lecture_6_12_oct_2010

lecture_6_12_oct_2010 - Open Ocean and Deep Sea P e la g ic...

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1 Open Ocean and Deep Sea Pelagic zones Epipelagic = surface to 200 meters (150 meters in Levinton) depth, seaward of the shelf-slope break. Mesopelagic = 200–1000 m depth, seaward of the shelf-slope Bathypelagic = > 1000 m; 79% of volume of Earth’s biosphere FIG. 1.13 A cross section of the ocean from the shoreline to the deep sea, showing the location of major marine habitats. Benthic zones Bathyal = along continental slope (200–4000 m) Abyssal = along continental rise and abyssal plain (4000–6000 m) Hadal = in deep sea trenches (> 6000 m) FIG. 2.11 Oxygen minimum layers: depth profiles of dissolved oxygen as a function of depth. Note the strong presence of oxygen minimum layers in the eastern Pacific, off the coast of California, as compared with their absence in the North Atlantic. (From Childress and Seibel, 1998, reproduced with permission of the Company of Biologists.) FIG. 2.12 An example of the pattern of exponential decline in light intensity with increasing depth in a coastal marine water column. Epipelagic zone High light intensity Temperature, oxygen, light decrease with depth Characteristics of epipelagic organisms fusiform body - reduces drag large stiff, forked caudal fin - powerful, generates lots of thrust “Flying fishes” Do not flap “wings” (fins) or “fly” Swim rapidly, leave water and glide away from predators such as mahi mahi
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2 Characteristics of epipelagic organisms Crypsis - difficult to hide in clear water Many are clear Many have bluish colors Countershaded fishes (dark above, light or silver below) Body reflects light so as to match background color Almost all light is from above Countershading is reverse of background light little light reflected from dorsal surface more light reflected from side and ventral surface obscures outline of fish by eliminating contrast of fish and background Epipelagic zone Floating objects are attractive to organisms (logs, seaweed, etc) Shelter, crypsis (hide in shadows beneath it, seek refuge when approached) Concentrations of food Floating Logs - tuna congregate near these in the tropical eastern Pacific Diverse group of organisms also present under and around logs Groswald 1995
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3 Epipelagic organisms - Pelagic Sargassum community Brown alga (Phaeophyta) Several benthic species Holdfast (for attachment to bottom) Air-filled spheres (hold plant erect) Atlantic species entirely pelagic no holdfast air-filled spheres keep plant at surface Epipelagic organisms - Pelagic Sargassum community Persistent in the pelagic realm, especially in the north Atlantic “Sargasso Sea” - central gyre of the north Atlantic Sargassum rafts common in this region Pelagic Sargassum community Forms huge rafts of floating algae Fishes, etc. associate with this as with other floating objects Persistence of pelagic Sargassum had led to the evolution of a community of
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lecture_6_12_oct_2010 - Open Ocean and Deep Sea P e la g ic...

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