Nekton Flashcards
What are Nekton
Organisms that can swim against an ocean current
General characteristics of Nekton
Larger body size
Greater swimming power
Most nektons are vertebrates
Most vertebrates are fish
Only the squid and a few species of shrimps are truly nektonic invertebrates
Include seabirds, reptiles, mammals but not amphibians
Importance of Nekton
Large nekton can influence marine communities
Important in current or historical harvests
Fishes of critical importance to world food supply
Vertical distribution
- Epipelagic countershading
– Countershading:
a nektonic organism is bicolored, dark above and light below - Holoepipelagic:
shark, tuna, ocean sunfish - Meroepipelagic:
herring, salmon
Morphological features of nekton at Mesopelagic zone
– Seldom exceed 10 cm
– Equipped with well developed teeth and large mouth
– Large light-sensitive eyes, uniformly black
– Photophores: light-producing organs
Morphological features of nekton at Abyssalpelagic zone
– Species-specific pattern of photophores
– Small with flabby, soft, nearly transparent flesh
supported by weak bones
– Oversized mouth
Nekton and reynolds numbers
- Ratio of inertial forces to viscous forces:
– Re=LV/ɷ
L=length
V=velocity
ɷ = viscosity - Water viscosity consistent, therefore Reynolds numbers change as a function of size and of velocity
- Small objects viscosity most important
- Large objectives inertia most important
Cephalopods - what are the two extant xub-classes
- Nautiloidea
- Coleoidea
Fishes: chondrichthyes, osteichthyes & Chondrichthyes
– Elasmobranchii (sharks, rays, skates, and sawfish)
– Holocephali (chimaeras)
* Osteichthyes
– Sarcopterygii (lobe-finned fishes)
* Coelacanths & lung fish
– Actinopterygii (ray-finned fishes)
Sea turtles
All sea turtles are nekton
Sea birds
All sea birds are nekton
Marine mammals - Sub order Pinnipeds
Family: Odobenidae
Family: Ottariidae
Family: Phocidae
Marine mammals - Order Cetaceans
Suborder: Mysticeti
Suborder: Odontoceti
Marine mammals - Order Sirenia
Family: Trichechidae
Family: Dugonidae
Nekton live in predictable environments, what are the factors
a)Iteroparous
b)Long-lived
c)Delayed maturity
d)Low-reproductive rates
e)Migratory
Iteroparity
Means living to reproduce repeatedly
* Sea Turtles
Return to natal beaches each year
* Cetaceans
Return to calving grounds annually
* Sharks
Site fidelity
Semelparity:
- Cephalopods
After mating & egg deposition both sexes die
Cold blooded
- Most fish are cold-blooded – poikilothermic
- Bodies same temperature as environment
- Not fast swimmers
Warm blooded
- Some are warm-blooded – homeothermic
- Found in warmer environments
- Helps them capture prey
Adaptations of Deep-Water Nekton
- Mainly fish that consume detritus or each other
- Lack of abundant food
- Bioluminescence
– photophores - Large, sensitive eyes
- Large sharp teeth
- Expandable bodies
- Hinged jaws
- Counterillumination
Marine Reptiles
- Ectothermic
- Covered with scales
- Breathe air with lungs
- Have specialized salt glands to excrete excess salt taken in from seawater
Marine Mammals
- Land-dwelling ancestors
- Warm-blooded
- Breathe air
- Hair/fur
- Bear live young
- Mammary glands for milk
Major marine mammal groups:
Order Carnivora, Order Sirenia, Order Cetacea, Order Cetacea
Order Carnivora
- Prominent canine teeth
- Sea otters
- Polar bears
- Pinnipeds
– Walruses
– Seals
– Sea lions
– Fur seals
Seals vs. Sea Lions and Fur Seals
- Seals lack prominent ear flaps
- Seals have smaller front flippers
- Seals have fore flipper claws
- Different hip structures
- Different locomotion strategies
Order Sirenia
- Herbivores
- Manatees
– Coastal areas of tropical Atlantic Ocean - Dugongs
– Coastal areas of Indian and western Pacific Oceans
Order Cetacea
- Whales, dolphins, porpoises
- Elongated skull
- Blowholes on top of skull
- Few hairs
- Fluke – horizontal tail fin for propulsion
- Adaptations to increase swimming speed
- Adaptations for deep diving
- Use oxygen efficiently
- Muscles insensitive to buildup of carbon dioxide
- Collapsible lungs
Order Cetacea, Suborder Odontoceti (toothed):
– Dolphins, porpoises, killer whale, sperm whale
– Echolocation to determine distance and direction to objects
– Determine shape, size of objects
Order Cetacea, Suborder Mysticeti
- Baleen whales
- Blue, fin, humpback, gray, right
- Fibrous plates of baleen sieve prey items
- Vocalized sounds for various purposes
