The Davis Strait - DCE - Nationalt Center for Miljø og Energi

8.5 Marine mammals and seabirds
The impacts of climate change on marine mammals and seabirds are likely
to be severe, and not so straightforward to estimate since patterns of changes
are non-uniform and highly complex (ACIA 2005). Laidre et al. (2008) compared
seven Arctic and four sub-Arctic marine mammal species with regard
to their habitat requirements and evidence for biological and demographic
responses to climate change. Sensitivity of the various species to climate
change was assessed using a quantitative index based on population size,
geographic range, habitat specificity, diet diversity, migration, site fidelity,
sensitivity to changes in sea ice, sensitivity to changes in the trophic web,
and maximum population growth potential (Rmax). Marine mammals dependent
on sea ice (e.g. hooded seal, polar bear and narwhal) appear to be
most sensitive. Species such as ringed seal and bearded seal are less sensitive,
primarily due to their large circumpolar distributions, large population
sizes, and flexible habitat requirements. Due to their dependence on sea-ice
habitat, the impacts of continued climate change will increase the vulnerability
of all polar bear sub-populations. Population and habitat modelling have
projected substantial future declines in the distribution and abundance of
polar bears (Lunn et al. 2010).
Arctic seabirds, which typically depend on large, energy-rich zooplankton,
are likely to be negatively affected by increasing temperatures and decreasing
ice cover, while more temperate piscivorous species may benefit from
these changes (cf. Kitaysky & Golubova 2000). Changes in the extent and
timing of sea-ice cover over the past several decades, for example, have led
to changes in phenology and reproduction of thick-billed murres in Canada,
with adverse consequences for nestling growth (Gaston et al. 2005). A circumpolar
study of population change of both thick-billed and common
murres showed that both species tended to decline following major changes
in sea temperature (Irons et al. 2008). Within the assessment area it is likely
that the breeding population of the partly planktivorous thick-billed murre
will be gradually replaced by the cold-temperate sibling species, the piscivorous
common murre (Gaston & Irons 2010). This will probably be a very
slow process due to pronounced site fidelity and human disturbance. Other
temperate species which may be favoured by increasing temperatures include
the recent immigrant, the lesser black-backed gull. In general, the timing
of spring migration and breeding of most species is likely to advance
substantially in the coming decades. North of the assessment area, the phenology
has already changed for common eider and thick-billed murre (AU &
GINR, unpubl.). This may also be the case for the assessment area, but so far
no data exist. Changing breeding conditions north of the assessment area,
e.g., phenology, prey availability or available breeding habitats, may lead to
changing numbers of wintering birds within the assessment area.
8.6 Conclusions
The examples given above clearly indicate that climate change has a large
potential to modify marine ecosystems, particular in high latitude regions,
either through a bottom-up reorganisation of the food web by altering the
nutrient or light cycle, or top-down reorganisation by altering critical habitat
for higher trophic level (Macdonald et al. 2005). Alterations in the density,
distribution and/or abundance of keystone species at various trophic levels
could have significant and rapid consequences for the structure of the ecosystems
in which they currently occur.
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