Antarctic Krill: Essential to the Food Chain
Krill are crustaceans found in waters all over the world. Existing near the bottom of the food chain, krill are an important source of nutrition for many marine species including whales, seals, penguins, squid, and fish. It has been estimated that Antarctic krill (Euphausia superba) make up a staggering 380 million metric tons of marine biomass. Krill are considered a “keystone species,” or a fundamentally essential species for its aquatic ecosystem. By feeding on plankton, krill unlock essential nutrition for other species.
A migratory species, krill are fished commercially in the Southern Ocean and around Japan. Their stock, a rich source of protein and omega-3 fatty acids, has a variety of uses as aquaculture feed, aquarium feed, bait in sport fishing, and human and animal consumption as nutraceuticals (such as krill oil supplements) or food (including Japanese okiami and Filipino bagoóng alamáng).
Mostly located in the southwest sector of the Atlantic Ocean, Antarctic krill are swarming animals that migrate to the upper levels of the ocean at night and retreat to deeper water during the day. Their numbers can reach from 10,000 to 60,000 per cubic meter.
Krill Depend on Sea Ice
It is believed that loss of sea ice due to climate change is adversely impacting krill populations, although a recent study found that Antarctic sea ice is not in decline. Loss of sea ice means less iron in the ocean due to fewer iron fluxes that result from the freezing and thawing of sea ice. Iron is a major food source for the phytoplankton on which krill feed, therefore it is likely that fewer hatching krill larvae would survive to maturity in a warming scenario.
Long-term monitoring of the Western Antarctic Peninsula (WAP) has shown steady loss of sea ice due to warming, whereas short-term studies from the late 1990s have observed growth in sea ice.
Precisely measuring the anthropogenic effects of climate change on krill at a local level is hindered by naturally occurring background variations, particularly when measured over short time intervals. This hindrance is likely to mask anthropogenic effects of climate change on krill populations until around the year 2100, according to a recent study. For example, although monitoring of the Western Antarctic Peninsula (WAP) over the long-term has shown steady loss of sea ice due to significant warming, other short-term studies from the late 1990s and early 2000s, have observed growth in sea ice.
In their attempts to distinguish “human-driven” changes from naturally occurring ones, the study’s authors used a tool called a Community Earth System Model Large Ensemble (CESM-LE), which incorporates atmosphere, ocean, land, and sea ice component models, in association with existing krill modeling for species dynamics and associated ecological and environmental processes and drivers.
Their research found, among other things, that during the summer, krill growth potential is affected by its level of tolerance of warmer waters. For instance, krill growth is strongly constrained by the boundary of the 5°C isotherm (a line connecting equal temperatures) coinciding with the Polar Front of the Antarctic Circumpolar Current (the planet’s largest ocean current) that is particularly marked by insufficient concentrations of chlorophyll for growth in this region.
The study suggests that a decline in the growth potential of krill could occur in association with warming trends along the WAP. An earlier study linked the decline in krill spawning habitat with significant changes in the advance of sea ice north of Marguerite Bay. The area around the WAP is likely to be the main spawning area for southwestern Atlantic kill.
Natural variation in the climate affects the reproductive ability of female krill, in turn producing fluctuations in krill populations every five to seven years.
Oceans are dynamic systems, and the effects of natural non-anthropogenic variations in the Southern Ocean have significant impacts on krill. An example of this natural oceanic variation is the Antarctic Circumpolar Current that is driven by the Southern Westerly Winds. These winds fluctuate naturally, with regard to their strength and position, in association with the Southern Annular Mode (SAM), the north-south movement of this wind belt.
Another natural pressure is the Multivariate El Nino Southern Oscillation Index (MEI) that includes sea-level pressure, surface wind, sea surface temperature, surface air temperature, and cloudiness of the sky. Such natural variation in the climate affects the reproductive ability of female krill, in turn producing fluctuations in krill populations every five to seven years.
Updated Data, Stronger Catch Limits Needed
The Southern Ocean surrounding Antarctica is a critical component of the global biosphere. It follows, therefore, that with its outsized contribution to marine ecosystems, krill must be protected. Growing concern over a marked increase in krill harvesting in the 1980s triggered the creation of the Convention on the Conservation of Marine Living Resources (CCAMLR). This development led to imposed catch limits on the industry. However, these limits are based on an assessment methodology that has been criticized for not taking into account anthropogenic climate change or, indeed, population fluctuations caused by natural variables.
Though CCAMLR now manages about 10% of Earth’s surface, only 4.6% of this area is designated as a Marine Protected Area (MPA), a situation that the Antarctic Krill Conservation Project wants to change. At present, there are two MPAs in place in the Southern Ocean, one being in the waters near the Orkney Islands and the other in the Ross Sea.
Current data on krill populations in the Southern Ocean dates from 2000 and is therefore likely to be unreliable. To address this inadequacy, the Antarctic and Southern Ocean Coalition (ASOC), as part of the Antarctic Krill Conservation Project, advocates for increasing mass surveys of krill populations. Made up of thirty non-government organizations including the World Wildlife Federation, ASOC is also pressing for greater transparency from the krill harvesting industry and the monitoring of fishing impacts on nearby krill-dependent species, such as whales.
Krill is now the major target species of the fishing industry in the Southern Ocean. The use of continuous pumping systems accounts for 80% of the annual krill harvest.
In the Southern Ocean, krill are now the major target species of the fishing industry, which has been growing locally in direct competition to aquatic species that depend on krill for food. This trend increased dramatically during the 2000s.
With new continuous pumping systems accounting for 80% of the annual krill harvest, it is important to have better data to inform krill conservation efforts going forward, according to a study led by Bettina Meyer of Germany’s Alfred Wegener Institute.
Though data on krill has accumulated in recent years, research efforts are hampered by weather and logistics, limiting research to the summer months and to a single season’s populations. Meyer and her team propose that coordinated international year-round research is needed to fill the data and knowledge gaps that impede our understanding of how and how much to protect this vital species.
*Robin Whitlock is an England-based freelance journalist specializing in environmental issues, climate change, and renewable energy, with a variety of other professional interests including green transportation.