bitte übersetzte nachfolgenden Text:      ECOSYSTEM CHANGES
Climatic changes on short and long time scales can
significantly impact on Antarctic ecosystems (Constable & Doust 2009). The most marked ecosystem
changes have been observed in the SW Atlantic
sector of the Southern Ocean. In this region, a pronounced change in environmental conditions, most
prominently sea ice decline and climate warming,
has occurred in the region where the main krill fishing grounds are located (Gascon & Werner 2009).
Signals of ecological change date back to the mid1990s, when simultaneous declines in krill stocks and
increases in salp populations were linked to climate
variability (Loeb et al. 1997). While krill populations
may have suffered from sea ice decline, salps likely
have benefited from warming surface waters during
the last century (Pakhomov et al. 2002, Atkinson et
al. 2004, Loeb & Santora 2012).
These changes may be caused by perturbations of
the physical environment, but also reflect changes at
the lower trophic levels of the food web. In the western Antarctic Peninsula (WAP) region, net primary
productivity has declined during the past 3 decades,
associated with a change in phytoplankton community composition, potentially impacting negatively
on krill and positively on salp grazing efficiency
(McClatchie & Boyd 1983, Moline et al. 2004,
Montes-Hugo et al. 2009, Schofield et al. 2010).
In the SW Atlantic sector, changes in krill biomass,
whether inter-annual or longer term, affect foraging, breeding success and population size of krilldependent predators (Croxall et al. 1999, Fraser &
Hofmann 2003, Trathan et al. 2007, 2011, 2012, Trivelpiece et al. 2011). At South Georgia, a number of
predator species, including penguins, seals and
whales, show responses to climate variability, with a
particular species response thought to be mediated
through the availability of krill (Forcada et al. 2005,
Leaper et al. 2006, Trathan et al. 2006). Farther south
in the Scotia Arc and in the WAP regions, penguins
are also showing responses to environmental variability, presumably mediated through reduced krill
availability and changing sea ice (e.g. Reid & Croxall
2001, Forcada & Robinson 2006, Trivelpiece et al.
2011, Lynch et al. 2012). A simple interpretation of
environmentally driven change is difficult to substantiate, however, and there is increasing evidence
to suggest that the effects of historical harvesting are
still important (Trathan & Reid 2009, Trivelpiece et al.
2011, Lynch et al. 2012, Trathan et al. 2012). For
example, certain populations of Antarctic fur seals
(Christensen 2006) and humpback whales Megaptera
novaeangliae (Nicol et al. 2008, IWC 2010) have
increased considerably over the past decades.
Also in the Indian Ocean and Pacific sectors of
the Southern Ocean, ecosystem changes associated
with changing sea ice extent and climatic conditions
have been reported (Dayton 1989, Cameron & Siniff
2004, Ainley et al. 2005, Jenouvrier et al. 2005). The
changes observed in the Indian and Pacific sectors of
the Southern Ocean have been related to periodic
climate fluctuations, such as the Southern Oscillation
Index (SOI; Jenouvrier et al. 2005, Trathan et al.
2007).
Increases in water temperature are expected to
result in changes in phytoplankton community structure, which in turn are expected to cascade upwards,
altering primary productivity, food web dynamics
and even the structure of marine food webs (Finkel et
al. 2010). This is important, because krill are regionally important grazers of the larger phytoplankton,
especially diatoms (Ross et al. 2000, Garibotti et al.
2003, Haberman et al. 2003a,b). A shift in phytoplankton community structure, from diatoms to
crypto phytes, has already been documented in some
years near the Antarctic Peninsula (Moline et al.
2004). The shift was observed during the austral
summer and was correlated in time and space with
glacial meltwater runoff and reduced surface water
salinities. Elevated temperatures will increase the
extent of coastal meltwater zones and the seasonal
prevalence of cryptophytes. This change in phytoplankton composition may enhance competition
of krill with gelatinous zooplankton, such as salps
(Moline et al. 2004).
Krill play a central role in several Antarctic marine
ecosystems; for example, in the southern Scotia Sea,