We discussed earlier how Euphausia superba are
extremely important in the functionality of the ecosystems of the Southern
Ocean. Shortages in krill populations have been shown to have widespread
impacts on a number of species that rely on these tiny creatures as a nutrient rich food source (Meyer 2012). As we look to the future of
climate change and the understood impacts decreased sea ice will have on
species, it is important to understand
the historical shortages of Euphausia superba and
the impacts it has had on individual species.
Adélie penguins (Pygoscelis adeliae)
A study published in 2008 quantified the effect
an Antarctic Krill population around the Flat Islands could have on a
neighboring colony on Adelie penguins located on Bechevervause Island in the
East Antarctic (Nikol et al. 2008). Adelie Penguins are known to forage
extensively on krill as they are found near nursing areas and therefore reduces
the amount of time needed for foraging trips (Trivelpiece et al. 1987). This
penguin species is known for the amount of time and energy it places on
preparing for pregnancy and caring for offspring once born. An ongoing acoustic survey of Euphausia superba had been conducted
for 15 years in the area (Nikol et al. 2008).
The research focused on two year, 2001 and 2003, and while the distribution
of the krill remained similar, the abundance in 2001 was three times that of
2003. For unknown reasons the summer of
2003 experienced a massive decline in overall krill biomass. During
these two years, the team of scientists collected land based data reflecting
the breeding performance of the penguin colony.
Also gut contents of the penguins were examined in both years. The results of this survey indicated that in
2003, the reduced abundance of Antarctic Krill resulted in:
- Increase in foraging trip duration- Penguins had to travel farther for food
- Decreased efficiency off foraging trips- less food brought back per trip
- Increased ratio of fish consumption as compared to 2001
- Increased chick mortality
In conclusion, this study showed the direct impact a year with low
krill abundance can have on the breeding success of the Adelie Penguin. This represent s the dependence this Antarctic species has on the availability of krill.
Chaos in the South Georgian Islands
The South Georgian Islands are located just north of the Antartic Penisula in an area of the Southern Ocean that has experienced some of the largest increases in average water and air temperatures over the past 50 years (King 1994). A long term study has been preformed on the populations of predator species on Bird Island from 1980- 2000 including Antarctic fur seals, black-browed albatross, gentoo penguins and macaroni penguins (Reid and Croxall 2001). All four species experienced dramatic declines in abundances, especially for the period from 1985-2000. Also, this study found significant declines in the proportion of krill in these the diet of macaroni penguins based on stomach samples. Lastly, the size of krill being consumed by all species were examined and displayed a very noticeable decrease in average krill length being consumed.
The general decrease in krill populations were proposed as a ultimate reason for the decline in these predator populations (Loeb et al. 1997). The decrease in size of the krill consumed can be related to the limiting factor sea ice plays on the recruitment of this species (Atkinson et al 2004). Recruitment can be described as the ability of juvenile organisms to survive to the age or size where they are recognized as as subsistence target for commercial and predator extraction.
All species have been known consumers of Antarctic Krill and also consume other species that rely on krill as their food source. This is enforces the idea that trophic levels are intricate systems and the role of Euphausia superba as keystone species results in its population dynamics having far reaching effects on species far above it on the trophic pyramid.
Southern Right Whale
Southern Right whales are yet another target of the decreased Euphausia superba populations found near the South Georgian Islands (Leader et al. 2006). Right whales is a baleen species that feeds heavily on krill and other plankton. A satellite study from 1981-1999 shows the increase in mean surface water temperatures as well as the variability by season. This was linked to the decreased krill availability tested via acoustic transects during the summer breeding months from 1996-1999 (Trathan et al. 2003). Krill biomass showed a negative relationship to the cooling of near shore waters, where krill nursing areas are common and shelve ice is receding. In a long term survey by the International Whaling Commission, right whale reproductive success and population dynamics were observed and related to the success of mature females summer feeding season during pregnancy (Cooke et al. 2003). The results indicated that there were significantly higher rates of calve failure in two periods- late pregnancy and early lactation (Leaper et al. 2006). This supports the idea that decreases in krill availability as a result of warmer waters and receding annual ice, has devastating effects on the breeding success of Southern Right Whales
The South Georgian Islands are located just north of the Antartic Penisula in an area of the Southern Ocean that has experienced some of the largest increases in average water and air temperatures over the past 50 years (King 1994). A long term study has been preformed on the populations of predator species on Bird Island from 1980- 2000 including Antarctic fur seals, black-browed albatross, gentoo penguins and macaroni penguins (Reid and Croxall 2001). All four species experienced dramatic declines in abundances, especially for the period from 1985-2000. Also, this study found significant declines in the proportion of krill in these the diet of macaroni penguins based on stomach samples. Lastly, the size of krill being consumed by all species were examined and displayed a very noticeable decrease in average krill length being consumed.
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| ORIGINAL FIGURE |
All species have been known consumers of Antarctic Krill and also consume other species that rely on krill as their food source. This is enforces the idea that trophic levels are intricate systems and the role of Euphausia superba as keystone species results in its population dynamics having far reaching effects on species far above it on the trophic pyramid.
Southern Right Whale
Southern Right whales are yet another target of the decreased Euphausia superba populations found near the South Georgian Islands (Leader et al. 2006). Right whales is a baleen species that feeds heavily on krill and other plankton. A satellite study from 1981-1999 shows the increase in mean surface water temperatures as well as the variability by season. This was linked to the decreased krill availability tested via acoustic transects during the summer breeding months from 1996-1999 (Trathan et al. 2003). Krill biomass showed a negative relationship to the cooling of near shore waters, where krill nursing areas are common and shelve ice is receding. In a long term survey by the International Whaling Commission, right whale reproductive success and population dynamics were observed and related to the success of mature females summer feeding season during pregnancy (Cooke et al. 2003). The results indicated that there were significantly higher rates of calve failure in two periods- late pregnancy and early lactation (Leaper et al. 2006). This supports the idea that decreases in krill availability as a result of warmer waters and receding annual ice, has devastating effects on the breeding success of Southern Right Whales
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