In the ocean, krill live together in swarms, some of them stretching for tens of kilometres. Krill swarms are some of the largest gatherings of life on the planet and this naturally poses some puzzling questions to science: Why are krill living together? How do they find each other? Why are some swarms enormous when others are more moderately sized?

In an effort to shed some light on the mystery, a team of British Antarctic Survey (BAS) researchers headed by Dr Geraint Tarling set out to study the composition and structure of 4525 separate krill swarms in the Scotia Sea. Despite its name, the Scotia Sea is not located close to home for these British scientists – it is a vast expanse of water situated partly in the Southern Ocean and partly in the Atlantic; between Argentina and the Antarctic Peninsula.

Using echo-sounding equipment, the Tarling team tracked down the krill living in this 900,000 km² area and what they found surprised them. According to this new research, krill normally gather into two different types of swarms. The first type is relatively small, typically not exceeding a length of 50 meters and a depth of 4 meters. In this comparatively small type of swarm, the density of krill isn’t very high – you will just find an average of ten krill per cubic meter.

The other type of swarm – dubbed “superswarm” by the researchers – is on the other hand a very densely packed group with up to 100 krill per cubic meter. These dense congregations are the ones that grow really big, often stretching over one kilometre in length and averaging almost 30 meter in depth.

“I was coming at it thinking there might be small swarms tightly packed, and then large swarms that were a bit more diffuse,” says Dr Tarling. “But what we actually found was the opposite. There were small swarms that were quite diffuse and large swarms that were tightly packed.”

This means that a majority of the krill living in the Scotia Sea at any one time will be found within one of just a few enormous superswarms.

“We talking trillions of krill in one aggregation,” explains Dr Tarling. “Ten or 12 swarms could explain 60 or 70% of the biomass in an area the size of the eastern Atlantic. It was astonishing how much biomass could be concentrated into such a small area.”

A fishing flee scooping up a whole swarm of krill may therefore be removing the majority of krill from the Southern Ocean in just one short fishing trip if they happen to target one of the superswarms instead of a small swarm.

How does a superswarm come about?

Although they weren’t able to fully answer this question, Tarling and his colleagues managed to pinpoint certain factors that make superswarms more likely to appear.

“The factors we identified included whether there was more likely to be a lot of food around or not, and when there wasn’t that much food around, they tended to form larger swarms,” says Dr Tarling.

Age is also of importance. The smaller, diffuse swarms typically contained adult krill, while the enormous superswarms consisted of densely packed juvenile individuals.

“Where the animals were less mature, they were more likely to form the larger swarms,” says Dr Tarling, adding that he doesn’t know why.

It might be a question of safety in numbers; it is common among prey animals to live in large groups to reduce the risk of getting eaten, and krill is after all a favoured meal by a long row of sea living creatures.

“All types of swarms are probably to a greater or lesser extent an antipredator response,” Dr Tarling says.

But although living in a swarm reduces the risk of being eaten, it also means having to compete with all the other members of the group for food. Juvenile krill are more buoyant than adults, which mean that they spend less energy swimming. Perhaps this is why adult krill prefers to live in smaller congregations; their negative buoyancy forces them to eat more so they can’t afford living in a huge swarm densely surrounded by competitors.

On the other hand, being in a swarm has been shown to be more energetically efficient than being isolated.

“For a juvenile that wants to grow very quickly, saving energy could be a bonus for them,” says Dr Tarling.

Night-time mystery

As a scientist, you often find yourself in a situation where new findings answer one question but simultaneously create three new ones. One of the new conundrums that Dr Tarling has brought back home from his research trip is the following: Why are superswarms more likely to form at night?

“That is more puzzling for us to explain,” says Dr Tarling. “Up until this point, most polar biologists believed that the swarms dispersed [at night], because that’s the time they feed. When daylight comes they get back into the swarm again for the antipredator benefit. But we found the opposite to that.”

The research has been published in the journal Deep Sea Research I.

As of August 12, 2009 the harvesting of krill in the in the Exclusive Economic Zone (EEZ) off the coasts of California, Oregon, and Washington will be prohibited by federal law.

Yesterday, the U.S. National Oceanic and Atmospheric Administration (NOAA) published a final rule in the Federal Register prohibiting the harvesting of krill in these three regions. All types of krill harvesting will be illegal, regardless of fishery and gear type.

“Krill are the foundation for a healthy marine ecosystem,” said Mark Helvey, NOAA’s Fisheries Service Southwest Assistant Regional Administrator for Sustainable Fisheries. “Protecting this vital food resource will help protect and maintain marine resources and put federal regulations in line with West-Coast states.”

Harvesting krill within three miles of the coastline of California, Oregon, and Washington has already been prohibited by state law, but the zone situated between three and 200 miles off the coast have lacked krill protection until now.

“This is a great success for protecting the entire California Current ecosystem“, said William Douros, West Coast Regional Director for NOAA’s Office of National Marine Sanctuaries. “This decision reflects strong teamwork within NOAA and a commitment to addressing the issues raised by the Pacific Fishery Management Council and Sanctuary Advisory Councils.”

The krill protection rule was adopted as Amendment 12 to the Coastal Pelagic Species Fishery Management Plan (FMP), which was developed by the Pacific Fishery Management Council (PFMC) under the Magnuson-Stevens Fishery Conservation and Management Act. Amendment 12 adds all species of krill under a new category: ‘prohibited harvest species’.

Vast amounts of creatures looking like jelly balls have begun to appear off the eastern coast of Australia, and researchers now suspect that these animals may help slow down global warming by moving carbon dioxide from the atmosphere to the ocean floor.

The proper English name for this “jelly ball” being is salp. A salp is a barrel-shaped free-floating tunicate that moves around in the ocean by contracting and relaxing its gelatinous body. Just like the other tunicates, the salp is a filter feeder that loves to eat phytoplankton and this is why it has caught the attention of scientists researching global warming.

Phytoplankton are famous for their ability to absorb carbon dioxide from the top level of the sea, and a salp feasting on phytoplankton will excrete that carbon dioxide in the form of faeces. The faeces will drop to the ocean floor; thus lowering the amount of carbon dioxide present in the upper part of the ocean. Since the carbon dioxide found in this level of the sea chiefly hails from the atmosphere, phytoplankton and salps are a great aid when it comes to removing carbon dioxide from the air. Salps will also bring carbon down to the ocean floor when they die, which happens fairly often since the life cycle of this organism is no more than a few weeks.

Salp species can be found in marine environments all over the world, but they are most abundant and concentrated in the Southern Ocean near Antarctica where it is possible to encounter enormous swarms of salp. Over the last 100 years, krill populations in the Southern Ocean have declined and salp populations seem to be replacing them in this cold ecosystem. According to researcher Mark Baird of the Australian Commonwealth Scientific and Research Organization (CSIRO), the amount of salps in the waters off Australia are also on the increase, at least according to a survey carried out last month by CSIRO and the University of New South Wales.

While salp may help slow down global warming, their increase may also cause problems. Salp has a fairly low nutrient content and salps replacing nutrient rich krill in the Southern Sea may therefore prove detrimental for oceanic animals higher up in the food chain.

By moving from the surface of the sea down to deeper layers, Antarctic krill transport carbon down from the surface to the depths of the ocean. Scientists from the British Antarctic Survey (BAS) and Scarborough Centre of Coastal Studies at the University of Hull have now discovered that Antarctic krill venture between the surface and the deep sea several times per night. Earlier, they were believed to do so only once per night. The more times they head for the deep with their bellies filled, the more carbon they will remove form the surface, so this is interesting news for anyone worried about too much carbon in the atmosphere and upper ocean. According to Dr Geraint Tarling from BAS, Antarctic krill transport an amount of carbon equivalent to the annual emissions of 35 million cars.

Krill swims to the surface to feed on phytoplankton (which must stay fairly close to the surface since they rely on photosynthesis) but they do not spend all their time close to the surface because that would make them easy targets for predators. Instead, krill regularly sink down to greater depths where the risk of being eaten is lower. When krill excrete carbon rich waste products at such depths, the waste will sink down to the ocean floor.

Other studies have shown that adding iron to the water could allow the krill populations to increase in size which would cause them to remove more CO2 from the atmosphere. Adding iron can also help trigger algae growth that further removes CO2 from the atmosphere and can help fight global warming. We do however know too little about the potential side effects of adding iron to the water to make it a viable alternative at this time.

According to an article published by The Guardian, scientists believe that krill have declined 80 per cent since the 1970s. Why this has happened remains unknown, but it might be due to global warming. According to estimates made by the British Antarctic Survey (BAS), there is roughly 100 million tonnes krill left, while krill harvesting companies place the figure at 400-500 million tonnes. The Convention on the Conservation of Antarctic Marine Living Resources allows 4 million tonnes of krill to be caught in the Southern Ocean per year. Until now, this number has seldom been reached; in a normal year, less than 20 percent of the permitted 4 million tonnes have been caught.

Today, the emerging interest in health products such as Omega 3 oil and Omega 3 fortified food is causing a boom in krill fishing. A majority of the fished krilled is used to produce Omega 3 oil and other health supplements, or as fish-farm feed. So called “suction harvesting” is now used to meet the demand for krill.

So, why care about a tiny crustacean? The truth is that entire ecosystems depend on krill and krill are also able to help us remove carbon dioxide from the atmosphere. Some species, such as the gigantic Blue Whale, feeds directly on krill. Other species, such as penguins and seals, are indirectly depending on krill since they feed on animals that feed on animals that eat krill.

If you want to learn more about krill and hear different experts explain their view on the current situation, read the full article at The Guardian: http://www.guardian.co.uk/environment/2008/mar/23/fishing.food