Antarctic Peninsula Climate – A Change in Krill Ecosystem
Antarctic Peninsula has been experiencing warming trends for over 40 years with an increase of 2-3 C, thus correlating with lower sea ice conditions in the Amundsen Sea and Bellinghausen Sea. Warming temperatures around the Antarctic Peninsula is changing the dynamics of the ecosystem. The rise in atmospheric temperature is causing increasing in melting of freshwater glaciers and ice shelves. Fresh water emerging into the sea counteracts the salinity within a regional area. Changes identified are;
• Decrease in sea water salinity up to 60 miles offshore
• Lower sea ice
• Decreased krill population
• Increased salp (open ocean tunicate that is reminiscent of a jelly-fish) population
• Increase in cryptophytes (single cell phytoplankton algae)
• Decrease in diatom phytoplankton
• Increase in carbon sequestering in deep ocean sinks
• Decrease in carbon availability in the food chain
The Antarctic Krill (Euphausia superba), a small shrimp like crustacean is the most important zooplankton species associated with the sea ice and plays a crucial role in the Antarctic food web. On a regional basis the amount of krill appear to be declining in the southern ocean. There are definitely lower trends in krill population during lower sea ice years around Antarctica. Part of the rational for the population decline is that ice algae rely on the sea ice for protection and growth. The krill need the sea ice in order to feed on the algae and phytoplankton.
Krill occur in groups or large swarms. They are less than 3 inches in size and feed primarily on phytoplankton and sea ice algae. Krill filter diatom phytoplankton out of the water column and scrape algae from the sea ice. Apart from frequenting the sea ice to feed, krill in particular juveniles, seek protection from predators in the many nooks and crannies formed by the deformed sea ice floes. Krill is the staple food of many fish, birds and mammals in the Southern Ocean. The biomass of Antarctic krill is considered to be larger than that of the earth’s human population.
Sea- ice algae utilizes atmospheric carbon dioxide for its energy source, the same as plants do on land. Krill diet of the sea-ice algae and phytoplankton is essential for converting the carbon for use in higher animals such as fish, birds, and whales. This carbon conversion is a very critical role in predatory nutrition. Additionally krill do eliminate some of the silica from the diatom shells and carbon in sticky balls that sinks nearly two miles into the deep ocean. These cold, deep waters are able to contain carbon dioxide and prevent the gas from rising to the surface, thus immobilizing carbon that is not passed into the food chain.
In recent years there have been increases in algae phytoplankton called cryptophytes. Mark Moline, California Polytechnic State University, states that the cryptophyte population correlates with warmer temperatures and lower salinity waters that are produced by the melting of the freshwater glacier. Cryptophytes measure around 2 mm, while other plankton in the Antarctic waters are much larger and measure 15 to 270 mm. Along with the increase in cryptophyte population an increase in salp, a pelagic tunicate, population has also occurred. There are differences between salps and krill. Salps feeding efficiency is capable of grazing on smaller food sources less than 4mm, whereas, the Antarctic Krill efficiency declines on any food less than 20 mm. The salps compete with krill for the phytoplankton and thus decrease the krill population. Additionally the salps feed on krill larvae, which also cause a decline in krill numbers.
The warming trend in the Antarctic Peninsula is showing a pattern of increasing cryptophytes over other phytoplankton and the increase in the salp. This influence is due to the low sea ice and the lowering of the salinity in the seawater. Salps and cryptophytes do better in the lower salinity, while the krill and other plankton are unable to tolerate the increased freshwater regime from the glacier ice melts. This selectivity gives preference to the salps as the dominant species while decreasing krill abundance. During lower sea ice seasons the density of krill declines while the salp population increases.
Carbon sequestering into the deep ocean from the algae and phytoplankton occur by both the salp and krill. Both species eliminate the atmospheric carbon received from the primary producing algae by producing fecal pellets by the salps and sticky balls by the krill, thereby, reducing the amount of carbon dioxide in the atmosphere. The salps though sequester more carbon into the cold deep ocean than the krill. However, the krill provides the most efficient pathway for carbon transfer up into the food chain. The cryptophyte dominated waters are less efficient in the food chain due to increased feeding by salps and the difficulty of the krill to utilize the cryptophytes as a food source. Migration patterns by penguins are changing, in part due to the changing krill population. Krill is a mainstay diet for penguins, and if the krill population changes, many other ecological changes occur with it.
Steve Bynum has worked at Palmer Station along the Antarctic Peninsula. He not only enjoyed the ecosystem along the Bellinghausen Sea but he has also witnessed the changing climate conditions.
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