Antarktis
Antarktis:
Major currents
- Area partially
separated from
other areas by the
hydrographical
features
Depths:
Hydrography
Deep ocean circulation
Ice and bottom water masses
- Polynyas
- Sea-ice formation (brine)
=> dense, i.e. Saline and cold watermasses
Transport:
- Watermasses in
clockwise rotation
- Several frontal
zones
Frontal systems
- Polar front
- ACC
- Antarctic Circumpolar
Current
Peninsula/Scotia Sea/South Georgia
- One of the best
studied areas of the
Antarctic
(USA & UK)
- High krill biomass
Frontal zones around SG
- Drake passage
- Topographical
forcing
- Weddel sea gyre
Other well studied areas:
- Antarctic peninsula
- Ross sea
- quite different biology, other groups more
important
- 0-meridian
- Indian ocean sector
Primary production and HNLC
- Seasonally high
light levels
- High levels of
nutrients
- Low production
- HNLC paradox
Iron limitation
- Iron hypothesized as the main limiting factor
- High patchiness
- Production highest
downstream of iron-sources
Iron enrichment
- Mesoscale experiments
suggests iron limiting
- But uncertain whether
increase in prod. Transl.
to increased export
- Suggested as mechanism
to combat global warming
- Commercial operators already selling CO2-quotas based on marine
iron-enrichment
Sea ice and seasonality:
Sea ice as a habitat:
- “Separate” food-chains
associated with the sea-ice,
i.e. with specialised flora and
fauna.
- Sympagic:
A sympagic environment is one
where water exists mostly as a
solid, ice
- Ice habitat also extremely
important to more generalist
species like E. superba, and
important for spring blooms
Food webs:
- Perceived as extremely
simple
- As usual a bit more complex,
but this gives a reasonable picture of energyflow
in some antarctic pelagic ecosystems
Antarctic krill
- Often used synonymously with E. superba
- E. superba relatively longlived (up to at least 7 yrs),
though only few attain this age.
- Maturity at 2-3 yrs
- Up to approx. 6 cm
- E. superba P/B ratio approx. 1
Antarctic krill
- Spawning in upper 100 m
- Clutch size 6.000-10.000 eggs, several clutches
- Spawning late spring and summer, mainly from
early January to mid February
- Eggs negatively bouyant, hatch from 500-2000m depth
- Note: eggs that hit bottom prob. lost
Antarctic krill
- Center of spawning around the Peninsula
- Eggs and larvae mature on the “conveyor belt”
- Stock at South Georgia perceived as “sink”
- Separate stock in Weddel Sea?
5 minutter krilltråling i
Antarktis. Bilder Einar
Loshamn
Fangst ca. 2 tonn. Bilder
Einar Loshamn, men
foreleser var faktisk tilstede
Krill behaviour
- Adults relatively strong swimmers (12-20 cm/s sustained)
- High escape speeds (1 m/s)
- Capability to utilise ice-algae, using legs to scrape algae from ice
- Ice especially important
for young krill
- Species primarily
herbivorous (i.e. uses
filter basket)
- Species found mainly
above 250 meters,
especially during
summer
Antarctic krill, behavior:
- Some describe the species as a obligate
swarmer
- High proportion of biomass found in swarms
- Purpose of
swarming?
Krill behaviour:
- Swarm densities exceeding 1000 ind/m3 reported
- Swarming/Schooling:
- Antipredator behaviour
-dilution of risk
-more eyes open
-effective against some predators (confusion..)
-hiding???
- Spawning
- Feeding
- Migration
Krill biomass
- Centered in the
Atlantic sector
(Figure from Atkinson
et al. In press)
Other important groups:
- Salps
- may dominate in some years and regions
- Copepods
- biomass generally
dwarfed by krill, but
around SG biomass
approx. 1/1
Salps
- Colonial chordates
- Filterfeeders
- Houses may clog
at too high dens.
of large phyto
Amphipods
- Themisto shallow
- Lots of other species in
deeper waters
Gigantocypris sp.
Bilder Einar Loshamn
Predators:
- Mainly air-breathing predators known to be
important, especially seals and penguins, but
this may be because this is the only group
we've got numbers for
- Pelagic and benthopelagic fish stocks
- Whales
Seals
- Crabeater seals krill specialists
- Krill also appear in the diets of other species,
especially fur seals
- Seal populations exploded after the commercial
whaling began, and was also exploited
commercially even prior to commercial whaling
Important seal species
- Fur seal
- Elephant seal
- Crabeater seal
- Leopard seal
Antarctic
fur
seal
- Major krill predator
- Population exploded after whales hunted, but
this species was also commercially exploited
Lobodon carcinophaga, Krabbeetersel
Hunner: 2.2-2.6m, 220kg.
Hanner noe mindre.
Ved fødselen: 1.2 m, 30kg.
Verdens mest tallrike selart:
trolig mer enn 15 millioner
individer. (Bestandsestimat på
inntil 50 millioner har vært
publisert.)
Tenner velegnet til å filtrere krill
fra vannet.
Opptrer i familiegrupper.
Hydrurga leptonyx, Leopardsel
Hanner: 2.5-3.2m, 200-455kg.
Hunner: 2.4-3.4m, 225-591kg.
Ved fødselen: 1.5-1.6m, 35kg.
Pakkis rundt hele kontinentet og
øyene.
Bestand ca 220,000 – 400,000.
Spiser andre sel, pingviner,
blekksprut og krill.
Slekten Mirounga Elefantseler
Mirounga angustirostris Nordlig elefantsel
Mirounga leonina Sørlig elefantsel
Hanner: 4.5m, 2,300kg. Hunner: 3.6m , 750kg.
Ved fødsel: 1.5m, 30kg.
ASM: Hunner 3-5 år, hanner 4-6 år, sosialt 9-12 år.
Bestand: 84,000 i US California, 32,000 i Mexico.
Hanner: 4,2 m, 2,200kg. Hunner: 2,7m, 500kg.
Ved fødsel: 1.3m, 50kg.
ASM Hunner 2-4 år, hanner: 3-6 år (sosialt 10 år).
Bestand: 600,000. Dykkedybde 2km, dykktid 2 timer
Begge arter sterkt overbeskattet historisk.
Nordlig var nesten helt utryddet, og det var
mindre enn 100 individer igjen på den
fjerntliggende mexicanske øya Guadalupe da
fangsten stoppet på slutten av 1800-tallet
Whales
- Several of the whale stocks have rebounded in
the later years, though not all. We saw only
humpbacks
-Despite this, whale populations are much lower
than before whaling started
- Many species follows ice-edge
- Krill biomass the main force behind feeding
excursions to the Antarctic
Baleen whale species in the
Antarctic
* Blue whale
* Minke whale
* Humpback whale
* Fin whale
* Southern right whale
* Pygmy right whale
Humpback whale
Nordkaper
Whaling
- Krill surplus theory
Først den ene, så den andre,…
30000
25000
Knølhval
Blåhval
Finnhval
Seihval
Sperm
Vågehval
20000
15000
10000
5000
0
1910
1930
1950
1970
1990
Statistikken
• I perioden 1910 - 1990 ble det tatt
•
•
•
•
•
•
103 000 knølhval
344 000 blåhval
694 000 finnhval
132 000 seihval
198 000 spermhval
118 000 vågehval
Penguins and other birds
- Chinstrap and macaroni penguins major
consumers of krill
- Prions and fulmars also dependent on krill
- Limited travel possibilites during breeding
season gives strong spatial variation in krill
predation
Important avian species
Important avian species
- In addition to penguins, also flying species:
- Petrels
- Albatross species
Fish and squid
- Unknown importance, biomass unknown, but
krill important in the diet of many species
Important fish groups
- Icefish
- Lack haemoglobin
- Mostly neritic/demersal
Mesopelagic fish
Antarctic food webs:
- Few levels, high trophic efficiencies
- Krill in a central position
Ross sea ecosystem
Salps and krill
Salps and krill
- Krill biomass correlated with
winter ice extent and duration
- Mechanism: young krill dependent
on ice-algae for survival?
- Salps and krill biomass inversely
related
Salps, krill and sea ice:
- Salps and krill biomass inversely related
- Krill population recruitment dependent on sea ice
- Krill reproduce near Peninsula
- Peninsula area among the most affected by global warming
- Krill/salp mechanism not
fully understood
- Ice con
Predation in the Scotia Sea
- Krill the most important food by weight
- Spatial variation, and these numbers
refer to Scotia sea ecosystem.
- E. superba less important in Ross Sea
Predation in the Scotia Sea
- Fish/squid consumption unknown
- The known biggest consumers
penguins and seals
- Whales comparatively low
- Air breathing predators with rearing
of young on land => high spatial
variation in predation
Antarctic krill:
- Several species
- Most important: Euphausia superba
- Other common species include E. triacantha, E. frigida, E.
crystallorophias and Thysanoessa species.
- Dominant in biomass in the Antarctic zone
- Biomass Atlantic sector: 37 – 200 mill tons
- Catch limit: 4.7 mill tons
- Current catches: 100-200MT
Products of Antarctic krill
- Aquaculture feed (e.g. protein)
- «Marine» oils (health products)
- Human food!
- Pigment for aquaculture
But high fluoride values in antarctic krill!
Other fisheries:
- Toothfish (line fisheries)
- Mackerel icefish
Problems of commercial catches
- Technical (quickly deteriorating, high fluoride
etc)
- Ecological/ethical (fishing down the food web,
interference/overlap with central place foragers
etc, slow growth in polar waters)
Paradigms?
Current paradigm, based on pel. studies since ca. 1980:
- System controlled by primary production, i.e. Bottom up
- Air-breathing predators the main top-down ”force”
- What about squid/fish? Will whales affect ecosystem
structure?
- How about sea ice?
- Increasingly clear that there is no «Antarctic ecosystem»,
but several ecosystems