Animals of the Pelagic Environment
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Making a living--Adaptations
Staying Above the Seafloor
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Eating
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Gas Containers
Floaters
Swimmers (nekton)
Mobility
Speed
Temperature
Group Behavior
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Reproduction
Schooling
Migrations
Adaptations
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To make a living organisms must meet
the following challenges:
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1) where to live
2) what food to eat and how to obtain it
3) how to avoid predators
4) where, how, when to reproduce
They are strongly influenced by the
usual factors: temperature, density, etc.
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Planktonic forms: Zooplankton
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Zooplankton are the animals of the
plankton. They cannot swim against
the currents.
Every major phylum of the animal
kingdom is represented
Their size ranges from micrometers
(protists) to tens of meters ("Jellies")
Zooplankton Continued...
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Zooplankton typically grow fast, and
this is very dependent on the food
supply
Distribution - Zooplankton typically
occur in patches with a high density of
organisms, but they may accumulate
along a particular depth e.g., the
pycnocline, DSL
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Common Zooplankton
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Copepods and euphausids (krill)
Foraminifera and radiolarians
Transparent forms or "Jellies". There
are the so-called true Jellies (Cnidaria)
and the Ctenophores, or comb-jellies
Salps and tunicates
True Nekton
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This group can regulate both their
horizontal and vertical position, and
include:
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Fish
Molluscs (squid, cuttlefish, nautilus)
Reptiles
Marine Birds
Marine Mammals (>50% of time at sea)
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Buoyancy
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4 groups, based on vertical positioning:
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Size-Independent
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This includes the smallest organisms
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Primarily the smaller zooplankton
So small they don’t sink very rapidly
Adaptations are size- and shape-related
Gas Containers
Floaters (no hard parts)-neutrally buoyant
Swimmers
Buoyancy: Gas Containers
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Use a gas chamber to regulate depth
(buoyancy)--similar to a diver’s BCD
Limited to about 500 m depth (the
crush depth) for nautilus
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Buoyancy: Fish Bladders
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A special case of gas containers, as
most fish swim instead
NOT found in fish that swim all the time
such as tuna
Below about 7000
m, the gas is
replaced by fat
Can be rapidly or
slowly adjusted
Buoyancy: Floaters
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Contain very little hard tissue
Includes:
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Coelenterates
Siphonophores
 Scyphazoans
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Tunicates
Ctenophores
Chaetognaths (usually placed in
zooplankton group)
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Coelenterates-->Siphonophores
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Bodies are more than 95% water
Use a pneumatophore for buoyancy
Colonial organism,
with specialized
individuals
Includes
nematocysts
(stingers)
Coelenterates-->Scyphazoans
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True jellyfish
Don’t contain a float-bag
Uses muscular
contraction of the bell to
provide movement
Capable of explosive
growth by asexual
budding
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Tunicates
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Also called sea
squirts, salps
Are chordates, but
don’t have a spine
Use jet propulsion
Can grow up to 40%
per day in size!
Can be important for
export of organic
material to depth
Ctenophores
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Also called “comb jellies”, sea
gooseberries
Always pelagic, marine
Carnivorous
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Chaetognaths
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Also called arrow
worms
very important
carnivores,
intermediate step
between small
zooplankton and
fish
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Nekton (true swimmers)
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Squid
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Fishes
Marine Mammals
All of these groups expend more
energy to maintain buoyancy
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Adaptations for Feeding
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Mobility and Speed are largely
dependent on 3 factors:
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Length:Width (barracuda vs. sunfish)
Caudal Fin morphology
Red vs. white muscle mass
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Body Temperature
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Tuna are an example of countercurrent
heat exchange systems
Body Temperature
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The opposite extreme are cold-water
fishes that use antifreeze
These glycoproteins bind to small ice
crystals in the cell, keeping them from
forming bigger crystals
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Marine Mammal Adaptations
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Marine Mammals: spend more than
50% of the time at sea
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Cetaceans (obviously)
Pinnipeds
Sea Otters
Sirenians (manatees, dugongs, Stellar
sea cow [extinct])
Polar Bears
Breathing
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Deep diving mammals have evolved to
reduce oxygen consumption by:
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Increasing blood volume, capacity
“gliding” as they dive
Shutting off unnecessary organs during
dives
Developing flexible ribs
No nitrogen narcosis
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Behavioral Adaptations
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Schooling: found in over 2000 species
of fishes
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Reduce the predator-prey encounter rate
Less likely to eat any given individual
May appear as a “single” organism
Confusing to predators
Can be reproduced
using simple rules on
a computer
Behavior: Migration
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Behavior: Abduction
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Some organisms “borrow” another one
to enhance survival
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