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Aquatic Ecology Course
Zoo 374
Biodiversity
• Despite the importance of marine
ecosystems, increased human activities
have caused significant damage or are
serious threats to the marine biodiversity.
These activities can be overfishing,
pollution, introduction of exotic species or
coastal development. For this reason,
conservation plans are necessary to save
the marine ecosystems from being lost.
Categories
• For the Coastal Zones the subcategories are:
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Rocky shores
Sandy shores
Continental shelf
Open oceans
Deep Sea
Sea ice ecosystems
Coral reefs
Seagrass meadows
Mangroves
Salt marshes
Estuaries
I- Rocky Shores
I- Rocky Shores
• A rocky shore is an intertidal area that consists of solid
rocks. It is often a biologically rich environment and can
include many different habitat types like steep rocky
cliffs, platforms, rock pools and boulder fields. Because
of the continuously action of the tides, it is characterized
by erosional features. Together with the wind, sunlight
and other physical factors it creates a complex
environment. Organisms that live in this area experience
daily fluctuations in their environment. For this reason,
they must be able to tolerate extreme changes in
temperature, salinity, moisture and wave action to
survive.
Zonation
• Each region on the coast has a specific
group of organisms that form distinct
horizontal bands or zones on the rocks.
The appearance of dominant species in
these zones is called vertical zonation. It is
a nearly universal feature of the intertidal
zone.
Supratidal zone
• When the tide retreats, the upper regions become exposed
to air. The organisms that live in this region are facing
problems like desiccation, temperature changes and
feeding. This upper region is called the supratidal or
splash zone. It is only covered during storms and
extremely high tides and is moistened by the spray of the
breaking waves. Organisms are exposed to the drying heat
of the sun in the summer and to extreme low temperatures
in the winter. Because of these severe conditions, only a
few resistant organisms live here. As fungi and microscopic
algae living together and sharing food and energy to grow.
Also snails which are well adapted to life out of the water
by trapping water in their mantle cavity or hiding in cracks
of rocks. Other common animals are isopods, barnacles.
Intertidal zone (littoral zone)
• Because the intertidal zone is a transition zone
between the land and the sea, it causes heat stress,
desiccation, oxygen depletion and reduced
opportunities for feeding. At low tide, marine
organisms face both heat stress and desiccation
stress. The degree of this water loss and heating is
determined by the body size and body shape. When
body size increases, the surface area decreases so
the water loss is reduced.
Subtidal zone (sublittoral zone)
• is the region below the intertidal zone and is
continuously covered by water. This zone is
much more stable than the intertidal zone.
Temperature, water pressure and sunlight
radiation remain nearly constant. Organisms do
not dry out as often as organisms higher on the
beach. They grow much faster and are better in
competition for the same niche. More essential
nutrients are acquired from the water and they
are buffered from extreme changes in
temperature.
Problems and adaptations
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Air
Light
Temperature
Salinity stress
Desiccation stress
Predation
Wave action
Problems and adaptations
• Air: Intertidal organisms are regularly exposed to
air and water. Air differs physically from seawater
in important features. This influences the ability to
exchange gas and their overall thermal balance
with the surrounding environment.
• Attachment and body changes are also
required. When exposed to the air, the organisms
directly absorb solar radiation. The buffering
capacity of water, because of the high rate of heat
conductivity, disappears and the body temperature
increases. In contrast to this, heat loss is much
lower in air than in water. An adaptation to heating
is the vaporization of internal water reserves.
Problems and adaptations
• Light: Sunlight is another parameter that
influences the organisms. When there is too much
sunlight, organisms dry out and the capacity to
capture light energy can be weakened. The light
that is not used or dissipated can cause damage
to subcellular structures. Too little sunlight
reduces the growth and reproduction of the
organism, because photosynthesis is reduced.
Algae can avoid absorbing too much light by
changing the amount of pigments they produce.
When free radicals are produced from an excess
of light, they can be scavenged and deactivated.
Problems and adaptations
• Temperature:. The organisms must be resistant to temp.
changes to survive. Most of the marine organisms are
ectothermic (need the warmth from the environment to
survive). When the air temperature is too low, the organisms
must cope with physiological threats associated with cold
stress. The body fluids can then reach their freezing point &
ice crystals develop. This causes damage to cell membranes
and increasing the osmotic concentration of the remaining
fluids. To avoid this cold stress, organisms can migrate to
habitats that are more suitable. For sessile organisms ,they
can develop physiological and behavioral adaptations such as
gaping shells (mussels). Some organisms have developed
antifreeze proteins. When the temperature is too high, heat
stress appears. Heat stress accelerates rates of metabolic
processes. This can be avoided by evaporative cooling
combined with circulation of body fluids.
Problems and adaptations
• Salinity stress: When the osmolality of
the cell is lower than the surrounding
medium, the cell loses water from the
internal fluids to the environment
(hyperosmotic stress). When the
intracellular osmolality is higher than the
environment, there is an influx of water
into the cell from the environment
(hypoosmotic stress).
Problems and adaptations
• Desiccation stress: Organisms are threat by
desiccation during emersion at low tides.
Dehydratation due to evaporative water loss is
the most common mechanism. Highly mobile
organisms can avoid the desiccation by
migrating to a region that is more suitable. Less
mobile organisms restrict various activities
(reduced metabolism) and attach more firmly
to the substrate. Physiological features by
reduction in water permeability of membranes,
reduction of metabolic and developmental rates.
Problems and adaptations
• Predation: strategies to escape from predation 1)
calcification. It makes them tougher and less nutritious.
2) production of chemicals, These chemicals can be
produced all the time such as toxins, but other chemicals
are only produced in response to stimuli (inducible
defense). 3) Bioluminescence, The light is used for
warning, blinding, making scare, misleading or attracting
the predator. 4) camouflage. This can be visually or
chemically. Visual camouflage means that the prey
becomes invisible to the predator by using the same
colors as the environment. Chemical camouflage is the
passive adsorption of chemicals. The predator does not
smell the prey anymore, because the smell is masked.
Problems and adaptations
• Wave action: permanent attachment (Bivalves).
But this strategy can not be used by organisms
that have to move to feed themselves. These
organisms have to make a compromise between
mobility and attachment. Another way to be
protected is to burrow themselves into the
sediment. But an alternative is to seek protected
habitats.
Why are rocky shores important?
• Providing a home for a lot of organisms
• Nursery area for many fish and crustacean
species
• Shelter in areas where seaweeds break the
waves power
• Providing food for fishes
• Algal beds important food source for rare and
threatened species like sea turtles
• Feeding ground at low tide for wading birds
• Stabilization inshore sediment
Chemical aspects of the sea
The chemical constituents of seawater
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dissolved gases
major elements
minor elements
organic matter