Aquatic Ecosystems
The types of organism in an aquatic ecosystem
are mainly determined by the water’s salinity.
SALINITY – the amount of dissolved salts that
water contains.
Two types of Aquatic Ecosystems:
 Freshwater Ecosystems
 Marine Ecosystems
Examples of Freshwater Ecosystems include:
 Lakes
 Ponds
 Freshwater Wetlands (marshes, swamps)
 Rivers
 Streams
Some Biotic Factors in an Aquatic Ecosystem
1. Plankton: Organisms that cannot swim
against currents, so they are drifters.
 Phytoplankton – drifting plants that
are the food base for most aquatic
ecosystems; most are microscopic.
 Zooplankton – drifting animals,
which may be microscopic or as
large as jellyfish.
2. Nekton: Free-swimming organisms.
 Fish, turtles, & whales.
3.Benthos: Bottom-dwelling organisms.
 Mussels, worms, & barnacles.
 Many benthic organisms live
attached to hard surfaces.
ORGANISMS CALLED DECOMPOSERS ARE ALSO
PRESENT IN AQUATIC ECOSYSTEMS. THEY
BREAK DOWN DEAD ORGANISMS.
LAKES & PONDS
 Structured into horizontal and vertical zones
o Littoral zone: nutrient rich; aquatic life
is diverse and abundant; plants are
rooted in the mud underwater, etc.
o Benthic zone: the bottom of the pond
or lake; cooler water; little sunlight;
bacteria & decomposers live on dead
plants and animals that drift down from
above.
How do nutrients affect a lake?
Eutrophication is an increase in the amount of
nutrients in an aquatic ecosystem. Algae and
plant grow due to nutrients in a body of water.
As the amount of algae and plants grow, so
does the amount of bacteria and decomposers.
These bacteria use the oxygen dissolved in the
lake water, eventually reducing the amount
available for oxygen-loving organisms.
FRESHWATER WETLANDS
 Covered with fresh water for at least part of
the year.
 Two types:
o Marshes – contain non-woody plants,
such as cattails.
o Swamps – dominated by woody plants,
such as trees and shrubs.
MANY WETLANDS HAVE BEEN DRAINED,
FILLED, OR CLEARED FOR FARMS OR
RESIDENTIAL/COMMERCIAL DEVELOPMENT.