new paths for invasions of boreal species in the Arctic.
Nekton
The benthic and planktonic organisms discussed above constitute food sources for higher trophic levels, which in the
Arctic are primarily nektonic vertebrates. Aside from marine
mammals and sea birds, this group is represented by a speciose community of fish. In the Arctic, there are 243 species of
fish (Bluhm et al. 2011a), comprising several key species
like polar cod and capelin (Hop and Gjøsæter 2013) as well
as species with unique traits including the longest living vertebrate, the Greenland shark (Nielsen et al. 2016).
The biogeography of this ecologically and economically
important group remained, unfortunately, largely unknown.
Only recently, Mecklenburg et al. (2011) have improved the
taxonomic identification of all Arctic species, thereby
improving the resolution available for the spatial structure of
their diversity. COI barcoding, combined with morphological analyses, allowed them to revise the biogeographic origin
of species, showing that some of the past fish records from
Arctic waters were misidentified. They found that a majority
Arctic fish species (59%) are cosmopolitan species with
boreal distribution, while the remaining 41% are Arctic,
mainly-Arctic, and boreo-Arctic species (Mecklenburg et al.
2011). Such detailed knowledge on the biodiversity is
required to trace the climate-change derived alteration of, for
example, species distribution. The study also shows the hidden potential of the simultaneous morphological-molecular
approach to taxonomy. In this particular case, it could be
used to resolve the cod mother identity, or to acquire data of
unprecedented species-resolution (Carr and Marshall 2008).
For some fish species like Arctogadus glacialis, Boreogadus
saida complete genomes are available (Breines et al. 2008).
There is a high interest in postglacial colonization of fishes
like Salvelinus fontinalis (Pilgrim et al. 2012), Coregonus
nasus (Harris and Taylor 2010) or Coregonu lavaretus
(Østbye et al. 2006). We can also find lots of studies about
genetic diversity of different species (Kai et al. 2011; Kovpak
et al. 2011), as in the future it might be crucial for adaptations to a changing environment.
The overall low number of species and distinctive morphology allow a relatively easy acquisition of high- resolution
data on marine mammal diversity by means of classic taxonomic methods. Furthermore, such approaches have already
revealed pronounced modifications in species ecology and
biology, by detecting shifts in distribution ranges, decrease
in body size and size of the separate populations, as well as
alterations of food migrations (Kovacs et al. 2010). All of
these changes might affect marine mammal species populations. Even though molecular research does not focus on biodiversity, it may cover a wide range of other aspects, like
evolution, population genetics or phylogeography.
Future Perspectives
The Arctic Ocean is warming three times faster than the
global average (IPCC 2014), thus further changes in species
composition and entire ecosystem functioning are inevitable.
Temperature has an impact on many aspects of physiological
processes and it can affect reproduction, growth, and survival. Changes in single species distributions can effect
entire ecosystems through all trophic levels, as was shown
for the case of a potential mismatch between phytoplankton
blooms and reproduction of Calanus glacialis in Arctic
waters (Søreide et al. 2010). Hence, using only traditional
methods might not be enough to timely observe what is
going on in this fragile ecosystem. Kędra et al. (2015)
emphasized the lack of biodiversity research in some Arctic
areas, especially in the deep-sea region, but also the lack of
research predicting direction of changes in species distribution resulting from global change.
DNA barcoding has been proven a useful tool in biodiversity assessment, however, the evolution of molecular methods is very fast, including the development of new approaches
such as metabarcoding. This method involves the extraction
K. S. Walczyńska et al.
the few examples of such studies, is Song et al. (2016), who
used combined morphological and molecular approach to
investigate the collections of Chinese National Arctic
Research Expeditions in the Bering Sea. By means of 16S
rDNA sequences, a new species, Sertularia xuelongi, was
described and the potential biogeographic origin of this species discussed. By comparing 16 sequences of S. xuelongi
and of other congeneric species from the northwest of
France, Iceland, and the Chukchi Sea, they suggested that
these species are of Pacific origin, but may in fact constitute
a significant part of the deep-sea benthic fauna of the Arctic
(Song et al. 2016).
As mentioned earlier, important factors in shaping nowadays Arctic diversity were glaciation processes, during which
species were forced into refugia in order to survive, what
caused long-term isolation and thus differentiation of the species. After glaciation ceased, some of the expanding species
went in secondary contact, however, undergoing processes
were much more complicated (Maggs et al. 2008). One of the
interesting examples is blue mussel, Mytilus edulis, which
was gone for a long time from Svalbard waters, however
warming of the Arctic enabled its re-appearance (Berge et al.
2005). It has been proven that blue mussels can create hybrids
with other species, like Mytilus trossulus and Mytilus galloprovancialis in different Arctic regions, what leads to local
adaptations (Mathiesen et al. 2017). This topic has not been
investigated well yet, nonetheless it requires more insight as
Mytilus spp. are ecosystem engineers and global warming
opens new paths for invasions of boreal species in the Arctic.
Nekton
The benthic and planktonic organisms discussed above constitute food sources for higher trophic levels, which in the
Arctic are primarily nektonic vertebrates. Aside from marine
mammals and sea birds, this group is represented by a speciose community of fish. In the Arctic, there are 243 species of
fish (Bluhm et al. 2011a), comprising several key species
like polar cod and capelin (Hop and Gjøsæter 2013) as well
as species with unique traits including the longest living vertebrate, the Greenland shark (Nielsen et al. 2016).
The biogeography of this ecologically and economically
important group remained, unfortunately, largely unknown.
Only recently, Mecklenburg et al. (2011) have improved the
taxonomic identification of all Arctic species, thereby
improving the resolution available for the spatial structure of
their diversity. COI barcoding, combined with morphological analyses, allowed them to revise the biogeographic origin
of species, showing that some of the past fish records from
Arctic waters were misidentified. They found that a majority
Arctic fish species (59%) are cosmopolitan species with
boreal distribution, while the remaining 41% are Arctic,
mainly-Arctic, and boreo-Arctic species (Mecklenburg et al.
2011). Such detailed knowledge on the biodiversity is
required to trace the climate-change derived alteration of, for
example, species distribution. The study also shows the hidden potential of the simultaneous morphological-molecular
approach to taxonomy. In this particular case, it could be
used to resolve the cod mother identity, or to acquire data of
unprecedented species-resolution (Carr and Marshall 2008).
For some fish species like Arctogadus glacialis, Boreogadus
saida complete genomes are available (Breines et al. 2008).
There is a high interest in postglacial colonization of fishes
like Salvelinus fontinalis (Pilgrim et al. 2012), Coregonus
nasus (Harris and Taylor 2010) or Coregonu lavaretus
(Østbye et al. 2006). We can also find lots of studies about
genetic diversity of different species (Kai et al. 2011; Kovpak
et al. 2011), as in the future it might be crucial for adaptations to a changing environment.
The overall low number of species and distinctive morphology allow a relatively easy acquisition of high- resolution
data on marine mammal diversity by means of classic taxonomic methods. Furthermore, such approaches have already
revealed pronounced modifications in species ecology and
biology, by detecting shifts in distribution ranges, decrease
in body size and size of the separate populations, as well as
alterations of food migrations (Kovacs et al. 2010). All of
these changes might affect marine mammal species populations. Even though molecular research does not focus on biodiversity, it may cover a wide range of other aspects, like
evolution, population genetics or phylogeography.
Future Perspectives
The Arctic Ocean is warming three times faster than the
global average (IPCC 2014), thus further changes in species
composition and entire ecosystem functioning are inevitable.
Temperature has an impact on many aspects of physiological
processes and it can affect reproduction, growth, and survival. Changes in single species distributions can effect
entire ecosystems through all trophic levels, as was shown
for the case of a potential mismatch between phytoplankton
blooms and reproduction of Calanus glacialis in Arctic
waters (Søreide et al. 2010). Hence, using only traditional
methods might not be enough to timely observe what is
going on in this fragile ecosystem. Kędra et al. (2015)
emphasized the lack of biodiversity research in some Arctic
areas, especially in the deep-sea region, but also the lack of
research predicting direction of changes in species distribution resulting from global change.
DNA barcoding has been proven a useful tool in biodiversity assessment, however, the evolution of molecular methods is very fast, including the development of new approaches
such as metabarcoding. This method involves the extraction
K. S. Walczyńska et al.