Climate change will alter marine ecosystems. However, the complexity of the food webs combined with the chronic undersampling, constrains efforts to predict their future and to optimally manage and protect the marine resources. The West Antarctic Peninsula (WAP) is the fastest winter warming place on Earth and it’s therefore a key place to study how polar marine ecosystems respond to climate change. The ocean has become warmer near the WAP and has been implicated as the main driver for the deglaciation seen in the region. This heat comes from deep water that intrudes onto the shelf region and it can be 4C warmer than Antarctic surface waters.
In part because of the heat and nutrients supplied by the warm deep water, the WAP hosts an extremely productive marine ecosystem supported by large phytoplankton blooms. There has been a shift towards smaller cells and an overall decrease phytoplankton biomass in the WAP linked with increasing cloud cover, deep mixed layers and decrease marginal ice zone. The shift in phytoplankton biomass and size has direct consequences for grazer communities, especially Antarctic krill (Euphausia superba). A shift in zooplankton population has also been observed, with increasing numbers of salps, a gelatinous tunicate, as they are more efficient at eating small phytoplankton. Because krill forms a critical trophic link between primary producers and top predators, the shift in zooplankton community structure suggests that there should be dramatic changes in the higher trophic levels (fish, seals, whales, and penguins and other seabirds).
These changes have been documented most dramatically in Antarctic pygoscelid penguins. In the past 30 years in the northern WAP, populations of ice-dependent Adélie penguins (Pygoscelis adeliae) have fallen by 90%, whereas those of ice-intolerant Chinstrap (P. Antarctica) and Gentoo (P. papua) penguins have risen in the northern and mid-Peninsula region. Declines in the polar species have been related to decreasing sea ice cover and its possible effects on prey availability.
Shifts in climate have thus had a cascading effect, with altered sea ice distributions disrupting the evolved life strategies of resident species, leading to changes in community structure and in the abundance of populations, and ultimately altering the nature of local and regional food webs.
 Mixed layer: layer in which active turbulence (usually winds) has homogenized some range of depths.
 Marginal ice zone: the transition between the open ocean and sea ice
 saps: gelatinous tunicates
Source: Schofield, O., Ducklow, H.W., Martinson, D.G., Meredith, M.P., Moline, M.A. and Fraser, W.R., 2010. How do polar marine ecosystems respond to rapid climate change?. Science, 328 (5985), pp.1520-1523. doi: 10.1126/science.1185779
Author: Filipa Carvalho