Changes in food webs and ecosystem function

Key drivers
Temperature
Ocean acidification
Dissolved oxygen
Ocean Circulation
What has happened?

Local and regional studies have attempted to assess ecosystem response to climate change. There are however limited long-term time series data, and even where time series data are available (e.g., suggesting a decline in Antarctic krill corresponding with changes in sea ice extent since the 1980s) there is often not clear consensus in the interpretation. 

Mid-level species, such as copepods, amphipods, salps, squid and mesopelagic fish (e.g., lanternfish) may potentially buffer impacts from changes in krill distributions for predator species that are able to switch prey source, maintaining ecosystem stability.

For high level species, changes in the suitability of breeding habitats could be affecting reproductive success, mortality and body condition. Changes in spatial and seasonal prey availability may also be affecting patterns of migration, distribution, foraging and reproduction, although high interannual variability, and at South Georgia, recovery from historic exploitation, makes it difficult to identify long-term trends. 

There is evidence that acidification in coastal waters is already having a detrimental effect on primary production and causing changes to the structure and function of the microbial communities at the base of the food web. 
 

CONFIDENCE LEVEL
MEDIUM

Low evidence, medium agreement

Changes in ecological systems at SGSSI and BAT are both documented and anticipated to occur more acutely in the future. There is however currently limited understanding of the preconditions or indicators of change that would help model/ pre-empt them.

What could happen?

The impact of climate change on benthic (seabed) ecology will differ depending on water depth. For shallower shelf areas, ice loss and increased iceberg scour, will favour fast growing algal species and species better adapted to disturbance. Reduced survival of long-lived, slow growing species could mean a net loss in benthic biodiversity. In deeper waters, the magnitude and timing of the seasonal pulse of organic nutrients from surface phytoplankton blooms and pelagic biomass may change, potentially impacting reproductive success in benthic animals.

Under high emissions scenarios, primary production is projected to increase in waters south of 65°S by 2100. Lower trophic level primary consumers such as krill, are expected to exhibit a corresponding move southward into a decreasing zone of cold and increasingly acidified water. There is an increased risk of declines in some krill predator populations (e.g., certain species of penguins). Ocean acidification will negatively impact growth and reproduction and reduce success in invertebrate early life-history stages.

Lanternfish, which play a key role in the foodweb, are predicted to move polewards. Less is known about larger seabed fish species, but differences in temperature tolerance (e.g., Patagonian vs. Antarctic toothfish) may result in latitudinal range shift with implications for future fisheries.

BAT and SGSSI host some of the largest concentrations of seabirds and marine mammals on Earth. Climate change impacts will vary according to life history traits (e.g., preferred nursery grounds), feeding strategies and habitat preferences (e.g., species that associate closely with ice habitats), which are highly species and region specific.

Changes to ocean temperatures and circulation could improve survival of non-native species to the detriment of native Antarctic species. 
 

CONFIDENCE LEVEL
LOW

Low evidence, medium agreement

Biodiversity projections and food web models are limited by uncertainty in the potential for organisms to tolerate or adapt to ecosystem change and the resilience of foodweb structures. There is significant uncertainty associated with natural variability and recovery from historic commercial exploitation.