Aquatic biomes occupy the largest part of the biosphere
Two major categories of aquatic biomes
Marine biomes
have salt concentration of ~ 3%
cover ~ 75% of the earth’s surface.
Freshwater biomes
have salt concentration of <1%
closely linked to the soils and biotic components of the terrestrial biomes through which they pass.
Vertical stratification of aquatic biomes.
Exhibited by many aquatic biomes
based on physical and chemical variables
light
photic zone
zone through which light penetrates and photosynthesis can occur.
aphotic zone
where very little light can penetrate.
Vertical stratification of aquatic biomes.
Exhibited by many aquatic biomes
based on physical and chemical variables
temperature
.
thermocline
narrow stratum of rapid temperature change
separates a more uniformly warm upper layer from more uniformly cold deeper waters.
benthic zone
bottom of any aquatic biome
contains detritus, dead organic matter.
Freshwater biomes
two categories
standing bodies of water
such as lakes and ponds
moving bodies of water
such as rivers and streams
Freshwater biomes
zonation in a lake
littoral zone
shallow, well-lit, and close to shore.
region in which rooted and floating plants flourish
limnetic zone
well-lit, open surface water, farther from shore
occupied by phytoplankton, zooplankton, higher animals
profundal zone
consists of the deep, aphotic regions.
Lakes
often classified according to their production of aquatic matter
oligotrophic
eutrophic
mesotrophic
Lakes
Oligotrophic
deep
nutrient-poor
phytoplankton are sparse, not very productive
don’t contain much life
.
waters often very clear
Lakes
Eutrophic
shallower
have increased nutrients.
Phytplankton more plentiful and productive
waters often murky
Lakes
Mesotrophic
have a moderate amount of nutrients
have moderate amount of phytoplankton that are reasonably productive.
Over long periods of time, oligotrophic lakes may become mesotrophic as runoff brings in nutrients.
Pollution from fertilizers can cause explosions in algae population and cause a decrease in oxygen content.
Streams and rivers
bodies of water moving continuously in one direction
headwaters
cold, clear and carry little sediment and relatively few mineral nutrients.
As the stream travels down,
it picks up O2 and nutrients on the way.
Nutrient content
largely determined by the terrain & vegetation of the area.
Many streams and rivers have been polluted by humans and have caused many environmental problems.
Wetlands
areas covered with water that supports many types of plants.
can be saturated or flooded
includes areas known as marshes, bogs, and swamps.
home to
many different
types of organisms,
from herbivores
to crustaceans.
Unfortunately,
humans have
destroyed them,
but many are now
protected in
many places.
Estuaries
areas where freshwater and salt water meet.
salinity of these areas can vary greatly.
are crucial feeding areas for many types of water fowl.
Zonation in Marine communities.
intertidal zone
where the land meets the water.
neritic zone
includes shallow regions over the continental shelves.
oceanic zone
extends past continental shelves, can be very deep.
pelagic zone
is the open water.
benthic zone
is the seafloor.
Intertidal zones
alternately submerged & exposed by 2x-daily cycle of tides
.
can be rocky or sandy and provide excellent examples of distributional limitations.
Inhabited by many types of organisms such as suspension -feeding worms, crustaceans, mollusks and others.
are often destroyed by pollution and human activity.
Neritic zone
of warm tropical waters contain coral reefs
which constitute a conspicuous and distinctive biome.
are dominated by coral
include a very diverse assortment of
vertebrates and invertebrates.
oceanic pelagic biome
includes most of the ocean’s water.
water is constantly mixed by ocean currents.
plankton live in the photic zone and are the producers for this biome.
includes a great variety of free swimming fish and mammals.
Benthos
the ocean bottom below the neritic and pelagic zones.
is extremely productive due to the great amount of nutrients found.
benthic communities consist of bacteria, fungi, seaweed and filamentous algae, numerous invertebrates, and fish.
Abyssal zone
very deep communities.
organisms are adapted to
continuous cold.
high pressure
low to no light
low nutrients
deep-sea hydrothermal vents of volcanic origin found here.
dark, hot, oxygen-deficient environment
producers are chemoautotrophs
In aquatic ecosystems, light and nutrients limit primary production
Production in Marine ecosystems
Light
is the first variable to control primary production in oceans since solar radiation can only penetrate to a certain depth (photic zone).
We would expect production to increase along a gradient from the poles to the equator; but that is not the case.
There are parts of the ocean in the tropics and subtropics that exhibit low primary production.
Why are tropical and subtropical oceans less productive than we would expect?
It depends on nutrient availability.
Ecologists use the term limiting nutrient to define the nutrient that must be added for production to increase.
In the open ocean, nitrogen and phosphorous levels are very low in the photic zone, but high in deeper water where light does not penetrate.
Nitrogen is the one nutrient that limits phytoplankton growth in many parts of the ocean.
Nutrient enrichment experiments showed that iron availability limited primary production.
Evidence indicates that the iron factor is related to the nitrogen factor.
Iron + cyanobacteria + nitrogen fixation à
phytoplankton production.
Marine ecologists are just beginning to understand the interplay of factors that affect primary production.
Production in Freshwater Ecosystems.
Solar radiation and temperature are closely linked to primary production in freshwater lakes.
During the 1970s, sewage and fertilizer pollution added nutrients to lakes, which shifted many lakes from having phytoplankton communities to those dominated by diatoms and green algae.
This process is called eutrophication, and has undesirable impacts from a human perspective.
Controlling pollution may help control eutrophication.