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Aquatic Biome Stratification
MP 2.1 and 2.2
Light Intensity
• Light intensity decreases rapidly with increasing
depth greatly influencing the communities that
can live at each level
• Zones in a lake are classified by whether or not
they receive light (photic) or not (aphotic)
Photic Zone
• Upper part of a lake or ocean where there
is sufficient light for photosynthesis
Aphotic (profundal) zone
• Deep lower parts of oceans or lakes where
no light penetrates
Benthic Zone
• Bottom of the lake or ocean at ANY depth
• Has special communities adapted to living on
the bottom
• The poop and bodies of decaying organisms (detritus)
fall like snow to the benthos (bottom) by gravity.
• Benthic bacteria convert the detritus into nitrates that
algae use as nutrients for photosynthesis.
• Currents bring these nutrients to the surface where
photosynthesis can take place (eutrophication)
• Differences in temperature
with increasing depth
• Usually gets colder quickly
• Effects the distribution of
aquatic organisms especially
Littoral Zone
• Part of the sea, lake or
river that is close to
• Also subdivided into
smaller areas.
• Dominated by
herbivorous fish
communities like Perch
and Bluegill and their
Limnetic Zone
• Part of the open water
in a lake that is in the
photic zone
• Off shore of the littoral
zone and above the
profundal zone.
• Communities would
include predators like
pike, trout or bass.