Oceanography 100
P Anderson
Chapter 12
The Marine Habitat
The diversity of marine life
• The ocean is home to a wide variety of organisms
• Marine organisms range from microscopic bacteria and algae to the largest animal in
the world (blue whale)
• Number of known marine species: 250,000
Classification of living things
• Organisms can be classified into one of three domains of life:
– Archaea
– Bacteria
– Eukarya
Classification of living things
• Organisms can also be classified into one of five kingdoms:
– Monera
– Protoctista
– Fungi
– Plantae
– Animalia
Classification of living things
• Taxonomic classification includes the following increasingly specific groupings:
– Kingdom
– Phylum (Division for plants)
– Class
– Order
– Family
– Genus
– Species
Taxonomic classification of selected organisms
Classification of marine organisms
• Marine organisms can be classified into one of three groups based on habitat and
mobility:
– Plankton (floaters)
•
Phytoplankton (drifting plants and algae)
•
Zooplankton (drifting animals)
– Nekton (swimmers)
– Benthos (bottom dwellers)
Life cycle of a squid
• Squid experience benthic, planktonic, and nektonic stages
• Squid are considered meroplankton (opposite = holoplankton)
Distribution of species on Earth
• The land has more species because it has greater environmental variability than the
ocean
• Most ocean species are benthic because of greater environmental variability compared
to pelagic environments
Adaptations of organisms to the marine environment
• The marine environment presents many challenges to organisms because seawater:
– Is dense enough to support organisms
– Has high viscosity
– Experiences variations in temperature and salinity
– Contains variable amounts of dissolved gases
– Has high transparency
– Has a dramatic change of pressure with depth
• Marine organisms have various adaptations for the conditions of the marine
environment
Need for physical support
• Condition:
– Seawater is dense enough to support marine organisms
• Adaptations:
– Many marine organisms lack rigid skeletons, appendages, or vast root systems
– Instead, they rely on buoyancy and friction to maintain their position within the
water column
Seawater’s viscosity controlled by temperature
• Condition:
– Seawater’s viscosity (resistance to flow) is strongly affected by temperature
– Cold water has higher viscosity than warm water, so is more difficult to swim
through
– Warm water has lower viscosity, so organisms tend to sink within the water column
Seawater’s viscosity controlled by temperature
• Adaptations:
– Many warm-water organisms have ornate appendages to say afloat
– Many cold-water organisms are streamlined to swim more easily
Seawater’s viscosity and adaptations of phytoplankton
• Condition:
– Phytoplankton must remain in sunlit surface waters
• Adaptations:
– Small size increases surface area to volume ratio
– Appendages increase frictional resistance
– Tiny droplet of low density oil increases buoyancy
Variations in temperature
• Condition:
– Coastal water temperatures vary more than the open ocean or at depth
• Adaptations:
– Many coastal organisms can withstand a wide temperature range (are
eurythermal)
– Most open ocean and deep-water organisms can withstand only a small temperature
range (are stenothermal)
Variations in salinity
• Condition:
– Coastal environments experience greater salinity variation than the open ocean or
at depth
• Adaptations:
– Many shallow-water coastal organisms can withstand a wide salinity range (are
euryhaline)
– Most open ocean and deep-water organisms can withstand only a small change in
salinity (are stenohaline)
Osmosis
• Condition:
– Osmosis is the movement of water molecules through a semipermeable membrane
from higher to lower concentrations
– Osmosis removes water from hypotonic organisms
–
Osmosis adds water to hypertonic organisms
Dissolved gases: Oxygen
• Condition:
– Marine animals need oxygen to survive
• Adaptations:
– Many marine animals use gills to extract dissolved oxygen from seawater
– Marine mammals must breathe air
Abundance of dissolved oxygen and nutrients with depth
Seawater’s high transparency
• Condition:
– Seawater has high transparency
• Adaptations:
– Transparency
– Camouflage
– Countershading
– Migration (DSL)
The deep scattering layer (DSL)
• Organisms within the deep scattering layer undertake a daily migration to hide in deep,
darker waters during daytime
Increase of pressure with depth
• Condition:
– Pressure increases rapidly with depth
• Adaptations:
– Most marine organisms lack large compressible air pockets inside their bodies
– Water-filled bodies exert the same amount of pressure as is pushing inward, so
marine organisms do not feel the high pressure at depth
Divisions of the marine environment
• Main divisions:
– Pelagic (open sea)
– Benthic (sea bottom)