antarktis - folk.uio.nofolk.uio.no/steinka/roya/antarctic_tak.pdf · hanner: 4,2 m, 2,200kg....

Antarktis

Antarktis:

Major currents

- Area partially separated fromother areas by thehydrographical 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 inclockwise rotation

- Several frontalzones

Frontal systems

- Polar front

- ACC- Antarctic Circumpolar Current

Peninsula/Scotia Sea/South Georgia

- One of the beststudied areas of theAntarctic(USA & UK)

- High krill biomass

Frontal zones around SG

- Drake passage

- Topographicalforcing

- 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 highlight levels

- High levels of nutrients

- Low production

- HNLC paradox

Iron limitation

- Iron hypothesized as the main limiting factor- High patchiness- Production highestdownstream of iron-sources

Iron enrichment

- Mesoscale experimentssuggests 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 andfauna.

- Sympagic: A sympagic environment is one where water exists mostly as a solid, ice

- Ice habitat also extremelyimportant to more generalistspecies like E. superba, andimportant for spring blooms

Food webs:

- Perceived as extremelysimple

- As usual a bit more complex,but this gives a reasonable picture of energyflowin 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 fromearly 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 importantfor young krill

- Species primarilyherbivorous (i.e. uses filter basket)

- Species found mainlyabove 250 meters,especially during summer

Antarctic krill, behavior:- Some describe the species as a obligate

swarmer- High proportion of biomass found in swarms- Purpose ofswarming?

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 Atkinsonet al. In press)

Other important groups:

- Salps - may dominate in some years and regions

- Copepods- biomass generallydwarfed by krill, but around SG biomassapprox. 1/1

Salps

- Colonial chordates

- Filterfeeders

- Houses may clogat too high dens.of large phyto

Amphipods

- Themisto shallow

- Lots of other species indeeper 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.

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

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.

Slekten Mirounga Elefantseler Mirounga angustirostris Nordlig elefantsel

Mirounga leonina Sørlig elefantsel

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,…

0

5000

10000

15000

20000

25000

30000

1910 1930 1950 1970 1990

Knølhval

Blåhval

Finnhval

Seihval

Sperm

Vågehval

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 dependenton ice-algae for survival?

- Salps and krill biomass inverselyrelated

Salps, krill and sea ice:

- Ice con

- 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 notfully understood

Predation in the Scotia Sea

- Krill the most important food by weight

- Spatial variation, and these numbersrefer to Scotia sea ecosystem.

- E. superba less important in Ross Sea

Predation in the Scotia Sea

- Fish/squid consumption unknown

- The known biggest consumerspenguins and seals

- Whales comparatively low

- Air breathing predators with rearingof young on land => high spatialvariation 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