The Pelagic Zone

Pelagic Zone: the water region of the ocean that is above the ocean floor and away from the shore.– In order to survive in the pelagic zone species have

evolved adaptations for defense, hunting and mating.

Section 1: Life Near The Surface and Life In The Deep

Hunting Adaptations in the Pelagic ZoneHow do organisms stay above the

ocean floor?• Larger organisms are more dense

than water.– Swimming stay above the ocean

floor requires a lot of energy.– Many organisms use gas-filled

organs to stay afloat.– Gas is less dense than water.

Hunting Adaptations in the Pelagic Zone• Swim Bladder: an internal, flexible, gas-filled structure.– Gases are added and removed through the blood which

will cause the swim bladder inflate or deflate.• Some fast moving fish do not have any gas-filled organs to

stay afloat.– Some fish are strong enough to continuously swim to stay

off the ocean floor.– Sharks have a specialized tail fin shape which provided lift

as they swim.

– Red Muscle: Contains myoglobin which is a red pigment that carries oxygen. More oxygen allows for long periods of muscle use.

– White Muscle: Provides great acceleration for short periods of time but fatigues much more rapidly than red muscle tissue.

•Mobility of a fish depends on the quantity and type of muscle•There are 2 types of muscles: red and white

Hunting Adaptations in the Pelagic Zone

Bony fish can be split into 2 groups based on mobility:1. Cruisers: Hunt by actively swimming and seeking

prey.– Contain mostly red tissue to swim long distances

2. Lungers: Sit and wait for food.– Contain mostly white tissue because they only

travel short distances in quick bursts.

Hunting Adaptations in the Pelagic Zone

Hunting Adaptations In The Deep• There is very little food available in the

deep sea.• Deep sea fish have developed

adaptations to conserve energy– Weak and flabby muscles (they mostly

sit and wait for prey to some by)– Deep water fish have swim bladders

filled with fat instead of gas which does not compress under pressure.

– Why couldn’t a fish from the deep sea have a swim bladder that is filled with air?

Hunting Adaptations In The Deep• Deep sea fish have large mouth and

expandable stomachs to consume large prey.• Anglerfish use bioluminescence to lure in prey.

Section 2: Defense Adaptations In The Pelagic Zone

Countershading: Fish living near the surface usually have a . . .

• Back that is black or blue.– A predator that is looking down will

not see the fish against the dark ocean floor.

• Belly that is white or silver.– A predator that is looking up will not

see the fish against the bright that is filter into the ocean.

• Photophores: Light producing organs.• Organism use photophores to match the

amount of light in the environment.• Similair to countershading.

Defense Adaptations In The Pelagic Zone

Sex in the Pelagic ZoneReproduction• 3 basic types of reproduction

1. Oviparous Reproduction: animals release eggs that develop and hatch outside the body.

– Most fish produce thousands of eggs because most will be consumed by predators.

– Some fish will only produce a few eggs, but they viciously defend their eggs.

– In seahorses, the male is responsible for carrying the eggs.

Sex in the Pelagic Zone2. Viviparous reproduction – mothers directly nourish their

unborn young through, and give birth to live young. – Some sharks, rays and all marine mammals reproduce

in this way– This is the way that is closest to human reproduction

Sex in the Pelagic Zone3. Ovoviviparous: animals develop and hatch from eggs,

inside the female, which gives birth to live young– Organisms are not directly nourished by the mother, they

consume egg yolks for nourishment.– This is the reproductive cycle of most cartilaginous fish– Once the sand tiger shark consumes all its egg yolk it eats

its brothers and sisters in the womb, then it begins to eat its mothers unfertilized eggs directly out of her ovaries.

Sex in the Deep• Finding a mate in the deep

sea can be more difficult than finding food.

• Challenge 1: Finding the same species– Different species use different

patterns of bioluminesence – Male Parasitism: male angler

fish bite onto the female and remains attached for the rest of his life.

Sex in the Deep

• Challenge 2: Finding the opposite sex.– Hermaphodites – many deep sea

organism produce both eggs and sperm.– Females release a chemical that males

can smell.

Schooling and Migration in the Pelagic zone

Schooling: a well defined social group of fish or squid.

• Common among many cruiser fish, hammerhead sharks and manta rays.

• Use vision, smell, and lateral line to form schools and move in unison

Schooling and Migration• Reasons for Schooling– Protection from predators• Predators are unable to target single individual• To intimidate or confuse predators

– Makes swimming easier by reducing drag.– Makes hunting or feeding easier.– Makes mating easier.

(Different fish have different reasons to school)

Schooling and MigrationMigration: regular mass movements from

place to place daily, annually, or once in a life time

• Reason to Migrate– Feeding

Ex: Tuna live in tropical waters but migrate to temperate waters to feed.

– Breeding• Salmon : live in saltwater but

migrate to fresh water to spawn.

Explain why deep sea fish do not form schools or migrate.

Section 2: Cartilaginous Fish vs. Bony Fish

Section 2: Cartilaginous vs. Bony FishCartilaginous fishes: Have a skeleton made of cartilage

which is a material that is lighter and more flexible than bone

• Belong to the Chondrichthyes class of organisms• There mouth is below there head• They have rough sand paper like scales• Ex: sharks skates and rays and ratfish’s

Cartilaginous vs. Bony FishBony fishes: Have a skeleton made of bone• Belong to the Osteichthyes class of organisms. • There mouth is usually at the front end of their head• They have smooth scales covered with a thin layer of

mucus • The great majority of fish in the pelagic region

Cartilaginous vs. Bony FishLocomotion

– Caudal fin: provides forward movement.

– Pectorals: helps in steering and breaking

– Pelvic fins: helps in steering and keeping balance

– Dorsal/anal: helps the fish stay upright

Both bony and cartilaginous fish have 4 sets of fins:

Cartilaginous vs. Bony FishLocomotion in Cartilaginous Fish• sharks use their fins for locomotion and buoyancy

(staying afloat)• bony fish use their fins only for locomotion because they

use swim bladders to stay afloat.• Sharks tend to sink because they don’t have a swim

bladder. • Heterocercal caudal fin - an asymmetric fin where the

top lobe is larger than the bottom lobe which provides lift.

Cartilaginous vs. Bony FishLocomotion in Bony Fish• 4 different caudal fin shapes– Rounder: good acceleration and

maneuverability, but not good at prolonged swimming

– Truncate: Similar to the rounder shaped caudal fin.

– Forked: not good at acceleration and maneuverability but ok at prolonged swimming.

– Lunate: worst at acceleration and maneuverability but best at prolonged swimming.

Cartilaginous vs. Bony FishFeeding in Cartilaginous Fish• Sharks eat by taking bites out of large

organisms, not swallowing smaller organisms

• Most sharks mouths are adapted to have rows of teeth that help them bite and tear off peaces of larger prey

• Only Whale sharks, Basking sharks, and Megamouth sharks are suspension feeders– Suspension feeding sharks have large

mouths with small teeth that is good for straining through large quantities of water

Cartilaginous vs. Bony Fish

Feeding in Bony Fish• Most bony fish are totally or mostly carnivorous and

so they have moths adapted to help them capture, grasp, and hold their pray which is usually swallowed whole

• What do they eat?

Cartilaginous vs. Bony FishRespiration in Cartilaginous Fish• Sharks need to swim in order

to breath• Sharks open and closer their

mouth while swimming which helps force water over their gill slits

• Since rays and skates are not constantly swimming they use a modified pair of gill slits called spiracles to help move water over their gills

Cartilaginous vs. Bony FishRespiration in Bony Fish• Boney fish have gill covers

that circulate water over the gills without swimming.

• The fish sucks in water through the mouth while the gill covers are closed.

• Then the mouth closes, the gill covers open, and the water is forced over the gills.

Cartilaginous vs. Bony FishRespiration in Bony Fish• Countercurrent system of flow: blood flows over the

gills in the opposite direction that water flows over the gills. – allows the most oxygen deprived blood to meet

the most oxygen rich water so the fish gets more oxygen.

Cartilaginous vs. Bony FishOsmoregulation: the ability of organisms

to regulate the amount of salt and water in their bodies

• Osmosis: the movement of water molecules through a membrane from high concentration to low concentration.

• Why can’t you drink saltwater if you are stranded at sea?

Cartilaginous vs. Bony FishOsmoregulation in Cartilaginous Fish• To prevent dehydration sharks and other

cartilaginous fish concentrate urea (one of the main components of urine) in their blood.

• Makes the concentrations of solutes in their blood close to or even higher than that of sea water

• Excess salt is secreted via the gills, skin and urine

Cartilaginous vs. Bony FishOsmoregulation in Bony fish– Urea is toxic to bony fish– Due to osmosis and diffusion, water leaves the fish

and solutes enter the fish causing dehydration.– Bony fish use kidneys to prevent dehydration by

excreting only a little water and a lot of solutes through urine

Cartilaginous vs. Bony FishSensory Structures in Cartilaginous Fish• Have a week sense of vision with little to no color

vision• Ampullae of Lorenzini: a special sense organ located

in the head of cartilaginous fish that can detect week electrical signals given off by the nervous systems of their pray

Cartilaginous vs. Bony Fish

Sensory Structures in Bony Fish• Have a good sense of vision but can

only focus by physically moving closer or further away

• Lateral line – a system of small canals that run along the body of the fish and allow it to sense vibrations in the water