marine ecosystems in the southern ocean sunlight and photosynthesis abyssal plain
TRANSCRIPT
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Marine Ecosystems in the Southern Ocean
Sunlight andphotosynthesis
Abyssal plain
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Marine life receives a gradient of light from the surfacethrough the photic zone, much absorbed
Sea ice complicates this in winter, reduces light penetration
Cold, dense water sinks below ice but also causes nutrientrich water from below to upwell
Increases productivity around Antarctica
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Continental Shelf in Blue: Narrow around most of Antarctica
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Continental shelf benthos has a surprising biodiversity
Now known that ~80% of species are endemic
Some groups (e.g., sea spiders or pycnogonids) are morediverse here than anywhere else
http://www.oikonos.org/
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Underwater in McMurdo Sound with an ice wall behind and many Antarctic scallops, several sea urchins, Sterechinus neumayeri and brittle stars, Ophionotus victoriae, and a white club-shaped sponge, Homaxinella balfourensis. https://en.wikipedia.org/
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Kelp in the Antarctic Peninsula
Bull kelp can reach lengths >20mStrongest in world to sustain heavy seas, but some
still break looseKelp community has highest diversity of inshore
marine environment, >90 spp. includingworms, molluscs, mites, sea-stars, sea-cucumbersand numerous crustaceans
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Kelp can also be a nice bed for seals…
http://www.antarctica.gov.au/
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Once thought simple, marine communities in Antarctica are quite diverse
http://www.lternet.edu
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Inshore surface waters are actually colder than deep waters,due to katabatic winds, ice that cool the water there
The average depth over the continental shelf is ~500 m
The average temperature of the water has risen by 1° C since 1950
This cold temperature limits species—e.g., no crabs on the shelf,predators are only slow moving starfish and urchins, but…
King Crab invasion video:
https://www.youtube.com/watch?v=rcwXGfTtW3U
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Sea Ice Drives Marine Productivity in Antarctica--when ice begins forming in late summer, it traps marine
algae in pockets in the ice--the algae remains dormant during the long winter, but
with spring sunlight, can grow in the ice--when ice melts, it releases all this algae into the marine
food web
Heavy ice years = high productivity, and vice versa
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Record sea ice extent, 2012, caused by warmer temperature overAntarctica and stronger katabatic winds producing more ice
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Marine Algae: Sea Ice versus Open OceanSea ice dominated by small pennate diatoms: Fragilariopsis cylindrus and Fragilariopsis curta; and prymnesiophyte Phaeocystis antarctica
Some grazers from the water can gain access to algae in ice via the brine channels, even in winter
https://web.duke.edu
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Lizotte (2001)
Sea Ice Zone
Marginal Ice Zone
Shelf water
Sea Ice
Primary production peaks in sea ice in November, beforeit peaks in marginal zone or open water, as it is primarily annual ice. Multi-year ice peaks later, as snow accumulationon the surface can block light early, and annual ice melts later
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Lizotte (2001)
Primary production in sea ice surface communities by month
These data show that most production is in the annual sea ice,which is mostly farther south near the continent
Multi-year ice
First year ice
Total Sea Ice
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Although offshore plankton production in the open ocean exceedsthat of sea ice algae, the blooms of sea ice algae differ in timing and distribution near the continent
Sea Ice is an important driver of productivity near the continent wherewater column productivity is negligible, providing food resources for higher tropic species
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Krill: A Keystone Species in the Southern Ocean
Euphausia superba
en.wikipedia.org
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Krill have a complex life cycle
--spawn in January to March--eggs laid in water at surface, sink to over 2000 m depth
and hatch after 10 days--larval krill grow and live up to seven years
en.wikipedia.org
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en.wikipedia.org
Krill feeding on algae under the sea ice
Krill occur in large swarms and filter-feed on algae, diatomsCan rake algae below sea ice, one krill can rake one square foot
in ten minutesSea ice production means more krill production (heavy vesus light
ice years, krill cohorts vary)
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Ice or Crystal KrillEuphausia crystallorophias
--smaller than E. superba--found farther south, 74 latitude and higher--eggs do not sink, larva and adults in same shallow water
associated with sea ice
pal.lternet.edu
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Krill Swarm--krill are keystone as they are extremely abundant--fed upon by fish, seabirds including penguins, seals, and whales--500 million tons of biomass in Southern Ocean each year
krillcruise.wordpress.com
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Euphausia superba
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http://www.arkive.org/antarctic-krill/euphausia-superba/video-00.html
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http://www.oceanographerschoice.com/
Salp, or tunicate
Salpa thompsoni
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Ice FishSuborder Notothenioidei
--dominant group on continental shelf of Antarctica--over 100 species, adapted to cold shelf waters, most
are endemic to Antarctica--benthic, no swim bladder--produce an antifreeze glycoprotein
www.fishesofaustralia.net.au
Lanternfish (Electrona risso)
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Antifreeze Glycoproteins--found in Notothenioids, but also some other vertebrates, plants,
fungi, bacteria--a class of polypeptides that bind to ice crystals and prevent growth--several types, all developed independently--first isolated and described in Antarctic fish by Dr. Art DeVries
https://bradyinantarctica.wordpress.com
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Antarctic SilverfishPleuragramma antarcticum
--another Notothenioid also known as a cod icefish--like krill, it is considered a keystone species--common prey item for seals, penguins and other seabirds--spawn near surface, larval and juveniles remain in upper
water column, then migrate to deep waters
blog.rinnovabili.it
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Hubold (1985)
Silverfish inhabit deeper waters with age and live up to 14 yrs.However, adults can occur in all depths of water (Hubold 1984).
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http://phys.org
Family Channichthyidae
--less than 1% hemoglobin in blood--gain oxygen through the skin, no scales--transparent
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Otoliths of Pleuragramma, Electrona, and other speciesare easily identified by shape and other characters
--can estimate size of fish in life from otolith dimensions--useful for quantifying diet in penguin and seal guano--otoline mineral structure with CaCO3 helps them preserve
well in stomachs
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Age (cal. yr BP)
0 2000 4000 6000 8000 10000
Mea
n d
18O
(‰
, V-P
DB
)
-8
-7
-6
-5
-4
-3
-2
Windmill Islands, East Antarctica
Oxygen isotopes in otoliths can be used as a proxy for changingocean temperatures over time
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Deep Sea Benthos
Not as isolated as Antarctic continental shelf, so fauna is not dominated by endemic species
Very little known about this region, but thought to havehigher diversity than continental shelf
ANDEEP, program to target deep sea benthos in SouthernOcean, 2002 and 2005
Many species may have originated from Ross and Weddell Seas, making the continental shelf around Antarcticaa ‘biodiversity pump’
Recent evidence for gene flow in bipolar species of Foraminifera
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Also get gigantism in Antarctic waters
Giant Isopod Glyptonotus antarcticus Can reach 20 cm length, 70 g weight
http://www.oikonos.org/
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http://depts.washington.edu/
Gigantism in many marine invertebrates in Antarctica may be related to the cold waters
Oxygen exchange in salt water is more difficult, but oxygen use in cold wateris slower, less demand
This may select or allow for larger body sizes in marine inverts in this region
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http://www.landcareresearch.co.nz/science/soils-and-landscapes/antarctic-soils
Readings on Antarctica soils for next time:
Read main section and first three subheadings under AntarcticSoils on left side of page
https://www.soils.org/discover-soils/story/climate-change-puts-spotlight-back-antarctic-soils
Read entire article on this site