Introduction Adaptation Distribution Importance

Organisms that have developed powers of locomotion; capable of movement at will These are the animals that we are most familiar with: Vertebrates Invertebrates

Dominated by fishes (bony fishes; cartilaginous fishes) Includes also other members of the vertebrate class (marine mammals, reptiles, birds) Includes also some members of the cephalopod mollusks

Buoyancy Gas or swim bladder (possessed by most fishes) Two types of gas bladder Physostome: Open duct exists b/w gas bladder & esophagus (e.g. Herrings, salmonids, catfishes) Physoclist: No duct is present (spiny-rayed fishes)

Buoyancy contd. Gas-filled cavities (lungs) --- in air-breathing nektonic animals Accessory air sacs (in some marine mammals; birds) Air trapped under feathers (penguins) Air trapped in dense wool undercoats (sea otters & fur seals)

Buoyancy contd. Replacement of heavy chemical ions (Na + ) in the body fluids with lighter ones (NH4 + ) --- in squids Lay down lipid (fat or oil) in the body---in fishes (muscles, liver, etc), marine mammals (below the skin as blubber)

Buoyancy contd. –Hydrodynamic mechanisms for producing buoyancy during movement Lifting surfaces in the anterior region (pectoral fins, flippers) Heterocercal tail (upper lope is larger than lower lobe) More primitive fishes tend to have hydrodynamic adaptations to create lift More advanced fishes appear to evolve static or passive means to achieve neutral buoyancy

Adaptation to create propulsive force Undulation of the body from side to side due to alternate contractions of the body muscles (fishes) Tail movement are up and down in whales Undulation of the fins: body remains stationary while fins are moved to effect forward motion

Tuna Sailfish

Speed, poisonous secretions, mimicry of other poisonous or distasteful species, camouflage, countershading, transparency Schooling –Many individuals maneuver as if one –Safety in numbers –Appears larger –Movements confusing to predator

Are well developed in nekton Lateral Line System in Fishes: rows of tubes open to the surface; contain sensory pits sensitive to pressure changes in water Ampullae of Lorenzini in Sharks & Rays: Sensitive to minute electric currents in water; use electroreception to find prey Geomagnetic sensory system in marine mammals for long-distance navigation Eyes: Well developed Olfactory senses (sense chemicals) Hearing senses (Inner Ear in fishes)

Most developed in cetaceans High Frequency Sounds used to locate objects in water (prey/predators); navigate around objects Toothed whales possess very large brains relative to their body size that enable them to process acoustical information rapidly

Holonektonic bony fishes spawn eggs that float and undergo development in the open ocean waters Eggs of some spp. have threadlike structures for adhering to floating debris Heavy losses of pelagic eggs occur due to predation Large Nos of eggs are produced to offset the losses Tuna produce 2 – 2.6 million eggs Marlin (13 million eggs) Ocean sunfish (300 million eggs)

Pelagic sharks produce a few large eggs or embryos Thresher shark: produce 2 embryos Blue shark: up to 54 eggs Eggs are large & retained in the female for much longer period of time so that at birth or hatching they will have relatively high probability of survival

Similar to their terrestrial relatives All produce shelled eggs; laid on land Marine birds often congregate in large #s to nest on islands or cliffs that are inaccessible to terrestrial predators This ensures that the helpless young (altricial) bird will survive until it is old enough to fly, although this makes the birds vulnerable to human predation or pollution

Practically all members of the nekton are carnivorous Planktivorous Toothed whales, tuna, and sharks are general carnivores eating both other vertebrates and invertebrates Piscivorous

This is a challenging environment to live in Extreme 3 dimensionality No solid substrate No landmarks to use for navigation

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

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

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 The caudal fin provides the major component of thrust

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

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

Color and Camouflage Countershading - dark dorsal side, light ventrally

Behavior Schooling behavior is a method of protection for small fish Flying Fish Use modified pectoral fins for gliding above the surface

Why are migrations made? Many animals undergo extensive migrations usually for feeding or reproduction Salmons 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

What influences nekton abundance? Bottom-up influences Intrinsic (physiological) influences Top-down influences How important are community-level interactions?

Planktonic community Climate change Long line fishing Seine nets Food web

Growth rates may be temperature dependent Size influences feeding success the number of eggs produced per female escape from smaller predators through growing too large to be eaten Is there evidence for temperature effects on nekton success?

Nekton-feeding fishes, birds & mammals dominate the open ocean nekton. Their diet includes fishes, squids, large crustaceans. Size of prey consumed increases with size of the predator Largest carnivore in the oceans is the sperm whale which preys on the giant squid The 2 nd largest carnivore of the nekton is the killer whale which preys on fishes, penguins, porpoises, seals, sea lions, & even large baleen whales Smaller toothed whales, seals, & sea lions feed on squids & fishes Pelagic marine birds feed mainly in the surface waters consuming small fishes and squids.