Water, water, everywhere

• Which organisms occur at a given place in the marine environment is determined by the physical and chemical properties of the surrounding water

• Marine organisms depend on water for metabolic demands, but also as a medium through which they must travel, hunt, reproduce, avoid predation, find mates, etc.

The unique properties of water• Water is the only substance that occurs

naturally in all 3 phases: solid, liquid and gas• In liquid water, hydrogen bonds hold most of

the molecules together Hydrogen bonds

The unique properties of water• As water cools, the movement of the

molecules slows and they pack together more tightly

• Colder liquid water is denser than warmer water

• Water freezes when the molecules move so slowly that the hydrogen bonds ‘take over’, locking the molecules into a 3-dimensional pattern

• Because the same mass of water now occupies more volume as ice than as liquid water, ice is less dense than liquid water and floats

• Extremely unusual and very important for aquatic (freshwater and marine) organisms living on, in, or beneath the ice!

Got water?

• In ice, the water molecules are held together by the hydrogen bonds in the ice crystal

• When ice melts, energy (in the form of heat) is required to break the hydrogen bonds and to increase the speed of the molecules

• Because of the hydrogen bonds, more heat is required to melt ice or to convert liquid water into water vapor; gives water a high heat capacity; how much heat is needed to raise a substance’s temperature by 1 degree

What does this mean for marine life?

• Because of water’s high heat capacity, marine organisms do not experience sudden swings in temperature that may occur on land (although shallow water ecosystems are more vulnerable)

• Because of water’s hydrogen bonds, water is also an excellent solvent; water can dissolve more things than any other natural substance

Ion insolution

Saltcrystal

Seawater

• The oceans contain enough salt to cover the entire planet with a layer more than 500 feet thick!

• The salts in seawater come from the chemical weathering of rocks (via river flow) and the out-gassing of hydrothermal vents

• The total amount of solid material dissolved in water is a measure of its salinity

Salinity of seawater

• The salinity of seawater is typically 3.5% • A salinity of 3.5% indicates that seawater

contains 96.5% pure water and 3.5% solutes• Only 6 ions compose 99% of the solids

dissolved in seawater, and of these sodium and chloride account for 85%

• More commonly, salinity is referred to as “parts per thousand” or ‰ (3.5% = 35‰)

Could you please pass the salt…

• The salinity of water greatly affects the organisms that live in it

• Most marine organisms will die in freshwater, and vice versa (we’ll come back to this)

• Salinity also influences the density of seawater; the saltier the water, the denser it is

• The density of seawater therefore depends on its salinity and its temperature

Dissolved gases in seawater

• Gases in the air easily dissolve in seawater at the ocean’s surface

• Organisms living in the ocean require these dissolved gases to survive

• The major gases in seawater are:– Nitrogen (N2)

– Oxygen (O2)

– Carbon dioxide (CO2)

Dissolved gases in seawater: Nitrogen

• Nitrogen constitutes ~48% of the dissolved gases in seawater

• Nitrogen is essential for organisms and can be a limiting factor for phytoplankton

• Most dissolved Nitrogen is unusable since it exists as N2 gas, a form that cannot be assimilated by most organisms

• Nitrogen can be a pollutant when added to seawater in large quantities!

Dissolved gases in seawater: Oxygen

• Oxygen constitutes ~36% of the gases dissolved in seawater

• Oxygen is essential for all aerobic life forms• Dissolved oxygen comes from photosynthesis

and diffusion from the atmosphere• Gases, such as oxygen, dissolve better in

colder water than in warm water, and so concentrations are highest in polar waters and in colder, deeper seawater

Dissolved gases in seawater: Carbon Dioxide

• Carbon dioxide comprises ~15% of the dissolved gases in seawater and is much more soluble in seawater than oxygen

• CO2 reacts chemically with water when it dissolves forming H2CO3 (carbonic acid), therefore seawater can hold a tremendous amount of CO2

• The ocean stores 50 times as much CO2 as the atmosphere!

• CO2 is used near the surface and produced at depth

• O2 is produced near the surface and used at depth

Let there be light!

• One of the most biologically important properties of seawater is its transparency, allowing sunlight to penetrate into the water

• This is vital because all photosynthetic organisms need light to grow and survive

• Sunlight contains all the colors of the rainbow, but not all the colors penetrate seawater equally

Wavelength (nm)

10–5 nm

Increasing energy

Visible light

650nm

10–3 nm 1 nm 103 nm 106 nm 1 m 103 m

380 400 500 600 700 750

Radiowaves

Micro-waves

InfraredX-rays UVGammarays

Light waves with shorter

wavelengths contain more energy and

penetrate deeper than those with

longer wavelengths.

However, by 300 meters, even blue

light has been absorbed and

darkness prevails

You light up my life…

• Where light penetrates, photosynthesis proceeds; very important!

• The thin film of sunlit water at the top of the surface zone is the photic zone and is dependent on the amount of suspended material in the water– <100 meters in open ocean– <40 meters in coastal regions– <600 meters in clear tropical regions

Hey, who turned off the lights???

• Ocean below the photic zone lies in blackness• Except for light generated by living organisms,

the region is in perpetual darkness• This dark water beneath the photic zone is

known as the aphotic zone– Dark– Cold– High pressure

Deep-sea shrimp: Survival adaptation

Eggs are red, too!

Sea no evil, hear no evil…

• Sound travels nearly 5 times faster underwater than on land (in the air)

• In water, sound is transmitted by water molecules; since water molecules are densely packed (more so than molecules in air), they transmit sound more quickly

• Because sound waves travel more efficiently underwater than light waves, marine organisms frequently rely on sound (hearing), much more so than light (vision)

Talk about singin’ the blues…

• Blue whales produce deep rumbling sounds; deep, low-pitched sounds that are the loudest noise produced by any animal

• You will feel a blue whale vocalization before you ever hear it

• Whale vocalizations can travel over entire ocean basins!!!

Under Pressure

• Another factor that changes dramatically with depth is pressure

• Organisms on land are exposed to 1 atmosphere of pressure at sea level

• Marine organisms, on the other hand, are under the weight of the water above them and as well as the atmosphere

• Pressure increases dramatically with depth; for every 10 meters of increased depth, another atmosphere of pressure is added

Under Pressure

• As pressure increases, gases are compressed• Gas-filled structures inside organisms, such as

air bladders, floats, and lungs shrink or collapse under the pressure

• Limits the depth range of many organisms• Others have evolved

physiological adaptations to survive in the depths (we’ll come back to this)