LSM3254_Lecture 9 the Open Ocean

8/3/2019 LSM3254_Lecture 9 the Open Ocean

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LSM3254 Ecology of Aquatic Environments

The open ocean

Peter ToddDept of Biological Sciences

By the end of this lecture you should be able to discuss variousas ects of nekton includin :

Learning outcomes:

What nekton is!

Movement and lift

Migration

Examples of invertebrate and vertebrate nekton

Zones of the marine environment

Artificial/utilitarian classification of marineorganisms is generally by habitat and mobility:

What lives there?

Plankton: passive drifters

Nekton: active swimmers

Benthos: bottom-dwellers


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Nekton consists of:

Cephalopod molluscs

Some crustaceans

Vertebrates:

Seabirds

Marine reptiles

Fishes

General characteristics

Movement

Swimming

Active swimming required for:

Movement from point to point.

Maintaining position against a current (e.g., damsel fish guardingterritory in coral reef)

Requires well-developed muscular systems

High energy requirements

Impressive feats of migration (e.g., for feeding; for reproduction)

Movement

Movement useful for:

Reproduction

Feeding (finding food and/orremaining in food-rich environment)

Protection (predator avoidance)

Respiration (aeration of gills)

Generate li ft


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Lift Nekton generally denser than seawater

Need to achieve lift (buoyancy)

Static lift Accumulation of materials of low specific density Reduction of heavy tissue Swim bladder

ynam c t Nekton which chase prey actively have generally dispensed with

buoyancy aids and maintain lift mainly through constantlocomotion

e.g. some sharks, tuna

Static lift

Materials of low specific densityLiver

Low density lipids (fats or oils) and hydrocarbon (squalene)accumulated in liver and muscle tissues of sharks and some bonyfishes Liver up to 1/4 of the body weight in some sharks Also serve as important stores of energy

Layer of blubber below the skin of whales and seals

Reduction of heavy tissue

Cartilaginous skeleton in chondrichthyians (sharks, rays, skates). Cartilage lighter than bone

Static lift

Fats, oils and some body fluids only slightly less dense thanseawater

For many small but active nektonic species expending energycarrying blubber, oil-filled liver, etc. may not be ideal

SOLUTION: internal gas-filled flotation organ

Swim bladder in bony fishes (osteichthyians)

Flexible and extensible containers (cf. cephalopods)

Original respiratory function - forerunner of tetrapod lung

Maintain neutral buoyancy (static lift)

Swim bladder

Physostomatous: connected topharynx by pneumatic duct(primitive condition); dorsal orventral connection to pharynx

Physoclistous: completelyisolated from digestive tract; gasgland and oval window to add andremove gas from bladder.


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Gas-filled buoyancy organs may be rigid and strong as in somecephalopods - can structurally resist the increased water pressuresfound at depth

Static lift

e.g. nautilus, cuttlefish

Cuttlefish has cuttlebone - organof buoyancy with a number of gaschambers laid down as theanimal grows.

Dynamic liftHeterocercal tail

Sharks (chondrichthyians) lack swim bladder unable to maintainbuoyancy and achieve lift by static means alone

Some buoyancy from high concentration of low density lipids andhydrocarbon (squalene) especially in liver; and cartilaginousskeleton

Compensate with dynamic lift (requires locomotion)

Heterocercal tail (dorsal lobe larger than ventral) providing upwardpropulsion, together with rigid, flattened, laterally-held pectoral fins,acting as hydrofoils, generates lift as fish swims

The larger upper lobe of a shark's tail cuts the oncoming water

slightly before the smaller lower lobe.

This creates a wake within a wake, giving the shark both thrust andlift, both forward and upward motion.

Wilga, C. D. & G. V. Lauder, 2004. Biomechanics:Hydrodynamic function of the shark's tail. Nature, 430: 850.

Sensory reception

Chemoreception-olfaction

e.g., salmon and sharks respond to very low concentrations ofodour molecules

nav ga on ur ng m gra on; prey e ec on

Balance/equilibrium

statocysts (invertebrates); otoliths (fishes) able to detect speed as well as gravity - two types of receptor,

one detects gravity, other detects acceleration

Vision nekton generally have large well-developed eyes


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Some mesopelagic fish have:

Tubular eyes very acute vision in directionthat eye is pointed. Retina extends upone side of e e to im rove and ex andlateral visual field. bristlemouth with tubular eye

Sensory reception Sound reception

Swim bladder of fish:

,

Sound-production in certain fish - communication, defence,courtship or echolocation

Sound detection in fish:

Inner ear and otoliths (ear stones)

Lateral line system detects vibrations in the water

Marine mammals can echolocate and

use sound for communication

Odonticeti have a fatty organ at thefront of the head called a melon,which focuses emitted sounds fromthe nasal sacs into a beam ahead ofthe animal.

The whale produces a beam ofrapidly emitted echolocation clicksto help it navigate and find food.

The clicks bounce back to thewhale from objects in its path.

Sounds are received andconducted through the lower jaw tothe middle ear, inner ear, and thento hearing centers in the brain via

the auditory nerve.

Sensory reception

Electro-reception/magneto-reception

Some organisms (e.g., sharks) detect weak electric and

Muscle contractions in swimming animals

Water currents moving past inanimate objects

Earths own magnetic field

Sharks, skates and rays have an extensive network of tiny poresor pits on tops of their heads

Each pit connects to a flask-shaped jelly-filled ampulla ofLorenzini that is associated with the lateral line system

Prey detection

Navigation


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Tiger shark

Ampullae of Lorenzini

Threshold of sensitivity as low as 5nV/cm. That is 5/1,000,000,000 of a voltmeasured in a centimeter-long ampulla

Defence and camouflage

Strongest adaptations for defence are those related to achievingast orwar movement n t e water co umn

Camouflage nevertheless possible and useful even in openwaters of pelagic environment

Some species of squid may be transparent, but difficult for mostnekton when the body is highly muscular

Cryptic colouration

Countershading

Countershading

Common in nekton; in many fishes, whales and squid

Darker green, grey or blue pigmentation on dorsal surface Viewed from above, the pigmented upper surfaces blend with the darker

ac groun eow

White or silvery ventral surface Viewed from below, difficult to distinguish from ambient light coming from

the sea surface above

Protection against predators Confuse prey

Migration Most nekton start life as plankton

Spawning sites provide planktonic larvae with access to nursery

In certain species, spawning and adult feeding sites may differ,making it necessary to have migrations

Migration circuits involvescircular movements to:

Spawning grounds Nursery grounds Adult feeding grounds


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Generalised migration circuit of migratory nekton

Adult population

Nursing areaSpawning sitePassive drift as plankton

Nektonic invertebrates

Cephalopod molluscs

Squid, cuttlefish, octopus, nautilus

comprise a major component of biomass globally

Agile swimmers, with complex nervous system

Molluscan shell reduced or lost

In some regions, vast numbers of small squid (less than 1m inlength) form important intermediate links in epipelagic food chains

The giant squid (Architeuthis) lives in deep waters

Giant squid, caught off Spain, Sept.02

90kg, 11m long

Bathypelagic squidFunny squid


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Cephalopod molluscs

Movement:

Water taken into mantle cavity and expelled at high speedsthrough a nozzel-like siphon (jet propulsion)

Siphon can be aimed in any direction for rapid course

correc ons an or manoeuvrng purposes

Also use undulating fins on sides of mantle

Excellent camouflage.

Crustaceans Shrimps/prawns and crabs

Antarctic krill (Euphausia superba)

Some workers regard adult Antarctic krill (Euphausia superba) asnekton

Movement: Prawns and krill use abdominal paired appendages (pleopods) and tail

fan (uropods)

Certain crabs, use flattened appendages, usually lined with setae (hairs)

Swimming crabs (Portunidae)

Light produced bymesopelagic species closelymatches background light.

Why the cleareye shield?

Nektonic vertebrates


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Marine reptiles Marine iguanas and saltwater

crocodiles

Littoral animals - rarely venture out ofsight of land

Sea turtles

Nine species - largest is theleatherback or leathery turtle

Long migrations - return to land to layeggs

Sea snakes

Laterally flattened tails, which arepaddle-shaped

Highly venomous (closely related tocobras)

Blue-lipped sea krait

Fishes

Bony and cartilaginous fishes

(osteichthyes os-te-ich-they-ez &

chondrichthyes cond-drik-they-ez)

Holoepipelagic: spend entire lives in the epipelagic

Most abundant in surface waters of tropics and subtropics

Meroepipelagic: spend part of life cycle in the epipelagic

Includes: Species that live in epipelagic but move inshore or into

freshwater to spawn, e.g. salmon, capelin

Species that migrate to epipelagic only at certain times tofeed, e.g. deepwater fishes

Hard body

Fish swim either by:

body and/or caudal fin (BCF) movements - greater thrust and acceleration.

median and/or paired fin (MPF) propulsion - generally employed at slowspeeds, offering greater maneuverability and better propulsive efficiency.

Fins - thrust

High speed cruisingswimmers (e.g. tuna):

Thin caudal peduncle

Large crescent or forkedshape caudal fin

(maximise thrust)

Fast acceleration and high. .

grouper):

Thicker peduncle

Truncate or rounded tail


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Fins Stabilisation offish

Paired fins (pectoral andpelvic fins) - counter pitch

Pectoral fins also used forbraking and steering (cf.stiff, inflexible pectoral finsof sharks and tunas usedas hydrofoils)

Unpaired fins (dorsal and

ana ns - counter yawand roll

Body form - examples of specialists:

Flat fish (flounder, sole) - bottom specialist

Excellent camouflage

Laterally compressed but look dorso-ventrally flattened

One eye migrates to top as fish develops

Deep sea dragonfish(Stomiidaemelanostomias)

Deep water fish

OCEAN DEPTHS

EPIPELAGIC(0-200m) sufficientlight for photosynthesis

MESOPELAGIC(200-1000m) - dim lightinsufficient for

photosynthesis

BATHYPELAGIC(1000-4000m) - no light

ABYSSOPELAGIC(4000-6000m)

HADOPELAGIC(below 6000m) Deep Sea


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Decreasing light, primaryproductivity, temperature, food,current strength, environmentalfluctuations.

Each zone presents different environmental conditions andtherefore supports different species communities.

Declining abundance withdepth: 5-10x lessorganisms at 500m,10x less at 4000m.

- Diversity!??

Increasing nutrients,pressure.

Deep sea fish adaptations

Mostly small-sized (not enough food to grow very big!).

Common features of deep sea fishes:

- large eyes in the mesopelagic, small below that.- photophores- large mouths with hinged/extendable jaws- sharp teeth- broad diet- small size, lightweight (no scales or spines)

- ess musc e, no sw m- a er- soft, weak bones- loss of defensive spines/scales- inactive swimmers.

FOOD ACQUISITION

Food capture. Some species have very large mouths and can consume preylarger than themselves e.g. swallowers and gulpers. Stomachs expandable toaccommodate prey. No scales, usually black, up 1m long.

Swallower eel

anglerfish

anglerfish

swallower

gulper

bristlemouth

devilfishGulper eel

Aristostomias sp.

The Malacosteid

family

(Loosejaws)


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Marine mammals

Marine mammals

Marine Mammals fall into 3 orders:

r er ren a - mana ees ugongs. Order Carnivora - seals, sea-lions, walruses, otters, bears Order Cetacea - whales, porpoises, dolphins;

They can also be divided another way:

Oceanic: whales, seals and sea lions Other marine mammals such as manatees, dugongs (Sirenia)

and sea otters (Carnivora) occupy inshore waters at all times Walruses relax and mate on Arctic ice floes. Polar bears spend

most of their time on Arctic ice (and may never touch land duringtheir lifetime).

Monophyletic group with two extant familes:

Sirenians (order Sineria)US FWS

Trichechidae (manatees) 3 speciesDugongidae (dugongs) 1 species

Wholly aquatic Once heavily hunted

US FWS ps are arge an mo e The only herbivorous marine mammal Closely related to elephants (and other sub-ungulates) Now vulnerable to habitat loss and propellers, etc.

'discovered in 1741

Georg Wilhelm Steller,physician, and VitusBering explorer.


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Pinnipeds (Order Carnivora, Suborder Pinnipedia)Latin words 'pinna' ('fin', 'flap' o r'wing') and 'pedis' ('foot'),

Or Order or Superfamily

Most found in polar, sub-polar and temperate waters.

Share their time between the water and the land (or ice)

On land they mate, rest, give birth, and moult.

They are streamlined - nostrils close underwater

Lots of blubber

Underwater, their heart rate slows down and arteries squeeze shut

so that only the sense organs and nervous system get the normal

blood flow

Harp SealPhoca groenlandica

South African andAustralian Fur Seals

Arctocephalus pusillus

Northern Fur SealCallorhinus ursinus

Hooded SealCystophora cristata

Leopard SealHydrurga leptonyx

Crabeater Seal

60-80,000 killed for fur

30,000 killed for fur

Lobodon carcinophagus California, Galpagos andJapanese Sea LionsZalophus californianus

seals vs. sea lionsSea lionsFamily OtariidaeExternal ear flapsRotate hind flippersSwim with front flippers

Family PhocidaeNo external ear flapsCannot rotate rear flippers

Swim with rear flippers

NOAA

NOAA

Family Odobenidae 1 species Odobenus rosmarus

Two subspecies: the North

The walrus

, ,North Pacific walrus. Bothare usually found above

58 degrees north.

No external ear flaps but swims with rear flippers

NOAA

Tusks are actually canine teeth (up to 1m long)

Males ~ 1500 kg, females ~ 850 kg

Benthic feeders - on mollusks (clams) especially


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Sea otters and polar bears (Order Carnivora)

Sea otters (Enhydra lutris)

Smallest of the marine mammals (~45kg) Coastal - max 4 km offshore Often associated with kelp beds (hold on!) Single pup birth in water Rest in single-sex rafts (can be 100s of otters)

Cute!

NOAA

NOAA

polar bear (Ursus maritimus)

Found in Arctic circle, semi-aquatic Biggest land predator To of food chain feed on seals Run at speeds close to 65 km/hr Can swim > 100 km

Also cute!

NOAA

US FWS

Order Cetacea (whales & dolphins)

Mostly marine Includes whales, dolphins, and porpoises

Found in all the world's oceans

NOAA

Nostrils are located on the top of the head

Specialized forelimbs = flippers

Hind limbs and pelvis are very reduced

As with pinnipeds, heart rate and blood flow alter when diving.

Order Cetacea (whales & dolphins)

Suborder Mysticeti (baleen whales) 11 species

Mysticeti (from the Greek words Mystaxmeaning "moustache" and Ketosmeaning sea monster").

Baleen whales capture preyitems by straining water

plates fixed to the upper jaw.These act as filters, collectingfood items.


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Suborder Odonticeti (toothed whales) 77 species

Chinese lake dolphinFamily Platanistidaeriver dolphins. Only 5 species, e.g. Beiji (orChinese lake dolphin) now extinct (?) because the Yangtze River hasbecomes less livable for both prey items and predators.

Beaked whales are deep-water,

medium-sized, deep-diving speciesthat are not often seen (speciesusually known from only a fewspecimens).

Family Stenidae. 16

species in all includingthe rough-toothed

Northern bottlenosed whale

dolphin, spotted dolphin,long-snouted spinnerdolphin, etc.

spotted dolphin

Family Delphinidae (25 species) includes common dolphin, Risso'sdolphin, bottlenose dolphin etc. also killer whales and pilot whales.

bottlenose dolphin

Dolphin vs. Porpoise

DolphinLong, sleek bodyWave-shaped dorsal fin

PorpoisePlump bodyTriangular dorsal fin

os rumConical teethLonger life span

Blunt snoutSpade-shaped teethShorter life span

Family Physeteridae, Genus Physeter: speciesmacrocephalus(sperm whale) and Genus Kogia:(pygmy sperm whale & dwarf sperm whale).

What is ambergris?

Left tooth or twotwisted upper teeth?

Family Monodontidae SpeciesMonodon monoceros(narwhal)are highly vocal with distinctive

sperm whale

belugaorn, up o m n eng .

Genus DelphinapterousSpeciesDelphinapterous leucas(whitewhale or beluga).

narwhal

Three main types of feeding behaviour

1. Rorqual whales feed by gulping lots of water containingcrus aceans, sc oo ng s es, sma squ e c. roa(ventral) grooves (pleats) expand that maximizes the waterand food capacity. The jaws are brought together, the throat

grooves contract, and the tongue is pressed up, forcing thewater to drain out the sides and front of the mouth.


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2. Gray whales also have throat grooves (but not so many)

and filter food through their baleen plates in a similar wayto rorquals (except they suck more!). However, first, greywhales dive to the bottom and suck in water, mud, and food(feed on gammarid amphipods, molluscs, crabs and

polychaete worms).

NOAA

3. Right whales swim at or near the surface of the water and

strain the water for small zooplankton such as copepods.Water and food enter the mouth through a gap in the front

baleen plates. Water exits through the sides of the mouth

and food is caught on the matted baleen fringes inside.

NOAANOAA

Humpbacks feeding (bubble corralling!)

Northern right whale feedingGrey whale in aquarium!

Plates on right often worn down

3 families (3 types of feeding)

Family Balaenopteridae (rorquals) are lunging feeders. This groupconsists of the Genus Balaenoptera, i.e. minke (pronounced minkee")w a e, se w a e (pronounce say ) , ry es w a e (pronounce"broodus") , blue whale, fin whale, plus the Genus Megaptera:humpback whale.

The grey whale is on its own in the Family Eschrichtidae, GenusEschrichtius, Species robustus

Famil Balaenidae: cruisin continuous filter feeders. This rouconsists of the Genus Balaena: the bowhead whale, and the GenusEubalaena(right whales): northern right whale, southern right whale,and the pygmy right whale.


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Baleen (or whale-bone) was used in19th century corsetmaking and demand

whaling industry.

Whale-bone traders

Probably right whale plates (2-4m)

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LSM3254_Lecture 9 the Open Ocean