The Nekton Realm Flashcards
Nekton
- Pelagic province: neritic and oceanic zones
- Active swimmers with specialised muscles for locomotion
- Can migrate long distances
- Adaptations to environmental conditions
3 clades of nektons
Molluscs, crustaceans, vertebrates
Molluscs
Second largest phylum of invertebrates. Invertebrate phylum with great morphological diversity
Features of molluscs
- 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
Molluscs- cephalopods
E.g. cuttlefish, squid , octopuses, nautiluses
Cuttlefish
- Internal cuttlebone, gas-filled shell used for buoyancy control
- Implodes at 200-600m
- Live in shallow or continental shelf benthic ecosystems
Squid
- 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
Nautilodia
- 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
Crustaceans
Phylum- Arthropods
Class- Crustacea
e.g. shrimp, krill
- Some swimming ability, restricted capacity to swim against currents
- Many benthic species
Vertebrates
Subphylum of Chordata
- Diverse group >100 species
- Depend on ocean for food - primarily ocean dwelling
Cetaceans
Whales, dolphins, porpoises
Sirenians
Manatees, duongs
Pinnipeds
Seals, sea lion, walruses
Otters
Sea otters, marine otters
Vertebrates - marine fish
Largest and most diverse group
3 classes:
- Agnatha: primitive jawless fish
- Chondrichthytes: cartilaginous fish
- Osteichthytes: bony fish
Agnatha
= 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
Chondrichthyes
- 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
Osteichthyes- group 1: Actinopteygii, ray finned fish
- Fins are webs of skin supported by bony spines
- Highly diverse group- 29,000 marine species
-Evolved ~ 400mya
Osteichthyes- group 2: Sarcopterygii, lobe finned fish
Fleshy, lobed paired fins joined to the body by a single bone
- Only 8 living species
- Tetrapodomopha evolved into tetrapods- vertebrates w legs
Epipelagic fish
- Most common
- Commercially harvested
Osmosis
Movement of water through a semi-permeable membrane that separates 2 solutions of different concentration
Hypotonic
Internal salinity= lower than external salinity
Osmoconformers
Marine inverterbrates, maintain internal salinity to equal surrounding seawater
Osmoregulators
Marine and freshwater fish tightly regulate body osmolarity
Internal salinity
Stays constant- may be lower or higher than surrounding water
Osmoregulation
Controls amount of water and mineral salts in blood. Fish must counteract effects of osmosis
Hypertonic
When internal levels of salt= higher than external levels
Marine fish
Hypotonic to surroundings- lose water, gain salt.
- Drink lots of water and excrete salt via gills
Freshwater fish
Hypertonic to surroundings - gain water, lose salt
- Don’t drink freshwater and absorb salt via gills, hypotonic urine to expel excess water
Buoyancy
- Fish, marine mammals, molluscs and crustaceans control their deoth habitat by counteracting their tendency to sink
- Maintain neutral buoyancy
Adaptations of sharks - buoyancy
- 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
Swim bladders
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
Disadvantage of swim bladders
-PROHIBIT rapid vertical movements or migrations
Sperm Whales
- 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
Locomotion
- Swimming = rapid locomotion
- 3 types of drag must be overcome for efficient swimming
3 types of drag
- Surface Drag
- Turbulent Drag
- Form Drag
Methods of locomotion to minimise drag
- Manoeuvrability
- Cruising
- Acceleration
Adaptation strategies
Defence and camouflage
- Light colour if viewed from below
- Dark colour if viewed from above
Echolocation
Adaptation : mesopelagic fish
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
Influences on migration
Temperature variations, water masses, ocean currents (transport system) ; breeding cycle
Diadromous fish migration
Migrate to select favourable conditions for feeding and reproduction- food and climate
Anadromous fish migration
fish lay eggs in freshwater and migrate to the sea to grow and mature, then return to spawn e.g. salmon
Catadromous fish migration
fish breed at sea and spend most of their adult life in freshwater e.g. American eel
