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Aquatic Ecosystems
Chapter 54
In general…
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Aquatic ecosystems are classified primarily on
abiotic factors:
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temperature, salinity, dissolved oxygen, current
These factors are often related to water depth
Three ecological categories of organisms:
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Plankton – at the mercy of current and waves:
• Phytoplankton – photosynthetic organisms
• Zooplankton – heterotrophic protozoa and animals
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Nekton – stronger swimmers (fish)
Benthic – live on or in the bottom (worms)
Freshwater ecosystems
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Flowing water
 Headwater streams are usually shallow, fastflowing, highly oxygenated. They depend
primarily on detritus for energy input
 Rivers – typically deeper, slower flowing, with
less dissolved oxygen
 Organisms in different locations are adapted
accordingly, especially for O2 levels and current
Freshwater ecosystems…
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Standing-water ecosystems
Ponds and lakes
Large lakes can be divided into zones:
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Littoral zone – shallow area around shore; may
contain emergent and nonemergent plants
Limnetic zone – deeper water; phytoplankton is the
base of the food chain
Profundal zone – below the depth of light penetration
Thermal stratification may occur in temperate
lakes and have areas of warm water over cold
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Thermocline – the zone of rapid temperature change
Turnover – in the fall and spring the waters mix
Freshwater ecosystems…
– transitional between aquatic
and terrestrial ecosystems
 Include hardwood bottomland forests,
prairie potholes, and peat bogs, as well as
swamps (with trees) and marshes (without
trees)
 Are important in flood control, breeding
sites for birds, recharge of groundwater
 Wetlands
Transitional ecosystems
– where freshwater and salt
water meet
 Salt marshes – in temperate locations
 Mangrove forests – in tropical areas
 Undergo marked changes in temperature,
salinity, current, and other abiotic factors
 Extremely productive areas
 Threatened by pollution and human
population growth
 Estuaries
Marine Ecosystems
zone – transition between land
and ocean between high and low tide
 Highly productive but very stressful habitat
 Intertidal
Marine ecosystems…
zone – ocean floor
 Seagrass beds – flowering plants adapted
to being submerged
 Kelp forests – the largest brown algae
 Coral reefs – very productive habitats;
restricted to shallow water because coral
polyps have a symbiotic relationship with
photosynthetic zooxanthellae
 Benthic
Marine ecosystems…
 Neritic
province – shallow waters close to
shore
 Euphotic region – the lit zone where
photosynthesis occurs
 Phytoplankton  zooplankton  nektonic
organisms
Marine ecosystems…
province – most of the ocean;
greater than 200 m deep
 Marine ‘snow’ – organic debris that ‘rains’
down into the darker regions
 Oceanic
Marine Ecosystems…
 Overfishing
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Many commercially important fishes have
reached commercial extinction due to
overfishing
 Pollution
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is a threat
is also a threat
Many of the world’s largest cities began as
ports
Garbage has long been dumped in the sea