I. Central Case: Collapseofthe Cod Fisheries A. No fishhashad moreof an impact on human civilization than theAtlantic cod.
B. This abundant groundfish (fish that feed on the bottomof theocean)was a dietarystaple in cultures on both sides of theAtlantic.
C. Cod provided the economic engine formanycommunities alongcoastal
NewEngland and Canada.
D. Afterdecades of technologicallyadvanced fishingtechniques harvested
manymaturebreedingadults, the cod populations in theAtlantic ―crashed.
E. Government officials in Canada, followed byU.S. officials, closed fishing areas to all commercial fishing. In most of the areas, the cod havenot rebounded.
1. It is believed that cod remain limited because the formerpreyof adultcod arenow competingfor food with youngcod and even eatingthembefore theycan mature.
2. A bright spot is that areas of theGeorges Bank arerecoveringdueto elimination ofdestructivepractices such as trawling. Some other species arerecovering, such as seascallops.
II. The Oceans A. Oceans cover most of Earth’s surface.
1. Theworld’s five oceans—Pacific, Atlantic, Indian, Arctic, and Southern— areallconnected, comprisingasingle vast bodyof water. This one―world ocean‖covers 71%of Earth’s surface and contains 97.5% ofits water.
B. Seafloortopographycan be rugged.
1. To comprehend underwatergeographic features, we can examinea stylized map that reflectsbathymetry (themeasurement ofocean depths) and topography (physical geography, or theshape and arrangement of landforms).
2. In bathymetricprofile, gentlyslopingcontinental shelves underlie the shallow waters borderingthe continents.
a. Continental shelves varytremendouslyin width but average80 km (50 mi) wide, with an averageslope ofjust1.9 m/km (10 ft/mi).
b. Theseshelves drop off at the shelf-slope break, wherethe continental slope angles moresteeplydownward to the deep ocean basin below.
3. Wherever reefs, volcanism, or otherprocesses create physical structure underwater, lifethrives.
C. Ocean water contains salts.
1. Ocean water contains approximately96.5%H2O bymass. Most of the remainder consistsof ions from dissolved salts.
2. Ocean wateris saltybecause theocean basinsarethe final repositories for waterthat runs offthe land.
3. Evaporation from theocean surfacethen removes purewater, leavinga higher concentration ofsalts.
4. Thesalinityof ocean watergenerallyranges from 33 to 37 parts per thousand (ppt), varyingfrom placeto placebecause of differences in evaporation, precipitation, and freshwater runoff from land and glaciers.
5. Seawater also contains nutrients such as nitrogen and phosphorus that play essential roles in nutrient cycling.
6. Another aspect of ocean chemistryis dissolved gas content, particularly the dissolved oxygen upon which gill-breathingmarine animals depend.
D. Ocean wateris verticallystructured.
1. Waterdensityincreases as salinityrises and as temperature falls, giving riseto different layers ofwater.
2. Thewaters of thesurfacezone areheated bysunlight each dayand are stirred bywind.
3. Thepycnocline is the region below thesurfacezonein which density increases rapidlywith depth.
4. Thedeep zoneof theocean lies beneath thepycnocline and is not affected bywind and sunlight.
5. Oceans help regulate Earth’s climatebyabsorbingand releasingheat to the atmosphere.
E. Surfacewater flowshorizontallyin currents.
1. Theocean surfaceis composed of currents—vast, river-like flows driven bydensitydifferences, heatingand cooling, gravity, and wind.
2. Currents transport heat, nutrients, pollution, and the larvaeof manymarine species.
F. Vertical movement of water affects marine ecosystems.
1. Upwellingis thevertical flow of cold, deep watertoward thesurface, bringingnutrients from the bottom.
2. Downwellingtransports warm water rich in dissolved gases downward, providingoxygen fordeep-waterlife. G. Currents affect climate.
1. Thethermohaline circulationis a worldwide current system in which warmer, fresherwatermoves alongthe surface and colder, saltier water (which isdenser) moves deep beneath thesurface.
a. As this water releases heat to the air, keepingEuropewarmer than it would otherwisebe, the water cools, becomes saltierthrough evaporation, and thus becomes denser and sinks, creatinga region of downwellingknown as the North Atlantic Deep Water (NADW).
b. Scientists hypothesizethat interruptingthe thermohaline circulation could trigger rapid climate change.
2. Another interaction between currents and climateis theEl Niño– SouthernOscillation(ENSO), asystematicshift in atmosphericpressure, seasurfacetemperature, and ocean circulation in thetropical Pacific Ocean.
3. El Niñoconditions aretriggered when air pressuredecreases in the eastern Pacific and increases in thewestern Pacific, weakeningthe equatorial winds and allowingthe warm waterto flow eastward.
4. La Niñaevents arethe opposite ofEl Nino events. In aLaNiña event, cold waters riseto thesurface and extend westward in the equatorial Pacific when winds blowingto thewest strengthen, and weatherpatterns areaffected in opposite ways.
H. Climate changeis alteringthe oceans.
1. Theocean’s surfacewatermaysoon become saturated with as much CO2
as itcan hold.
2. As ocean watersoaks up CO2, itbecomes more acidic. Asocean acidificationproceeds, manyseacreatures havedifficultyformingshells because the chemicals theyneedareless available.
III. MarineandCoastalEcosystems 1. Regions of ocean waterdiffer greatly, and somezones support morelife than others.
a. Theuppermost 10 m(33 ft)of water absorbs 80%of solar energy, so nearlyallof theoceans’ primaryproductivityoccurs in thetop layer, or photic zone.
b. Habitats and ecosystems occurringbetween the ocean’s surface and
floor aretermed pelagic.
c. Those thatoccuron the ocean floorare calledbenthic.
A. Open-ocean ecosystems varyin their biodiversity.
1. Much ofthe ocean’slifeis concentrated near thesurfacein areas of nutrient-rich upwelling. These areas include avarietyof photosynthetic species and manyfree-swimminganimals.
2. In the deep ocean, animalshave adapted to deal with extreme water pressures andto livingin the dark.
3. Some extremelydeep ecosystems cluster aroundhydrothermal vents. B. Kelp forestsharbormanyorganisms.
1. Kelpis a large, brown algae; some typescan reach 200 feet in length. C. Coral reefs aretreasuretroves of biodiversity.
1. A coral reefis a mass of calcium carbonate composed of theskeletons of tinycolonial marineorganisms calledcorals.
2. Corals aretinyinvertebrate animals related to sea anemones and jellyfish.
3. Coral animals capture food with stingingtentacles and also derive nourishment from symbiotic algae, known aszooxanthellae, which inhabit theirbodies and produce food through photosynthesis.
4. Coral reefs host anincrediblediversityof life, and theyprotect shores from damagebywaves andstorms.
5. Coral reefs areexperiencingworldwide declines, probablydueto increased seasurfacetemperatures andthe influxof pollutants.
D. Intertidal zones undergo constant change.
1. Theintertidalorlittoralzonelies alongshorelines between low tide and high tide.
2. Tidesarethe periodic risingand fallingof theocean’s height at agiven
location, causedbythe gravitational pull of themoon and sun.
3. Theintertidal zoneis a tough placeto makealiving, but is hometo a remarkable diversityof organisms.
4. The rockyintertidal zoneis so diversebecauseenvironmental conditions changedramaticallyfrom the lowpart ofthe intertidal zoneto thehigh part.
E. Saltmarshes linetemperate shorelines.
1. Alongmanyof theworld’s coastsat temperate latitudes,salt marshes
occurwherethe tides wash over gentlyslopingsandyor siltysubstrates.
2. Saltmarshes boast veryhigh primaryproductivityand provide critical habitat forshorebirds, waterfowl, and manycommerciallyimportant fish and shellfish species.
3. Saltmarshes also filterpollution and stabilizeshorelines againststorm surges.
F. Mangroveforestsline coastsinthe tropics and subtropics.
1. Mangrovesaresomeof the few types of trees that aresalt-tolerant. They haveunique types of roots that curveupward likesnorkels to attain oxygen lackingin themud or that curvedownward likestilts to support thetreein changingwaterlevels.
2. Other than servingas nurseries for fish and shellfish that people harvest, mangroves also provide materials that peopleuse for food, medicine, tools, and construction.
G. Freshwatermeets saltwaterin estuaries.
1. Manysalt marshes andmangroveforestsoccurin or nearestuaries, areas whererivers flow into theocean, mixingfresh waterwith saltwater.
2. Sheltered from crashingsurf, the shallow waterof estuaries nurtures eelgrassbeds and otherplant life, producingabundant food and resources.
3. Estuaries everywherehavebeen affected bycoastal development, water pollution, habitat alteration, and overfishing.