Post on 22-Dec-2015
Ecology of Sandy BeachesEcology of Sandy Beaches
ExpectationsExpectations? ??
ObjectivesObjectives• 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 The early neglect of sandy beach ecosystem was due toto• Rocky shore
• 1- Obvious life-presenting 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.
• Sandy Shore• 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
Tardigrada
Nematodes
AnnelidsGastrotrichs Harpacticoida
Ostracoda
Foraminifera
Turbellaria
M
EI
O FA
UNA Nemertina
• In Contrast:
• Typical permanent intertidal sandy beach MACROFAUNA
Very Few Species of
Polychaete
Two or few Crustacea species
MolluscaDonax sp.
Although of this distinction, macrofauna has intensively studiedOur knowledge about meiofauna and microbiota are poor.
• The importance of developing and understanding of sandy shore ecosystems
¾ of the world’sIce free coastline Consists of sandyShores.
Beaches and duneSystems are fragile ecosystems need management.
Appropriate management& successful conservativeCan only be achieved.
• Physical Environment• Sandy Coastal line = Shores +Beaches
• It is Dynamic environment
Physical Habitat Structure is determined by
Sand
Water
Air
• Sandy Beach is one of the most stable dynamic coastal line (why?).
• Due to its ability to absorb wave energy.
•
Wave driven sand transport
Sediment transport in Surf zone by wave action.
Aeolian (wind) transport
Sediment transport in Dunes by wind action.
Beach is characterized by
Sand
Terrestrial OriginQuartz (Silica)Erosion of land
Go to sea by rivers
Marine Origin)Carbonate sand(
Biogenic sourcesAnimals skeleton&
Sea cliff erosion
Originates from
The most important characteristic of sand particles
Sand grains (Ф = mm)Ф= log2 diameter
Permeability determine the amount of flushing through sand
Penetrability related to % silt, clay& Water content
Porosity = Volume of void space / sand ≈30-40% of total volume for sand.
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
Wind Surfacetension
undulation
wavesDistortion 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
Wind
Under water avalanches
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 Size of surf zone
Wave Heightflatten Size of surf zone
Affect sediment transport between Beach and Dunes
• ً��
•Summary
• Sand Movement
Sand moves in two ways
Bed LoadIt is moving close to the bed
Coarser materials
Suspended LoadIt 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