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I. I.Physical Environment C. C.Salinity Usually expressed in ‰ (g per kg) “Average” sea water ~34.7 ‰ 33-37 ‰ in open ocean (very consistent) Fresh water.

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Presentation on theme: "I. I.Physical Environment C. C.Salinity Usually expressed in ‰ (g per kg) “Average” sea water ~34.7 ‰ 33-37 ‰ in open ocean (very consistent) Fresh water."— Presentation transcript:

1 I. I.Physical Environment C. C.Salinity Usually expressed in ‰ (g per kg) “Average” sea water ~34.7 ‰ ‰ in open ocean (very consistent) Fresh water < 0.5 ‰ Brackish water – ‰ Consistent in open ocean Variable in shallow areas and near sources of fresh water Ion composition consistent throughout ocean Osmoregulation energetically expensive Most marine organisms are osmoconformers

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4 Fig. 4-5

5 I. I.Physical Environment D. D.Pressure Increases predictably with depth 10 m = 1 atmosphere (14.7 psi) 3700 m = 5450 psi Affects gas-filled structures Constrains vertical movements of many animals

6 I. I.Physical Environment E. E.Density Sea water 830x denser than air Reduces need for substantial support structures Marine organisms have adaptations for buoyancy, not support Examples: Fishes have light, flexible bones and swim bladders filled with gas/lipid Whales have hollow bones filled with lipid Most marine plant species are microscopic, floating organisms Many marine macrophytes use gases for buoyancy Many organisms live in permanent suspension (bacteria, viruses) High density of sea water also influences: Locomotion (less energy required than in air) Feeding (enables suspension feeding) Communication (efficient sound transmission)

7 I. I.Physical Environment F. F.Gas Availability Oxygen concentrations in sea water much lower than in air (~0.001% vs. 21%) More soluble at lower temperatures Concentrations affected by biological activity Aerobic organisms may be limited in design, metabolic activity and distribution by Oxygen availability Ability to carry out rapid gas exchange

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9 I. I.Physical Environment G. G.Viscosity Stickiness to objects due to adhesion Objects moving through water drag some water with them Many aquatic animals have adaptations to manipulate drag Reduce: fast-swimming species (squid, tuna) Use: some suspension feeders Link

10 I. I.Physical Environment H. H.Surface Tension Stickiness at the surface due to cohesion Water surface can support weight of very small organisms Air-water interface supports numerous organisms Microbes in surface films Halobates Fig. 4-2

11 I. I.Physical Environment I. I.Water vs. Air Dehydration not a problem (most terrestrial organisms expend energy avoiding desiccation) Some marine organisms expend energy getting rid of water J. J.Nutrient Availability Food availability decreases with depth Sea water contains many dissolved chemicals that can be absorbed directly

12 II. II.Zonation Important concept in biological oceanography Construct created by humans, but zonation has a basis in ecological reality A. A.Pelagic/Benthic Pelagic = “open sea” Benthic = “bottom” “Reverse benthic” B. B.Neritic/Oceanic Neritic zone overlies continental shelf Bounded by land and 200 m isobath (typically), representing edge of continental shelf Exception: Ross Sea (shelf to 800 m depth) Some neritic zones are wide (E. Coast of US); others are narrow (W. Coast of S. America) Oceanic zone overlies deeper water Overall, 92% of World Ocean is oceanic

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14 II. II.Zonation C. C.Depth Zones Limits subjective & variable, ecologically- based 1. 1.Pelagic a. a.Epipelagic (0-200 m) Definition based mainly on downwelling light intensity Functionally similar to euphotic zone Nearly all photosynthetic marine organisms Epipelagic organisms adapted to well-lighted environment with few horizontal obstructions Air-sea interface important to some organisms

15 II. II.Zonation C. C.Depth Zones 1. 1.Pelagic b. b.Mesopelagic ( m) Extends from lower limit of epipelagic zone to nominal depth of maximum sunlight penetration Organisms typically non-photosynthetic Some may migrate into surface waters periodically Organisms adapted to low-light, fairly high-pressure environment with limited food availability and relatively cold temperatures c. c.Bathypelagic ( m) Extends from lower limit of mesopelagic zone to ~mean depth of ocean Organisms typically non-migratory Low densities and difficulty of sampling limit knowledge of organisms

16 II. II.Zonation C. C.Depth Zones 1. 1.Pelagic d. d.Abyssopelagic ( m) Conditions similar to bathypelagic zone Organisms living in association w/sea floor show very different adaptations vs. purely pelagic organisms Bottom-associated (benthopelagic, nektobenthic) animals often active scavengers and/or predators, skilled at detecting, localizing & utilizing scarce food Benthopelagic species typically w/larger eyes and less watery tissues than species not associated with sea floor e. e.Hadopelagic ( ,000 m) Includes trenches; maximum depth of ocean Pelagic trench fauna very poorly studied Food resources often more plentiful than in abyssopelagic zone

17 II. II.Zonation C. C.Depth Zones 2. 2.Benthic a. a.Supralittoral (Above mean high water) “Splash zone” (Ex: La Bufadora) May be immersed during storms and unusual high tides Organisms adapted to almost constant exposure to terrestrial conditions but also must be able to cope with aquatic conditions periodically Conditions may be highly variable Harsh conditions  few organisms in this zone b. b.Littoral/Intertidal (Mean high water to mean low water) Immersed at high tide, exposed at low tide Organisms must be able to cope with complete exposure and complete immersion every day High light levels may support extensive populations of photosynthetic organisms


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