page_title: Marine food web
section_title: Polar webs
hierarchical_section_title: Marine food web / By habitat / Polar webs
caption_attribution_description: English: Sea ice food web and the microbial loop. AAnP = aerobic anaerobic phototroph, DOC = dissolved organic carbon, DOM = dissolved organic matter, POC = particulate organic carbon, PR = proteorhodopsins. The microbial loop here is re-drawn and abridged from: Azam, F., Fenchel, T., Field, J.G., Gray, J.S., Meyer-Reil, L.A. and Thingstad, F. (1983) "The ecological role of water-column microbes in the sea". Marine ecology progress series, 10(3): 257–263. Fenchel, T. (2008) "The microbial loop–25 years later". Journal of Experimental Marine Biology and Ecology, 366(1-2): 99-103. doi:10.1016/j.jembe.2008.07.013.
context_page_description: Compared to terrestrial environments, marine environments have biomass pyramids which are inverted at the base. In particular, the biomass of consumers is larger than the biomass of primary producers. This happens because the ocean's primary producers are tiny phytoplankton which grow and reproduce rapidly, so a small mass can have a fast rate of primary production. In contrast, terrestrial primary producers, such as mature forests, grow and reproduce slowly, so a much larger mass is needed to achieve the same rate of primary production.
  Because of this inversion, it is the zooplankton that make up most of the marine animal biomass. As primary consumers, zooplankton are the crucial link between the primary producers and the rest of the marine food web.
  If phytoplankton dies before it is eaten, it descends through the euphotic zone as part of the marine snow and settles into the depths of sea. In this way, phytoplankton sequester about 2 billion tons of carbon dioxide into the ocean each year, causing the ocean to become a sink of carbon dioxide holding about 90% of all sequestered carbon.
context_section_description: Arctic and Antarctic marine systems have very different topographical structures and as a consequence have very different food web structures. Both Arctic and Antarctic pelagic food webs have characteristic energy flows controlled largely by a few key species. But there is no single generic web for either. Alternative pathways are important for resilience and maintaining energy flows. However, these more complicated alternatives provide less energy flow to upper trophic-level species. "Food-web structure may be similar in different regions, but the individual species that dominate mid-trophic levels vary across polar regions".
  Arctic
  The Arctic food web is complex. The loss of sea ice can ultimately affect the entire food web, from algae and plankton to fish to mammals. The impact of climate change on a particular species can ripple through a food web and affect a wide range of other organisms... Not only is the decline of sea ice impairing polar bear populations by reducing the extent of their primary habitat, it is also negatively impacting them via food web effects. Declines in the duration and extent of sea ice in the Arctic leads to declines in the abundance of ice algae, which thrive in nutrient-rich pockets in the ice. These algae are eaten by zooplankton, which are in turn eaten by Arctic cod, an important food source for many marine mammals, including seals. Seals are eaten by polar bears. Hence, declines in ice algae can contribute to declines in polar bear populations.
  In 2020 researchers reported that measurements over the last two decades on primary production in the Arctic Ocean show an increase of nearly 60% due to higher concentrations of phytoplankton. They hypothesize that new nutrients are flowing in from other oceans and suggest this means the Arctic ocean may be able to support higher trophic level production and additional carbon fixation in the future.
  Antarctic
caption: Sea ice food web and the microbial loop. AAnP = aerobic anaerobic phototroph, DOC = dissolved organic carbon, DOM = dissolved organic matter, POC = particulate organic carbon, PR = proteorhodopsins.[92][93]
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