Food web – a complex of interrelated food chains in an ecological community
We teach these two terms in elementary school so it is not surprising to read the latest scientific studies that link the decline of two Antarctic penguin species with climate change and the decline of a major food source in the region.
At the heart of the food web in Antarctica is krill. This shrimp-like crustacean live in large schools called swarms. These swarms can reach concentrations of between 10,000 – 30,000 organisms per cubic meter. As a biomass they are certainly one of the most successful species at about 500 million tons on the planet.
Whether an animal feeds directly or indirectly, krill is at the center of the Antarctic ecosystem. While there is some indication that the reemerging whale and seal populations are in competition for krill with the penguins, the study indicates that it is the decline of the krill population that is having the most impact on the Adelie and chinstrap penguin populations.
Antarctic krill is also the target of commercial fishing. Studies show that the loss of food at the bottom of the oceans food chain will harm a range of species that can result in malnutrition, death of offspring or the disruption of breeding patterns. However, the biggest impact on the krill population seems to be the warmer temperatures and its impact on sea ice. Krill feed on phytoplankton which is basically ice algae found beneath the sea ice pack. As the ice habitat disappears so do the tiny plants that grow among the ice crystals. Each year the ice forms later in the season covering less area, and it melts earlier each Antarctic spring.
The big losers from this decline seem to be the Adelie and chinstrap penguins with the chinstraps fairing the worst. It was first thought that they would be more successful with the retreat of the ice but it seems that their food source has been impacted as well. Before the reduction of the krill, 50% of young penguins returned to the rookeries to breed. As the abundance of krill shrinks only about 10% of young penguins survive to breed in their second and third years.
Like in the lessons taught in my elementary classroom, when you remove one important element from an ecosystem it can have a major impact on the entire web. Our ocean system is interconnected, and Antarctica seems to be a canary in the tunnel giving us an important warning!
If you have an interest in these issues and more here are some websites to visit:
Antarctic Heritage Trust http://www.nzaht.org/