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