In the marginal ice zone, faecal pellet flux can reach greater depths 5. Krill also release moults, which sink and contribute to the carbon flux 6. Nutrients are released by krill during sloppy feeding, excretion and egestion, such as iron and ammonium 7, see Fig.
Some adult krill permanently reside deeper in the water column, consuming organic material at depth 8. Any carbon as organic matter or as CO 2 that sinks below the permanent thermocline is removed from subjection to seasonal mixing and will remain stored in the deep ocean for at least a year 9.
The swimming motions of migrating adult krill that migrate can mix nutrient-rich water from the deep 10 , further stimulating primary production. Other adult krill forage on the seafloor, releasing respired CO 2 at depth and may be consumed by demersal predators Larval krill, which in the Southern Ocean reside under the sea ice, undergo extensive diurnal vertical migration 12 , potentially transferring CO 2 below the permanent thermocline.
Krill are consumed by many predators including baleen whales 13 , leading to storage of some of the krill carbon as biomass for decades before the whale dies, sinks to the seafloor and is consumed by deep sea organisms.
Vertical migrations can also shunt carbon to depth when krill occupy deeper layers and respire carbon consumed at the surface, a process termed active carbon flux.
This occurs especially in younger developmental stages of E. Larval DVMs may follow a normal pattern of ascent during the night and descent during the day 46 , or a reverse pattern of ascent during the day and descent at night DVM patterns in adult krill are less clear, and a range of behaviours may be exhibited, including normal and reverse DVM as well as remaining at particular depths throughout the diel cycle 47 , 48 , so their biogeochemical role may differ depending on the depth they inhabit or migrate to.
Even so, where DVM does take place in adults, they generally remain above the permanent thermocline, within the surface mixed layer Difficulties in resolving the complex DVM of Antarctic krill means that estimates of the total contribution of this species to active carbon flux have yet to be fully resolved 41 , 48 , There are further additional mechanisms by which krill might contribute to the carbon sink.
For instance, in winter adult E. Metabolism of their lipid reserves to CO 2 when residing in deeper waters in winter, as observed in copepods 54 , releases surface-produced carbon to the deep ocean. This process is termed the lipid pump and is significant in that it moves carbon to depth without depleting surface concentrations of potentially limiting nutrients over winter e. Finally, some E. The contribution of all these processes to carbon transport is potentially significant but remains unquantified.
Iron is an important trace element in the oceans and its low availability limits primary productivity in large areas, including much of the ice-free Southern Ocean 56 , The largest sources of new iron to the Southern Ocean surface waters are deep winter mixing 58 and the seasonal melting of sea ice Following the depletion of this winter-spring iron pulse, further primary production depends increasingly on recycled iron The iron concentration in an individual whole adult krill ranges from 4.
Eventually, the iron retained in individual bodies can be released back into surface waters when baleen whales and other vertebrates consume E. Thus, in the iron-limited Southern Ocean iron recycled via krill and their predators is important for stimulating primary production Fig. Upon digestion of phytoplankton, E. Therefore, the cycling of iron via krill is closely linked to the fate of their faecal pellets, which may sink to great depths without being consumed 37 , A study on salps showed that iron was not readily leached from their faecal pellets 66 , and, if also true for krill, their pellets would need to be fragmented to release dFe into the water column as the pellet sinks.
Nevertheless, the feeding activity of the abundant E. Such fertilising processes mediated by krill may explain why phytoplankton blooms downstream of the island of South Georgia last longer and are more intensive during years with high krill abundances on-shelf Krill also release macronutrients such as ammonium Fig.
Regions of frequently high but spatially variable E. At South Georgia, grazing was sufficient to suppress phytoplankton biomass toward the east of the island 68 , yet E. In addition, E. Krill grazing can also fragment phytoplankton cells or other particulate matter releasing dissolved organic matter into the water termed sloppy feeding, Figs.
This process reduces the flux of carbon to the deep ocean, although, thus far a link between sloppy feeding and increased microbial activity has not been explicitly shown for krill. In addition to shunting carbon to deeper waters, krill are also involved in the vertical and lateral transport of other nutrients.
For instance, adult E. For instance, fluoride concentrations in live E. How quickly these nutrients are released from shedded exoskeletons moults and their possible contribution to biogeochemical cycles has yet to be quantified. Krill can also mix nutrients; mass migrations of krill swarms from deep nutrient-rich water, particularly in localised, permanently or temporarily oligotrophic waters, could mix nutrients to the surface and stimulate phytoplankton growth 42 , 78 Fig.
Conversely, the carbon transferred by krill from the surface to below the mixed layer is subjected to remineralisation by bacteria and detritivores, which convert dissolved organic carbon to CO 2 6 , The depth at which this remineralisation occurs, or the depth of krill respiration, is crucial for determining the longevity of CO 2 storage in the deep ocean; i.
The length of time CO 2 or nutrients will remain in the deep ocean also depends on the water mass it enters owing to ocean circulation For E. Currently we do not know whether nutrients released by Southern Ocean organisms make a significant contribution to production elsewhere. The contribution of larval krill to biogeochemical cycles is different to that of adults due to their unique pattern of growth and development, smaller size and feeding ecology Larval E.
Furthermore, DVM in larval E. The pronounced DVM patterns of larval krill in the proximity of ice may be responsible for the low attenuation of krill faecal pellets with depth in the marginal ice zone of the Atlantic Southern Ocean 6 , 37 Fig.
Larvae may be more likely to contribute to active transport of carbon via egestion and respiration at depth, although the mass and sinking potential of larval faecal pellets have yet to be characterised.
In summary, E. Whilst there has been some focus on the contribution of E. Nonetheless, the substantial biomass, diurnal vertical migrations and broad horizontal distribution of E. Quantification of these rates, as well as better constrained estimates of krill biomass, are critical to provide meaningful data so biogeochemical modellers can sufficiently parameterise the influence of E.
A better understanding of krill—nutrient interactions will also allow assessment of the impact of human activities, particularly fishing, on biogeochemical cycles and help to identify management approaches that will minimise these impacts. The complex biogeochemical roles of E. In this section, we detail the possible impacts harvesting krill could have on the Southern Ocean carbon sink given current knowledge. We also briefly discuss the biogeochemical implications of potential changes in krill biomass owing to the recovery of whale populations and to climate change.
As discussed, large, fast-sinking krill faecal pellets can form a large proportion of total particulate organic carbon flux in the Southern Ocean 6 , If krill are removed from the ecosystem, this faecal pellet flux will decrease.
To estimate the reduction in this sink owing to the removal of E. We estimate that the decline in the E. If the trigger- or catch limits in Area 48 0. These calculations contain certain assumptions e. Map of Antarctica and fishing areas for E.
Numbers in grey are subareas not fished and those in black are fished. The above faecal pellet flux calculations consider adults only and do not include any active transfer via DVM or the lipid pump. As larval E. Given that migrating larvae will also respire CO 2 deeper and eventually become the next generation of adults, larval biomass is important to protect.
Currently, the fishery only targets adult E. As it is not currently known if larvae are caught by the fishery, CCAMLR should initiate research to determine whether the current fishery is catching larval krill as bycatch and, if so, adopt regulations to prevent this happening in the future.
Fishery-driven declines in adult E. The ratio of phytodetrital aggregates to faecal pellets in particle flux varies globally but is generally low in the Southern Ocean where pellets dominate 6. However, we do not know to what extent removing krill may increase the magnitude of aggregate flux. Whilst removing krill may increase phytoplankton biomass through a decline in consumption rates, it would also decrease the fertilisation effects of krill e.
As we are unable to quantify many of the other aspects of the carbon cycle e. Another unknown regarding the impact of the fishery is which zooplankton i. Copepods, which have a higher production rate than E.
Yet, E. The size of krill gives them a strong swimming ability allowing swarm formation, which we speculate contributes to their efficiency in pellet export, alongside large pellet size and associated high sinking speed. Also relating to body size is an ability to feed on a very wide range of particle sizes using a large but fine mesh filter 46 , including large, iron-storing diatoms and lithogenic particles.
While these functions of recycling nutrients are partially available to smaller grazers 49 , the size and swarming behaviour of krill results in different impacts on biogeochemical cycles than zooplankton.
Thus, the biogeochemical role of krill would not be replaced like-for-like by copepods. Salps are non-selective feeders, can exist in swarms and have fast-sinking pellets and caracases 89 and thus could potentially fill part of the biogeochemical niche of krill, if they replaced E.
Although salp particle flux is generally thought to be high, it can be variable with high attenuation rates observed in the Southern Ocean 90 , and thus the contribution of salps to biogeochemical cycles is an area for future research.
Krill biomass is also influenced by the abundance of their predators. Exploitation of Southern Ocean organisms since the late s has severely perturbed the krill foodweb and thus krill biomass, via the sequential extraction of fur seals, baleen whales and endemic fish species 91 , For example, the reduction in whales potentially increased krill grazing pressure on phytoplankton diatoms in particular 92 , and so decreased iron recycling With the rapid recovery of baleen whales 94 E.
Because ecosystem change associated with recovering baleen whales is occurring alongside human-driven warming it will be complicated to tease apart the factors that might be changing krill biomass in the future. There is an urgent need to better understand the recovery of baleen whales in the Southern Ocean and the ecological consequences of their return. There are concerns for the future of E. The Southwest Atlantic sector warmed rapidly during the last century 96 , 97 , and this is both the main population centre for E.
There are reports of declines in krill density within this sector 98 , 99 , , , particularly in the northern part of the Southwest Atlantic, with evidence of a more stable population toward the south, including over the continental shelf of the Western Antarctic Peninsula Recruitment to juvenile E.
Population dynamic models predict further declines in krill populations, particularly around the high phytoplankton biomass and carbon export region of South Georgia 97 , With the possible exception of increased acidification , most of the projected future climate change scenarios, such as trends in temperature, sea ice cover and climatic modes are likely to have a negative impact on adult E.
Each of these observed and potential future changes has implications for biogeochemical cycles. A larger mean body size of the krill population may increase pellet size and sinking speeds, yet a decline in krill biomass is likely to reduce the role of krill in biogeochemical cycling. Investigating how perturbing the foodweb via commercial harvesting, together with climate change and changing predator populations, is important to assess the future of state of biogeochemical cycles.
Box 2 The fishery is managed by CCAMLR Commission for the Conservation of Antarctic Marine Living Resources , and a range of Conservation Measures regulate mandatory notification of intention to fish, minimisation of seal and bird bycatch, reporting, scientific observation and annual catch limits CCAMLR is mandated to apply ecosystem-based management with no explicit measures to regulate fishery impacts on biogeochemical cycles.
Rather, management relies on catch limits that are low relative to estimates of pre-exploitation biomass. CCAMLR has also established much lower trigger levels in most surveyed areas, that cannot be exceeded until sufficient information is available to avoid localised concentration of the catch.
The trigger level in the Southwest Atlantic sector, where almost all current fishing occurs 19 , has been subdivided into further catch limits in each of the individual subareas and for the last 4 years the catch in subarea Management trigger level 0. Compiling our current knowledge of E. This includes some hitherto neglected areas, such as the contribution of larval E. These include quantifying the extent to which adult E. In addition, determining if krill contribute to mesoscale nutrient mixing requires combining laboratory mixing experiments with estimates of vertical migrations, and answering such questions as; what proportion and what age e.
Future research priorities on E. The pyramid illustrates the rates and states of krill life history, habitat and biogeochemical function, which need to be prioritised as areas of key research in the coming decade. The underlying ones, namely biomass including spatial and temporal variations and the residence depth of krill, are listed at the top of the pyramid. Determining the influence of climate change on all of these processes is vital.
Autonomous vehicles fitted with biogeochemical sensors and cameras and acoustics will be instrumental in collecting data on this cryptic species. These key areas of research are needed to be able to parameterise krill in both ecosystem and biogeochemical models.
Whilst there is a clear need for more understanding on the role of E. As discussed in Box 1 , sampling for krill is sporadic, seasonal, spatially and temporally patchy and based on different methods nets or acoustics , contributing to uncertainty in krill biomass estimates. Other key information surrounding biomass include the biomass of larval krill in open water and under ice , the daytime residence depth of all krill life stages and the proportion of krill undergoing ontogenetic migrations.
Better estimates of biomass would help constrain the potential scale of the impact krill have on all biogeochemical cycles. These could be achieved through improved conversion factors between acoustic return and biomass, experimental comparisons between the results of nets and acoustics, synoptic surveys in regions outside of the Atlantic sector of the Southern Ocean, and new technologies such as remote acoustic samplers and long-range sonars and cameras attached to remotely operated vehicles These should be combined with biogeochemical experiments to determine the biogeochemical function of different krill populations residing at or transiting to different depths.
To produce circumpolar E. Some key parameters needed for this are food availability e. These approaches have been attempted individually with varying success , , , but are yet to be assimilated and used together to estimate E. Primary production can provide an upper limit on krill population biomass , but foodweb models are needed to fill gaps where data are sparse and variable for krill predators Foodweb and fishery models are also useful for investigating how krill biomass may change owing to fishing pressure, climate change or predator biomass changes , Aggregation of lower trophic levels is often necessary to reduce uncertainty related to incomplete trophic information These models Table 1 are focused on the Antarctic Peninsula where the information required to parameterise krill life stages is available, while system-specific information for krill is unavailable for regions such as the Indian sector where few foodweb models exist Whilst E.
The benefit of biogeochemical models though is that the low trophic level organisms e. With temperature and nutrient concentrations projected to change globally , more progress is necessary on coupling foodweb and biogeochemical models to build an end-to-end model from nutrients to top-predators A current example for the Southern tracks organic carbon through the ecosystem from phytoplankton to penguins, including an explicitly parameterised krill group Ideally end-to-end models will be able to incorporate nutrients and physical water circulation to make spatial projections of the impacts of climate change and fishing on biogeochemical cycles and vice versa.
To understand fully the role of a fishery or the changing climate on E. We also need to account for spatial heterogeneity, because climate change may make lower latitudes uninhabitable and open new habitats in the south. Laboratory experiments should be combined with newer and advancing technology such as autonomous vehicles e.
Using multiple approaches to study krill will be vital to gain all the information needed on these cryptic organisms. Collaborating with the krill fishing fleet by providing them with biogeochemical sensors, and possibly autonomous vehicles, would widen the temporal and spatial coverage of data Box 2. The large body size, high biomass and swarming ability of E.
The vertical migratory habits of E. As the Southern Ocean has a disproportionately important role in the global carbon sink, and productivity is limited in iron-deplete areas, the cycling of carbon, iron and ammonium by E. However, the life-history traits of all krill e.
We have shown that the role of E. Particularly crucial are ongoing efforts to estimate the absolute E. Whilst the E. Globally, measures to maintain biomass and productivity of stocks of fished species indirectly help to preserve their biogeochemical role. However, fishery management needs to consider the influence of harvesting on biogeochemical cycles. An amendment to this paper has been published and can be accessed via a link at the top of the paper. Falkowski, P. Biogeochemical controls and feedbacks on ocean primary production.
Science , — CAS Google Scholar. Pauly, D. Primary production required to sustain global fisheries. Nature , The role of phytoplankton photosynthesis in global biogeochemical cycles. Robinson, C. Phytoplankton biogeochemical cycles. OUP, Steinberg, D. Bacterial vs. ADS Google Scholar. Belcher, A. The role of particle associated microbes in remineralization of fecal pellets in the upper mesopelagic of the Scotia Sea, Antarctica.
Cavan, E. Role of zooplankton in determining the efficiency of the biological carbon pump. Biogeosciences 14 , — Zooplankton and the ocean carbon cycle. Google Scholar. Ratnarajah, L. Pelagic iron recycling in the southern ocean: exploring the contribution of marine animals. Davison, P. Carbon export mediated by mesopelagic fishes in the northeast Pacific Ocean. Copepod faecal pellet transfer through the meso- and bathypelagic layers in the Southern Ocean in spring. Biogeosciences 14 ,— Remineralization of particulate organic carbon in an ocean oxygen minimum zone.
Polar Operations Our operational strategy Our operational teams Operational collaborations Engineering and technology Polar fieldwork opportunities How to apply Pre-deployment training. Search the site. Also in Antarctic wildlife Penguins Albatross Other birds. Whales and seals Fish and squid Krill. Land animals Plants. Euphausia superba krill from the Bellingshausen Sea continental shelf. This ice in here is just standard party ice in a chamber in this tank, and it is keeping these krill cold.
But the trick is that the centre core here is filled with a super salty brine. Rob, I know that we've got some school children watching here at the Antarctic Division today, and — they're asking us, can krill shrink? And these kids obviously know quite a bit about krill. So, do you want to answer that question? Krill can shrink. If you take all food from krill, you can shrink it down from a large size back to a juvenile again. They'll also sexually regress — they'll lose their sexual characteristics and go back to looking like a juvenile.
So, krill switch to chasing around zoo plankton and doing other things, but they can also shrink if they get really desperate. So yes, shrinking is a trick, and it makes them the most successful crustacean in the Southern Ocean today. What do krill taste like? Whales and penguins have an enzyme to break it down. So, be cautious about how many krill you eat. Thanks Rob. And we're very cautious about how much is caught in the ocean because we want them to be there for a long time.
Thanks for joining me on this tour. We're going to leave you now with our lovely krill tank here, and thanks so much for joining us here at the Antarctic Division. Krill is a general term used to describe about 86 species of crustaceans found in open oceans. They belong to the group of crustaceans called euphausiids. Antarctic krill is one of 5 species of krill that lives in the Southern Ocean, south of the Antarctic convergence. Krill are mostly transparent, although their shells have a bright red tinge from small pigment spots.
Their digestive system is usually visible and is often a vivid green from the microscopic plants they have eaten. They have large black eyes. They range in size from small tropical species of less than 1 cm in length , to 6 cm for the largest pelagic krill species in the Southern Ocean.
There is one deep-sea benthic krill species that can reach 14 cm. There are 5 species of krill found in Antarctic waters. The most dominant of these species is Antarctic krill, Euphausia superba. Antarctic krill is one of the most abundant and successful animal species on the planet. They are frequently found in such abundance that they colour the sea a reddish-brown. They may be small individually, but there is an estimated million tonnes of Antarctic krill in the Southern Ocean.
Antarctic krill aggregate in schools or swarms, where the density of the animal can be as high as 30, individuals per cubic metre. The swarms occur in larger groupings or patches. Scientists are still determining the social structure of the swarms. It seems that some krill swarms may be made up of entirely of juveniles, while other swarms may consist of all females or all males. Krill can change from adults into juveniles. It is estimated that Antarctic krill live for 5 to 10 years, but determining the age of the animals presents quite a problem for scientists.
Crustaceans usually grow by moulting their hard shell exoskeleton , expanding the new one and then growing into it. When the exoskeleton becomes tight again, the moulting and growing process starts once more. In most crustaceans, the moulting tends to slow down as the animal grows older, and stops altogether in adulthood.
This means that scientists can usually tell the age of an animal from its size. On average, the larger the creature the older it is. Antarctic krill are an exception to this rule. Because they live in the cold, dark Southern Ocean, they must survive the winter months when food is scarce.
They do this very successfully. Laboratory studies have shown that Antarctic krill can survive more than days of starvation. Krill retain the ability to moult for life. They use this ability to continue growing and reducing their body size to help them survive. All species of krill seem to share this adaptation. At the end of summer adult krill begin to lose their sexual characteristics. After a series of moults they again resemble two-year-old juveniles, giving no indication that they were ever adults.
In spring, adults once more begin to develop sexual characteristics and become mature before the spawning season. Antarctic krill are thought to lay a number of broods of eggs, with as many as 8, eggs per brood. The season may last as long as 5 months. Krill usually feed on the surface of the water at night and often sink deeper in the water column in the daytime. The primary food of krill is phytoplankton, which are microscopic ocean plants suspended in the upper water column where light is sufficient to allow for growth.
In winter, krill have to use other food sources such as the algae which grows on the underside of the pack ice, detritus on the sea-floor or the other animals in the water. Krill can survive for long periods up to days without food.
They shrink in length as they starve. Most of the larger Antarctic animals seals , whales , seabirds , fish and squid depend on Antarctic krill, directly or indirectly. Why live in Antarctica? How many people? Take a tour of the Antarctic krill aquarium Video transcript Nick Good morning everybody, and welcome to a very wintry day in Hobart, the Antarctic Gateway city down to Antarctica. Rob So, while we're coming into those bases, we're also travelling over the prime krill territory really, which is all of this around east Antarctica, south of 60 degrees, is teaming with krill.
Elanor Hi Nick, Hi Rob. Nick Do you want to tell us a little about the work you do, and especially how it is you get an insight into how whales live in the Southern Ocean and interact with the krill? Elanor Absolutely, Nick. Elanor What one of the exciting things we do is, we can use technology, such as satellite tagging, to track whales and work out where they're going to find their food, how deep they dive, how often they dive, what type of krill they're targeting.
Nick Fantastic. Thanks so much Elanor. Elanor Bye, Nick. Rob Yeah, I mean the work we're doing in the lab that we're going to see shortly, is all about getting data to put into things called models, and models are really how we predict the future.
Nick Well, the specialist in this field is Jess Melbourne-Thomas. Welcome Jess. Jess Hi Nick, Hi Rob. Jess Yeah, definitely. Nick All right. Nick Okay. Nick We're dropping out a bit now, so for those of you who have just joined us, you're at the Australian Antarctic Division in Hobart in Tasmania.
We're doing a tour of the — Jess An absolute pleasure. Have fun. Nick See you later. Rob Yeah. And remember everyone to please — But we'll be getting to answer some of your questions in just a moment. Rob Yes.
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