I. Physical Environment

C. Salinity• Usually expressed in ‰ (g per kg)• “Average” sea water ~34.7 ‰

• 33-37 ‰ in open ocean (very consistent)

• Fresh water < 0.5 ‰• Brackish water – 0.5-17 ‰• 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

Fig. 2-4

Fig. 4-5

I. Physical Environment

D. Pressure• Increases predictably with depth

• 10 m = 1 atmosphere (14.7 psi)• Pressure @ 3700 m = 5450 psi

• Affects gas-filled structures• Constrains vertical movements of many

animals

I. Physical Environment

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)

I. Physical Environment

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

I. Physical Environment

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

I. Physical Environment

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

HalobatesFig. 4-2

I. Physical Environment

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. Nutrient Availability• Food availability decreases with depth• Sea water contains many dissolved

chemicals that can be absorbed directly

II. Zonation

• Important concept in biological oceanography• Construct created by humans, but zonation has a

basis in ecological realityA. Pelagic/Benthic

• Pelagic = “open sea”• Benthic = “bottom”• “Reverse benthic”

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

Fig. 2-24

II. Zonation

C. Depth Zones• Limits subjective & variable, ecologically-

based1. Pelagic

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

II. Zonation

C. Depth Zones1. Pelagic

b. Mesopelagic (200-1000 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. Bathypelagic (1000-4000 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

II. Zonation

C. Depth Zones1. Pelagic

d. Abyssopelagic (4000-6000 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. Hadopelagic (6000-11,000 m)• Includes trenches; maximum depth of ocean• Pelagic trench fauna very poorly studied• Food resources often more plentiful than in

abyssopelagic zone

II. Zonation

C. Depth Zones2. Benthic

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. 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