Transcript Ecology of Sandy Beaches

Ecology of Sandy Beaches
Expectations
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Objectives
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The Biological Study of Sandy Beaches
Typical sandy Beach animals (Characters & features)
Cryptic animals
Meiofaunal Vs Macrofaunal Sand Sample
The importance of developing and understanding of sandy
shore ecosystems.
Physical Environment.
Sand.
Waves: Surface gravity, Internal & Edge waves.
Wind.
• The Biological Study of Sandy Beaches
• When has the biological study started?
• It started only fifty years ago after intensive
studies of rocky shore.
• Why was there an early neglect of sandy beach
ecosystem?
• It seems always devoid of life (why?).
The early neglect of sandy beach ecosystem was due
• Rocky shore
to • Sandy Shore
• 1- Obvious lifepresenting fascinating
prospect to scientific
research.
• 2- Plants & animals are
large and highly colored.
• 3- Many animals are
sessile or very slow
moving, easy to collect
and study.
• 1- No attached plants.
• 2- Animals are so small.
3- Few species of
macrofauna are cryptic.
• 4- On sheltered beaches
burrows excavated by
Arenicola and Callianosa
(evidence to life).
• 5- On exposed beaches,
sand is unstable to
support burrows
intertidal.
• 6- Animals are highly
mobile to maintain their
position.
• Cryptic animals
• They are hiding within sand.
• They appear only when necessary to feed,
perform other vital functions.
• Mobility and cryptic mode of life render sandy
beach observations.
• Typical sandy Beach animals
(Characters & features)
• 1- Millimeter or so in length. Small enough to
live and move between sand grains.
• 2- Migrating up and down through the sand
column in response to environmental factors.
• 3- Those animals are named MEIOFAUNA
• 4- Although the collection and identification of
meiofauna is difficult than macrofauna, the
diversity of meiofauna is higher than
macrofauna.
• Meiofaunal Vs Macrofaunal Sand Sample
• A single sand sample
Numerous species of
A Nemertina
N
U
Tardigrada
M
Turbellaria
E
Nematodes
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A
O
Foraminifera
F
Ostracoda
Annelids
Gastrotrichs Harpacticoida
• In Contrast:
• Typical permanent intertidal sandy beach
MACROFAUNA
Very Few Species of
Polychaete
Mollusca
Donax sp.
Two or few Crustacea species
Although of this distinction, macrofauna has intensively studied
Our knowledge about meiofauna and microbiota are poor.
• The importance of developing and understanding
of sandy shore ecosystems
¾ of the world’s
Appropriate management
Ice free coastline
& successful conservative
Consists of sandy
Can only be achieved.
Shores.
Beaches and dune
Systems are fragile
ecosystems need
management.
• Physical Environment
• Sandy Coastal line = Shores +Beaches
• It is Dynamic environment
Physical Habitat Structure is determined by
Sand
Air
Water
• Sandy Beach is one of the most stable dynamic
coastal line (why?).
• Due to its ability to absorb wave energy.
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Beach is characterized by
Wave driven sand transport
Aeolian (wind) transport
Sediment transport in
Surf zone by wave action.
Sediment transport in
Dunes by wind action.
Sand
Originates from
Terrestrial Origin
Quartz (Silica)
Erosion of land
Go to sea by rivers
Marine Origin
(Carbonate sand)
Biogenic sources
Animals skeleton &
Sea cliff erosion
The most important characteristic
of sand particles
Sand grains (Ф = mm)
Ф= log2 diameter
Porosity = Volume of void space / sand
≈ 30-40% of total volume for sand.
Permeability determine the amount
of flushing through sand
Penetrability related to % silt, clay &
Water content
Waves
Surface gravity
waves
Internal wave
Edge waves
• Surface Gravity Waves:
• 1-Generated by wind stress on water surface.
• 2-Friction (wind & water)
• 3-A viscous drag
4- Stretches the surface like an elastic membrane
undulation
Wind
Distortion
waves
Surface
tension
Restoration
• What happens if strong wind blows up?
• 1-Waves grow.
• 2-Gravity replaces surface tension.
• 3-Waves move off before the wind.
• 4-Waves transfer energy from wind at sea to
coastal zone.
• Internal waves
• They occur at the boundary between water layers
of different densities.
Generated by
Tide
Under water
avalanches
Wind
Internal waves may causes fluctuations in surf zone
• Edge waves
• They are waves running along the shore and
contained in surf zone.
• ًWind
• They are important in shaping wave characteristics.
• Surface water movement is about 2% of wind speed.
• Strong on shore winds
• Off shore winds
Wave Height
Wave Height
flatten
Size of surf zone
Size of surf zone
Affect sediment transport between Beach and Dunes
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•Summary
• Sand Movement
Sand moves in two ways
Bed Load
It is moving close to the bed
Coarser materials
Suspended Load
It is transported above Bed
Finer materials
The steeper the waves and the beach,
the greater the tendency for accretion.
• In Practice:
• Strong erosion or sea ward movement of
sediment for short periods
Is balanced
by
Gradual accretion or land ward