Which creature on Earth has the largest bio-mass (the combined weight of all the members of the species)? Not blue whales. Not elephants. Not humans. It's krill, a small, zoo plankton found in most of the oceans but most abundantly in Antarctica. (The part of the krill in this photo is being played by a Sea Dragon seahorse, only found around Australia, because they are more attractive....)
The future of the mammal, bird, and fish populations in Antarctica depends on the future of the krill population, and it probably will come as no surprise that global numbers of krill are falling, although they are not dangerously depleted yet. Rich in protein and fat, krill are the main food source for many of Antarctica's species. Those that don't eat krill directly tend to chow down on those who do, so now would be a good time for biologists to learn as much as possible about these simple organisms in order to understand and protect them.
It will also come as no surprise that the depletion of krill stocks could come because people have suddenly discovered a use for them. Driven by the manufacturers of nutritional supplements, there has been a suggestion that krill oil is better than fish oils at lowering HCL or "bad" cholestrols and controlling some symptoms of Pre-Menstrual Syndrome. The problem with krill as a human food source until now is that they are very difficult to preserve and eat: as soon as krill die, their bodies begin to break down and become toxic. Also, their shells contain levels of fluoride that are toxic to humans and so they must be peeled before eating. Not that easy when they tend to be no bigger than a couple of inches long.
Plankton are the organisms that spend their lives floating in the top layers of the ocean. Zoo plankton such as krill feed on the phyto plankton (plant life) found in these layers, particularly the algae that grow on the undersides of the sea ice. Huge swarms of krill float close to the shores where penguins and other birds have their nests, forming the main food source for parents and baby birds. Further out in the ocean, the massive blue and other baleen whales swim through the krill swarms, sucking them in through their baleens. A blue whale can consume up to four tons of krill at a time. Different krill predators eat varying sizes of krill at different depths of the ocean, ensuring that the supply stays constant.
Krill still hold a number of mysteries, including how long they can live and why they sometimes make radical changes in their behaviour: usually they spend the day at the lower depths of the ocean, rising at night to the surface. But sometimes, for a not-yet discernible reason, they surface during the day. Like other crustaceans, krill grow by shedding their exoskleton but they can also shrink when there is a food shortage. Krill have been known to live for 200 days with no obvious food source: they don't have reserves of fat to live off, so there must be some other way they stay alive. In the laboratory, krill can live as long as eleven years but it is very difficult to keep them alive in lab conditions.
Besides nutritional supplements, much of the commercial krill catch is used to feed farmed and domestic aquarium fish. Some is quick frozen at sea and used for animal feed as well. The former Soviet Union was the main krill fishing nation, but now Norway, South Korea, Ukraine, Russia, and to a lesser extent, Japan have vessels in the southern ocean. China has recently sent two ships as well. Fishing limits are set and enforced by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR or "Camlar"), an international body that sets policy in consultation with its scientific advisors. So far, the quotas exceed the number of krill harvested by quite a lot, but activists such as Sea Shepherd say that this is beside the point. Animals like penguins that depend on krill to feed their young cannot move their nests to follow the krill, so fishing vessels must be prevented from operating in those areas altogether. And this is without the environmental impact of the industrial vessels on the pristine Antarctic seas. The United States banned krill fishing on its shores decades ago to protect biodiversity.
The main threat to krill and the species that feed on them is probably not commercial fishing, though. It's climate change: the less sea ice there is, the less algae and therefore less food for krill and consequently less food for seals, whales, penguins, and others. Krill are a tiny but hugely important part of the food chain and we know that their numbers have declined by as much as 80% since 1970. They deserve to be understood and protected before it's too late.
In other ocean news, Google Earth has jumped into the water. Beginning on 2 February, you can see the ocean floor and explore its reefs on your computer screen. We know more about the topography of Mars than we do about our oceans, but that may be about to change. The National Oceanic and Atmospheric Administration (NOAA) Office of Ocean Exploration and Research has made data available to a layer on Google Earth which shows the ocean floor and explores 13 U.S. marine parks in depth (no pun intended....) Other maps show marine debris, weather patterns, algae blooms, currents, and shipwrecks, including Titanic.