UNIT ENERGY IN 6 THEOCEAN - tyburnscience.educationtyburnscience.education/MarineBio/18.pdf · currents have kinetic energy, the energy of motion. Waves crashing on a beach produce

UNIT

6ENERGY INTHE OCEAN

The ocean is a storehouse of energy. Waves and

currents have kinetic energy, the energy of

motion. Waves crashing on a beach produce sound

energy. Hot water boiling up from hydrothermal

vents on the seafloor gives off heat energy. Energy

is the ability to do work, and work involves move-

ment. For example, when a wave crashes on the

beach, work is done because water is moved.

Energy is interchangeable; that is, one form

can change into another form. When sunlight

strikes the ocean surface, some of its energy is

absorbed by the water and changed into heat.

And some of the light energy is absorbed by

marine plants and changed into the chemical

energy stored in glucose. In this unit, you will

learn how energy, temperature, and pressure

affect the ocean environment and the various

life-forms within it.

CHAPTER 18 Temperature and Pressure

CHAPTER 19 Light and Sound in the Sea

CHAPTER 20 Tides, Waves, and Currents

441

When you have completed this chapter, you should be able to:

DESCRIBE the relationship of kinetic energy to heat in the sea.

DISCUSS the effects of temperature and pressure on divers and marineorganisms.

EXPLAIN how aquatic organisms regulate osmotic pressure.

If you ever have swum in the ocean, you know that the water feelscooler than the air above it. And if you have been in a lake, you prob-ably noticed that the deeper you swim the cooler the water feels.Temperature is an important factor that affects properties of oceanwater. Differences in temperature affect water density, the mixing ofwater layers, and the kinds of organisms that can live in different partsof the ocean. Temperature is a measure of the average kinetic energypossessed by the particles of a substance. In the ocean, temperaturesvary from below 0°C to above 100°C.

As soon as you dip below the ocean’s surface, you feel pressure onyour face and body because water exerts pressure. Pressure is definedas the force per unit area. When you swim underwater, you can feelthe water pressure all around you. Underwater pressure increases at apredictable rate with increasing depth.

Most aquatic organisms cannot survive the low temperatures andhigh pressures found in the great ocean depths. Humans certainly can-not withstand such conditions without the use of special equipment.However, some marine animals are equipped to live under extreme pres-sure and cold temperatures. In this chapter, you will study how tempera-ture and pressure vary in the ocean and how they affect living things.

442

18.1Kinetic Energyand Heat in the Ocean

18.2TemperatureVariations in the Ocean

18.3PressureUnderwater

18.4Osmotic Pressure andAquatic Adaptations

Temperature and Pressure1818

18.1 KINETIC ENERGY AND HEAT IN THE OCEAN

Due to the way that the sun heats Earth, you will recall, ocean sur-face temperatures at the equator are warm, whereas water tempera-tures at the poles are very cold. Water is warm when its moleculeshave more kinetic energy, and cold when its molecules have lesskinetic energy. Kinetic energy is the energy a substance has due tothe motion of its molecules. When the kinetic energy of a substanceis transferred to another substance, it is called heat. In the ocean,the greatest amount of heat is found at the hydrothermal vents,where temperatures of 350°C and higher have been recorded. Thelowest amount of heat is found at the poles, where the water tem-perature is at, or slightly below, the freezing point.

You may also remember learning that the ocean takes longer toheat than the land does because it has a higher specific heat, or heatcapacity. The water also takes longer to cool. As a result, there is agreat difference in heat capacity (also called heat storage ability)between the ocean and the land. Specific heat is the amount of heatneeded to raise the temperature of one gram of a substance onedegree Celsius. Heat is measured in calories. A calorie is the amountof heat required to raise the temperature of one gram of water onedegree Celsius. Thus the specific heat of water is one calorie pergram-degree Celsius (1 cal/g-°C), which is the standard againstwhich other specific heats are measured. (See Table 18-1.)

Temperature and Pressure 443

TABLE 18-1 SPECIFIC HEATS OF COMMON MATERIALS (CAL/G-°C)

Material Specific Heat

Water 1.0

Ice 0.5

Water vapor 0.5

Dry air 0.24

Basalt 0.20

Iron 0.11

Copper 0.09

Lead 0.03

Different States of Water

The temperature in the ocean varies so much that ocean water canexist in three different phases, or states: solid (ice), liquid (water),and gas (water vapor). The temperatures at which changes of state inwater occur are shown in Figure 18-1. When one gram of waterchanges into one gram of water vapor, 540 calories of heat areabsorbed by the water. The change in state from a liquid (water) to agas (water vapor or steam) is called vaporization; the energyabsorbed when this process occurs is called the heat of vaporiza-tion. Normally, evaporation occurs at the ocean surface at tempera-tures well below the boiling point. Heat is then released into theatmosphere, along with the water vapor. In fact, most of the watervapor in the atmosphere comes from the ocean through evapora-tion. Where in the ocean does the water actually boil? On activevolcanic islands, such as Hawaii, lava flows into the ocean. On mak-ing contact with the water, the molten lava boils it into billowingclouds of steam. Of course, the main phases of water in the oceanare liquid and solid (ice), not gaseous.

If the temperature falls below its freezing point, water changesinto ice. When one gram of water freezes, 80 calories of heat are lostby the water. The change of state from a liquid (water) to a solid(ice) is called fusion; the energy lost in this process is called the heatof fusion. Likewise, when one gram of ice melts into one gram ofwater, 80 calories of heat are gained by the water.

444 Energy in the Ocean

0

100

Time (heat added)

Solid

Liquid

Melting

Vaporization

Gas

Tem

pera

ture

(°C

)

Figure 18-1 Changes ofstate in water: from solidto liquid and from liquidto gas.

Ice in the Ocean

Much of the ocean at the North Pole and around the South Pole iscovered by ice. There are two kinds of ocean ice: sea ice and ice-bergs. Sea ice is formed when water on the ocean surface dropsbelow the freezing point, which is about –2°C for seawater. (The saltin ocean water lowers the water’s freezing point.) Sea ice canbecome a hazard to navigation when coastal waterways freeze. Pow-erful ships called icebreakers are used to smash through sea ice up to3 meters thick.

An iceberg is a chunk of ice that breaks off from the end of aglacier. (A glacier is a mass of moving ice formed on mountains fromcompacted snow.) Glaciers that reach the shore become undercutby waves. Wave action erodes the base of the glacier and pieces of ice“calve,” or break off into the sea. A good-sized iceberg can be 50 to100 meters high and several hundred meters long. (See Figure 18-2.)Icebergs can be a menace to navigation because they often float outinto shipping lanes. What makes them particularly dangerous is that


Figure 18-2 An iceberg isa very large chunk of icethat has broken off fromthe end of a glacier at theshore. Most of an icebergactually floats below theocean surface.

the part you see above the water is, literally, just the “tip of the ice-berg.” About 80 to 85 percent of an iceberg floats below the surface,and that is the part that can split the hull of a ship. As you mayrecall from Chapter 1, the Titanic sank after colliding with an ice-berg in the North Atlantic.

18.1 SECTION REVIEW

1. What is the definition of a calorie? How is it related to the spe-cific heat of water?

2. In what different states of matter can ocean water exist?

3. For water, which process requires more calories of heat, vapor-ization or fusion? Why do you think this is so?

18.2 TEMPERATURE VARIATIONS IN THE OCEAN

Much of the sun’s radiant energy that reaches Earth is absorbed atits surface and changed into heat. But, as you know from Chapter17, the heating of the planet is not uniform. As a result, surfaceocean temperatures vary with latitude. Surface water temperaturesrange from –2 to 29°C.

Variations With Depth

The temperature of the ocean also varies with depth (particularly inthe middle latitudes). You may have experienced a temperature dif-ference while diving in either an ocean or a lake. The deeper youdescend, the colder it gets. The relationship between depth and tem-perature is shown in the graph in Figure 18-3. As depth increases,water temperature decreases. But the decrease is not uniform. Thereis a very steep drop in temperature between 200 and 1000 meters.This layer of ocean water is called a thermocline. The thermoclineis a permanent boundary that separates the warmer water abovefrom the colder, denser water below. Seasonal thermoclines between


100 and 200 meters deep also occur. They are more common in thesummer, when the water is heated more by the sun. Due to thisheating, the surface water is less dense than the cold water below, soit floats on top in a distinct layer. As a result, there is very little mix-ing of water between the two layers. When the surface water cools,it sinks and displaces the bottom water, causing an “overturn” ofwater layers (and the minerals within them).

Oceanographers use several instruments and methods to mea-sure seawater temperature. To get a temperature profile of the ocean,scientists use a bathythermograph (a narrow torpedo-shaped can-ister that is lowered into the ocean to make continuous tempera-ture readings), a reversing thermometer (in a Nansen bottle), andthermistors (electrical temperature sensors towed on a cable). Seasurface temperatures are obtained from ships, floating buoys, andremote sensing by satellites (provided by the U.S. Navy, NASA, andthe European Space Agency).

The Effects of Temperature on Ocean Life

Temperature affects the functioning of living things. If you have a tropical fish tank, you may have noticed that when the watertemperature is high, the fish are more active than when the water


2400

1800

1200

600

0

Dep

th (

met

ers)

Temperature (°C)5 10 15

High latitudes (about 53°N)

Middle latitudes (about 35°N)

Figure 18-3 The relation-ship between water depthand temperature at highand middle latitudes: thesteepest drop in tempera-ture occurs (at middle lati-tudes) between 200 and1000 meters in depth.

temperature is cooler. This occurs because, for fish and many otherectothermic animals, when the temperature of the external envi-ronment changes, their internal body temperature changes, too.When the water temperature increases, the organism’s internalenergy level, or metabolic activity, also increases.

The metabolic activity of an animal can be determined by mea-suring the amount of carbon dioxide given off during respiration. Aswater temperature increases, the amount of CO2 exhaled by a fishalso increases, indicating an increase in metabolic activity. As a gen-eral rule, for every 10°C increase in temperature, there is a doublingof metabolic activity. However, at very high temperatures, enzymesare inactivated and metabolism decreases.

What happens to organisms in extremely cold ocean environ-ments? Below-freezing temperatures are about as extreme as youcan get. Marine biologists have discovered that several species oficefish survive in frigid Arctic and Antarctic waters because of aunique adaptation in their blood; the fish have glycoprotein, a bio-logical “antifreeze” that lowers the freezing point of body fluids,preventing the tissues from freezing. Glycoprotein also coats icecrystals, which prevents them from enlarging in the body. Very coldtemperatures can harm living tissues by destroying the enzymesthat enable cellular chemical reactions. Scientists found that the ice-fish can breathe through its skin even while encased in ice. A richnetwork of blood vessels in its skin allows the fish to supplementbreathing through its gills by taking in oxygen through its bodywall. (See Figure 18-4.)

In shallow tropical waters, some snails have ridges on theirshells. These ridges help radiate heat and keep the snails cool. Snailswith light-colored shells also tend to be found in warmer waters.


Icefish

Figure 18-4 The icefishcan survive in frigid polarwaters because it has anatural “antifreeze” in itsblood.

CONSERVATIONKeeping the Chinook Chilly

1. Why is the chinook salmon an endangered species of fish?

2. How is the chinook salmon affected by temperature changes?

3. Describe one measure undertaken to save the chinook salmon.

QUESTIONS


A degree or two can mean the differencebetween life and death for the chinook salmon,an endangered species that spawns in theSacramento River in California. The chinook cansurvive only in cold water; they begin to die ifthey are exposed to water temperatures above14°C. In fact, when the Sacramento’s watertemperature rose to about 16.5°C during a1976–1977 drought, thousands of these salmonperished. During a recent winter run, only 2000adults were counted traveling to their spawninggrounds, as compared with 117,000 that werecounted making the run in 1969.

The Sacramento River has warmed due tothe construction of the Shasta Dam—a 180-meter concrete barrier located about 320 kmnorth of San Francisco. The dam, which createdLake Shasta, was built in the 1940s to provideelectricity to the area. The hydroelectric systemtakes in and releases the warmer water fromLake Shasta; in doing so, it blocks the naturalflow of colder water from the lake bottom to thesalmon’s spawning grounds in the river below it.

Fortunately, the hydroelectric facility andlocal government biologists became concernedabout the decrease in the salmon population.The chinook salmon are important to both theeconomy and the ecology of California’s riverand marine communities. As a result, the Fed-eral Bureau of Reclamation constructed an $80million temperature-control system on the

Shasta Dam. This new water-intake system,bolted to the dam, permits colder water fromthe lake bottom to flow through huge louversinto the Sacramento River.

Taxpayers may complain that the $80 mil-lion project, which comes to $40,000 per fish, istoo high a price to pay. But environmentalistspoint out that the dam has blocked the salmonfrom reaching their historical spawning groundsin the Cascade Mountains farther north. Thus,the Sacramento River below the dam must bemaintained as a suitable habitat for the breed-ing population of this fish; and part of thateffort means keeping the water temperaturewithin a safe range for the salmon returningfrom the sea.

The light color reflects more sunlight than dark colors do; thus, thelight color also helps to keep the snails from overheating. Tempera-ture differences in the ocean also affect the distribution and featuresof certain microorganisms. For example, Oithona and Calanus aretwo types (genuses) of copepods. Oithona lives in warm water,whereas Calanus lives in cold water. Since warm water is less densethan cold water, objects floating in warm water tend to sink moreeasily. However, Oithona has long, frilly appendages that increase itssurface area, helping to keep it afloat. In contrast, Calanus does nothave these “extra frills,” since it lives in cold water, where it is easierto stay afloat.

Marine mammals such as cetaceans and pinnipeds are adaptedto survive in cold water because they have thick layers of fatty tissue(blubber) under their skin that insulate against heat loss. (In addi-tion, pinnipeds have fur.) These defenses against the cold helpwhales and seals (which, as mammals, are endothermic) maintain astable body temperature.

Humans are also endothermic. However, we do not have thespecial adaptations of marine mammals for retaining body heat inwater. A person loses body heat 25 times faster in water than in airof the same temperature. Exposure to very cold water leads to anexcessive loss of body heat, which can quickly cause a life-threat-ening condition called hypothermia. The body tries to make up forheat loss by generating heat through the involuntary contractionof its muscles, that is, by shivering. If heat loss is not stopped, a per-son’s body temperature drops farther and the person may becomeunconscious. By getting out of the water, removing wet clothes,and keeping warm, people can restore their body temperature tonormal.

18.2 SECTION REVIEW

1. What is a thermocline? Why are some more common duringthe summer?

2. How does a change in water temperature affect an animal’smetabolism?

3. How is the icefish specially adapted to live in cold polar waters?


18.3 PRESSURE UNDERWATER

When you turn on the faucet, water gushes out. Water exerts pres-sure. Pressure is defined as a force applied over a given area, and canbe calculated by using the following formula:

Pressure (P) = Force (F)/Area (A)

Pressure is measured in units called pascals (Pa). Force is measuredin units called newtons (N). One pascal is equal to one newton of forceper meter squared (N/m2). One newton is the force needed to accel-erate a one-kg mass one meter per second squared. The force exertedby an object equals its weight. Weight is defined as the product of itsmass (m) times acceleration (a), or F = ma, where acceleration due togravity is 9.8 m/s2. An object with a mass of one kg has a weight orforce of 9.8 newtons, as shown in the following formula:

F = ma

F = (1 kg) (9.8 m/s2)

F = 9.8 newtons

Look at the container of water shown in Figure 18-5. Waterspurts out farthest from the hole at the bottom of the can. Why?


100 mm

100 mm

Figure 18-5 Water pres-sure is greatest at thebottom of the containerbecause of the mass ofwater above it.

There is more pressure at the bottom than at the top because thereis more water above the bottom hole than above the top holes. Ifthe mass of the water in the container is 0.5 kg, what is the waterpressure at the bottom of the container? First you calculate the forceor weight of the water:

F = ma

F = (0.5 kg) (9.8 m/s2)

F = 4.9 newtons

Substituting the 4.9 newtons into the formula for pressure, youhave:

P = F/A

P = 4.9 newtons/A

The area (A) at the base of the container is the length (100 mmor 0.1 meter) times width (100 mm or 0.1 meter), which equals 0.01meter squared. Substituting the area into the formula you have:

P = 4.9 newtons/0.01 m2

P = 490 pascals

The pressure at the bottom of the container is 490 pascals.The water pressure in the middle of the container would be less,

because there is half the mass of water pressing down at that point.Substitute 0.25 kg of water mass to calculate the force:

F = ma

F = (0.25) (9.8 m/s2)

F = 2.45 newtons

The pressure in the middle of the container would be:

P = F/A

P = 2.45 newtons/0.01 m2

P = 245 pascals

There is energy in water pressure. The water in the containerhas the energy of position, called potential energy. When the plugs are removed, water spurts out. When the water flows out,


potential energy is changed into kinetic energy, the energy ofmotion.

Depth and Water Pressure

The mass of several kilometers of air exerts atmospheric pressure onEarth’s surface. Under normal conditions, the atmospheric pressureat sea level, expressed as one atmosphere of pressure, is equal toapproximately 101 kilopascals (kPa). Pressure exerted by the water’smass (due to its density) is called hydrostatic pressure. Scientistsknow that for every 10 meters of depth, water pressure increases by101 kPa (one atmosphere). What is the hydrostatic pressure on adiver at a depth of 60 meters? The hydrostatic pressure would beequal to six atmospheres, or nearly 608 kPa.

The atmosphere also presses down on the diver. The total pres-sure, or ambient pressure, on the diver is the sum of the atmos-pheric pressure plus the hydrostatic pressure. Thus, the diver at 60meters depth is under an ambient pressure of 709 kPa. Pressures atdifferent depths are summarized in Table 18-2.

Table 18-2 shows that as depth increases at regular intervals,pressure also increases. This relationship between water depth andpressure is shown in Figure 18-6 on page 454. As you can see from


TABLE 18-2 OCEAN DEPTH AND WATER PRESSURE

Depth Atmospheres* Hydrostatic Pressure Ambient Pressure (meters) (kPa) (kPa)

0 1 0.0 101.325

10 2 101.325 202.650

20 3 202.650 303.975

30 4 303.975 405.300

40 5 405.300 506.625

50 6 506.625 607.950

60 7 607.950 709.275

*1 atmosphere = 101.325 kPa = 14.7 lb/in.2

the graph, there is a direct relationship between pressure and depth.For every change in depth, there is a uniform change in pressure.

The Effects of Pressure on Ocean Life

Marine organisms live at many different levels in the water column.In what ways are they adapted to differences in water pressure? Div-ing mammals, such as dolphins, possess a very flexible rib cage thatcan expand and contract in response to pressure differences as theanimal swims up and down. At greater depths, where the pressure isstronger, a dolphin’s rib cage and lungs can collapse without dam-age.

Many deep-sea fish, such as the hatchetfish, cannot swim freelybetween the bottom and top layers of the ocean. Like many otherbony fishes, the hatchetfish has an air-filled swim bladder thatinflates and deflates to regulate movement through the water col-umn. When the swim bladder takes in air, the fish rises. When thevolume of air in the swim bladder decreases, the fish sinks. By regu-lating the size of the swim bladder, a fish can maintain a neutralbuoyancy without actively swimming—an important adaptation forenergy conservation. The great pressure differences, however,between the top and bottom of the ocean keep deep-sea fish likethe hatchetfish “prisoners” of the depths, since their swim bladderswould expand and burst if they rose to shallower waters.

Another animal whose movements are affected by differencesin water pressure is the chambered nautilus. The nautilus is a mol-


0 10 20 30 40 50 60

1

2

3

4

5

6

7

Pre

ssur

e (a

tmos

pher

es)

Depth (meters)

Figure 18-6 There is a direct rela-tionship between water depth andpressure.

lusk whose shell contains spiral chambers filled with air. The ani-mal rises and falls in the water column, between depths of 100 and500 meters, by taking in and releasing water from its outermostchamber. The nautilus does not live below 500 meters, because thecrushing effects of the deep-sea pressure would crack its shell.

People and Underwater Pressure

We are fascinated by the challenge and mystery of the deep ocean.The effects of pressure, however, limit the depths to which humanscan descend. The Ama pearl divers of Japan attain the upper limit ofhuman underwater endurance. They can make repeated free dives,without the aid of scuba tanks, down to 18 meters and remainunderwater for as long as one minute. With the aid of scuba, how-ever, divers have been able to descend to greater depths and staydown much longer. The current depth record for scuba diving is 132meters. (The record free dive of 104 meters was made by JacquesMayol in 1983.)

Scuba diving has opened up the underwater world to a varietyof human activities. Scuba divers (using special gas mixtures fordeep dives) carry out scientific research on the ocean floor, do sal-vage work on sunken ships, make repairs to ships’ hulls, and installoffshore oil rigs. Recreational scuba diving is also a rapidly growingindustry. However, scuba diving is not without its risks. Exposureto underwater pressure can lead to various injuries.

Barotrauma

Any diving injury associated with pressure is called a barotrauma.There are three kinds of barotrauma: injuries occurring on descent,injuries occurring on ascent, and nitrogen narcosis.

Injuries on Descent: As soon as a diver goes underwater, ambientpressure exerts a force over the entire surface of his or her body. The body’s thin membranes are the first to feel the effects of pres-sure. The eyes and the eardrums are pushed slightly inward. Thesinuses, which are membrane-covered cavities in the bones of theface and forehead, also feel the effects of pressure. As the diverdescends, pressure increases on these membranes, which may cause


discomfort or pain. Pain in the ear is called ear squeeze, and painin the forehead is called sinus squeeze.

The pain can be eliminated by relieving (equalizing) the pres-sure by blowing through the nose while keeping the nostrils closed.When the discomfort is eliminated, the diver can continue todescend. If ear or sinus squeeze recurs, the diver can ascend slightlyand clear the sinuses again by blowing through the nose. Earsqueeze and sinus squeeze are two examples of barotrauma that canoccur to both scuba divers and snorkelers.

Injuries on Ascent: Coming up from the bottom too quickly canproduce a serious injury to scuba divers called the bends. Whenscuba divers breathe air under pressure, the gases dissolve in theirblood at that pressure. If a diver ascends too quickly, there is a sud-den decrease in pressure. This decrease, called decompression, cancause gases to come out of solution and form small bubbles in theblood—similar to the way bubbles appear in a bottle of soda when itis opened. The gas bubbles can travel to tissues and joints, causingthe diver to bend over in pain (hence the name “the bends”). Thebends is an example of a decompression illness; if severe, it can crip-ple or kill a diver.

Another dangerous effect of decompression illness occurs whena gas bubble, or air embolism, in the blood blocks a blood vesselin an important organ such as the brain. An air embolism can occurif a scuba diver ascends too quickly and mistakenly holds his or herbreath during ascent. As in the bends, when the diver rises to thesurface, the air inside the lungs expands as ambient pressure on thediver decreases. If the diver doesn’t exhale sufficiently while ascend-ing, the air in the lungs may rupture through the air sacs and passinto the bloodstream. Air bubbles in the blood can block circula-tion, cause fainting and paralysis, or even cause death.

To prevent decompression illness, scuba divers must alwaysbreathe normally while ascending, and the rate of ascent should beabout 10 meters per minute to allow enough time for the dissolvedgases in the bloodstream to be exhaled. Decompression illness doesnot happen to people who are snorkeling (that is, skin divers), becausethey are not breathing compressed air (air that is under pressure).

Decompression illness can be treated by placing the afflicteddiver in a decompression chamber, which is made with thick steelwalls. In the decompression chamber (also called recompressionchamber), air pressure is first increased to redissolve the bubbles


inside the person’s body. Then the pressure is gradually decreasedover a period of several hours, until the dissolved gases slowly comeout of solution and are safely exhaled.

Nitrogen Narcosis: Scuba divers who make deep dives below 30meters may experience what ocean explorer Jacques-Yves Cousteaucalled “rapture of the depths” or nitrogen narcosis, a kind ofbehavioral effect that resembles alcohol intoxication. The diverappears drunk, has difficulty concentrating, and is not able to carryout simple tasks. This confused state can pose a threat to the diver’ssafety. Nitrogen narcosis results from breathing nitrogen gas (N2)under pressure.

Nitrogen gas, which makes up 78 percent of the air we breathe,is biologically inert when inhaled under normal atmospheric pres-sure. However, when N2 is inhaled under pressure from a scuba tankat great depths, it can have a narcotic effect similar to that producedby nitrous oxide (laughing gas), a painkiller that some dentists giveto patients. Changing the mixture of gases in the scuba tank—byremoving nitrogen and adding helium, which is also biologicallyinert—reduces the incidence of nitrogen narcosis. This step alsoincreases the bottom time (the amount of time a diver can stayunderwater) for divers who work at depths below 40 meters.

18.3 SECTION REVIEW

1. What is the ambient pressure on a diver at a depth of 70meters? Show your calculations.

2. Why does decompression illness occur among scuba divers butnot among snorkelers?

3. What causes the bends and how can a diver prevent itsoccurrence?

18.4 OSMOTIC PRESSURE AND AQUATIC ADAPTATIONS

In addition to hydrostatic pressure, the water balance of an organ-ism affects its survival. A sea star placed in a freshwater tank woulddie. And a goldfish placed in a marine tank would die, too. Most


saltwater animals such as the sea star cannot live in freshwater. Andmost freshwater animals such as the goldfish cannot live in saltwater. However, some aquatic organisms such as the salmon can, atdifferent stages in their lives, live in both types of water.

Osmoregulation in Aquatic Animals

The ability of aquatic organisms to maintain a proper water balancewithin their bodies (in either salt water or freshwater) is calledosmoregulation. Osmoregulation is related to the process of osmo-sis. As you learned in Chapter 6, osmosis is the movement of watermolecules from an area of high concentration to an area of low con-centration through a semipermeable membrane. If a sea star wereplaced in freshwater, the water molecules would move from wherethey are more concentrated (outside the sea star) to where they areless concentrated (inside the sea star). (See Figure 18-7.)

In freshwater, the water molecules are more concentrated out-side the sea star, because the sea star contains dissolved salts withinits cells that take the place of water molecules. The sea star is unableto eliminate the excess water that enters due to osmosis. Theincreased water pressure, or osmotic pressure, inside the sea starupsets cell function and causes death. The sea star is unable to adjustto waters of very different salinities and so is considered to be a poorosmoregulator. When the sea star is in its normal saltwater environ-ment, it can regulate its osmotic pressure because the salt concentra-tion of the sea star’s body is closer to that of its external environment.


Freshwater (inward osmosis)

Watermolecules

Figure 18-7 The con-centration of water mole-cules is higher outsidethe sea star (than in thefreshwater), so inwardosmosis occurs.

However, salinity changes may occur in the sea star’s naturalenvironment. In 1982, along the shores of the Gulf of California (abody of water that contains higher-than-normal salinity), the seastar population suddenly declined. Marine biologists discovered thatthe drop in the number of sea stars coincided with heavy rainfalls,which were unusual for this dry coastal region. Evidently, freshwaterrunoff from the land lowered the gulf’s salinity, causing some seastars to die and others to move to deeper, more saline waters.

The goldfish is also a poor osmoregulator when placed in a salt-water environment. (See Figure 18-8.) If a goldfish were surroundedby seawater, the concentration of water molecules would be greaterinside the fish than outside, because the salt outside the fish takesthe place of water molecules. Since the osmotic pressure is greaterinside the fish than outside, water would leave the fish by osmosisthrough its gill membranes. The goldfish, unable to compensate forthe water loss, would die of dehydration. In its normal freshwaterenvironment, the goldfish can regulate its osmotic pressure—its kid-neys remove excess incoming freshwater.

Osmoregulation in the Salmon

The salmon is a good osmoregulator because it can adjust to aquaticenvironments that vary greatly in salinity. The salmon is a migra-tory fish. During its life cycle, it travels from a freshwater river tothe ocean and back again to spawn. Salmon are born in rivers; theyswim downstream to the ocean where they spend several years


Salt water (outward osmosis)

Watermolecules

Figure 18-8 The con-centration of water mole-cules is higher inside thegoldfish (than in the saltwater), so outwardosmosis occurs.

maturing into adults. When the salmon are in the ocean, the salin-ity of their body tissues is 18 parts per thousand (ppt), while thesurrounding ocean water has a salinity of 35 ppt. Since there is animbalance in salinity, the concentration of water molecules isgreater inside than outside the fish. As a consequence, outwardosmosis occurs and water leaves the fish through the gill mem-branes. To counter this water loss, the salmon drinks seawater. Tomaintain a proper osmotic balance, the salmon excretes excess saltfrom its gills and also produces salty urine.

When mature salmon swim upstream to spawn, they encountera salinity near zero ppt, while the salinity of their body tissues isstill 18 ppt. Since the salinity is greater inside than outside the fish,the concentration of water molecules is greater outside than insidethe fish. This difference in the concentration of water moleculescauses water to enter the fish by inward osmosis. To counter thisintake of excess freshwater, the salmon excretes water in the form ofa dilute urine. The salmon is a good osmoregulator because it iscapable of adjusting to large differences in salinity. However,osmoregulation in the salmon is a gradual process of adjusting towaters of different salinities. This process occurs over a period ofweeks or months as the fish migrates between ocean and river.

18.4 SECTION REVIEW

1. Why would a sea star die if placed in freshwater?

2. Why can’t a goldfish adapt to a marine environment?

3. How does the salmon function as a good osmoregulator?


Laboratory Investigation 18

PROBLEM: How do temperature and salinity affect the density of oceanwater?

SKILL: Graphing scientific data.

MATERIALS: Temperature-Salinity Diagram (Figure 18-9), ruler, pencil.

PROCEDURE

1. Two seawater samples, labeled A and B, were taken and tested for tempera-ture and salinity. The results were plotted as two dots, A and B, on the Tem-perature-Salinity Diagram (Figure 18-9). Find the temperature and salinityvalues for A and B and record them in a copy of Table 18-3 in your note-book. (See page 462.) Record the density for each sample in your table.

Effects of Temperature and Salinity on Water Density


0

5

10

15

20

33.5 34.0 34.5 35.0 35.5 36.0 36.5

Tem

pera

ture

(°C

)

Salinity (parts per thousand)

1.02

90

1.02851.0280

1.02751.0270

1.0265

1.02601.0255

1.02501.0245

A

B

Temperature-Salinity Diagram (lines of density in g/cm3)

Figure 18-9 Both temperature and salinity have an effect on water density.


2. Record in the water sample table the temperature and salinity of water sam-ple C that would result if equal volumes of samples A and B were mixedtogether. (Hint: Mixing one liter of 10°C water with one liter of 30°C waterresults in two liters of water at 20°C.)

3. Plot the new sample C by placing a dot on the Temperature-Salinity Dia-gram. Next, record in the water sample table the density of sample C.

4. On the Temperature-Salinity Diagram, draw a straight line between thepoints representing samples A and B. The point representing any possiblemixture of these seawater samples, including sample C, would fall some-where on this straight line.

OBSERVATIONS AND ANALYSES

1. How does an increase or decrease in temperature affect density?

2. How does an increase or decrease in salinity affect density?

3. Does sample C have a density that is equal to, less than, or greater than thedensities of sample A and sample B prior to mixing?

4. Which water samples would sink and which would float above the others?

TABLE 18-3 TEMPERATURE/SALINITY/DENSITY OF WATER SAMPLES

Sample Temperature Salinity Density(°C) (parts per thousand) (g/cm3)

A

B

C

Answer the following questions on a separate sheet of paper.

Vocabulary

The following list contains all the boldface terms in this chapter.

air embolism, ambient pressure, barotrauma, bathythermograph,bends, decompression, heat of fusion, heat of vaporization,hydrostatic pressure, hypothermia, metabolic activity, nitrogennarcosis, osmoregulation, osmotic pressure, thermocline

Fill In

Use one of the vocabulary terms listed above to complete each sentence.

1. Pressure exerted by the density of water’s mass is ____________________.

2. Scientists use a ____________________ to measure ocean temperatures.

3. The total pressure on a diver is called the ____________________.

4. The bends is a type of ____________________ that can cripple a diver.

5. The boundary between warm and cold water is the ____________________.

Think and Write

Use the information in this chapter to respond to these items.

6. Describe some adaptations of ocean life to cold water.

7. How do dolphins adjust to changes in hydrostatic pressure?

8. Explain why the salmon needs to be a good osmoregulator.

Inquiry

Base your answers to questions 9 through 11 on the following experi-ment and on your knowledge of marine science.

A marine science student hypothesized that an increase in watertemperature would cause an increase in cardiac activity in theshore shrimp. The heartbeat of the shrimp, as measured in beatsper minute, was observed at room temperature (20°C) for the con-trol group and at higher and lower temperatures for the exper-imental groups. The results are shown in the table on page 464.

Chapter 18 Review


Control Experimental Experimental Trial Group Group Group

(at 20°C) (at 28°C) (at 10°C)

1 116 235 142

2 174 396 114

3 114 377 100

4 140 300 144

5 216 276 123

6 138 285 106

Total 898 1869 729

Average 150 312 122

9. The results of this experiment show that a. as watertemperature decreases, cardiac activity remains the sameb. as temperature increases, cardiac activity increasesc. as temperature decreases, cardiac activity increasesd. as temperature increases, cardiac activity decreases.

10. Which statement represents a valid conclusion that can bedrawn from this experiment? a. The student’s hypothesis issupported by the data. b. The hypothesis is not supportedby the data. c. The hypothesis could not be tested.d. There are insufficient data to draw any conclusion.

11. Which is an accurate statement regarding the data in the table?a. Temperature does not affect heartbeat rate in the shoreshrimp. b. The trial with the most cardiac activity occurredin the control group. c. The trial with the least cardiacactivity occurred in the control group. d. The trial with theleast cardiac activity occurred in an experimental group.

Multiple Choice

Choose the response that best completes the sentence or answers thequestion.

12. Aquatic organisms maintain a proper water balance bymeans of a. hypothermia b. metabolic activityc. osmoregulation d. decompression.

13. Snorkelers do not get air embolisms on ascent because theya. do not breathe compressed air b. hold their breathc. do not dive deep d. come up too fast.


Base your answers to questions 14 through 16 on the graph in Figure 18-6on page 454.

14. According to the graph, you can conclude that a. as depthincreases, pressure also increases b. as depth increases,pressure decreases c. as depth decreases, pressure increasesd. as depth increases, pressure remains the same.

15. According to the graph, what is the pressure in atmospheresat a depth of 50 meters? a. 4 b. 5 c. 6 d. 7

16. There is a pressure of one atmosphere at zero meters’ depthbecause a. water exerts pressure on the atmosphere b. airexerts pressure on the water surface c. water pressure ispushing upward d. air and water pressure cancel out.

17. In this diagram, the concentration of water molecules ishigher inside the fish than outside the fish, so you couldexpect the occurrence of a. inward diffusion b. outwardosmosis c. inward osmosis d. hypothermia.

18. Descending in the water while snorkeling or using scuba gearmay cause a. sinus squeeze b. decompression illnessc. the bends d. an air embolism.

19. A recreational scuba diver normally breathes a. compressedair b. pure oxygen c. a special mixture of gases d. air atatmospheric pressure.

20. Hypothermia is more likely to occur in humans than inmarine mammals because humans a. have less hair b. arewarm-blooded c. are cold-blooded d. have no blubber.

21. Unlike icebergs, sea ice a. comes from glaciers b. isformed when ocean water freezes c. cannot be smashed byicebreakers d. is not a menace to navigation.

22. Which statement is true? a. As depth increases, temperatureincreases. b. As depth decreases, temperature decreases.c. As depth increases, temperature decreases. d. As depthincreases, temperature remains the same.

Research/Activity

Report on a marine organism that lives under extreme conditionsof temperature and/or pressure. Use the Internet to find data on afish or invertebrate that lives in the deep ocean or polar seas.


Documents

UNIT ENERGY IN 6 THEOCEAN - tyburnscience.educationtyburnscience.education/MarineBio/18.pdf · currents have kinetic energy, the energy of motion. Waves crashing on a beach produce