Climate change impacts and vulnerability in Europe 2016

Climate change impacts on environmental systems
4.1.5 Distribution shifts of marine species
Key messages
• Increases in regional sea temperatures have triggered a major northwards expansion of warmer water plankton and a
northwards retreat of colder water plankton in the North-east Atlantic. This northerly movement has amounted to about
10 ° latitude (1 100 km) over the past 40 years, and it seems to have accelerated since 2000.
• Sub-tropical species are occurring with increasing frequency in Europe's seas, and sub-Arctic species are receding
northwards.
• Wild fish stocks are responding to changing temperatures and food supply by changing their distribution. This can have
impacts on those local communities that depend on those fish stocks.
• Further changes in the distribution of marine species, including fish stocks, are expected with the projected climate
change, but quantitative projections of these distribution changes are not widely available.
Relevance
Most marine organisms are 'ectotherms' that rely
on the temperature of their environment to function
optimally and are adapted to the temperature regime
of their existing distribution range. Because of this
relationship between the physical environment and
species' life requirements, the redistribution of species
has emerged as one of the most significant and visible
species responses to climate change (Sunday et al.,
2012).
Climate velocities (the rate and direction that isotherms
shift through space) can be up to seven times higher
in the ocean than on land (Poloczanska et al., 2013).
Combined with fewer dispersal barriers in the
marine environment, this allows marine species to
seek out optimal temperature regimes faster than
most terrestrial species (Pinsky et al., 2013). Changes
in species distribution can therefore be used as
an indicator of climate change impacts in marine
ecosystems, bridging the gap between observed
changes in physical conditions of the sea and observed
changes in biological parameters.
As the distribution and abundance of a species
changes, so will the role of that particular species in the
local or regional marine community. Changes in species
distribution can, in turn, change the overall productivity
and stability of the local ecosystem, thereby ultimately
affecting the food available to (other) fish, birds and
marine mammals (Thackeray et al., 2010; Cardinale
et al., 2012).
Changes in species distribution will also create
challenges for local communities that depend on fish
stocks and other marine resources. For example, the
recent mackerel dispute between the EU and the Faroe
Islands was caused by the fact that the mackerel stock
had increased the time it spent in the waters of the
Faroe Islands rather than in EU waters. This caused
a heated discussion on stock allocation between
countries. Ultimately, it led to an increase in the Faroe
Islands' total allowable catch from 5 to 13 %, with
further increases planned (Hartman and Waibel, 2014).
Such disputes will most likely occur again as coldwater
species retreat northwards. New opportunities may
arise as new species come in from the south, but it is
uncertain whether these will be of a similar commercial
value to the receding ones.
In addition to changes in species distribution, rising sea
surface temperatures are also causing changes in the
phenology of marine species (see Box 4.3).
Past trends
Increases in regional sea temperatures have triggered
a major northwards movement of species. As a result,
sub-tropical species are occurring with increasing
frequency in European waters, and sub-Arctic species
are receding northwards. However, in areas with
geographical constraints, i.e. where a coastline hinders
northwards movement, some species shift into deeper
and cooler waters (Dulvy et al., 2008; Brattegard, 2011;
Pinsky et al., 2013). Some examples are provided below.
Plankton in the Greater North Sea have shown a
northerly movement of about 10 ° latitude over the
past 40 years. This corresponds to a mean polewards
movement of around 250 km per decade, which
appears to have accelerated since 2000 (Beaugrand,
2009). As a result, the ratio of the coldwater Calanus
finmarchicus to the warmwater Calanus helgolandicus
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