Download PRINCIPLES OF BIOLOGY: LECTURES 3 and 4

Marine Biology: June 2, 2008
Epipelagic Zone: Birds (briefly) and Mammals (Antarctic plus…)
I.
II.
III.
Antarctic penguins (previous lecture): Yep, they are birds!
Key non-penguin seabirds of the Antarctic Peninsula (briefly): focus on links within
Antarctic food web
A.
South polar skua
1.
Gull relatives
2.
Colonies nearby those of Adelie penguins
a)
Feed on Adelie eggs and chicks
b)
Work in groups to distract Adelies
c)
Also feed on Antarctic silverfish
3.
Highly aggressive to intruders
B.
Blackbrowed albatross (and other albatross species)
1.
Can forage over thousands of kilometers; primarily feed on krill when in the
Antarctic
a)
May use olfaction; detect other feeding groups via the odor of
crushed-up krill as well a visually; will displace smaller birds on
feeding grounds.
2.
Surface and near-surface feeders
C.
Southern giant petrel
1.
Young can fend for themselves: gacking
2.
Primarily feed on krill
D.
Wilson’s storm petrels
1.
“Jesus birds”: feed on near-surface zooplankton (smaller krill species,
copepods, amphipods)
E.
Blue-eyed shags
1.
Feed on fish and squid (links to krill?); deep divers
2.
Have heavy bones like penguins.
F.
Kelp gulls
1.
Feed on limpets
a)
Part of intertidal rather than epipelagic food web.
Order Pinnipedia: Seals, sea lions and walruses (NOTE: walruses are Arctic only)
A.
Family Phocidae: true (earless) seals
1.
Phocid characteristics: highly adapted to aquatic environment
a)
no external ear
b)
short foreflippers: not useful for land mobility; cannot stand up.
c)
hindlimbs held parallel, work together for propulsion
d)
relatively short neck for streamlining
e)
Sex organs retractable; testes internal
f)
Best divers are in this group (Elephant seals = deepest diving pinnipeds)
2.
Reproduction (shared features of Phocidae)
a)
Females usually give birth to one offspring per year after maturation;
generally mate at end of weaning period.
b)
Females and males may fast or feed little during periods of mating and
lactation.
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
Why not eat? (Adaptive value)
Milk is rich in fat, sometimes close to 50%
Young can grow and wean quickly

Why important? (Adaptive value)
3.
Antarctic species
a)
Crabeater seals

>90% of diet is krill (mostly E. superba)

Specialized tricuspids with small spaces for straining krill
b)
Elephant seals

Squid (and fish) eaters

Large breeding colonies

Sexual dimorphism; highly skewed reproductive success in
males (Blue planet…)
c)
Leopard seal

Only phocid that eats seabirds and other seals

Also feeds on krill (specialized dentition in lateral teeth is
similar to crabeater seal’s teeth)

Probably has the broadest trophic position of any seal
d)
Weddell seals

Live within pack ice even in winter; keep ice holes open with
their teeth

Feed on fish and squid during long foraging journeys beneath
the ice.

Well-studied for their deep diving physiology and behavior
e)
Ross Seals (relatively rare)
B. Family Otariidae: sea lions, fur seals
1.
Otariid characteristics: a bit more terrestrially-adapted
a)
small external ear
b)
long foreflippers used for standing (on land), and for propulsion
c)
hindlimbs can be splayed apart, turned under body for support on land
d)
Flexible neck: predation
e)
Sex organs retractable; testes external
2.
Reproduction (compare with Phocidae!)
a)
Sometimes annual births, sometimes every other year (single pup)
b)
Females feed during lactation
c)
Milk is less fatty than for Phocidae
d)
Pups grow more slowly than for Phocidae

More mobile and able to escape terrestrial predators
e)
Sometimes nursed up to two years, but usually less
3.
Antarctic species
a)
Antarctic fur seal; Subantarctic fur seal

Feed on…krill, fish, squid and penguins
c)
d)
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IV.
C. Family Odobenidae: walruses: 1 species, circumpolar (N. Pacific and N. Atlantic
subspecies; no Antarctic species)
1.
Odobenid characteristics
a)
No external ear
b)
Foreflippers short in comparison to otariids but can stand (sort of) on them

Used for foraging
c)
Can turn hindflippers under body

Swim like seals; also used for stability while foraging on the bottom
d)
Sex organs retractable; testes internal
e)
Tusks=enlarged upper canines

Role in feeding for predatory walruses; possibly aid in clam-digging

Help them move on the ice

Also for display in mating, other social contexts (poem!)
2.
Reproduction
a)
Births every other year or even longer intervals (single pup)
b)
Females and males feed throughout breeding and lactation
c)
Milk tends to be relatively low in fat compared to Phocidae
d)
Slow growth rate of pups (longest of all the pinnipeds)

Nursed for 2 years or more
Order Cetacea
A.
Suborder Mysticeti: the baleen whales. Antarctic Mysticetes were greatly
reduced in numbers during the late 19th and early 20th century.
1.
Major characteristics
a)
Baleen plates for filter-feeding
b)
Most common Antarctic species use a method called compressionfiltration (just like the krill they eat!)
B.
Key species of Antarctic Mysticeti (baleen whales)
1.
Baleen
a)
Upper jaw only
b)
Baleen is composed of keratin
c)
Distinct baleen plates are stacked together

Portion facing inside of mouth is frayed to form fine bristles

Bristles are coarse or silky depending upon prey; so it is the baleen’s
texture/thickness that determines prey type, not the size of the whale.
2.
Minke whales
a)
Small
b)
Throat grooves and similar feeding mechanisms as the humpback whales

Feed on…krill!
c)
Most abundant of the baleen whales, with higher reproductive rates

Can they be “fished” sustainably?
3.
Humpback whales
a)
Largest pectoral fins of any whale, up to 1/3 of body length, broadly serrated
on leading edge.
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b)
V.
Distinctive throat grooves allowing for enormous throat expansion during
feeding

Feed primarily on krill in the Southern ocean

Use a technique called “bubble-netting”

May eat 2 tons in 24 hours
c)
Migration: cold waters to tropics (Why?

Males sing primarily on breeding grounds

Same song sung by all males of a population, but the song changes
over time; complete turnover of phrases in ~5 years.

A single song lasts from minutes to near an hour.

Focus on Australian populations

Note mixing in feeding grounds, separation on return to
W. vs. E. Australia.

Song dialect change due to “lost” males…
4.
Blue whale
a)
Distribution: Once worldwide, now the largest populations are found off
coastal California

Migrate to tropical waters for calving

Appear to avoid coastlines, so they are difficult to track

System of fixed hydrophones throughout the NE Pacific were used in
this study to detect the whale calls (US Navy, SOSUS array)

Frequency and intensity of calls used to approximate the blue
whale density in a particular area

Data suggests that they follow krill populations from south to north in
fall (opposite to gray whale migration)
b)
Largest animal ever (note: you don’t have to memorize these stats!)

Can be up to 24.5 meters (female)

Max weight: 190 tons

Heart the size of a VW bug

Spray from blow is about 6 meters high.

Larger prior to mechanized whaling

Loudest and deepest voice of any animal (180 dB, 10 Hz)
c)
Diet is almost exclusively…KRILL!
Suborder Odontoceti: toothed whales
A.
Antarctic species = Orcas!
1.
Prey on all the seal species
a)
commonly eat crabeater seals due to their high abundance
b)
Will even eat leopard seals
2.
Prey on whales
a)
Probably once a more important food resource
3.
May prey on penguins
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B.
Orcas in the Arctic: Orcas in some parts of Alaska (i.e. Aleutian Islands) are linked to the
decline of pinniped and otter populations, and also to the decline of kelp forests
a)
What changed ~1990 that led to increased predation by orcas on sea
otters?

Megafaunal collapse and the role of humans
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Study questions
1.
Describe the key food sources/position in the food web for each species of Antarctic bird
described.
a.
Which species rely directly on krill?
b.
Which species rely indirectly on krill via food web connections?
c.
Which species are least linked to the epipelagic food web. Explain.
2.
Compare the characteristics of the Families Phocidae, Otariidae, and Odobenidae within the
Order Pinnipedia. In particular, be sure to describe similarities and differences for
a.
Ears
b.
Limbs
c.
Neck
d.
Sex organ retractability
e.
Key aspects of reproduction (especially number of young per year; length of lactation
period, relative fat content of milk)
f.
NOTE: Relate these to their relative adaptability to the terrestrial vs. aquatic environment.
3.
Why is the lactation period especially short for certain species of Arctic phocids?
4.
To which of Phocidae family do most Antarctic pinnipeds belong? Describe the key food
sources/positions in the food web for each species of Antarctic pinniped described. Also describe
any special adaptations they have for feeding on their particular food resource. Also, which
pinniped species has the broadest diet in terms of trophic levels.
5.
Be able to name several Antarctic mammal and bird species that feed on…krill! Name others that
do not eat the krill, but rely on them indirectly (perhaps via other food web links).
6.
Name the two suborders of the Order Cetacea, and describe the major difference between them.
Be able to provide examples for each group.
7.
Describe the feeding behavior of humpback whales as well as their primary food resource within
the Antarctic.
8.
Briefly describe the migratory behavior of humpback whales (similar pattern as many other
Mysticetes.) What is the potential adaptive value of these migrations?
9.
What method has been primarily used to study the blue whale migrations along the Pacific coast?
What appears to be the adaptive value of their migratory pattern?
10.
Which species of Mysticetes can arguably be “fished” in a sustainable way, and what makes this
species different than others that are probably more vulnerable to overfishing?
11.
What is the role of song in humpback whales? Which whales sing, and when? Do humpbacks
worldwide sing the same song? Does the song change over time?
12.
What is the role of orcas in Antarctic food webs?
13.
Explain how orcas are linked to the decline of kelp forests in the Aleutian Islands, providing a
step-by-step explanation of the chain of events, including the role of humans.
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