Oceans: Environmentfor Life

13.113.213.313.413.513.613.7

13.813.913.1013.1113.12

Buoyancy and FlotationO smotic ProcessesTemperaturePressureGasesNutrientsLight and ColorSunlightBioluminescenceColorCircula tionBarriers and BoundariesBottom T ypesE nvironme ntal ZonesClass ificati on of Organisms

The river is within us; the sea is all about us;The sea is the land's edge also, the graniteInto which it reaches, the beaches where it tossesIts hint s of earlier and other creation.The starfish, the hermit crab, the whale's backbone ;The pools where it offers to our curiosityThe more delicate algae and the sea anemone.It tosses up our losses, the torn seine,The shattered Iobsrerpot; the broken oarAnd the gear of foreign dead men. The sea has many voices,M any gods and many voices.

T. S. Eliot,from "T he D ry Salvages," The Four Qllartelt

Box: Spartina: Valnab!e and Produ ctiue or Invasiv eand Destructive ?

13.13 Practical Considerations: Modification andMitigation

SummaryKey TermsStudy QuestionsSuggested Readings

1\ sc hoo l of small fish iPum priacunthus ransonnetii gree t ;I diver ill Indonesia .

333

A ~omplex variety of env ironments for living organismsIS provided by the oceans and coastal seas ofthe soorid. A t

the surface, conditions range ji'om polar to tropical; over depth,from light to total and constant darknes s; and around the world,

from open ocean to sheltered bays. Currents and w av es, 7'isingand falling tides, sandy bottoms and rocky shores all contribute

to the v ariati on. Light-dark cycles as well as the tides modijj anenvironment over the day; seasona l cycles modifY it over the

y ear, and other cycles take much longer. Some changes are grad­ual and extend over long distances; other changes occur quickly

in a small area. Th is chapter introduces the ocean as a habitat

by reviewing the properties ~rthe soorld oceans that produce thisspecial environment [or life. Since the topics discussed here are

considered in other chapters, tbeir p resentation is briefand keyed

to their interaction with the marine organisms.

Org anis ms of the marine environment have much in

common with the organisms ofthe land, but th ey also hav e 'IJe1)'

different problems and have developed unique solutions to cop e

with them. This chapter also explains some ~r the characteristicsthat enable organism: to liv e in th e sea.

Organi sms that make their home on land requi re structuralstrength to support their bodies in air and against gravity.Tre es must be able to hold up their canopies of leaves, andanimals need skeletons and muscl es to give the ir bodiesshape and the ability to move. The salt water surroundingmarine organi sms has a den sity similar to the tissues ofman y of the organisms. The buoyancy of objects in sea ­wa ter is due to its densit y , and helps to keep the floatingorgani sms at the surface. It supports the bodi es of thebottom-living crea tures and lessens the energy expended byswimmers.

Many organisms have ingenious adaptations to helpthem stay afloat. Some jellyfish-type animals, for examplethe Portugu ese man-of-war and the by-the-wind-sailor(ch apter 15, fig. ]5.1 3) , secre te ga ses into a float thatenables them to stay at the sea surface . Some seaweedssecrete gas bubbl es and form gas-filled float s , which helpthem keep their frond s in the sunlit sur face waters whilethey are anch ored to the seafloor. One flo atin g snail pro­duc es and stores intestinal gase s; another form s a bubbleraft to which it clings. The chambered nautilu s (fig. 13.1a),a relative of the squid , continually add s ch amb ers to itsshell and moves to the last chamber as it grows . A special­ized tissue rem oves the ion s from the empty chamber s,cau sing water to diffuse out, then the chamber fills withga s, mainly nit rogen , from ti ssue fluids . Th e cuttle fish,another rel ative of the squid, has a soft, porous , intern al

Cuttlefish

Chambered nautilus(a)

shell or "bone"; it regulates its buoyancy by controlling therelati ve amounts of gas (also mainly ni trogen) and liquidwithin the shell (see fig . 13.1b).

Many fish hav e gas- filled swim bladders that keepthem neutrally buoyant. Some fill their swim bladders bygulping air at the surface ; oth er s rel ease gas from theirblood through a gas gland to the swim bladder. When a fishchanges depth , it adjusts the gas pressure in its swim blad­der to compe nsa te for the pressure ch ange in the water,limiting its vertical swimming speed. If a fish with a swimbladder is forced sudde nly to swim deeper, the increasedex ternal water pressure compresses the air, the bladdershrinks , and the fish s inks. If the fish is not able to read­just its system, it tire s as it is forced to swim upward con­tinu ally to compensate for the loss of buoyancy . A deep­swimming fish brought quickl y to the surface with a fishingline will show bulging eyes ancl a distended body, as thegas in the swim bladd er expands with decreasing pressure .Active, continuously swimming predatory species such asthe mackerel, some tuna, and the sharks do not have swimbladders ; bottom fish also lack swim bladders.

Small members of floating plant and animal popula­tions store their food reserves as oil droplets that decreasetheir density and retard sink ing. Large sur face are a-to­volume ratios that slow sinking are characteristic of smallspheres, and sing le-ce lled organisms, parti cularly plants,take advantage of this by keeping their size sm all. Manyhave devel oped spines , ruffles , and feathery appendagesthat increase surface area and decrease their sinking rate,allo wing them to more easily remain at or near the seasurface .

Figure 13.1(a) Chambered nautilus. (b ) Cuttlefish. The chambered shel l thai prov idesbuoyancy is show n ill each organism.

B oya cy and F 0 arion13.1

334 Oceans:EnvironmentfOrLife

7

The tissues of most large marin e anima ls are moredense than seawa ter. To reduce the density of its body tis­sues , the g iant squid excludes the more-dense ions from itsbod y flu id s an d re p laces th em with less-d ens e ion s .Another squid species has one pair of its arms filled withlow-density body fluids. Whales and sea ls dec rease theirdensity and increase their notation by storing large quantitiesof blubber, which is mainly low-density fat. Sharks and someother varieties of fish store oil in their liver and muscle.

Seabirds float by using fat deposits in combinationwith light bones and air sacs developed fo r flight. Theirfeath ers are waterproofed by an oily secretion called preen ,which acts as a barrier to seal air between the feathers andthe skin. Thi s is important in keeping the birds warm, and italso helps to keep them afloat.

Mechanical strength is not a prerequisite for successin the marin e enviro nme nt. Marin e organisms fl oat andmove with the water, and except where breakin g waves areencountered at the surface or along the shore, the mechani­cal stresses of the water are slight. Many marine organismsare exceedingly delicate and frag ile but survive and func­tion well as long as they are surrounded by water.

Spec ial problems are posed for living creatures if the saltcontent of their body fluids differs from the salinity of thewater that surrounds them. The body fluid s of living plantsand animals are separated from the seaw ater by membranebound aries that are semipermea ble , alJowing some mole­cules [0 move across the membrane bound aries while othermolecules cannot. Molecules that move across these mem­branes do so along a gradient from a region of high concen­tration of a substance to a reg ion of low concentration ofthat substance, a process called diffusion . Water moleculespass across the membranes in a spec ial type of diffusionknown as osmosis, which was discussed in chapter 5.

Most fish have body fluids with a salt concentrationthat is about halfway betweeo that of fresh water and sea­water. In salt water, their tissues tend to lose water as itmoves along an osmotic gradient from an intern al highwater concentration and low salt concentration to the lowerwater co ncentration and higher salt co nce ntra tion of theocea n environment. Fish must constantly expend energy toprevent dehyd ration and an increase in the salt concentra­tion of their tissues. Fish stay in fluid balance by drinkingseawa ter nearly continually and excreting its sa lt acrosstheir gi lls . Sh ark s and rays do not ha ve thi s problem ,because their body fluid s have the same approximate saltcontent as seaw ater , so that there is no osmotic gradient.These fish main tain a high concentration of urea in thei r tis­sues . The urea allows their tissue to retain water, preventsthe mov em ent of sa lt into their bodi es, and keep s bod yfluid at approximately the same salt content as seawater.

The body fluids of many bottom-dwelling organisms,such as sea cucumbers and sponges , are also aLthe samesalt concentration as the seawa ter. There is no concentra­tion grad ient; the water dif fuses equally in both direction s

Waler lossby osmosis

Water Waterloss gain

(a)

across the mem branes , and the salt content remain s thesame on both sides of the membranes. The fish, which doeshave to overcome an osmotic gradient, and the sea cucum­ber , which does not, are compared in figure 13.2.

Species may be limited in their geographic distribu­tion by changes in salinity, for many organisms can main­tain their salt-fl uid balan ce ove r only limited sa l inityranges. Since there is little change in salinity in deep water,species living below the surface layers are dispersed overlarge areas with respect to salinity. The surface-dwellingform s are more likel y to find salinity barri ers in coastalwa ters, si nce the sa linity varies in bays and estuaries .Successful es tuarine animals such as crabs are able to stabi­lize their osmotic processes by regulating the intake of saltions . In some areas, a few spec ies are able to survive inh igh- salinit y lagoon s and sal t mar shes , but th ey a reunlikel y to re pro duce , and so the population must berepleni shed by ne w recru its from the sea. Some animalshave an extraordinary ability to adapt to large cha nges insalinity over their life history. Sa lmon spawn in fresh waterbut move down the rivers as juv enil es to live their adultlives in the sea . After several years (the time depends onthe spec ies), the salmon return to their home streams. TheAtlanti c common ee l reverses this process by migratingdownstream to spawn in the Sargasso Sea. The new genera­tion of eels spends one to three years at sea, then returns tofresh water to live for up to ten years before migrating sea­ward. Other fis h and crust acean s use the low-salinity

. ~. ~ ~?~~'.~. •@ · W,~·, . , -

( '~.::::~Water by gillsand salt gainedby drinking

(b)

Figure 13.2(a) The sail concentration of the sea water is the same as the saltconcentration of the sea cucumber's body fluids (35%0) . The waterdiffusing out of the sea cucumbe r is balanced by the water diffusing into it.(b) The sail concentration in the tissues of the fish is much lower (18%0)than thaI of the seawa ter (35%0). To balance the water lost by osmosis, thefish drin ks salt water, from which the sal! is removed and exc reted.

Osmotic I rocesses13.2

Osmotic Processes 335

coastal bays and estuaries as breeding gro unds and nurseryareas for their young, then as adults they migr ate fartheroffshore into higher-salinity waters .

The temperature of the deep oceans is low and nearly con­stant. At the surface and close to shore the water tempera­ture varies with seaso nal climate changes and geographiclatitude zones. Temperature, like salinity, affec ts the den­si ty of the seawater and also affects its viscosity; densityand viscosity are discussed in chapter 4. At polar latitudes,the surface water is cold, more dense, and more viscous ,and organisms floa t more eas ily. In trop ic latitud es , thewarm, less-dense , less-viscous water is home for spec ieswith more appendages, larger surface are as, and grea tergas-b ubble produ ction, for the water is less buoyant andoffers less resistance to sinking.

When surface conditions produce a warm, low-densitysurface layer overly ing denser wate r, the water column isstable, and floating organisms stay in the sunlit upper lay­ers. Under these condi tions, floatin g plant cells increasetheir rates of photosynthesis and reproduction. When sur­face waters coo l and increase their density, they beco meunstable ; the waters mix, ove rturn, and take the float ingorganis ms with them into deeper water and away from thesunlight. The photosy nthesis and reproduction of plants aredecreased.

Plants and marine animals other than birds and mam­mals do not control their body temperatures. They are cold­blooded and thei r body temp eratur es vary with environ­ment al conditions. The physiol ogy of marine organisms isregulated by the temperature of the water, and within limit smetabolic processes proceed more rapidly in warm waterthan in cold water. Cold-water forms frequently grow moreslowly, live longer, and atta in a larger size . T o somespec ies, changes in temperature act as signa ls to spawn orto become dormant. Although the heat capacity of the waterrestr icts temperatu re fluctuati ons, the geog raphic distribu­tion of seawater temperatures is sufficient to affect the dis­tribution of marine organisms .

Seabirds and mammals are warm-blooded and main­tain 'nearly constant body tempe ratures that are well abovethe temperature of the seawater. Because these animals areless restricted by the temperature of the water, they oftenhave wider geograp hic ranges , for exa mple , the annualmigrati on of wha les be tween polar and trop ical waters .So me fish, although cold-blooded, are able to conserveheat in their swimming muscles, elevating (heir body tem­peratures. Beca use their muscles work more efficiently athigher temperatures , these fish are able to swi m rapidlyand cruise long distan ces in the co ldes t wate r, maki ngthem efficien t pre dators. Fish of th is type incl ude sometuna, mackerel-sharks, the grea t white shark, and the dol­phin fish.

At the greater depths, the uniformity of temperaturewith lat itu de crea tes an oceanwi de env ironment tha t isunaffected by seas ona l changes . At the sea surface, the

13.3 Ten pent re

temperature changes with latitude much the same as the cli­mate changes on land. Annual changes in open sea-surfacetemperatures are small at the very high and very low lati­tudes; at the middle latitudes the annual changes in sea-sur­face temperature show a seasonal fluctuation. Ocean areasclose to land undergo still grea ter changes in surface tem­perature, due to their shallowness and the influence of thegreater annual temperature changes over the adjacent land­masses. Seaso nal fluctuation in surface. temperature at them iddle latitudes is reflec ted in periods of spring and sum­mer reproduction and growth and in winter dor mancy.

On land , the general pattern of climate zones encoun­tered by approaching the poles is also observed by increas­ing the altitude; the clim ate at sea leve l in polar zones issimilar to the climate at the top of a high mountain peak ata lower latitude. In the ocea n, conditions in surface water atpolar latitudes are similar to those found at deeper depths atlower latitudes. Some sha llow -wa ter species of the polarseas are fo und at grea ter depths at the lower latitudes.

13.4Deep-living organis ms, such as wo rms, crustaceans, andsea cucumbers , are unaffected by the pressure, beca use theydo not have gas-filled cavi ties or lungs that must be main­tai.ned at high pressure or mechanically protected againstthe pressure of the overlying water. It is possible that pres­sure may alter metabol ic rates and growth at grea ter depths,but little is known about such effects.

When humans desce nd into the sea , they need eitherprotectio n from the pressure that will collapse their chestcav ities and lungs or air supplied to the lungs at a pressureequal to the outside water pressure. Submarines and sub­mersibles provide the first type of protection, while scuba(Se lf -Conta ined Underwater Breathing Apparatus) andother commercial divi ng equipment supply the second type.After breathing gase s under press ure, hum ans may experi ­ence the serious problems of decompression sick ness andnitrogen narcosis. Divers breathing air under high pressurefor ex tended periods absorb large quanti ties of-gas, particu­larly ni trogen, into their blood and tissues. If they return toshallow dept hs of less pressure too quickly , these excessgases form bubbles in the body tissues and blood vessels,caus ing extre me pai n, paral ysis , and some times death .Exces s nitrogen disso lved in the bloodstream also has anarcotic effect, which confuses the diver and restricts his orher ability to function norma lly. The 1990 depth record foran open dive in seawater using air is 137 m (452 ft).

Air-brea thing marine mammals make dives of spec­tacular depth and duration without encountering such diff i­culties, beca use of thei r abilities to adjust their physiology.Record diving depths and duration for some of the whalesand seals are given in tab le 13.1. These anima ls have aphysiology that perm its their blood to absorb more oxygenand to tolerate higher concentrations of carbon dioxide thanland ma mmals . They also have a larger blood volume thannon divin g mamm als and a vasc ular shunt sys tem thatdirec ts the blood flow thr ough only the bra in and heart

336 Oceans: Environment/or Life

3025

Nitrate-NitrogenN03--N

Concentration (lLg-at/L)

10 15 205

Phosphate-PhosphorousP04-3_P

oO,..-----.,=-,----,----,----,-----,~---,

200 -

100

250

aQ)

o

50

e~E~__ 150 --

Table 13.1

Diving Depths anel Durations for Some Marine Mammals

Mammal Diving Durationrecord record(m) (minutes)

sea liun 168 30

porpoise 300 6

bottle-n osed dolphin 450 120

fin whale 500 30

Weddell seal 600 75

elephant seal (male) 1530 77

sperm whale 2250 90

300 L - - - _

Figure 13.3Nitrate and phosphate distribution in the main basin of Puget Sound in thelate summer. The low surface values are the result of nutrient utilizationby unicellular marine plants .

while underwater. Their muscles store additional oxygenand are able to tolerate the buildup of waste products fromexertion to a greater degree than those of other animals.DUling their dives their lungs collap se completely, forcingthe air out and preventing the blood from absorbing com­pressed gases at high pressure; therefore they do not sufferfrom diving illnesses and are able to rapidly change theirdepth .

13.6 N tri ents

Life in the water requires carbon dioxide and oxygen, asdoes life on land. Carbon dioxide is required by the plantsfor photosynthesis; it is contributed by the animals and bydecay processes, and it is absorbed by the water from theatmosphere . Because seawater has the capacity to absorblarge quantities of carbon dioxide, there is no shortage ofcarbon dioxide for the plant life. Also, carbon dioxide'srole as a buffer limits the ocean's pH range, which keeps ita stable environment for living organisms (see chapter 5).

Oxygen is required by all organisms to liberateenergy from organic compounds. Oxygen is available onlyat the ocean surface as a by-product of photosynthesis andfrom the atmosphere. Life below tile surface depend s on thevertical circulation processes (discussed in chapter 6) toreplenish the oxygen at depth. The amount of oxygen in thewater influences the distribution of organisms and is influ­enced by the temperature , salinity, and pressure of thewater. Shallow tidal pools and bays on warm, quiet daysincrease in temperature and salinity, decreasing the abilityof the water to hold oxygen, forcing motile animals out ,and limiting these areas to the organisms that can success­fully tolerate these changes . The bottoms of deep , isolatedba sins may be so low in oxygen that only non-oxygen­requiring, or anaerobic, bacteria can survive there (referback to chapter 5).

SunlightWithout light there are no plants; therefore the distributionof plant s in the oceans is light limited. Plant life isrestricted to the photic zone where there is sufficient lightenergy for the proces s of photosynthesis. The depth of thephotic zone, about 200 m (660 ft ) in clear ocean water, iscontrolled by factors discussed previously in chapters 1, 4,and 6, including (1) the angle at which the sun's rays hit the

Nitrate (N03- ) and phosphate (P04- 3) nutri­ents are required by the sea's plant life. They are the fertil­izers of the sea and are stripped from the surface layers bythe plants, which incorporate them into their tissues . Thesenutrients are liberated at depth by the decay of plant as wellas animal tissues , or they are returned to the water in theform of waste products of herbivores and carnivores (seefig. 13.3) . Vertical circulation and mixing transport thenutrients back to the surface in upwelling areas where lifeis abundant. Estuaries and coastal waters, where nutrientsare supplied by land nmoff and mixing from the continentalshelf's shallow seafloor, are also rich with organisms. Plantpopulations are limited by the lack of any essential nutrient ;if the concentration of such a nutrient falls below the mini­mum required, the population's growth ceases until thenutrient is replenished. Nutrients were introduced in chap­ter 5 and nutrient cycles will be discus sed in chapter 14.

13.5 Gases

13. 7 Lighta d Co 0

Light and Color 337

ColorSome sea animals are transparent, allowing them to blendwith their water background, for example, jellyfish andmost of the small floating animals in the surface layers,while other animals , particularly the fish, use color in manyways. In the clear waters of the tropics, where light pene­trates to deeper depth s , bright colors play their great estrole . Some brightly colored fish match the colors of thecorals so well they become nearly invisible, and bold col­orati on increase s during the breeding periods of somespecies. Othe r fish conceal thems elves with bright colorbands and blotches that disrupt the outline of the fish andmay draw the predator's attention away from a vital area toa less important spot, for example, a black stripe over theeye and an eye spot on a tailor fin. Another use of brightcolor is to send a warning; organi sms that sting, taste foul,have sharp spines, or poisonous flesh are often striped andsplashed with color, for ex ample , sea slugs and somepoisonous shellfish. Among fish that swim near the surfacein the well-lighted surface water, for example, herring,tuna , and mackerel, dark backs and light undersides arecomm on. This color pattern allows the fish to blend withthe bottom when seen from above and with the surfacewhen seen from below. See figure 13.5.

In temperate regions, coastal waters are mo re produc ­tive and more turbid, and there is less light penetration.Drab browns and grays are concealing against the kelp bedsof temperate waters, and cold-water bottom fish are usuallyuniform in color with the bottom, or speckled and mottledwith neutral colors. The flatfish are well known for theirability to change their color, having skin cells that expandand contract to produce color changes (see fig. 13.6). Theirextraordinary color-chan ging ability enables them to con­ceal themselves by matchin g the bottom type on which theylive (see fig. 13.7). Squid may be the ocean 's masters of

reaction that produces ligh t with a 99 % effi ciency . Thesame phenomenon is seen on land in the flashing of a fire­fly or the ghostly glowing of a fungus in the woods.

In the sea, the agitation of the water disturbs micro ­scopic bioluminescent organi sms, causing them to flash andproduce glowing wakes and wave crests. Anim als that feedon these organi sms often concentrate the chemicals in theirtissues and also glow . Jellyfish glow in this way and so doone's hands if the y come in contact with crushed tissue.Other bioluminescent organisms in the sea include squid,shrimp, and some fish. Many middepth and deep-water fishcarry light-producing organs, or photophores; some havepatt erns on their sides , possibly for identification. Othe rsshow photophores on their ventral surfaces , makin g themdifficult to see from below against the light surface water,and stil l others have glowing bulb s dangling belo w theirjaw s or attached to flexible dorsal spines, acting as lures fortheir prey . The fla shlight fish , found in the reefs of thePacific and Indian ocean s, has a specialized organ beloweach eye that is filled with light -emitting bacteria. Thesefish are known to use the light to see, communicate, lureprey, and confuse predators .

Percentage of solar energy

20 40 60 80

","

'"//

I' Clear ocean waterI• I Turbid coastal water

JJ,

IIII,I

70

60

20

10

~30e

*.s40.I::0.Ol -

a 50

80 lL- ---.J

Figure 13.4The percentage of solar energy available at depth in clear and turbid water.

earth's surface, which is related to latitude and change ofseason; (2) the different rates at which the wavelengths oflight are absorbed, which is determined by the propertiesof water ; and (3) the suspended particul ate mater ial pre­sent, which affect s the rate of absorption. Below the photi czone is the aphotic zone, the zone in which there is nophotosynthesis.

Ho wever, the presence of light d oes not guaranteeplant life; nutrients must be available. It is becaus e of a lackof nutrients that so much of the open ocean , exp osed tohigh-intensity sunlight , is considered for all practical pur­poses a biological desert. Life is more abundant along thecoa st s and over the continental shelves because of thelarger quantities of dissolved nutrient s. Waves and current sof the coastal zone stir the bottom and mix up silt with thenutrients . The silt particles absorb and scatte r light , reduc­ing the depth to which it penetrate s. As the single-celledplants reproduce, their increased numb ers also act to limitlight penetration , so that the photic depth may be reducedto less than SO ill (167 ft ). The penetrati on of sunlight inclear and turbid seawater is comp ared in figure 13.4.

Bioluminescence:wother source of light is present in the oceans, the organ­Isms themselves. On a dark night , when the wake of a boatis a glowing ribbon , and disturbed fish leave a trail of light ,or the water flashes as oars dip and a person 's hands glowbrie~y as a net is hauled in, living organisms are producingthe light. The light is bioluminescence produced by theinteraction of the compound luciferin and the enzym eluciferase. Thi s phenomenon is often incorrectly referredto as phosphorescence; it has nothing to do with phospho­rus or with the absorption of radiation, but is a chemical

338 Oceans: Environmentfor Life

II

Some species of deep-water shrimp are red whenseen at the surface, but below the level of penetration of redwavelengths of light their red pigment absorbs blue andgreen light ; little is reflected and the animals are dark andinconspicuous. In the deep ocean without light, color is oflittle importance except perhaps when combined with bio­luminescence . Of course, we do not know how the animalssee the colors , and there may be roles that color plays in the .sea we do not know or understand. Color is thought to beimportant in specie s recognition, courtship, and possibly inkeeping schools of fish together.

The ocean's water is in constant motion. It is moved andmixed by currents (chapter 8), waves (chapter 9), and tides(chapter 10). Below the surface layers, the ocean environ­ment is very uniform, providing marine organisms withsimilar conditions of temperature and salinity in any oceanat any time. Oceanic circulation brings food and oxygen,repleni shes nutrients, and removes waste; it disperses float­ing organisms and scatters the reproductive stages of swim­mers and attached forms.

Those plants and animals that drift rather than swimare carried along by the currents and run the risk of beingcarried out of a suitable habitat by either vertical or hori­zontal movement. However, analysi s of their remains onthe seafloor and observations of living populations showthat this does not always happen. Populations of driftinganimals appear to take advantage of their ability to move inthe vertical direction either by swimming or by changingtheir buoyancy. They are able to maintain their place hori­zontally in ocean space by moving away from the surfaceduring the day to depths where a current flows in a direc­tion opposite to the surface current. They then moveupward at night to be carried back to their starting position.Organisms also appear to maintain their position by addingto their population on the upstream side of a current to bal­ance losses on the downstream side. This pattern is relatedto the new supply of food and nutrients brought into thepopulation by the current upstream, in contrast to the food­depleted water downstream.

Vertical water motions in the sea are much slowerthan horizontal motions, but small displacements of organ­isms in the vertical direction can mean substantial changesin light, salinity, temperature, and nutrient supply. If thevertical flow is upward, it counteracts the tendency oforganisms and other particulate matter to sink. In this way,light-dependent organisms are he1d in the photic zone. Theupward motion of the water also supplies nutrients to thephotic zone to promote plant growth. At the same time,these upward flows decrease the temperature of the surfacewaters and return water with a low oxygen content to thesurface, where oxygen is replenished by photosynthesis andatmospheric exchange.

eire lation13.8

Rockfish

Chinook salmon

color change; they are able to flash and change color pat­terns with great rapidity, expanding and contracting pig­ment cells. Many squid also have bioluminescent cells, andsome have colonies of light-emitting bacteria covered by aflap of skin. When combined, these allow the squid to dis­play hundred s of different and complex color patterns andsequences, allowing them to change color and disappearalmost instantaneously.

Figure 13. 7The winter flounder resting on a checkerboa rd pattern shows its use ofcam ouflage.

Figure 13.5Viewed from above, the dark dorsal surface of the fish blends with theseafloor; viewed from below. the light ventral surface blends with the seasurface. This type of coloration is known as countershading.

Figure 13.6Pigment cells from a section or fish skin.

Circulation 339

A downw ard vertical flow under an area of surfaceconvergence accumulate s a population of organisms as thesurface flows move toward the area of downwelling. If theorganisms cannot increase their buoyancy to compensatefor the downward current , they are carried down to changesin light, temperature, salinity, nutrients, and gases. Areas ofdownwelling are usually regions of low plant growth, but atthe surface convergence , the accumulation of organ ismsprovides a rich feeding ground for carnivores.

In the sea, species and populations are isolated from oneanothe r by barriers where the properties of the waterchange abruptly. Near-surface boundari es in the water col­umn may be sharp; for example, rapid changes with depthin temp eratu re (th ermocline) , den sity (pycnocline) , andsalinity (halocJine) (refer to chapter 6). Light intensity alsochanges rapidly in the vertical direction (refer to chapter 4).Th ese boundaries are barrier s for marine or ganism s,because they do not survive if displaced through such aboundary. The effects of these barriers decreases at deeperdepth s, where water properties become more homogeneous.

Similar barri er s exi st in the hori zontal direction,where surface water of one type is adjacent to surface waterof another type (refer again to chapter 6). These boundariesare often associated with zones of surface convergence anddi ver gen ce in the oce an and al so occur in estu ari e s,betw een land-derived fre sh wate r and seawate r in thecoastal zone. When they are associated with a rapidly flow­ing current of one type of water moving through or adjacentto another type, the boundaries are sharp; for example, pop­ulations that do well in the warm , saline waters of the GulfStream may die if they are displaced into the cold, less­saline Labrador Current water between the coast and theGulf Stream.

Other boundaries are controlled by the topogr aphy ofthe seafloor (see chapter 2). Ridges that isolate one deep­ocean basin from another prevent the deeper water in thebasin s from freely exch anging , and water of dissi milarcharacteristics and populations may exist on either side of asubmarine ridge. In other cases, the water and the popul a­tions in the two basins may be similar, but the populationsare not able to move between the basins because the eleva­tion of the ridge that separates them forces the animals tochange their depth and pass upward into water with proper­ties that they cannot tolerate. Isolated seamounts with theirpeaks in shallow water may support spec ific isolated com­munities of sea life in much the same way that mountaintops on land support wide ly separated arcti c and alpinecommunities.

Lateral topographic barriers also isolate populations.Near-surface and surface spec ies of the tropic regions areprevent ed from moving between the Atlantic and Pacificoceans by the land barrier of Central America. Trop ical sur­face species such as sea snakes cannot migrate around thecontine nta l landm asse s of North and South Am eri ca,because to do so they must pass through regions of much

colder water. Africa also acts as a barrier, keeping the tropi­cal species of the Indian Ocean from communicating freelywith the tropical species of the Atlantic, because the watersouth of Africa is too cold for the tropical species of eitherocean .

Because the marine environment is so large and complex,biological oceanographers , marine biologists, and ecolo­gists interestecl in the sea divid e the marine environmentinto subunits called zones. The zone class if ications usedhere are based on the system developed by Joel Hedgpethin 1957; they are shown in figure 13.8. The water environ­ment is the pelagic zone, and the seafloor environment isthe benthic zone. The pelag ic zone is divided into thecoastal or neritic zone above the continental shelf, and theoceanic zone, or deep water away from the influence ofland. The oceanic zone is then subdivided by depth as fol­low s. The sur face wat ers to 200 m (660 f t) a re th eepipelagic zone; the meso pelagic zone is the twilight zonebetween 200 m (660 ft ) and 1000 m (3300 ft); the batby­pelagic zone ex tends to 4000 m (13, 20 0 ft) , and theabyssopelagic zone extends to the deepest depths . All

Bottom Types

E vironme al Zo es

13.10

13.11

Although the properties of the seawater are critical for thesurvival of marine organisms, for many plants and animalsthe type of ocean bottom-rock, mud , sand, or gravel- isequally important. A seaweed that requires rock for attach­ment is unable to live in sand, and a burrowing worm froma mud flat or a shrimp from a sand beach cannot survive ona rocky reef. The material of the seafloor, or substrate,provides food, shelter, and attachment sites, each substratetype providing suitable living space for a different group oforganisms. Substrates show greater variety along the shal­low coas tal areas ; sandbars , mud flats, rocky points, andstretches of grav el and pebble are frequently found alongthe same strip of coastline. Further seaward, as the seafloorbecomes more distant from the sea surface, the particle sizeof the sediments and the amount of organic matter associ­ated with the substrates decrease; the substrate becomesmore uniform, The decline in the variety of the substrate ismatched by a decrease in the animal mass.

Organi sms living attached to the seafloor often mod­ify their habitats, providing food, she lter, and additionalsurfaces for the attachment of still other organisms. Forestsof large seaweed attached to rocky bottoms in 20 m (66 ft )of water and eel grass beds in shallow, quiet, sandy, ormuddy bays both provide such environments, but for quitedi fferent popul ations of organisms. Some crabs movingacross the seafloor carry anemones attached to their backs,and some sea anemon es harbor specialized fish within theirtentacles. The most outstanding example of biological mod­ification of a substrate is the tropical coral reef; here theorganisms create a spec ialized environment over the stonyske letons of other organisms (see chapter 17).

Boundariesers aBa13.9

340 Oceans: EnvironmentjOrLift

Coastal zoneFigure 13.8Zones of the marine environment.

200

oro'"0

2000 {

ro~

4000

- - --- 6000

Aphotic zone

---~---\ Abysso-

pelagiczone

--- 1000

Bathypelagiczone

Oceanic zone

Mesopelagiczone

tEpipelagic Photic zone

___~~~ L__Neritic zone I

I

-~ :Sublll10r I zone /(subtidal zona)

Outer edge ofcontinental shelf

PelagicBenthic water

i

/Suprali lt oral \

zonotsplash zona)

Littoralzona

(intertklzona)

13.13

oceanic subdivisions, except for the epipelagic zone, areaphotic, or without light. The photic zone coincides roughlywith the epipelagic and neritic zones. Locate each zone infigure 13.8.

The seafloor, or benthic environment, is subdividedinto comparable zones. Tidal fluctu ations at the shorelinedefine the supralittoral zone, or splash zone, which liesjust above the high-water mark and is covered by the seaonly during the highest spring tides or by wave spray, andthe littoral zone, or intertidal zone, which lies betweenhigh and low water and is covered and uncovered once ortwice each day . The sublittoral zone, or subtidal zone,extends out along the continental shelf. The supralittoral ,littoral, and inner portion of the sublittoral zones occupythe same area as the benthic photic zone because sufficientlight is present to support single-celled plants and largebenthic plants.

Within the aphotic zone are the deeper portions of thesubtidal zone; the bathyal zone, extending from 200 m(660 ft) to 4000 m (13,200 ft) and coinciding with the con­tinental slope , and the abyssal zone, between 4000 m and6000 m, or roughly the area over the abyssal plain. Thehadal zone lies below 6000 m (19,800 ft) and is associatedwith the trenches and deeps (see again fig. 13.8).

The properties of the littoral and epipelagic zones arekeyed to latitude; keep in mind that these zones differmarkedly , depending on whether they are at polar, temper­ate, or tropic latitudes. Substrate plays a basic role in ben­thic zones, and there is much less variety in substrates inthe deeper zones . Life in all the zones is influenced by vari­ations in temperature, light, dissolved gases, nutrients, andall the factors discussed in this chapter.

13.12 Classification of. OrganiS1l1S

All of these ocean zones together mak e up the variedmarine environment, which is inhabited by a wide varietyof organi sms uniquely adapted to it. These organi sms aredivided into groups to promote ease of identification and toincrease our under standing of the relationships that existamon g them. Classi c taxonomic categories are listed intable 13.2 . A s imple and practical method divides allmarine organisms into three group s, based on where andhow they live. Plants and animals that float or drift with themovements of the water are the plankton. Those that liveattached to the bottom or on or in the bottom are the ben­thos, and the animals that swim freely and purposefully inthe sea are the nekton. Chapters 15, 16, and 17 use thisthree-part system.

Practical Consideratio IS:

Modification andMitigation

At the sa me time that we have been acquiring greaterunderstanding of how the physical, chemical, and geologi­cal factors discussed in this chapter interact to produce themany and different environments of the ocean, we havebeen bringing greater and lastin g changes to these oceanenvironments, especially in coa stal ba ys and estuari es ,where environments are typically small-scaled and varied .In some cases, using our knowledge of organisms and theirpreferred habitat s, we have altered an area to enhance the

PracticalConsiderations: Modification and M itigation 341

Table 13.2

Taxonomic Categories of Some Marine Organisms

PacificNorthern (Japanese)

Killer whale fur seal oyster Giant octopus Sea lettuce Giant kelp

king dom Animalia Anima lia An imal ia Anima lia Plantae Plantae

ph ylum Chordata Chordata Mollusca Mollu sca C hlo rophy ta Phacoph yta

cla ss Ma mma lia Ma mmalia Biva lvia Cephalopoda Chlo rophyeae Phae ophycae(pelecypoda)

order Cetacea Carn ivora Anisornyuria Oc topoda Ulvales Laminar iales

(P innipedia)

fam ily Delphinidae Oiariidae Oxtreidae Oc topodidac Ulvaceae Lessoniaceae

ge nus Orcinus Callorhlntts Crassostrea OCIOP!!.\" Viva Macrocystis

species Orcinus orca Callo rhinus Crassostrea Octopus Viva Macrocystisursinus gigas dofleini lactuca pyrifera

popul ations of organisms we consider desirable over thosewe consider undesirable. We build artificial reefs using oldcar bodies, bags of old shells, or chunks of fractured con­crete to encourage the growth of organisms that not only dowell in a ree f's protected nooks and crannies, but are wellsuited to recreational and sport fishing as well as commer­cial harve sting.

Developm ent and modification of estuaries and baysis often done at the expense of wetl and s and mud flats;refer bac k to chapter 12. Our engineering techniques allowus to move sediment, change the slope of the bottom, andalter subs trates. We deepen channels, bu ild marin as andprotective breakwaters, and bulkhea d the land to prevent itserosion. T hese act ivities do not remove marine habitat s asmuch as they chan ge them, substituting a new hab itat andits biological communities for the previous habitat com­plex. In some cases our activities resul t in the creation ofnonm arine uplands, and in this case there is a true loss ofmarine environment.

Our abi li ty to modify or reengin eer the oc eans'shall ow-water env iro nme nts also all ows us to cre atenew marshes , tide flats, and special habitats from less­pro ductive or less-desirable areas and to reest ablish com­munities of marine plants and anima ls. We can and dochoose which habitats and which orga nisms are to be con­served and which are to be sac rificed.

Present policies at national, state, and local levels, ata minimum seek to conserve our existi ng marine habitats ,and to improve them when possible, while at the same timeinc reasing population s promote de velopme nt of co as talzones. Attempting to balance hum an and natural needs hasled planners and dev elopers to the co as tal-ma nage mentconcep t of mitigation.

When development projects alter or destroy an env i­ronment, mana gement authorities at the local , sta te, or

342 Oceans: Environmentfor Life

federal level may choose to enforce mi tigati on of theseeffects by requiring the developer to purchase an area of thesame type as that to be developed and to arrange for it to beheld in its natural sta te, or the developer may be required toreengineer an area to resemble what has been lost. Suchrequired projects are examples of compensa tory mitigation;compensation is paid for change and destructi on. Projectsthat are vo lunt ari ly undertaken to improve coas ta l andshore areas are considered noncompensatory mitigation.

A successful mi tigati on project requi res a thorou ghknow ledge of the physical requiremen ts need ed to suppor tthe communities of plants and animal s that the mitigationseeks to enhance . Any characteristics of the new environ­men t tha t interfere wi th the mitigation process mu st becha nged if the mitigated area is to sus tain itself in thefuture . After the area has been restructured it must be moni­tored, and changes must be made as needed to maintain thenew environment. If these preproject and pos tprojec t stud­ies are not made, the mitigation effort is likely to fail.

While miti gat io n does preser ve some habi tats andspec ies, it can only approximate the lost environment, notduplicate it. The result is still a shift or a change in habitatproduced by hum an pressures.

Developm ent pressures in deep-sea areas asso ciatedwith min ing and ene rgy proj ect s are s till in the future.Tropical OTEC plants (chapter 6) will force cold, nutri ent­rich water to the sea surface, changing the surface produc­tivity ; and man ganese nod ule mining (cha pte r 2) willincrease deep-sea turbidity, changing the environment forbottom organisms in mined areas. However, because of thevast size of deep- sea areas wi th co mmon properties,changes in deep water are likely to be less significant thancha nges in the coastal zo ne. Ho w mitigation mi ght beundertaken in the open ocean has not yet been considered.

Spartina: Valuable and Productive or Invasiv e and Destructive?

Spartina alte rniflora , known as smoothcordgrass, many spiked cordgrass, and saltmarsh cordgrass, is a deciduous, perennialflowering plant native to the Atlantic andGulf coas ts of the United States. It is thedominant native species of the lower saltmarshes along the Atlantic seaboard fromNewfoundland to Florida, and on the GulfCoast from Florid a to East Texas. It growsin the intert idal zone from mean higherhigh water to 1.8 m (6 ft ) below meanhigher high water.

These natural salt m ar sh e s areamong the most produ ctive habitats in themarine environment. Nutrient-rich wateris brought to the we tla nds during eachhigh tid e, making a hi gh rate of foodprodu ction possibl e. As the seaweed andmarsh gras s lea ves die, bacteria breakdown the plant material, and in se ct s,s ma ll shrimp like organi sm s , fiddlercrabs, and marsh snails eat the decayingplant tissue , digest it, and excrete wasteshigh in nutrients. Numerous in se ct soccupy the marsh, feeding on living ordead plant tissue, and red-winged black­birds, spa rro ws , rod ents, rabbit s , anddeer feed direc tly on the cordgrass. Eachtidal cycle carries plant material into theoffshore water to be used by the subtidalorgani sms.

Spartina is an exceedingly competi­tive plant . lt spread s primarily by under ­ground stems; colonies form when piec esof the root system or whole plants flo atinto an area and take root, or when seedsfloat into a suitable area and germinate. Itestablishes itself on substr ates rangingfrom sand and sil t to grav el and cobbleand is tolerant of salinities ranging fromnear fresh to salt water (35%0). Spartinais able to tolerate high salinities becausesalt glands on the surface of the leavesremo ve the salt from the plant sap, leav­ing visibl e white salt crystals. Because ofthe lack of oxygen in marsh sedime nts,they are high in sulfides that are toxic tomost plants. S. aiterniflora has the abilit yto take up sulfides and conv ert them tosulfate, a form of sulfur that the plant canuse; thi s abili ty makes it easier for thegrass to colon ize marsh environme nts.Another adaptive adv antage is its bio ­che mical photosynthetic pathway thatuses carbon dioxide more efficiently thanmost other plant s.

These chara cteristics make Spart inaalterniflora a valuable component of thees tuaries where it occurs naturally. Th e

1.\ .,f\,h' iBoxfigure 13.1A naturall y occurring Spartina marsh .

plan t functions as a stabilizer and sedi­ment trap and as a nursery area for estua­rine fish es and shellfishes . Once estab­lished, a stand of Spartina begins to trapsediment, changing the substrate eleva­tion, and eventually the stand evolves intoa high marsh system where Spartina isgradually disp laced by higher-elevation,bracki sh- wat er spec ies . As el evationincreases, narro w, deep channels of waterform throughout the marsh (see Box fig.13.1) . Along the East Coast Spart ina isconsidered valuable for its ability to pre­vent erosion and marshland deteriorati on;it is also used for coastal restoration pro ­ject s and th e creation of new wetl andsites.

Spartina alterniflora has been intro ­duced to and naturalized in Washington,Oregon , California, England, Fr an ce ,New Zea land, and China. Spartina wascarried to Wa shington State in packingmaterial for oysters transplanted from theEast Coast in 1894. Le aving its insect

predators behind, the cordgrass has beenspreading sl o wl y an d steadily alongWashington' s tidal estuaries , crowdingout th e native plants and drastic allyalterin g the land scap e by trapping sedi­ment. It turn s tid al mud flat s into highmarshes inhospitable to many fish andwaterfowl that depend on the mud flats .By 198 8 it covered 1650 ac res inWashington's Will apa Bay ; it had spreadto 2500 acres by 1991 , and state officialspredict that by 20 I0 it will cover most ofthe bay' s 30,000 acres if left unchecked(see Box fig. 13.2). It is already hampe r­ing the oyster harv est, and it in terfereswith recreational use of bea ch es andwaterfronts.

Sp artina ha s been transplanted toEngland and New Zealand for land recla­mation and shorel ine s tabil iza t ion. InNew Zealand the plant ha s s pre adrapidly , changing mud flat s with marsh yfringes to exten sive salt meadows andredu cing the number and kind s of bird s

continued

Boxjig1/1oe 13 .2Circul.u patehe.' o f Spartiu« spread a1()I11,' the mud flats of Willupa Bay. Washington. The large circle at lower left is thoughr ro be the oug inal colony. Thisphotugruph was laken with infrared film arul i:-a fal:-e co lor image.

Spartina-continued

and animals that use the marsh. Anotherspecies of Spartina (S. maritima) occursin marshes along the coast s of Europeand Africa. S. altemiflora was introducedinto Great Britain from eastern NorthAmerica in about 1800 and spread toform large colonies. The native speciesand the introduced specie s existedtogether throughout the nineteenth cen­tury , and by 1870 a sterile hybrid thatreproduced by underground s temsappeared . About 1890, a vigorous seed­producing form was deriv ed naturally

from this hybrid and spread rapidly alongthe coasts of Great Britain and northwest­ern France.

Efforts to control Spartina outside itsnatural environment have included burn­ing, flooding , shading plants with blackcanvas or plastic, smothering the plantswith dredged materials or clay, applyingherbicide, and repeated rnowings . Littlesu ccess has been reported in NewZealand and England; Washington Statehas declared Spartina a "noxiou s weed"and set up tests using mowing and herbi­cide applications to control its spread.

Preliminary work has begun to determinethe feasibility of using insects as biologi­cal controls, but effective biological con­trols are considered ten years away. Evenwith a massive effort it is doubtful thatcomplete eradication of Spartina fromnonnative habitat s is possible, for it hasbecome an integral part of these shore­lines and estuaries during the last 100 to200 years . A management plan thatincludes mowing for small , acce ssiblepatches and biological controls for long­term regulation may be the most realisticapproach.

necessarily scattered, but keep their place due tomovements between surface currents and deeper currents.Upwellings supply nutrients and hold plants in the surfacelayers. Downwellings are regions of low plant growth.

Barriers for marine organisms include waterproperties, light intensity , zones of convergence anddivergence, seafloor topography, and geography. Differentsubstrates provide food, shelter, and attachment fordifferent groups of organisms.

The marine environment is subdivided into zones.The major environments are the benthic and pelagic zones;there are numerous subdivisions of each of these zones.

The organisms of the sea are classified foridentification and relationship. Organisms are also groupedas plankton, nekton, and benthos .

Development of marine areas , with the consequentloss of habitat and therefore populations, has led to theconcept of mitigation, under which developers are requiredto preserve or replace habitats in an effort to maintain andpreserve species.

Summary

Organisms living in the sea are buoyed and supported bythe seawater. Adaptations for staying afloat include low­density body fluids, gas bubbles, gas-filled floats, swimbladders, oil and fat storage, and extended surface areasand appendages.

Most marine fish lose water by osmosis. They drinkcontinually and excrete salt to prevent dehydration. Sharkshave the same concentration of salt in their tissues as thereis in seawater. They therefore do not have a water-lossproblem. Salinity is a barrier to some organisms; others canadapt to large salinity changes.

Temperature affects density, viscosity, and thewater' s buoyancy, as well as the stability of the watercolumn. The body temperature and metabolism of allmarine organisms, except for birds and mammals, arecontrolled by the sea temperature. Some fish conserve heatin their body muscles and elevate the temperature in thesemuscles. Temperatures at depth are uniform; sea-surfacetemperatures change with latitude and seasons.

Changes in pressure affect organisms with gas-filledcavities. Marine mammals have a unique ability to undergolarge pressure changes due to their physiology and bodychemistry. The swim bladders of fish are affected bypressure changes, and the fish must change depth slowly.

The carbon dioxide-oxygen balance in the oceansinfluences the distribution of all organisms. The availabilityof nutrients and light limits plant populations. The depth oflight penetration in the oceans is controlled by the angle ofthe sun's rays , the properties of the water, and the materialin the water. Light limits plant life, but nutrients are alsorequired. Some organisms produce chemical light, knownas bioluminescence. Animals use color for concealment andcamouflage and also to warn predators of poisonous fleshand bitter taste.

Winds , tides , and currents mix the water. Movingwater carries food and oxygen, removes waste, anddisperses organisms. Floating populations are not

buoyancyosmosisanaer obicphotic zoneaphotic zonebioluminescenceluciferinluciferasephotophoresubstratepelagic zonebenthic zoneneritic zoneoceanic zone

Key Terms

epipelagic zonemesopelagic zonebathypeiagic zoneabyssopelagic zonesupralittoral zone/splash zonelittoral zone/intertidal zonesublittoral zone/subtidal zonebathyal zoneabyssal zonehadal zoneplanktonbenthosnektonmitigation

Key Terms 345

Study Questions

L How do so many delicate and fragile organisms exist inthe oceans without damage?

2. What will happen to the body fluids of a frog placed inseawater? A sea cucumber placed in fresh water'!

3. Discuss the effect of temperature on the distribution oforganisms. Consider changes with latitude and withdepth .

4. Although seals and whales are mamm als, they do notsuffer from either decompressio n sickness or nitrogennarcosis during deep dives of long duration. Explain why .

5. How does the role of bioluminescence dif fer from the roleof sunlight in the sea?

6. Compa re the flotation problems of a many-armedorganism with those of an organism without arms but ofthe same density. Consider both organisms in 4°C waterand in 20°C water.

7.m what ways does upwell ing contribute to increasing thepopul ations of surface organisms? What properties ofseawater act as barriers for marin e organisms?

8. Explain why the substrate of the seafloor becomes lessdiversified as one moves from the shore to the deepocean.

9. What characteristics determine whether a plant or ananimal belongs to the plankton , the nekton, or thebenthos?

10. What properties of seawater act as barriers for marineorgan isms?

11. Why are Spartina marshes along the eas t coast conside redproductive while those along the west coas t areconsidered destructive?

346 Oceans: EnvironmentfOr Life

12. Why is the neritic zone of prim ary importance to theworld's commercial fishing industries?

13. Find an example of mitigation being used in yourcommunity and discuss its effect.

14. How does countershading aid the survival of fish innearshore areas?

15. How do rapidl y increasing populations of single-celledplants limit their own growth?

Suggested ReadingsBertness, M. D. 1992. T he Eco logy of a New England Salt Marsh .

American Scientist 80 (3) : 260-68.Fitzgera ld, L. M. 1990. Seven Under water Wonde rs of the World . Sea

Frontiers 36 (6): &--2 1.Lerman, M. 1986. Marine Biology, Environment, Diversity and Ecology .

Benjamin -Cummings, Menlo Park, Calif. 535 pp.Lire ill I I II' Sea, readings from Scientific American , 1982. Freem an, San

Francisco. 248 pp. (Art icles on marine organisms, the conditi on inwhich they live , and their food resources.)

MacLeish, W. H. ed. Fa ll 1980 . Oceanus 23 (3). (Issue include s articleson the various sen ses of org anisms of the sea.)

Nealson, K., and C. Arneson. 198 5. Mari ne Biolumin escence: About toSee the Light. Oceanus 28 (3): 13- 18.

Nybakken, J. 1989. Muri ne Biology, All Ecological Approach, 2d ed.Harper & Row , New York. 5 14 pp.

Siezen, R. 1986. Cuttlebo ne: The Buoyant Ske leton. Sea Frontiers 32 (2):115- 22.

Sumich, J. L. J992 . An Introduction to lire Biology ofMar ine LIf e, 5th ed.Wm. C. Brown. Dubuque, la. 449 pp .

Wa rd. P., L. Gree nwald. and O. E. Greenwa ld. 1980. The Buoyancy of theCha mbere d Na utilus. Scien tific American 243 (4) : 190--203.