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Nekton

Accomplished Swimmers

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What are Nektonic Animals?

Organisms that have developed powers of locomotion; capable of movement at will

These are the animals that we are most familiar with: Vertebrates

Invertebrates

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Nekton Feeding Biology Practically all members of the nekton

are carnivorous Planktivorous

Toothed whales, tuna, and sharks are general carnivores eating both other vertebrates and invertebrates

Piscivorous

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The Epipelagic Environment

This is a challenging environment to live in Extreme 3 dimensionality

No solid substrate

No landmarks to use for navigation

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Adaptations of the Nekton To be successful,

nektonic animals must develop:

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Staying Afloat Like plankton, nekton also incorporate lipids into their tissue Sharks concentrate high oil levels in a large liver

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Staying Afloat• Fishes use stiff fin elements with movable spines

• These fins are used as wings to generate lift

• Heterocercal tails are used in sharks to generate lifts

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Staying Afloat Hammerhead sharks possess a large wing

(hydrofoil) on the front of their head

http://www.divedarwin.net/hammerheadnew.jpg

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Staying Afloat

Image source: http://www.pskf.ca/sd/images/dcp_4932.jpg

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Faster Swimming Speeds All nektonic animals are evolving mechanisms

to swim faster In many cases, speed is what determines if the prey

escapes or if the predator eats Adaptations are directed towards decreasing

drag and increasing forward propulsion Elimination of protuberances and a streamlined body

shape helps Fast swimmers tuck fins into grooves

The caudal fin provides the major component of thrust

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A Swimming Machine

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Faster Swimming Speeds The best swimmers contain a high

amount of red muscle Red muscle gets its color from a high

concentration of myoglobin which is great at storing oxygen

Red muscle is best used for long periods of exertion

A difference seen when you compare a tuna versus a flounder

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Faster Swimming Speeds Some pelagic sharks and

large tuna have the ability to conserve the heat their muscles generate

This trick of the circulatory system allows cold oxygenated blood to pass closely with the warm deoxygenated blood

There is a transfer of heat to the cold blood before it enters the muscle

Benefit: a warm muscle is more efficient than a cold muscle

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Defense Mechanisms There is no cover to hide in the

epipelagic This is a very intense selective pressure, everyone

is evolving mechanisms of defense Sense Organs

Sight Lateral line Otoliths Echolocation Ampullae of Lorenzini

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Defense Mechanisms

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Defense Mechanisms

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Defense Mechanisms

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Defense Mechanisms Color and Camouflage

Countershading - dark dorsal side, light ventrally

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Defense Mechanisms Behavior

Schooling behavior is a method of protection for small fish

Flying Fish Use modified pectoral fins for

gliding above the surface

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Migrations Why are migrations made?

Many animals undergo extensive migrations usually for feeding or reproduction

Salmon Sea Turtles

Tuna undergo extensive migrations to fully exploit food resources

Marine mammals (baleen whales) make migrations in a north and south fashion for feeding and calf rearing

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Tuna Migrations

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Baleen Whale Migrations

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Migrations How do marine animals

make migrations? Use variations in water

temperature Walker et al. (1984) found

tuna use the earth’s weak geomagnetic field

Magnetite (Fe3O4) crystals transduce the geomagnetic field to the nervous system

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The Subtidal

Life on the Continental Shelf

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The Continental Shelf

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Exclusive Economic Zone Biologically, the continental shelf is the

richest area of the ocean

Countries have extended their borders to protect natural resources

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Shelf Habitats The continental shelf shares many

similarities with the intertidal community

Unlike the intertidal, the animals that live on the shelf are never exposed to air

The deeper areas have different physical conditions

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Sampling the Benthic Habitat

• Bottom trawls• Grabs • Dredges

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Soft-Bottom Subtidal Communities

This substrate dominates the world’s continental shelves

Animals that live here share many traits with animals that live in the sandy intertidal

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Abiotic Factors Abiotic factors are linked to two

fundamental characteristics of the shelf:

1. Ergerg2. Earert

Temperature Currents

Turbulence

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Recruitment & Lifestyles

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Soft-bottom Subtidal Communities

Notable absence of large plants and algae There is little

primary production so the filter feeders and suspension feeders rely on detritus flushed from estuaries

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Seagrass beds Areas that are

carpeted by flowering plants

They develop best in sheltered shallow areas along the coast

Eel grass is our most common representative

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Seagrasses Thick mats of eel

grass provide lots of habitat for animals to hide

By stabilizing the sediment it decreases the turbidity Dead sea grasses

provide lots of detritus that benefit suspension, deposit and filter feeders

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Sea Grass Food Web

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Hard-Bottom Subtidal Communities

Animals that are present have the same characteristics as those of the rocky intertidal

Red and brown algae dominate Zonation related to

sunlight penetration

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Kelp Distribution

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Kelp Structure

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Kelp Zonation

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North Atlantic Kelps