Marine Ecology: May 19-30, 2008
Epipelagic Zone: General/Antarctic marine ecosystem 1
NOTE: Although detailed, this is not a full transcript of the lecture. Refer also to your notes!
I.
II.
Overview
A.
The epipelagic zone [opening figure, Ch. 15]
B.
Epipelagic food web (simplified) [Fig. 15.4]
C.
“Classic” herbivore food chains vs. microbial loop: [Fig. 15.25]
Focus on phytoplankton (general)
A.
What is phytoplankton?
1.
Photosynthetic Prokaryotes: Bacteria & Archaea
2.
Photosynthetic Protista: diatoms, dinoflagellates, prymnesiophytes and
cryptophytes
B.
Variability of productivity in the ocean
1.
Differences primarily due to phytoplankton productivity, although macroalgae
also considered here…
C.
Which abiotic factors promote phytoplankton growth?
1.
Light
a)
Highly seasonal in polar regions; more consistent near equator
b)
Some species able to photosynthesize at lower light levels (i.e.
Phaeocystis antarctica)
2.
Nutrients
a)
Key factor in determining global marine primary production (figure from
Ecology text)
b)
Brought to surface in several ways

upwelling (coastal and equatorial)

3.
4.
deep mixing of winter storms (quite important in the Pacific
northwest as well as Antarctica)

runoff from land (in Antarctica, bird and seal colonies produce
lots of nutrient-rich waste)
c)
In the Antarctic, abundant at beginning of season, but certain ones may
become depleted as a result of blooms

Depletion of certain nutrients can cause a shift in the types of
phytoplankton seen
Shallow pycnocline
a)
Reduction of deep mixing; heating of surface waters so that the layering
due to temperature is distinct (important in Pacific Northwest and other
areas)

Important for phytoplankton to be held up close to light.
b)
In the Antarctic, the melting of sea ice contributes to a shallow
pycnocline (think about salinity…)
c)
Storms will deepen the pycnocline and thus can disrupt phytoplankton
blooms
Importance of ice
a)
Sets up shallow pycnocline (see above) in zone of melting ice
b)
“Seeds” water column with spores that have been frozen into the ice
c)
Reduces effects of wind
d)
Seasonal and interannual variability in ice extent causes drastic
changes in temporal and spatial extent of phytoplankton among
years.
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D.
III.
IV.
V.
Major groups of Antarctic phytoplankton
1.
Diatoms
2.
Prymnesiophytes (Phaeocystis antarctica)
3.
Cryptophytes (small, of lesser importance to krill)
E.
Variability in phytoplankton community composition
1.
Both spatial and temporal variations occur
a)
At different times and places, one or the other species may be dominant.

Different nutrient mixes favor one or the other type.

Different light levels may favor one or the other type

Phaeocystis fares better than diatoms in stormy
conditions/ lower light levels

Higher temperatures may favor Phaeocystis

Role of grazers?
Zooplankton: overview
A.
Crustaceans dominate!
1.
Copepods: Most abundant type of zooplankton, and most numerous animals on
earth!
a)
Can be herbivorous, carnivorous or omnivorous [Fig. 15.7]
b)
Species composition of copepods clearly shifts with temperature
changes.

Does this matter if there are still copepods in the area for higher
order consumers?
2.
Krill: Dominate the earth in terms of biomass: A single species, the Antarctic
krill (Euphausia superba) has greater biomass than all humans on earth.
B.
Gelatinous zooplankton (examples)
1.
Salps
2.
Larvaceans
a)
Both salps and larvaceans feed on picoplankton and nanoplankton (the
smallest plankton; small phytoplankton as well as various types of
bacteria.)
3.
Ctenophores
a)
Key predators! Have wiped out other zooplankton, including fish larvae,
in the Black Sea

But ctenophore-eating ctenophores (i.e. Beroe) actually seem to
mitigate the situation…
C.
Meroplankton (already covered…)
Focus: The Antarctic marine food web [Fig. 10.14 and slides!]
A.
Note key species and their relationships
B.
Note key role of KRILL!
1.
Other krill species play similar roles worldwide.
Focus on Antarctic krill
A.
Basic anatomical features
B.
Feeding behavior
1.
Feeding basket
2.
Compression-filtration
C.
Feeding preferences
1.
My experiments showed that they selectively graze on diatoms in preference to
the Phaeocystis
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a)
VI.
Phytoplankton availability could thus impact krill growth and
reproduction.
b)
Phytoplankton species composition may be affected by global change
such as increased uv radiation and increases in temperature.
D.
Schooling behavior
1.
Shape and size of schools
2.
Why school?
E.
Life-history (separate diagram)
1.
Spawning at surface, spring and summer
a)
Females can spawn multiple broods
b)
Hypothesis: number and size of broods is directly tied to food intake
during spring and summer.
2.
Eggs sink (why important?)
a)
Escape from predators
b)
Go to warm, deep layer where development is faster (due to slightly
higher temperatures)
3.
Nauplii (relatively early larval stage) move back to surface to feed
4.
Juveniles overwinter on the underside and crevices of pack ice
a)
Must feed on ice algae
5.
Adults overwinter outside of the shelf break
a)
Adults can go without food for the winter. A variety of survival
mechanisms have been suggested:

Decreased metabolic rate

Use of lipid stores

Shrinkage

Consumption of alternate food resources (controversial)
6.
Reach sexual maturity at 3 years. Can live for 6-8 years.
a)
Very long-lived compared to other zooplankton.
b)
Adaptive value of this lifespan? (Compare to cycle of ice)
F.
Decline of krill in the Antarctic?
1.
Study by Angus Atkinson published in Nov. 2004 issue of Nature: Suggests that
krill populations along the Antarctic peninsula are only 20% of what they were in
the 1970
a)
Global warming and an increased incidence of low ice years are likely to
be the causal factor.
b)
Difficult to estimate krill populations…
c)
Some higher krill years since paper was published…
Seabirds 1: Penguins of the Antarctic Peninsula
A.
Three major species (Adelie, chinstrap and gentoo): We will focus on the Adelie
penguins.
B.
Adaptations for diving
1.
Solid bones (no air spaces as in flying birds = non-pneumatic)
2.
Hindlimbs
a)
Swung far rearward to serve as a rudder
b)
Webbed, of course!
c)
Sharp toes for gripping ice
3.
Forelimbs are modified into flippers
4.
Air sacs minimized to reduce buoyancy
5.
Feathers
a)
Covered with three layers of scale-like short feathers
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

6.
C.
Trap air for warmth (on land)
No flight feathers…
b)
Squeeze air out of feathers prior to a dive

See a stream of bubbles!
Larger species are deeper divers:
a)
Less metabolic demand/gram of body tissue (so can hold breath longer)
b)
Larger wings mean more absolute movement forward
Warmth
1.
2.
3.
D.
E.
Blubber
Air in feathers (on land only)
Special oils
Breeding behavior of Adelie Penguins (Penguin taxon advisory group)
1.
Nest in large colonies of up to half a million birds on nearshore islands close to
the Antarctic continent. Nests are small depressions lined with pebbles that are
carefully selected (smooth, of correct size) and brought to the nest site.
2.
Nests are started by males at the beginning of the season (they arrive at the
breeding sites first) and then added to by both birds after the pair is formed.
a)
Adelies are faithful to site and (often) to their mate.
3.
Usually two eggs are laid.
4.
Both male and female parent share incubation and chick rearing duties.
a)
The parents first alternate when the chicks are small, but after chicks are
larger both parents are needed to feed the chicks in order for them to
successfully fledge. The chicks are left alone in crèches where they
huddle for warmth and for protection against predators.
5.
The young must eat a diet comprised primarily/solely of krill.
a)
Adults can survive on fish, but not the young.
b)
Krill are high in necessary lipids that the chicks need to grow.
c)
Adults grab krill within schools individually in their beaks when they
feed.
6.
The chicks are ready to fledge about 2 months after hatching.
a)
Nests that get started late in the season are unlikely to be successful
Declines/shifts in penguin populations
1.
More northern colonies are being abandoned (see work of Stephen Emslie) and
the center of the population is shifting southward (work of Bill Fraser)
a)
In five colonies near Palmer Station, numbers of breeding pairs have
dropped from 15,200 to 9,200 in 25 years, while some smaller colonies
have disappeared altogether.
b)
In regions further south, Adelie penguin colonies are actually increasing
in size.
2.
Why this change?
a)
Thought to be linked to the reduction in sea ice  reduction of krill
populations.

Related to role of ice in the food web as well as to ice-related
changes in krill distribution.
b)
Increased snowfall is also a cause of increased penguin mortality in
regions with low ice.

Moisture usually locked up in the ice is instead in the
atmosphere and falls as snow. The penguins build nests on the
snow, but when the snow melts, the nests are inundated by water.
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Study questions
*NOTE 1: There is a bit of repetition in these questions. Hopefully that will be helpful to you in
mastering the material!
*NOTE 2: There are also some questions within the body of the lecture outlines. Be sure you can answer
those questions too!
1.
What is phytoplankton? Be sure you know which major groups of organisms have some members
that are phytoplankters.
2.
In a general sense, where are the most productive areas of the ocean on a “per unit area” basis?
The least productive?
3.
List and describe the abiotic factors that affect phytoplankton growth. Be sure to include the
particular “condition” of each factor that promotes phytoplankton growth, and the mechanism/role
of each of these factors. (For example, does phytoplankton require high or low nutrient levels? If
levels need to be high, why?)
4.
What is the pycnocline? What causes a pycnocline to be shallow? What causes a pycnocline to be
deep? What role does the pycnocline play in phytoplankton growth?
5.
Describe three major processes that bring dissolved nutrients to surface waters.
6.
Describe the major roles of ice in promoting phytoplankton growth in the Antarctic.
7.
List/briefly describe the major groups of Antarctic phytoplankton (focus on Protista.)
8.
How consistent is a particular type of phytoplankton in space and time? What factors might make
the phytoplankton community composition variable? You should be able to think of at least three
factors.
9.
What role does krill play in the Antarctic food web? You should be able to answer this in a
general way as well as provide specific examples.
10.
What is the most abundant type of zooplankton in terms of numbers? What is the most abundant
type of zooplankton/organism on earth in terms of biomass?
11.
To which phylum and subphylum to salps and larvaceans belong? On what do they feed?
12.
What is the key feature of a ctenophore? On what do ctenophores feed? Describe the impact of
ctenophores on other organisms in the Black sea, as well as the effects of Beroe (the ctenophore
that preys on other ctenophores.)
13.
Describe how a krill feeds. Which type of phytoplankton appears to be selected for by the
Antarctic krill and why might this be important?
14.
In what ways is ice important to the Antarctic krill? Think about its importance to both adults and
juveniles.
15.
During what time of year do krill reproduce? Which factor(s) are likely to determine brood size
and the number of broods a female krill spawns in a season?
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16.
What happens to the fertilized eggs immediately after the female releases them? Why is this
important for the new krill’s’ survival? What behavior does the early nauplii larvae exhibit, and
why is this important to their survival.
17.
Why is a larger proportion of the “young of the year” krill likely to survive in a winter with a
larger ice extent?
18.
Putting together what you know about ice, phytoplankton and krill, explain why two “high ice”
years in a row are likely to allow for maximal reproductive success in krill. Start with the ice and
work your way up the food chain… (HINT: Reproductive success is not simply the # of young
produced, but should also take into account the survival of those young.)
19.
Krill populations along the Antarctic Peninsula are estimated to have dropped considerably in the
past 30 years. What are the likely causes of this change?
20.
Briefly describe several adaptations penguins have for swimming and diving.
21.
Briefly describe the key adaptations of penguins for staying warm in polar climates.
22.
Describe the basic breeding behavior of Adelie penguins, being sure to mention:
a.
Colony size (potential)
b.
Establishment of the nest
c.
Parental care of young, especially gender roles at various stages (similarities and
differences)
d.
Crèches (What are they and why are they necessary.)
e.
Major food for young (and why important)
23.
Adelie penguin populations along the Antarctic Peninsula are estimated to have dropped
significantly in the past 30 years. What is/are the likely cause(s) of this change?
24.
NOTE: Be sure you can put it all together! Focus on the importance of ice in the links from
phytoplankton to krill to penguins in explaining changes in these populations.
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