the open ocean chapters 6, 10, 12, 17. regions of the open sea vertical zonation depends on...

The Open Ocean

Chapters 6, 10, 12, 17

Regions of the Open Sea

• Vertical zonation depends on penetration of sufficient sunlight to support photosynthesis– photic zone—receives enough light for

phytoplankton to survive– aphotic zone—light rapidly disappears until

the environment is totally dark

• Epipelagic zone—the location of pelagic animals in the upper 200 m of the ocean

Life in the Open Sea

• Classification of plankton– taxonomic groups

• seston—particles suspended in the sea• tripton—non-living seston• phytoplankton—primary producers• zooplankton—heterotrophic eukaryotic microbes

that float in the currents• bacterioplankton—archaeans and bacteria• viriplankton—free viruses (the most abundant

plankton of all)


• Classification of plankton (continued)– functional groups

• akinetic—plankton that don’t move at all• kinetic—plankton that can move

– size• original scheme (based on collection method):

macroplankton, microplankton, nanoplankton• newer classifications: femtoplankton, picoplankton,

mesoplankton, macroplankton, megaplankton


• Classification of plankton (continued)– life history

• holoplankton—organisms that are planktonic throughout their lives

• meroplankton—planktonic larvae that will grow into non-planktonic organisms


• Classification of plankton (continued)– spatial distribution

• neritic—distinguished by presence of meroplankton and diverse diatoms

• oceanic—less diverse diatoms or invertebrate meroplankton; more salps, larvaceans, arrowworms and sea butterflies

• neuston—plankton that life close to the water’s surface

• pleuston—plankton which break the surface of the water with their gas bladders or bubbles


• Patchiness in the open sea– plankton occur in patches (localized

aggregations), often around upwellings– micropatchiness occurs throughout the photic

zone when marine microbes become attached to particles of organic matter, especially marine snow

• marine snow—strands of mucus secreted by zooplankton that form translucent, cob-webby aggregates


• Plankton migrations– many open-ocean zooplankton migrate from

the surface to nearly 1.6 km deep each day• provides access to phytoplankton in the photic

zone• reduces predation by plankton-eating fishes in the

epipelagic zone

– deep scattering layer—a mixed group of migratory zooplankton and fishes that are densely packed

Plankton

• Diatoms

• Dinoflagellates

• Foraminiferans

Plankton

• Protozoans


• Megaplankton– cnidarian zooplankton

• largest plankton are jellyfishes


• Megaplankton– molluscan zooplankton

• pteropods (sea butterflies) have a foot with 2 large wing-like projections and a greatly reduced (thecosome pteropods) or absent (gymnosome pteropods) shell

• pteropod ooze—calcareous sediments formed from shells of dead thecosome pteropods

• purple sea snails produce bubble rafts• nudibranchs


• Megaplankton (continued)– urochordates

• salps• pyrosomes—close relatives of salps that produce

colonies name up of hundreds of individual animals joined to form a hollow cylinder up to 14 m long

• larvaceans


• Nekton– invertebrates

• squids

– fish• billfish—species with an enlongated upper jaw (bill)

and no teeth• tuna• ocean sunfish• sharks• manta rays

Fishes

• Fishes are vertebrates—animals that possess vertebrae, a series of bones or cartilages that surround the spinal cord and help support the body

• Primitive fishes lacked paired fins and jaws

• Adaptation of jaws and paired fins allowed fish to more efficiently obtain food

Jawless Fishes

• Class Myxini (hagfish) and class Cephalospidomorphi (lampreys)

• Lack both jaws and paired appendages

• Have skeletons of cartilage (no bone)

• Lack scales

• Hagfish also lack vertebrae (some scientists consider them invertebrates)

Cartilaginous Fishes

• Class Chondrichthyes– e.g. sharks, skates, rays, chimaeras

• Skeleton of cartilage• Possess jaws and paired fins• Have placoid scales• 2 major groups:

– holocephalans (chimaeras or ratfish)– elasmobranchs (2 body forms: streamlined or

dorsoventrally flattened)

Sharks

• Excellent swimmers with streamlined bodies– swim with powerful, sideways sweeps of the

caudal fin (tail)– heterocercal tail—caudal fin in which the

dorsal lobe is longer than the ventral

• Males have claspers—modified pelvic fins which transfer sperm from the male to the female

Sharks

• Maintaining buoyancy– sharks sink if they stop swimming– large livers produce squalene—an oily

material with a density less than seawater– squalene offsets the shark’s higher density to

help maintain buoyancy

Shark Sensory Systems

• Vision– a clear nictitating membrane covers and protects

each lidless eye– many species seem to have color vision

• Olfaction– more important than vision – almost 2/3 of the

shark’s brain cells are involved in processing olfactory information

– sharks are sometimes referred to as “swimming noses”


• Lateral line system– consists of canals running the length of the

animal’s body and over the head– canals open to the outside at regular intervals,

allowing free movement of water over the neuromasts (sensory receptors) within

– neuromasts detect vibrations in the fluid which alert the shark to movements in the water, possibly made by prey animals


• Ampullae of Lorenzini– organs scattered over the top and sides of the

animal’s head – sense electrical currents in the water

Digestion in Sharks

• Blade-like, triangular teeth in the mouth grasp prey and tear off chunks

• Food is swallowed whole (sharks cannot move their jaws back and forth to chew)

• Food passes through stomach to a short intestine containing a spiral valve– spiral valve—a structure which aids in

absorption by slowing the movement of food and increasing the surface area

Osmoregulation in Sharks

• Maintain an internal solute concentration > or = to the seawater– retain large amounts of nitrogenous wastes,

mostly urea and trimethylamine oxide (TMAO)

• Gills and rectal gland (a large structure that empties into the intestine) work to excrete excess sodium chloride

• Kidney excretes other salts

Reproduction in Sharks

• Sperm produced in paired testes are transferred to the female through grooves in the claspers

• Oviparity– most primitive mode– eggs are laid outside the body and the

embryos develop in a protective case– e.g. whale sharks, bullhead sharks


• Ovoviviparity– most common mode– eggs hatch within the mother’s uterus but no

placental connection is formed• young are nourished by yolk from the egg

– e.g. basking sharks, thresher sharks, saw sharks, sand tiger


• Viviparity– most recent mode to evolve– either the young directly attach to the

mother’s uterine wall or the mother’s uterus produces “uterine milk” that is absorbed by the embryo

– e.g. requiem sharks, hammerhead sharks

Skates and Rays

• Have flattened bodies adapted to a bottom existence

• Greatly enlarged pectoral fins that attach to the head

• Reduced dorsal and caudal fins• Eyes and spiracles (openings for the passage

of water) on top of the head• Gill slits on the ventral side• Specialized pavement-like teeth are used to

crush prey (e.g. invertebrates)

Differences between Skates and Rays

Rays: swim by moving fins up and down

Skates: create a wave from the forward to backward fin edges

streamlined tails with venomous barbs or spines

fleshier tails with small fins and no spines

larger size smaller size

ovoviviparous mostly oviparous

Defense Mechanisms

• Electric rays have electric organs that can deliver up to 220 V

• Stingrays have hollow barbs connected to poison glands– treatment for stingray wounds: submerge in

hot water to break down protein toxin

• Sawfishes and guitarfishes have a series of (non-venomous) barbs along their pointed rostrums

Bony Fishes

• Class Osteichthyes

• Very diverse 25,000 species

• Most forms have: swim bladder (or lung), bone, bony scales, and fin rays

• 2 major lineages:– lobefins (subclass Sarcopterygii) –

coelacanths, freshwater lungfish– ray-finned fishes (subclass Actinopterygii)

Ray-Finned Fishes

• 2 major groups:– subclass Chondrostei – primitive forms with

heterocercal tails, primarily cartilage skeleton, ganoid scales

• ganoid scales—thick, heavy scales which give the fish an armored appearance

Ray-Finned Fishes

– subclass Neopterygii – homocercal tails, cycloid or ctenoid scales, more maneuverable fins

• homocercal tails—tails with dorsal and ventral flanges nearly equal in size; vertebral column usually does not continue into the tail

• cycloid & ctenoid scales—scales that are thinner and more flexible; less cumbersome for active swimmers

Ray-Finned Fishes

• Possess unpaired median fins and paired fins, providing better control of movements

• Median fins consist of 1 or more dorsal fins, caudal fin, and usually anal fin– help maintain stability while swimming

• Paired fins consist of pectoral and pelvic fins– both used in steering– pectoral fins also help to stabilize the fish

Body Shape

• Fusiform body shape—streamlined shape with a very high and narrow tail– efficient movement for active swimmers

Body Shape

• Laterally compressed or deep body– allows

navigation through grass or corals

Body Shape

• Depressed or flattened bodies– bottom-dwelling fishes

Body Shape

• Globular bodies, enlarged pectoral fins– appropriate for sedentary lifestyle

Body Shape

• Long, snake-like bodies, absent or reduced pelvic and pectoral fins– useful for burrowing, living in tight spaces

Fish Coloration

• 2 basic types of fish colors:– pigments (biochromes)– structural colors

• Pigments—colored compounds found in chromatophores – chromatophores—irregularly-shaped cells, usually

appearing as a central cell body with radiating processes

– fish can alter color by moving pigments between the central core and processes

Fish Coloration

• Structural colors—colors produced by light reflecting from crystals located in specialized chromatophores– iridophores—chromatophores used to

produce structural colors– colorless, relatively immobile crystals produce

mirror-like silver or iridescence

Fish Coloration

• Countershading is seen in open ocean fish– obliterative countershading—coloration in

which the back (dorsum) is dark green, dark blue or gray, and the shades grauate on the sides to the belly’s pure white

• Disruptive coloration—background color of the body is usually interrupted by vertical lines; may be an eyespot– more difficult for predators to see the fish

Fish Coloration

• Cryptic coloration—coloration which blends with the environment– used for camouflage

Fish Coloration

• Poster colors—bright, showy color patterns– may advertise territorial ownership, aid

foraging individuals to keep in contact, or be important in sexual displays

– aposematic (warning) coloration—bright coloration to warn predators that the fish is too venomous or spiny to eat

Buoyancy Regulation

• Most fish use a swim bladder—a gas-filled sac that helps offset the density of the body and regulates buoyancy– the fish can adjust the amount of gas in the

swim bladder to maintain depth– gas is added as the fish descends and

removed as it ascends

Buoyancy Regulation

• 2 methods for adjusting the amount of gas in the swim bladder– gulping air from the surface or spitting air out as

needed– gas gland—a specialized gland which fills the

swim bladder from gases dissolved in the blood• fish with a gas gland empty gas from the swim

bladder through diffusion into the blood

• Active swimmers do not have swim bladders, and must keep swimming

Nervous System and Senses

• Nervous system consists of: brain, spinal cord, peripheral nerves, and various sensory receptors

• Olfaction– olfactory pits—blind sacs opening to the

external environment that contain olfactory receptors

– size varies with dependence of fish on olfaction


• Taste and hearing– taste receptors may be located on the surface

of the head, jaws, tongue, mouth and barbels (whisker-like processes about the mouth)

– bony fishes have a lateral line system for detecting movement in the water

– ears are internal and have a detection range of 200 to 13,000 hertz

• human range = 20 to 20,000 hertz


• Vision– no eyelids– usually don’t need to adjust pupil size

because of the low quantity of light– entire lens moves back and forth to focus– eyes are usually set on the sides of the head– most have monocular vision– shallow-water species can perceive color

Feeding Types

• Carnivores (e.g. pufferfish, groupers)– most bony fishes are carnivores– prey are usually seized, swallowed whole

• chewing would block water flow past gills

• Herbivores (e.g. surgeonfish, parrotfish)– feed on a variety of plants and algae– teeth often broad and flat with a sharp edge to

scrape food from surfaces– may have gizzard-like stomach to grind vegetable

matter

Feeding Types

• Filter feeders (e.g. anchovies, larvae)– feed on plankton– typically use gill rakers—projections from the

gill arches which filter phyto- and zooplankton from seawater

– most travel in large schools, and are an important food source for larger carnivores

Adaptations to Avoid Predation

• Many exhibit elaborate camouflage• Pufferfishes and porcupinefish inflate their

bodies to deter predators• Flying fishes use enlarged pectoral fins to

glide through the air and escape• Pearlfish hide in other organisms• Parrotfish secrete a mucus cocoon• Surgeonfish are armed with razor-sharp

spines

Adaptations to Avoid Predation

• Clingfishes use a sucker to attach to rocks so predators can’t dislodge it

• Triggerfish projects spines to deter predators or wedge itself into cracks

• Scorpionfish and stonefish have venom glands for self-protection

Reproduction in Bony Fishes

• Gonads are paired structures suspended from the roof of the body cavity by mesenteries (membranes)

• Sperm and eggs pass to the outside through ducts, except in salmon

• Egg and sperm development is usually seasonal

• Variation in the level of pituitary and gonadal hormones controls the reproduction process


• Pelagic spawners (e.g. tuna, wrasses)– release vast quantities of eggs into the water

for fertilization by males– fertilized eggs drift with the currents– no parental care

• Benthic spawners (e.g. smelt)– non-buoyant eggs with large yolks– no parental care– pelagic or benthic embryos/larvae


• Brood hiders (e.g. grunion)– species that hid their eggs in some way but

exhibit no parental care

• Guarders (e.g. damselfish)– species that care for their offspring until they

hatch and, frequently, through their larval stages

• Bearers (e.g. jawfish, seahorses)– species that incubate their eggs until they hatch

(in the mouth or a special pouch)


• Hermaphroditism—individuals have both testes and ovaries at some time in their lives– occurs in at least 14 bony fish families– synchronous—possessing functional gonads

of both sexes at one time– sequential—changing from one sex to another

• protogyny—changing from female to male• protandry—changing from male to female


• Nekton (continued)– reptiles

• yellow-bellied sea snakes

– birds and mammals• penguins• whales

Characteristics of Marine Mammals

• Class Mammalia• Most have an insulating body covering of

hair• Homeothermic

– allows activity day and night, and adaptation to a wide range of habitats

• Mothers feed their young with milk– mammary glands—special glands in the female

that secrete milk

Characteristics of Marine Mammals

• Most marine mammals are placental mammals—animals that retain their young inside their body until they are ready to be born– placenta—an organ present only during

pregnancy that sustains the young

• Feed at various trophic levels

Sea Otters

• Have thick fur with an underlying air layer for insulation (instead of blubber)

• Short, erect ears

• Dexterous 5-fingered forelimbs

• Well-defined hind limbs with fin-like feet

• Usually stay within a mile of shore, near coastal reefs and kelp beds

Sea Otters

• Females normally give birth to 1 pup on shoreline rocks, and it soon follows its mother into the sea

• Consume nearly 25% of their body weight in food each day– eat sea urchins, molluscs, crustaceans, some

species of fish

• Diurnal, gregarious, vocal and playful• Nearly hunted to extinction for fur

Pinnipeds: Seals, Sea Lions, and Walruses

• Suborder Pinnipedia (e.g. seals, elephant seals, sea lions, walruses)– pinniped—”feather-footed”

• Have 4 limbs like terrestrial animals, but are more at home in the water

• Come shore to give birth and molt– most also mate on shore, and some sleep on

land or ice floes to avoid entirely aquatic predators

Pinnipeds: Seals, Sea Lions, and Walruses

• Eat fish, invertebrates; some eat other homeothermic animals

• Eaten by sharks, killer whales and humans

Pinniped Characteristics

• 3 families:– eared seals (Otariidae)– true seals (Phocidae)– walruses (Odobenidae)

• Eared seals have small external ears and swim using their forelimbs

• Phocids (true seals) lack external ears and swim with a sculling movement of their hind flippers

Pinniped Characteristics

• Walruses swim with a combination of the 2 methods

• Pinnipeds have spindle-shaped bodies

• Many have several thick layers of subcutaneous fat

• Round is carried on a distinct neck

• Large brains, well-developed senses

• 2 pairs of limbs are modified into flippers

Swimming and Diving

• Fast swimmers and expert divers

• Adaptations for diving– exhale before diving to decrease buoyancy– metabolism slows by 20% and heart rate

decreases while under water– blood redistributed to direct oxygen to vital

organs such as the brain and heart

• Weddell seals and northern elephant seals known for deep diving

Reproduction in Pinnipeds

• Most congregate on well-established breeding beaches to mate/give birth

• Some species are polygynous—bulls establish harems of 15 or more females

• Males arrive to establish territories; females arrive, give birth to pups, then mate again

Reproduction in Pinnipeds

• Gestation = 9-12 months

• Lactation period (length of time pups nurse) depends on species and habitat– coldest habitats = shortest lactation– nursing stresses the mother and she loses

weight– some breed on pack ice, and must wean pups

before it breaks up and becomes dangerous to the pups

Eared Seals

• Sea lions– e.g. California sea lion, the intelligent trained seal

seen in zoos and circuses– highly social; congregate when on shore

• Fur seals– distinguished from sea lions by thick, wooly

undercoats– coats are prized in the fur market, so hunting is

limited to avoid decimating the population of fur seals

Phocids, or True Seals

• Forelimbs are set closer to the head and smaller than the hind limbs– less adapted to life on land– move on land by dragging their bodies

• Most congregate during breeding season; males establish territories but mate with only 1 female

• Most abundant: crabeater seal, which actually eats plankton such as krill


• Harbor seals are a familiar type

• Harp seal pups have a white coat, and are thus prized in the fur market


• Leopard seal is the only phocid that eats homeothermic prey, including other phocids, penguins, and seabirds


• Elephant seals are the largest, and bulls have a unique proboscis that amplifies their roar and attracts mates

Walruses

• Lack external ears but have a distinct neck and hind limbs that can be used for walking on land

• Canine teeth of the upper jaws of males have developed into tusks– used to fight with other males or hoist the

animal onto ice floes

• Typical family group = 1 dominant bull with a harem of up to 3 females and 6 calves of various ages

Walruses

• Reproduction– 11-month gestation period– 1 or 2 calves stay with the mother until they are

4 or 5 years old– old bulls sometimes kill young

• Found in the Arctic region• Eat fishes, crustaceans, molluscs and

echinoderms• Eskimos are allowed to hunt them for meat,

but not for their tusks

Sirens: Manatees and Dugongs

• Order Sirenia (sirenians)

• Confined to coastal areas and estuaries of tropical seas

• Similarities to whales– streamlined, practically hairless bodies– forelimbs that form flippers, tail flukes– vestigial pelvis without hind limbs

• Completely aquatic

• Gentle and often trusting of humans

Dugongs

• Strictly marine

• Live in coastal areas of Indian Ocean

• Feed on shallow-water grasses

• Dugongs are distinguished anatomically from manatees by:– larger heads– shorter flippers– notched tail

Manatees

• Inhabit both the sea and inland rivers and lakes

• Have smaller heads, longer flippers than dugong, and rounded tails

• Mate and give birth under water– male remains with female after breeding

• Strict vegetarians that consume large amounts of shallow-water plants

• Motorboat propellers are the greatest danger to northern manatees

Steller’s Sea Cow

• This Arctic sirenian is now extinct• Species was first observed and recorded by

Georg Wilhelm Steller• After his expedition brought furs from the

Commander Islands, this area developed a reputation for furs which attracted hunters

• The hunters used Steller’s Sea Cow as a food source, and hunted the species to extinction

Cetaceans: Whales and their Relatives

• Mammals most adapted to life at sea

• E.g. whales, dolphins, porpoises

• Cetaceans have fascinated humans for centuries

• Cetaceans have frequently appeared in art and literature

General Characteristics of Cetaceans

• Thought to have evolved from terrestrial carnivores (now extinct)

• Bodies closely resemble those of fishes and are very streamlined– blowhole—nostril at the top of the head– uniformly thick layer of subcutaneous blubber– streamlining of body results in lack of neck,

inability to move head separately– internal ears with wax plugs

General Characteristics of Cetaceans

• Bodies closely resemble those of fishes and are very streamlined (continued)– essentially hairless, except for a few hairs on the

head– lack of sweat glands conserves water– forelimbs modified into stabilizing flippers– tail composed of flat flukes composed of dense

connective tissue is the main organ of propulsion

– countercurrent circulatory system with cold blood directed to un-insulated flippers conserves heat

Adaptations for Diving

• Prior to dive, a whale inhales an enormous breath, oxygen is rapidly transferred to blood, and the whale exhales to reduce buoyancy

• Proportionately large lungs with many alveoli—small air sacs– increases internal lung surface area exposed to

blood vessels– allows for more efficient diffusion of gases into

and out of blood


• Lungs and rib cage structured to collapse easily upon descent– contain little air during a dive– animal avoids problems of compression and

decompression while diving/surfacing

• During a dive:– metabolism and heart rate decrease– blood is preferentially shunted to vital organs

and tissues (e.g. brain, spinal cord)


• Medulla oblongata is less sensitive to CO2 levels in blood– can hold breath without urge to breathe

• Large amounts of hemoglobin and myoglobin– hemoglobin—molecule in red blood cells

responsible for carrying oxygen– myoglobin—molecule in muscle tissue that is

a reservoir of oxygen for muscle activity


• Muscles less sensitive to lactic acid– lactic acid—a waste produced during vigorous

or extended muscle activity in the presence of insufficient oxygen

• Exhalation of mucus from blowhole upon surfacing helps eliminate nitrogen from inhaled air, preventing the bends– the bends—condition in which nitrogen gas

dissolved in blood comes out of solution and forms gas bubbles


• Water is prevented from entering respiratory passages– larynx opens into the nasal chambers instead

of the back of the throat– cetaceans can open their mouths under water

without food or water entering respiratory passages

Reproduction and Development

• Many travel in pods (groups) of adults and young

• Usually bear 1 offspring at a time

• Nursed on extremely rich milk– 40-50% fat, 10-12% protein– infant grows rapidly– can produce sufficient body heat until blubber

layer has developed

Types of Whales

• 2 suborders– Mysticeti – baleen whales– Odontoceti – toothed whales

• Baleen whales lack teeth, and filter food from the water using baleen– largest whales are of this type

• Toothed whales feed on larger prey– e.g. dolphins, killer whales

Baleen Whales

• Enormous plates of baleen– each plate has an elongated triangular shape

and is anchored at its base to the gum of the upper jaw

– composed of keratin—a tough protein—in fibers fused except at the inner edge, where they form a fringe

– hundreds of plates form a tight mesh– used to capture plankton, especially krill, and

fish

Baleen Whales

• Whale feeds by swimming open-mouthed through the water, then straining out water through baleen– bubble net—a ring of bubbles blown by a

humpback whale to trap krill near the surface for collection

• Baleen is protected by the underlip when the whale is not feeding

Baleen Whales

• Right whales (family Balaenidae)– lack dorsal fins and grooves on throat and

chest– name derived from identification of these

whales as the “right whales” for hunting– one species, the Greenland or bowhead

whale, is the rarest of all whales

Baleen Whales

• Rorquals (family Balenopteridae)– have dorsal fin and ventral grooves

• ventral grooves allow the throat to expand while the animal is feeding

– slender, streamlined, fast swimmers– blue whale is the largest whale– fin whale is second largest– humpback whale has hump on its back, bosses

(bumps) on its snout, and very long pectoral fins

Baleen Whales

• Gray whale (Eschrictius gibbosus)– only eastern Pacific population survived after

western Pacific and Atlantic populations were hunted to extinction

– migrate from summer feeding grounds in Bering Sea to waters off Baja California to mate and give birth

– referred to as mossback whales owing to large accumulations of barnacles on their skin

Toothed Whales

• Sperm whales (Physeter macrocephalus)– 3rd largest animal with massive blunt snout– have a series of humps on the rear third of the

body, no real dorsal fin– aggressive attackers of squid and fish– polygynous – males accompanied by several

females– named for spermaceti—an oily, wax-like

substance in the animal’s head

Toothed Whales

• Sperm whales (continued)– ambergris—a digestive product; a secretion

thought to function in protecting the enormous digestive system from undigested squid beaks and cuttlefish cuttlebone

– spermaceti was sought as a high-grade wax; ambergris, as a base for perfumes

Toothed Whales

• White whales (family Monodontidae)– beluga whales are unique for their white color,

are found in northern polar seas– male narwhals have a tusk developed from 1

of 2 tooth buds; narwhals also inhabit Arctic waters

Toothed Whales

• Porpoises (family Phocaenidae)– porpoises have a rounded head with no beak

(dolphins have a beak)– harbor porpoises are small cetaceans known

for great intelligence, and have a wide distribution in the North Atlantic

– Dall’s porpoise is perhaps the first animal to be protected by law – Europeans once considered it a rare delicacy

Toothed Whales

• Dolphins (family Delphinidae)– collectively referred to as delphinids– common dolphin has a definite beak separated

from the snout by a groove; known for encircling and following ships

– bottlenose dolphins are used in research on cetacean intelligence, and as performing animals at aquariums

– orca (killer whale) is the largest dolphin; only cetacean that eats homeothermic prey (e.g. seals, sea lions, penguins)

Toothed Whales

• Dolphins (continued)– pilot whales have a globular head, projecting

forehead, and muzzle that forms a small beak• known for beaching themselves in large numbers

Echolocation

• Ears are modified to receive a wide range of underwater vibrations

• Echolocation allows cetaceans to distinguish and hone in on objects

• Dolphins emit clicking sounds– orientation clicks—low-frequency clicks that give

the animal a general idea of its surroundings– discrimination clicks—high-frequency clicks that

give the animal a precise picture of a particular object

Echolocation

• No vocal cords; sounds are produced by a ring of muscles in the larynx, which allows control of air flow

• Sounds are directed by being focused in the melon– melon—an oval mass of fatty, waxy material

located between the blowhole and the end of the head

• Clicking sounds bounce off objects; echoes picked up by sensitive areas on the lower jaw

Echolocation

• Echoes provide 4 types of information:– direction from which echo is coming– change in frequency– amplitude– time elapsed before the sound returns

• This reveals object’s range, bearing, size, shape, texture and density

• Traveling dolphins move their heads side to side and up and down, scanning for objects

Survival in the Open Sea

• Remaining afloat– swimming methods

• flagella, cilia, and jet propulsion– dinoflagellates, coccolithophores, silicoflagellates, and

blue-green bacteria swim with flagella– tintinnids, ciliates, and larvae use cilia– jellyfish, siphonophores, salps, and squid use jet

propulsion

• appendages– appendicular swimmers—organisms that use

appendages to swim (e.g. copepods, pteropods)

• undulations of the body– e.g. arrowworms, larvaceans, worms, fish, whales


• Remaining afloat (continued)– reduction of sinking rates

• frictional drag – can be increased by decreasing volume, flattening the body or increasing body length

• buoyancy – increased by storage of oils, increasing water content of the body, exchange of ions, and use of gas spaces


• Avoiding predation– benefit of being less conspicuous

• countershading—having dorsal surfaces that are dark blue, gray or green and ventral surfaces that are silvery or white

• many planktonic species are nearly transparent


• Avoiding predation– safety in numbers

• animals such as siphonophores (e.g. Portuguese man-of-war) increase chances of survival by forming colonies

Ecology of the Open Sea

• Open sea is a pelagic ecosystem—one in which the inhabitants live in the water column

• Small, primary producing organisms have a relatively high surface area– allows them to absorb more nutrients from

surrounding seawater


• Productivity– all higher forms of life rely on plankton– water near the surface receives plenty of

sunlight, but few nutrients from land or the sea bottom (except in rare areas of upwelling)

– phytoplankton productivity is low in tropical waters

• arrangement of water in layers with little circulation between prevents nutrients from being brought from the sea bottom


• Food webs in the open sea– dissolved and particulate organic matter

• phytoplankton release photosynthetic products as DOM into surrounding seawater

• heterotrophic bacteria recycle DOM as they eat it and then are eaten by nanoflagellates

• bacterial loop—process in which bacteria metabolize DOM and return it to the water in an inorganic form available to phytoplankton

• lysis of bacteria by viruses releases DOM and particulate organic matter (POM)


• Food webs in the open sea (continued)– efficiency of open-ocean food webs

• surprisingly efficient• entire phytoplankton or bacterial production may

be consumed daily• conversion rates (food to biomass) may be high• food webs may have food chains with 5-6 links• few large animals are supported away from

upwelling areas because of limited rate of primary production and declining conversion efficiency along the food chain

the open ocean chapters 6, 10, 12, 17. regions of the open sea vertical zonation depends on...

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open oceanchapters

open seavertical zonation

abundant plankton of

sea butterfliesneustonplankton

marine microbes

reduced thecosome pteropods

invertebrate meroplankton