The Nekton Realm

Question 1

Nekton

Answer 1

• Pelagic province: neritic and oceanic zones
• Active swimmers with specialised muscles for locomotion
• Can migrate long distances
• Adaptations to environmental conditions

Question 2

3 clades of nektons

Answer 2

Molluscs, crustaceans, vertebrates

Question 3

Molluscs

Answer 3

Second largest phylum of invertebrates. Invertebrate phylum with great morphological diversity

Question 4

Features of molluscs

Answer 4

• Mantle with a significant cavity for breathing and excretion
• Radula: feeding apparatus used for cutting or scraping food before entering the oesophagus
• Structure of the nervous system- paired nerve chords

Question 5

Molluscs- cephalopods

Answer 5

E.g. cuttlefish, squid , octopuses, nautiluses

Question 6

Cuttlefish

Answer 6

• Internal cuttlebone, gas-filled shell used for buoyancy control
• Implodes at 200-600m
• Live in shallow or continental shelf benthic ecosystems

Question 7

Squid

Answer 7

• Catch > 2 million tonnes/year
  Can swim 10ms-1
• Water jet propulsion via mantle and siphon- rotates for agility and speed
• Intelligent
• Eat 15-20% of body weight/day
• 5cm-20m
• Long distance migration: 4000km yr-1

Question 8

Nautilodia

Answer 8

• Chambered Nautilus
• Free swimming (slowly) cephalopods w up to 90 tentacles
  Jet propulsion- expel water from the hyponome
  Keeps external shell
• Large body chamber w subchambers filled with gas similar to air
• NEUTRALLY BUOYANT
• Jaws= beak like- feed on crustaceans
• 5 species exist today

Question 9

Crustaceans

Answer 9

Phylum- Arthropods
Class- Crustacea
e.g. shrimp, krill
- Some swimming ability, restricted capacity to swim against currents
- Many benthic species

Question 10

Vertebrates

Answer 10

Subphylum of Chordata
- Diverse group >100 species
- Depend on ocean for food - primarily ocean dwelling

Question 11

Cetaceans

Answer 11

Whales, dolphins, porpoises

Question 12

Sirenians

Answer 12

Manatees, duongs

Question 13

Pinnipeds

Answer 13

Seals, sea lion, walruses

Question 14

Otters

Answer 14

Sea otters, marine otters

Question 15

Vertebrates - marine fish

Answer 15

Largest and most diverse group
3 classes:
- Agnatha: primitive jawless fish
- Chondrichthytes: cartilaginous fish
- Osteichthytes: bony fish

Question 16

Agnatha

Answer 16

= without a jaw
- Evolved 550 mil years ago
E.g. Sea lamprey- skeletons= cartilage and are parasitic feeders on blood and body fluids
E.g. Hagfish- enter bodies of dead animals and eat from inside

Question 17

Chondrichthyes

Answer 17

• Cartilaginous skeleton, jaws, paired fins, paired nares, scales, heart with chambers in series
• Appeared 450 mil years ago
• 300 species e.g. sharks, skates, rays

Question 18

Osteichthyes- group 1: Actinopteygii, ray finned fish

Answer 18

• Fins are webs of skin supported by bony spines
• Highly diverse group- 29,000 marine species
  -Evolved ~ 400mya

Question 19

Osteichthyes- group 2: Sarcopterygii, lobe finned fish

Answer 19

Fleshy, lobed paired fins joined to the body by a single bone
- Only 8 living species
- Tetrapodomopha evolved into tetrapods- vertebrates w legs

Question 20

Epipelagic fish

Answer 20

• Most common
• Commercially harvested

Question 21

Osmosis

Answer 21

Movement of water through a semi-permeable membrane that separates 2 solutions of different concentration

Question 22

Hypotonic

Answer 22

Internal salinity= lower than external salinity

Question 23

Osmoconformers

Answer 23

Marine inverterbrates, maintain internal salinity to equal surrounding seawater

Question 24

Osmoregulators

Answer 24

Marine and freshwater fish tightly regulate body osmolarity

Question 25

Internal salinity

Answer 25

Stays constant- may be lower or higher than surrounding water

Question 26

Osmoregulation

Answer 26

Controls amount of water and mineral salts in blood. Fish must counteract effects of osmosis

Question 27

Hypertonic

Answer 27

When internal levels of salt= higher than external levels

Question 28

Marine fish

Answer 28

Hypotonic to surroundings- lose water, gain salt. - Drink lots of water and excrete salt via gills

Question 29

Freshwater fish

Answer 29

Hypertonic to surroundings - gain water, lose salt - Don't drink freshwater and absorb salt via gills, hypotonic urine to expel excess water

Question 30

Buoyancy

Answer 30

- Fish, marine mammals, molluscs and crustaceans control their deoth habitat by counteracting their tendency to sink - Maintain neutral buoyancy

Question 31

Adaptations of sharks - buoyancy

Answer 31

- Reduced specific gravity of bodily fluids - Cartilage skeletons - No swim bladders - Oils and lipids concentrated in tissues and organs (lipids=incompressible) - Dynamic lift from forward motion and fins- control depth by swimming

Question 32

Swim bladders

Answer 32

Only found in ray-finned fish - Control buoyancy by adding or removing gases from the blood at different depths - Lacking in bottom-dwelling fish - Reduced in continuously swimming fish e.g. tuna

Question 33

Disadvantage of swim bladders

Answer 33

-PROHIBIT rapid vertical movements or migrations

Question 34

Sperm Whales

Answer 34

- Dive 300-800m up to 1-2km to feed - Spermaceti: Changes in specific density regulate buoyancy and facilitate long deep dives - Hold breath for up to 2 hours

Question 35

Locomotion

Answer 35

- Swimming = rapid locomotion - 3 types of drag must be overcome for efficient swimming

Question 36

3 types of drag

Answer 36

- Surface Drag - Turbulent Drag - Form Drag

Question 37

Methods of locomotion to minimise drag

Answer 37

- Manoeuvrability - Cruising - Acceleration

Question 38

Adaptation strategies

Answer 38

Defence and camouflage - Light colour if viewed from below - Dark colour if viewed from above Echolocation

Question 39

Adaptation : mesopelagic fish

Answer 39

Scarcity of life= - large eyes- maximum light - Bioluminescence- camouflage, predator defence, attract prey, communication Scarcity of food= - Large mouth, hinged jaw - Increased prey choice - Large ingestions capability, slow growth

Question 40

Influences on migration

Answer 40

Temperature variations, water masses, ocean currents (transport system) ; breeding cycle

Question 41

Diadromous fish migration

Answer 41

Migrate to select favourable conditions for feeding and reproduction- food and climate

Question 42

Anadromous fish migration

Answer 42

fish lay eggs in freshwater and migrate to the sea to grow and mature, then return to spawn e.g. salmon

Question 43

Catadromous fish migration

Answer 43

fish breed at sea and spend most of their adult life in freshwater e.g. American eel