I. Who are the nekton? A. Greatly vertebrates 1. Invertebrates --cephalopods– (mollusca) -- squid 2. Fisha. Sharks (Class Chondrichthyes, cartilaginous fishes)b. Rays (Class Chondrichthyes, cartilaginous fishes)c. Bony fish (Class Osteichthyes) 3. Reptilesa. Turtlesb. Sea snakesc. In ancient seas (60 million year ago) were plenty of marine reptiles(ichthyosaurs,mosasaurs, plesiosaurs) 4. Birds (example, penguins) 5. Mammals (next week)a. Whales (Order Cetacea)b. Seals and also sea lions (Order Carnivora)c. Manatees and also dugongs (Order Sirenia)d. Sea otters (Order Carnivora)
B. An overwhelming to study
C. Functional teams of pelagic fish 1. Holoepipelagic fish a. Regularly lay floating eggs and have epipelagic larvaeb. Most abundant in tropics and subtropics 2. Meroepipelagic fish–only part of their life bike in the epipelagica. Might spawn inshoreb. Might spawn in freshwaterc. Might only be in epipelagic at details times -- migrate to surface ar tofeed at night
II. Environmental Conditions and Adaptations A. Buoyancy 1. Many nekton space closeto neutrally buoyant 2. Squid replace heavy ionsin their body fluids with lighter persons 3. Numerous fish have a swimor gas bladdera. Can regulate to readjust buoyancyc. Two key types(1) physostome – has actually an open duct in between gas bladder andesophagus (2) physoclist – no duct; rely on the gas gland and also the retemirabile – a network of small blood vessels
4. Lungs have the right to also help toregulate buoyancy (marine mammals) 5. Birds have actually bones withair channels; deserve to trap air under the feathers 6. Lipid reserves in fishwithout swim bladders (e.g., sharks, mackerels, bluefish, and also bonito)a. Spread throughout the bodyb. Localized(1) pelagic sharks -- enlarged liver through lipids(2) naval mammals deposit lipid (blubber) listed below the skin 7. Many fast fish have actually nogas bladder and also get lift from your body shapea. Pectoral fins or flippersb. Heterocercal tail (has a larger upper lobe)c. Former (anterior) portion of the body have the right to be inclined in ~ an edge -provide lift B. Osmotic regulation – · most marineinvertebratesare isosmotic with sea water · sharks regulatethe amount of urea in your blood - isosmotic or evenhyperosmotic · most marine fisheshave human body fluids that are much more dilute 보다 seawater and also tend come losewaterby osmosis (hyposomotic)o have impermeable skin (integument)o drink seawatero create a little amount of pee (kidneys) – maintain watero excrete excess salt in urine and also gills (chloride cell on gills) · birds and also turtleshave lower concentrations of salts than seawater; remove excess saltthrough salt-secreting glands in the orbit of the eye
C. Locomotion 1. Mechanisms because that creatingpropulsiona. S shaped contractions (undulations relocating from head to tail) of bodyortail(1)speed relies on speed of muscle contraction waves(2) various other fins carry out maneuverabilityb. Undulating the fins(1) rays – wing like pectoral fins; some squid; ocean sunfish(2) some elongated fish that hold their body rigid and also undulate thedorsalfin (oarfish and ribbonfish)(3) generally fairly slow motionc. Paddling movement of forelimbs, hindlimbs or bothmarine turtles, seals, sea lions, penguinsd. Jet propulsion using water -- squids -- have the right to move quickly
2. Instrument forreducingresistance (air much more dense than water, so there is an ext resistance)a. Varieties of resistance(1) frictional resistance -- proportional come the quantity ofsurfacearea in contact with the water (least because that a sphere -- least SA/V);(2) kind resistance -- traction while moving is proportional to thecross-sectional area the the object in contact with the water(a) large for a sphere(b) smaller sized if long and thin(3) Induced drag – turbulence (vs. Smooth laminar flow) createsvortices (eddies) and also increases the dragb. Generally useful to maximize laminar circulation – smooth or absentscales;covered through slime --streamlined body surface c. BUT, if the animal is big and fast, girlfriend can’t protect against turbulentflow– have controlled turbulence(1) swordfish: rough sandpaper-like skin ontheir sword(2) tunas: scale behind the head (corselet) d. Most streamlined bodies have actually a teardrop form balance betweenfrictionalresistance, form resistance and also induced traction -(1) offers the lowest resistance because that the biggest volume(2) ratio of largest diameter to length is about 0.22 (whales, dolphinsand tunas)
e.Fast swimmers outperform subs and torpedos by behavior mechanisms D. Defense and Camouflage 1. Quick movement 2. Camouflagea. Alteration of body form -- visibility of a ventral keel b. Crypticcoloration -- countershading 3. Flying fish -- largepectoral fins -- escape predators 4. Schooling
E. Sensory solution 1. Vision 2. Hear – inside ear;swim bladder amplifies in part fish 3. Olfaction –olfactorysacs; taste buds 4. Lateral present of fish– finding vibrations in the water 5. Ampullae the Lorenzini(sharks and rays) – perceptible to electrical currents 6. Geomagnetic sensorysystem(marine mammals and also some other organisms-- lengthy distance migration) 7. Echolocation in marinemammals (more in mammal lecture) F. Reproduction and Life cycle 1. Holonektonic bony fish(e.g., tuna and marlin) often tend to spawn eggs that float and undergodevelopmentin the open oceana. Room subject to big predation ratesb. Produce huge numbers of eggsc. Expansion rate an extremely rapid and also life spans fairly short (5-10 years) 2. Pelagic sharks -- produceonly a few large eggs or embryos and also retain in the female for a longperiod;may live 20-30 year 3. Maritime birds and turtlesproduce shelled eggs that are laid on land a.young space then inaccessible to terrestrial predators b.susceptible to person predation and pollution G. Migrations 1. Fish --a. Salmon migrate earlier to freshwater to generate (anadromous fish)(1) can return come the exact same stream in which castle hatched(2) may use land features, currents, salinity, temperature, the sun ormagnetic ar to gain close to land(3)sense of smell(4) dice after spawning(5) young return to the seab. Other naval fishc. Catadromous fish – each other at sea and migrate right into rivers togrowand mature – freshwater eelsd. Tunaanatomical basis because that magnetotaxis -- magnitite 2. Turtlesmigrate long distances to breeding beaches, sometimes on islandspossible homing mechanismsa. Ability to recognize magnetic areas (some vary with latitude)b. Orient to wave propagation or directionc. Follow chemical cues 3.
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Sea birds --may have an extremely long migrations; patchy prey (tubenoses)
III. Ecology of Nekton · Planktivorous-- consume zooplankton o--e.g., part fish -- flying fish, sardines, herrings, menhaden, whalesharks,basking sharks and megamouth sharks andsome naval mammals (baleen whales)o most abundant nektono usually these space size-specific and also do no specialize o numerous mesopelagic small fish migrate into the epipelagic in ~ night tofeedon plankton · Mostspecies of nekton consume various other nektono generally depends on body size -- larger types take bigger preyo sharks take bites from prey that can be bigger than themselveso many other fish consume food wholeo pelagic birds feeding on small fish andsquid in the surface ar waters