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Marine Ecology

Classification of Organisms by Environment

horizontal: neritic | oceanic


epipelagic (top) / euphotic (good)

mesopelagic (middle) / disphotic (low)

bathypelagic (deep) / aphotic (without)

abyssopelagic (bottomless)

Divisions of the Marine Environment Figure 9-1

Classification of Organisms by Lifestyle

Scientists have established another classification scheme to categorize biota on the basis of lifestyle. The major groups are:

plankton (floaters)

nekton (swimmers)

benthos (bottom dwellers)

Distribution of Marine Lifestyles

16.7% of Earths animals are marine

2% inhabit pelagic environment (most of the oceans are cold and dark)

98% are benthic!


Plankton are weak swimmers, and are known as drifters, unable to counteract currents. The group includes:

Phytoplankton (plants)

Zooplankton (animals)


Nekton are active swimmers capable of counteracting currents. The group includes a diversity of organisms including:



The benthos includes organisms attached to or living on or in the sea bed. This group includes plants and animals.

Epiflora or epifauna live on the sea bottom.

Infauna live in the sea bottom.

Benthic plants are restricted to shallow waters because of their requirement for light.

Benthic animals occur everywhere from shallow depths to the deep sea.

Research Video Clip: Live fast, die young...

and the story of the Tubeworm Barbecue

Varying Lifestyles

Although convenient, there are always exceptions to a classification scheme.

life style of a species may change as it ages.

Many benthic animals, e.g., crabs, clams, starfish have a planktonic larval stage.

Basic Ecology

factors regulating the distribution and abundance of organisms in the ocean.

influence of physical and chemical parameters on organisms in the various ecosystems that constitute the ocean.

An ecosystem includes both the living (biotic) and non-living (abiotic) portions of the environment.

Examples include: salt marshes, estuaries, coral reefs, the North Pacific Gyre.

Temperate and salinity important in controlling growth of organisms, as well as their distribution

Hydrostatic Pressure

Hydrostatic pressure is the pressure caused by the height of water.

It is a function of the density of water and the total heig ht of the water column.

Pressure generally increases at a rate of 1 atm per 10 m of water.

Hydrostatic pressure is enormous in the deep sea yet animals live there.

Animals do not contain gases.

However, mesopelagic fish which have gas-filled swim bladder s to help maintain neutral buoyancy are unable to move rapidly between depths because the pressure change could cause the bladder to explode.

Diffusion: molecules move from high to low concentrations


internal fluids of marine organisms also contain salts

a chemical gradient reflecting the concentration of salts inside the body relative to the surrounding seawater is established.

As a result salts will diffuse from an area of high concentration to low concentration.

Diffusion is important in the process of nutrient uptake and the elimination of waste products.

Diffusion (Cont.)

Diffusion is also the mechanism by which water molecules pass through cell membranes. This is called osmosis.

If an animals body fluid is less salty than the suurounding seawater water, water will diffuse out and the animal will dehydrate

If an animals body fluid is more salty water will diffuse in to the body leading to the swelling of cells.

Diffusion/Osmoregulation - Figure 9-12

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