Coastal environment

1. Coastal Environment
Topic 2 A-level Physical Geography

2. Introduction
• Coastal environments are the interface
between 3 natural systems: Atmosphere,
Ocean, Land
• Coastal zone refers to an area influenced
by proximity to the coast

3. Introduction
• Offshore zone refers to the portion of the profile where
there is no significant transport of sediment by wave
action
• Littoral zone refers to the portion of the coastal profile
where sediment can be transported
• Shore/ beach: Area of the coast sub aerially exposed
some of the time but remains subjected to wave action

4. Introduction
• Foreshore: Subjected to wave action periodically during
non-storm conditions
• Backshore: Subjected to wave actions during storms
• Swash zone: Zone of wave run-up on the beach and
return of water in the form of backwash
• Intertidal zone: Zone between high and low water (tide)
• Shoreline: The intercept of the mean water level along
the beach but it is often used loosely as swash limit or
landward edge of the backshore

7. Content
1. Coastal Processes
2. Characteristics and formation of coastal
landforms
3. Coral Reefs
4. Sustainable Management of Coasts

8. Factors influencing Coasts
• Lithology/ rock types
• Geological Structures
• Processes
• Sea-level changes
• Human Impacts
• Ecosystem types

9. Lithology
• Hard rocks
– Granite, Basalt
– Rugged landscape
• Soft rocks
– Sands/ gravels
– Flatter landscape

10. Geological Structure
• Concordant Coast Discordant Coast

11. Processes
• Tides/ diurnal fluctuation of sea level
• Wave action: Erosion/ Deposition
• Currents (Longshore/ Rip)
• Winds

12. Sea-level Change
• Interacts with points/ rates of erosion and
deposition
• Advancing coast (deposition/ relative
change in sea level)
• Retreating coast (erosions/ relative
change in sea level)

13. Human Impacts
• Modification by humans
• To protect settlements near the coast
• Mitigate problems of erosion
• Primary industries/ agriculture/ aquaculture
• Industries/ Tourism
• Mining
• Impacts of externality

14. Ecosystem Types
• Influences the rate of weathering
• Some can act as wave barriers
• Coral Reefs
• Mangroves
• Saltmarshes
• Sand Dunes
• Rocky Shores

15. Coastal Zones
• All areas from the deep ocean to point
around 60 km inland
• Inland areas can affect coastal areas by
controlling sediment supply and on-land
pollution sources
• Inland areas can also be affected by
coastal processes e.g. sea breeze can
affect land temperature

16. Upper beach/ Backshore
• Limit of high water to dunes/ inland limit (60 km)
• Only affected by waves during storms/ unusual
high tides
• Well-sorted/ well rounded sediments
• Coarse and medium sands

17. Foreshore
• Region between the high and low water marks
• Sediments may include:
• Soft, mobile/ semi mobile sediments (sand, mud,
shingle)
• A different case for
rocky shores

18. COASTAL PROCESSES

19. Wave
• A result of the friction between the wind and the
sea
• Forward surges of energy
• The water particles are not moving
• They move in circular orbit
• Wave orbit is the shape of the wave: Circular or
elliptical
• Diameter or orbit decreases with depth

20. Wave
• Wave Crest: Highest point of a wave
• Wave base: Point at the bottom of a wave
where there is no movement related to
wind energy
• Wave length: Distance between two
successive crests/ troughs

21. Wave

22. Wave Characters
• Waves are characterized by their height,
length and period
• Height: distance between trough and crest
• Length: distance between two wave crests
• Period: the time for 2 consecutive wave
crests to pass a given point
• Amplitude: distance from wave base to
crest

23. Wave Energy
• Carriers of energy
• Imparted to them by wind
• Energy per unit surface area of waves is
proportional to the wave height square
• Speed = wave length/ wave period

24. Breaking Waves
• Energy for movement of waves come from the
open ocean
• Differences in atmospheric pressure creates a
gradient down which the air flows
• Flow of air is known as wind
• The friction between the wind and the surface of
the ocean pushes water in certain directions

25. Breaking Waves
• The energy is propagated in the form of
swell waves
• Wave energy oscillates, moving water
particle in an elliptical or circular motion,
and then returning it back to its position
• As the waves reach the shore, they
become breakers

26. Breaking Waves
• The consistency of wave motion is
disrupted as it approaches the changing
topography of the shoreline

27. Shoaling
• As wave approaches shoreline, its base grazes
the ocean floor
• The friction causes the wave base to slow down
• However, movement of water particles at the
wave crest continues
• This causes multiple waves to combine
• Thus increasing the height and amplitude of the
waves
• This is shoaling

28. Shoaling
• Occurs as waves enter shallow water
• Speed/ length decrease
• Wave height increases
• Crest becomes too steep – unstable
• Curls forward and breaks on the shore

29. Breakers
• Breaking waves are waves whose
amplitudes reach critical levels at which
some processes occur to transform wave
energy into turbulent kinetic energy
• 3 types:
• Spilling breakers
• Plunging breakers
• Surging breakers

30. Spilling Breakers
• Ocean floor has gradual slope
• Wave steepens
• Crest becomes unstable
• Turbulent whitewater spilling down wave face – slowly
dissipating wave energy
• Gentle wave is created
• Takes longer time to break

31. Plunging Breakers
• Steeper ocean floors – sudden changes in depth
• Crest becomes much steeper
• Curls over and drops onto trough
• Breaks with more energy

32. Surging Breakers
• Long period gentle wave with steep beach
profile
• Rapid movement of wave base up sop and
wave crest disappearing
• The wave slides and swells up the shore

34. Constructive Waves Destructive Waves
Low Gradient High gradient
Low Wave height High wave height
Long wave length Short wavelength
Wave frequency 6 – 8 / minute Wave frequency 10 – 14 / minute
Swash > Backwash Backwash > Swash
Spilling breakers Plunging/ Surging breakers
Sheltered Coasts Exposed Coasts

35. Tide/ Tidal Cycle
• Regular movements of the sea surface
caused by gravitational pull of the Moon
and the Sun on the ocean
• Gravitational pull of the moon causes
water to bulge at the area of the earth
surface facing the moon
• The opposite side of the earth surface is
similarly affected by the centrifugal force

36. Tidal Cycle

37. Tidal Cycle
• At full moon and new moon (syzygy – when
earth moon and sun align), the gravitational pull
is maximized by the pull of the sun
• These times between new moon and first
quarter moon and full moon and third quarter
moon are known as Spring tides – maximum
height of tide
• The other times, there is only moon’s pull and
the tide is lower – Neap tide

38. Tides and shorelines
• Tides are greatest at bay and funnel
shaped coastline – less area thus water
pile up more : Tidal bores
• Northern hemisphere, water deflected to
the right
• Every decrease in 10 millibars = 10 cm
rises

39. Tidal Range
• Difference between high and low tide
• Highly variable
• 15 m in bay of Fundy Canada
• Varies with distance from amphidromic
points (areas where there is no tidal
range)/ shape of coasts

40. Tidal Range
• Microtidal < 2 m
• Mesotidal 2 > x > 4 m
• Macrotidal > 4 m

41. Impacts of Tides
• Vertical range of erosion/ deposition
• Weathering
• Biological activities
• Velocity of tidal flows can affect erosional/
scouring rate
• Can cause rip currents

42. Storm Surges
• Changes in sea level caused by intense low
pressure/ high wind speed
• During intense low pressure, pressure can drop
by 100 mb – surges reaching up to 1 meter
• During cyclones/ storms, surges are common
• Can cause casualties in flooding
• Can inundate farmlands/ residential areas

43. Wave Refraction
• Bending of waves due to varying water
depths
• Areas closer to shores are shallow
• Thus waves in those areas slow down
• So the waves seem to be slowing down to
break parallel to the shore
• Waves will wrap around the island

44. Wave refraction
• Refraction can be incomplete, causing
longshore drift
• A process of sediments transportation
causing by the waves hitting the shore at
an angle to the prevailing wind

46. Marine Erosion
• Waves can erode materials and sediments
on shores
• Hydraulic action: waves hit against cliffs,
air trapped in cracks/ joints/ bedding
planes – placing them under pressure
• Wave retreats
• This creates explosive forces
• Known as cavitation

47. Marine Erosion
• Stresses reduce rock coherence
• Highly effective against well jointed/
bedded rocks: limestone, sandstone,
granite, chalk
• Or poorly consolidated rocks: clays/ glacial
deposits
• AKA wave pounding

48. Marine Erosion
• Abrasion: pebbles/ shingles hurled at
surfaces
• Attrition: materials worn themselves down
• Solution: chemical erosion
• Calcareous rocks: waves may remove
materials with acidic water
• Organic acids from organisms like
barnacles/ limpets

49. Factors affecting rate of erosion
Wave Energy
Waves
Wave Steepness – steep destructive waves have greater
abrasive/ hydraulic power
Wave should also break close to cliff base for highest energy
Tides Tides can affect zones of erosion/ powerful tides have scouring
effects
Currents Longshore/ rip current erode materials
Winds
Onshore wind can erode beaches to form dunes
Offshore winds erode dunes to nourish beach
Longer fetch = greater wave energy

50. Factors affecting rate of erosion
Material factors
Sediment Supply
Abrasion can only occur with continual supply
However, oversupply can form effective protections
Width of platform Platforms before cliffs can absorb wave energy, longer
platforms = less wave energy
Rock resistance
Granite = highly resistant
Unconsolidated volcanic ash = less
Overlying rocks with different resistance promote differential
erosion
Rock structures/
dip
Well jointed/ bedded/ faulted rocks susceptible to cavitation
Horizontal/ vertical structures = steeper cliffs
Strata dipping away from sea = stability = gentle slopes

51. Factors affecting rate of erosion
Shore Geometry
Offshore
Topography
Steep seabed = higher/ steeper waves
Longshore bars cause offshore breaking = loses energy
Orientation of
coast
Headlands affected by refraction: energy concentrated
Degree of exposure influences rate of erosion
Direction of Fetch Longer fetch – great potential for wave erosion

52. Sub-Aerial Processes
• Cliff face processes
• Salt weathering: Sodium/ magnesium compounds
expand in cracks/ joints
• Freeze thaw weathering: Water freezes and thaws, the
cycle of expanding and contracting weakens the rocks
and allow deeper penetration
• Biological weathering: Molluscs, sponges, sea urchins
• Solution weathering: organic acids from organisms
• Slaking: Material disintegrated when exposed to water:
hydration cycle
• Mass movements

53. Marine Transportation/
Deposition
• Sediment sources vary in beaches
• Beach deposits, Offshore marine deposits,
river deposits, glacial deposits, materials
from mass movement, wind-blown
sediments/ artificial beach nourishment

54. Marine Transportation/
Deposition
• Beaches can be made of many materials
• Sandy beach, shingle beach, volcanic ash
beach
• Sediments are transported in 4 forms
• Like in river transports

55. Marine Transportation/
Depositions
• Bedload: Traction (dragging of large
materials) or saltation (discontinuous
jumping) – pebbles/ shingles
• Suspended loads: Turbulent flows carry
grains – silt, sand
• Wash loads: Clay/ dissolved materials in
constant suspension

56. Sediment Cell
• Coastal sediment budget/ cell is the
system of identification of sediments
sources and sinks
• Quantifications of amounts/ rates of
sediments erosion, transportation/
deposition within a defined area
• Helps engineers to project future shoreline
changes

57. CHARACTERISTICS AND
FORMATION OF COASTAL
LANDFORMS

58. Erosional Landforms

59. Cliffs
• Waves erode the base of the cliffs
• This creates notches
• It also leaves overhangs
• The overhangs soon collapse

60. Notches/ Geos
• These can form at the bases of steep cliffs.
• Usually located in the intertidal range where
wave energy is the strongest and most
concentrated.
• Wave action cuts a small depression at the
base of the cliff face.
• Water will continue to crash in the
depression, widening the gap.

61. Caves
• Caves can form at cliff bases or headlands
• The erosion of seawater creates caves
and caverns
• This landform may start as a small tunnel
before widening to form large caves
• Develop from notches and geos

62. Arches
• If the sea caves are formed at the base of
headlands, erosion may continue to the
point where the caves reach the other side
of the headlands
• Two caves formed at either side of the
headland will join to form arches.

63. Stacks
• Overhang of the arch soon collapses
• Leaving a tower-like landform disjointed
from the mainland

64. Stumps
• Stacks may be further eroded at bases
• This leads to the stack falling over
• Leaving a stump

65. Rocky Shores
• An intertidal area of sea coasts where
solid rocks predominate
• Biologically rich
• Consists of cliffs, platforms, pools, boulder
fields
• Most features are erosional
• Controlled by actions of tides, wind, wave
and insolation

66. Rocky Shores
• Variations in morphology due to:
mineralogy, lithology, tectonic history,
climate, wave actions, tidal ranges
• Rocky shores will consist of the platform
and the cliffs

67. Platforms
• Can be horizontal with steep sea ward
edge (Sub horizontal)
• Or gently sloping to the sea
• Sloping platforms: macro tidal range with
dominant wave action
• Sub horizontal platform: micro tidal range

68. Platforms
• Resistance platforms can be enhanced by
carbonate precipitation at limestone
formations of silica/ iron elsewhere
• Platform erosion occurs as a result of
waves and currents
• Chemical weathering plays an important
role in the sub-aerial processes

69. Cliffs Profiles
• Dip of the bedding affect cliff profiles
• Vertical dip = sheer cliff face
• Seaward dip = shelving cliffs prone to
landslide
• Model of cliff evolution will take in account
the dynamic between wave action and sub
aerial processes

70. Processes that impact rocky
shores
• Mechanical wave erosion
• Weathering
• Bio-erosion
• Mass movements

71. Mechanical wave erosion
Erosion Loose materials removed by wave
- Energetic wave
condition
- Microtidal range
Abrasion
Wave-induced flow with mixture of
sediments scour surfaces
- Soft rock for cliffs/
platforms
- Energetic waves
- Supply of sediments
(thin layer)
- Microtidal range
Hydraulic
Action
Wave-induce pressure, cavitation
widens rock cracks/ joints
- Weak rocks with joints/
bedding planes
- Energetic wave
conditions
- Microtidal range

72. Weathering
Physical Frost action/ cycle of wet-dry
- Cool climate
- Sedimentary rocks
Salt
Volumetric growth of salt crystals
widen cracks/ joints in rocks
- Sedimentary rocks
- Warm/ dry climate
Chemical
Carbonation
Hydrolysis
Oxidation
Hydration
Solution
- Sedimentary rocks of
specific mineral
compositions
- Warm/ wet climate
Water layer
leveling
Physical, salt and chemical
weathering combine in actions at
edges of pools
- Sedimentary rocks
- Warm/ wet climate with
high rate of
evaporation

73. Bio-erosion
Biochemical Chemical weathering caused by
products of metabolism
- Limestone
- Tropical climate
Biophysical
Burrowing
Grazing
Digging
- Areas of fair
biodiversity and
species abundance

74. Mass Movement
Rockfalls/
Toppling
Rocks fall/ roll straight down cliff faces
- Well jointed rocks
- Undercutting by waves
Slides Deep seated slope failures
- Deeply weathered
rocks
- Some moistures
- Serious undercutting/
loading
Flows Flow of loose materials
- Unconsolidated
materials or regolith
- Moisture
- Undercutting or loading

75. Composite Cliffs
• Cliffs that are composed of more than one
rock types
• Profiles of such cliffs may be influenced by
differential erosion
• Relative strength and permeability of such
rocks

76. Uniform cliffs
• Cliffs with uniform rock types
• Cliff recession will be steady and uniform
• Weaker rocks = faster retreats
• Glacial tills = fast retreats, vice versa for
granite

77. Cliff Profiles
• In composite cliffs, the interactions
between sub aerial processes and wave
actions are essential
• If weaker rocks overly stronger rocks, the
cliff will see higher erosion at the top of the
cliffs
• On the other hand, undercutting will cause
cliffs with underlying weak rocks to recede
fast

78. Permeability
• If permeable rocks overly, the cliffs risk
becoming prone to chemical weathering
and becoming saturated
• Such cliffs will e at risk of mass movement

79. Strata
• Strata dipping in land is more stable than
sea ward dipping strata

80. Bevelled Cliffs
• A cliff whose upper part has been trimmed to a relatively
low angle
• Formed under three stages:
1. Pre-glaciation
2. Glaciation
3. Post Glaciation

81. Pre glaciation
• Vertical cliff formed during the last
interglacial warm period
• Sea level higher than it is today

82. Glaciation
• Glacial period – water stored as ice onland
• sea level dropped
• solifluction/ freeze thaw trimmed upper
part of the cliffs
• Forms bevelled edge
• materials accumulate at the bottom wave
cut platform

83. Post-Glaciation
• Sea level rose again
• Renewed wave action erodes
accumulated material
• Steepen cliff base
• Leaves upper part at low angle

84. Coastal Platform
• Many experts claimed that the sea level
during post glacial time has not been
consistent enough to erode many of the
wave cut platforms around the world
• There is a theory that they are in fact
ancient relict of the time when sea level
was more consistent

85. Coastal Platform
• After isostatic recovery, some waves/ tidal
actions still have minor impacts
• Sub aerial processes within and above the
inter tidal ranges maintain the platforms

86. Depositional Features

87. Beaches
• The accumulation of materials deposited
between the High Water Mark (HWM) and
Low Water Mark (LWM)
• Typical beach has 3 zones: Offshore,
foreshore, backshore

88. Formation of Beaches
• Strengths/ characteristics of waves
determine the processes of deposition
• When waves bring sediments to shore,
those sediments can be deposited or held
in suspension

89. Sources of the sediments
• Longshore currents
• Headlands/ other landforms
• Corals/ other biological organisms

90. Wave Types
• For constructive waves: There are sufficient
periods between crests so that materials can
settle
• For destructive waves: periods between crests
too short – materials not allowed to settle and
taken away by drifts in suspension
• Stronger backwash also removes materials
• Constructive waves increase steepness
• Destructive waves make beaches more gentle

91. Role of sediments
• Eroded particles increase viscosity,
volume, density and abrasive quality of the
water
• So turbid water also increase erosive
power of wave

92. Role of sediments
• Beaches with larger particles allows
greater percolation, reducing power of
backwash and maintaining steepness
• Beaches with compact sand allow more
defenses against wind and wave erosion

93. Deposit forms
• Littoral deposits will drop at foreshore
zones where wave energy remains higher
• High turbidity in coastal areas increase
rate of attrition and allows for formation of
neritic deposits
• Neritic deposits are found offshore where
energy is only consistent above wave
bases

94. Berm
• Fine, dry deposits found above the HWM
• Can be deposition from storm waves or
relicts from when sea level was higher
• It is usually sloping
• May have dunes

95. Shingle Ridges
• Ridges of coarse materials pushed up by
spring tides or storm waves
• Far above the HWM
• May form storm beaches

96. Cusps
• Can be caused by scalloped edges of
swash
• Actions of two wave fronts from opposite
directions
• Usually has arches of coarse materials

97. Cusps
• Cusps are self perpetuating
• Swash can be broken, concentrating
energy on the cusps but allowing
deposition of fine sediments at the
embayment
• Cusps: Develop in high tidal range –
waves approach shore at right angle

98. Fulls
• Ridges of sediments pushed up by
constructive waves
• Run parallel to water line
• Varies with height of tides

99. Swales
• Troughs/ depressions
• Separate fulls

100. Bayhead Beach
• Sediments are deposited in bay area due
to low energy
• Sediments can come from nearby
headlands
• Beaches will be more stable due to lower
wave action
• More of a closed system with less waves/
currents

101. Offshore Bars
• Long narrow ridge of materials lying
parallel to the coasts
• Friction of low lying shoreline may cause
wave to break early
• Materials are deposited
• Once initiated the ridge self perpetuates
by causing waves to break more
• Offshore bars may grow and form lagoons

102. Swash-aligned coasts
• Oriented parallel to crests of prevailing
waves
• Closed system
• No longshore drift
• No littoral drift

103. Drift-aligned coasts
• Oriented obliquely to the crest of the
prevailing waves
• Controlled by longshore drift processes
• May lead to formations of spits, bars,
tombolos

104. Localized Depositional Features
• Spit
• Creeks
• Bars
• Tombolo
• Cuspate forelands
• Offshore Bars
• Barrier Beaches
• Coastal Dunes
• Saltmarshes
• Mangroves

105. Conditions for depositional
features
• Abundance of shingles and sands
• Irregular/ transverse coastline
• Vegetation
• Estuaries and main rivers

106. Spit
• Develop at indented coastlines with bays
or estuaries
• Wave energy reduced in those areas
• Sands are deposited in the direction of
longshore drifts
• Drift-aligned features
• Always joined at one end to mainland

107. Spit
• Refracting waves can give spits curved
ends
• Recurved spits and recurved compound
spits can be formed
• The area between spits and mainland may
become saltmarshes

108. Creeks
• Sediments accumulate in the marshes
• Yet channels still exist
• These are called creeks

109. Bars
• A ridge of materials connecting two
headlands
• Spits continuing to grow
• Onshore movements of materials can also
form bars

110. Tombolo
• A ridge linking an island to the mainland
• Wave refractions form spits
• Grow to link up to the islands
• Wave refractions/ diffractions cause more
deposition around the islands

111. Cuspate foreland
• Shingle ridges deposited in triangular
shape
• May be a result of two sets of storm waves
• Can also be two spits joining

112. Barrier beaches
• Gently sloping/ low lying coasts
• Beaches/ ridges/ dunes form at the
continental shelves
• Sea level rose and flood areas behind
dunes
• A lagoon is formed
• Landward migration of barrier beaches
begin

113. Coastal Dunes

114. Coastal Dunes
• Form when there is:
• Reliable supply of sand
• Strong onshore wind
• Large tidal range
• Vegetation to trap sand

115. Formation
• Onshore wind transports dry sands inland
• Vegetation slows down wind by friction
• Sands trapped by vegetation
• Forms small piles of sands

116. Formation
• Create more substantial wind breaks
• Cause more sand deposits
• High wind speed means dunes move
inland, low wind speed means it remains
static
• High supply of sand encourages formation
of new dunes seaward

117. Sand dunes succession
• Salt spray from sea makes the dune’s
ecology harsh
• Rotting seaweeds may provide nutrients
• Plants like marram grasses are adapted
• Young dunes: yellow dunes
• Grey dunes: high humus content

118. Sand Dunes Succession
• Coastal Sand dunes (psammoseres) – provides
habitats for plants/ animals
• Closer to beach conditions are harsh due to lack
of moisture/ nutrient and salt spray, wind
abrasion and instability
• Toughest pioneer plants dominate it: marram
• As dunes move inland, more species appear
due to increases in moisture, nutrient and
humus content

120. Pioneer - Foredunes
• Sand crouch grass/ Lyme grass
• Tolerant to salt – waxy coating to retain
water
• Roots bind sand producing more stable
wind break
• Increase in sand deposits may soon bury
the grasses

121. Yellow Dunes
• As Dunes move further back, the less
tolerant but stronger marram grass takes
over
• Marram grasses grow quickly and reach
out from dunes
• Plants may grow in patches
• As wind speed reduces due to increase
dune height, evapotranspiration reduces,
increasing moisture

122. Grey Dune
• Plants cover the dunes in continuous
pattern by now
• Humus layer from decaying vegetation
help retain moisture
• Grey-green lichens colonize the dunes
• Shells provide supply of calcareous
materials

123. Grey Dune
• Rain water leaches the nutrient making
dunes acidic
• High quantity of quartz grain makes soil
acidic

124. • http://www.countrysideinfo.co.uk/successn
/primary2.htm
• http://www.landforms.eu/Lothian/dune%20
succession.htm

125. Saltmarshes

126. Saltmarshes
• Occurs on low-energy shorelines
• Temperate, high latitudes
• Characteristic depends on sedimentation and
subsidence rate
• Mud/ sand flats nourished by sediments from rivers/
streams
• Embankments, estuaries, barrier islands and spits
• Mangroves in tropics – subtropics (Salt tolerant trees
instead of herbaceous plants)

127. Saltmarshes
• Low topography – low elevation – vast wide
areas
• Popular to human population
• Deltaic marshes, estuarine marshes, back-
barrier marshes, open coast marshes,
embayment marshes, drowned valley marshes

128. Formation
• Tidal flats gain elevation from sediment
accretion
• Rate/ duration of tidal flooding decreases
• Plants/ pioneer species colonize exposed
surface
• Rivers and streams arrive – rate of
discharge reduces due to low gradient –
more sediments settle

129. Formation
• Filamentous blue-green algae fix silt/ clay
• Increase erosion resistance of sediments
• Assists sediment accretion
• Roots of plants retain sediments from rising tides
• Creating a sediment terrace
• Reduces depths of and duration of flooding
• Allowing other plant communities to grow

130. CORAL REEFS

131. Corals
• Corals are made up of organisms called
polyps
• They have mineral (calcium) skeleton
• Symbiotic relationships with the
Zooxanthellae – photosynthesize and pass
food to the corals
• This supply of food allows corals to grow
into massive reefs structures

132. Development of Coral
• Begin as polyps (like sea anemones)
• Attach themselves to hard surfaces in shallow
seas (sufficient light)
• Polyps exude calcium carbonate  forms
skeleton
• Zooxanthellae grow inside the polyps
• Zooxanthellae gets shelter
• Polyps get photosynthesis
• Symbiotic relationship

133. Rate of Growth
• Tropical reefs: 2.5 – 60 cm per year
• This can form huge structures
• The oldest/ largest living systems on earth

134. Conditions required
• Temperature
• Depth
• Light
• Salinity
• Sediment
• Wave action
• Exposure to the air

135. Types of Corals
• Fringing reefs
• Atoll reefs
• Barrier reefs
• Patch reefs

136. Fringing reefs
• Directly attached to a shore – borders it
with intervening channels/ lagoons

137. Atoll reefs
• Circular/ continuous barrier reef extends
around a lagoon without a central island

138. Barrier reefs
• Reef separated from mainland by deep
channel/ lagoon

139. Theories of Origins
• Most of the Corals today are formed in the
last glacial period
• Changes in sea levels during the
Pleistocene is usually taken into account

140. Darwin-Dana - Subsidence
• Darwin observes that coral polyps flock together
and grow upward
• Thus fringing reef grows from the bases of the
volcanic islands, stopping at low tide level
• Land begins to subside due to tectonic forces
• However reefs continue to grow from the bases:
bedrocks

141. Darwin-Dana Subsidence
• Reefs cannot survive in deep water – must grow
• Reef grows slow near coast but vigorous away
from coast
• A lagoon is formed, and reef is now barrier
• Sediments accrete on the lagoon – keep land
level constant
• Original island fully subside, leaving an atoll

142. Evidences for
• Data from deep drilling confirms that corals do
grow on bed rock
• Bikini atolls in the Pacific Ocean
• Positive correlation age of corals and ocean
depths
• Submerged valley east Indonesia
• Subsidence explains why corals are not buried
by sediments – they accumulated at subsiding
lagoon bottom

143. Evidences Against
• Some areas of reefs, such as Timor, show no
evidence of subsidence
• Some lagoons with depths of 40 – 45 m but wide
lagoon cannot be explained by subsidence
• Some barrier and fringing reefs grow close
together – subsidence is a continuous process
and should affect them at equal stages

144. Murray – Stand Still Theory
• Corals grow on submarine platform
• No change in sea level
• No subsidence or uplift
• Submarine platform is either eroded by
wave action or had sediments deposited
on
• Coming up to an optimum depths

145. Murray – Stand Still Theory
• Corals start growing
• Starting with fringing reefs
• Grow outward to form barrier reefs
• And then atoll

146. Evidence For

147. Evidence Against
• Submarine platforms are not common
• Optimum depth indicated in the theory is
not universal
• Without subsidence, lagoon should’ve
been filled with deposits
• Marine deposition and erosion at the given
depth is contradictory

148. Daly
• Corals formed during the Pleistocene ice
age
• Corals die after fall in sea level
• This leaves a wave cut platform made of
the coral limestone
• Sea level rises again
• This allows reefs to grow from the wave
cut platform

149. Daly
• At narrow platforms, fringing reefs grow
• Broader platforms see growth of barrier
reefs
• Isolated island peaks saw growth of atoll

150. Value of Corals
• Coastal protection
• Biodiversity
• Economic
• Social

151. Coastal Protection
• Reefs have the effects of causing waves
to break offshore
• This reduces the erosive effects of wave
breaking on shore
• They also slow down storm waves and
surges
• Protect mangroves and sea grasses from
erosions

152. Biodiversity
• Rainforest of the sea
• Highly productive ecosystem
• Some animals feed on sea grass
• Some may use corals as shelters/
protection/ breeding
• Reef biomass and species diversity
positively correlated

153. Economics
• Role in the fishery industry
• Role in the Tourism industry
• Source of raw materials
• Role in the conservation industry

154. Fishery industries
• Corals provide habitats for fishes and
other marine animals
• They may be important to fishing
industries and aquaculture
• Subsistence livelihood may be directly
dependent on this

155. Tourism Industry
• Southeast Asian Reef System and Great
Barrier Reef
• In the former, LEDCs depend on Coastal
tourisms
• Aesthetic quality of reefs and biodiversity
are important to the economy
• Since tourism makes up a large proportion
of some country’s economic sector

156. Source of Raw Material
• Although most corals are being conserved,
they can also be mined for limestone
• High biodiversity means possibilities of
researches
• For medicines, genetic alleles etc.

157. Social Importance
• Many atolls – Timor, Maldives, Philippines,
Australia are home to indigenous
population
• In Maldives, sea level changes and
erosion threaten many atolls
• Tsunamis can destroy vast areas of reefs

159. Cultural Importance
• Parts of the livelihood of indigenous
population
• Many hunt and fish at corals
• The area has formed a part of their
indigenous cultures

160. Threats to coral reefs
• Changes in sea temperature and
bleaching
• Pollution and Sedimentation
• Fisheries and transports
• Invasive Species
• Eutrophication and Red Tide
• Tourism
• Overfishing

161. Sea temperature
• Global warming cause rises in sea temperature
• El Nino such as the one in 2016 can cause
changes in temperature
• This is beyond Coral’s optimum
• Relationship between corals and Zooxanthellae
broke
• Corals lose their white colors – bleaching
• Makes them more susceptible to diseases

162. Ocean Acidification
• CO2 released into the atmosphere
• Combines with water to form Carbonic
acid
• Acidic water can dissolve the calcium
carbonate skeleton

163. Pollution and Sedimentation
• Water pollution encourages invasive
species
• Makes water toxic and reduce biodiversity
• Reduces nutrients level
• Oil spill can block sunlight and prevent
photosynthesis
• Releases of nutrients and fertilizers can
lead to overgrow of algae

164. Pollution and Sedimentation
• This leads to eutrophication and red tide
• These organisms can ‘steal’ reefs’
nutrients
• Sedimentation from sea floor dredging,
sand mining or coastal construction can
make water murky
• Blocks sunlight for corals

165. Tourism
• Tourism encourages boats which may
release oil
• Careless tourists may stunt coral growths
by touching them
• In some cases bring home as souvenirs

166. Invasive Species
• Crown-of-Thorn Starfish
• May thrive in polluted water
• Eat corals
• Steal nutrients

167. Overfishing
• Reduce biodiversity
• Bombs to kill fishes can damage reefs

168. Coral bleaching
• When higher water temperature leads to
severing of symbiotic relationship between
Zooxanthellae and polyps, thus corals lose
their colors, leaving white skeletons

169. 1998 bleaching
• 1998, coral bleaching reported all over the world: Pacific,
Indian, Red, Mediterranean, Caribbean
• Indian corals most severely impacted
• Affected up to 50 m at depth
• The first globalized event
• Coincident with high sea temperature
• Unclear what caused rise (could be El Niño but link
unclear for Indian ocean)
• Global warming mentioned
• However, noted that other factors weakened reefs

170. 2004 Global assessment

171. Initiative in Climate Change and
Coral Reefs 2010

172. 2011 Assessment

173. Climate change, coral and
people

174. Evidence of climate-change
damage to coral reefs

175. Management strategies to
protect coral reefs

176. SUSTAINABLE MANAGEMENT
OF COASTS

177. Management
• Defense against flooding, erosion and sea
water encroachment
• Large number of population occupy
coastal zones – need protections
• Rich I resources and economically
significant

178. Shoreline Management Plans
• Large scale assessment of risks
associated with coastal processes and
helps to reduce these ricks to people and
the developed historic and natural
environment

179. Coastal defense
• Engineering methods to defend against
erosions
• May be hard engineering or soft
engineering

180. Human Activities and Coastal
Zones Problems

181. Urbanization and Transport
• Can release sediments by dredging
• Disrupt sediment cells
• Urbanization means mining for sands
• Loading of nearby cliffs
• Increase in domestic pollution
• See Case Studies for more

182. Agriculture
• Using of coastal land areas e.g.
Saltmarshes/ Mangroves for aquaculture
• Releases of fertilizers
• Eutrophication/ redtides

183. Tourism and Recreation
• Can damage coral reefs
• Increase domestic pollution
• Transportation need

184. Fisheries/ Aquacultures
• Aquaculture: Use land area
• Boats release oil
• Trawls/ nets damage reef systems

185. Industry
• Release of pollutants
• Chemicals and toxic materials

186. Hard-Engineering

187. Cliff-base management
• Defense of waves

188. Seawalls
• Wall used to defend against wave action
• Static feature going against the natural dynamic
• Used in high energy coastline
• Physically stop erosive actions of waves
• The fact that it goes against natural dynamics
mean erosional problems increase elsewhere
• Sea level rises can render sea walls useless

189. Seawalls
• They are expensive to maintain
• They are not vetted for extreme storm
events
• Calculation of wave strengths do no take
in account outliers
• Unappealing to tourists

190. Revetments
• Sloping structures placed on cliffs to absorb energy of
incoming waves
• Defend against crashing waves
• Low Cost
• Wooden revetments were used, now replace by
concretes
• Not effective in storms
• Regular maintenance required
• Make beaches inaccessible
• Unappealing to tourists

191. Gabions
• Cage or box filled with rocks and
concretes
• They have strong structures
• Can conform to subsidence
• Dissipate energy of flowing water/ resist
washing away

192. Gabions
• Low cost – easily constructed
• Flexible
• Unappealing to tourists
• Labor intensive

193. Groynes
• Low wall built out in the sea to check
erosion and drifting
• Effective in reducing longshore
• But a direct intervention in the sediment
cell transport

194. Rock armour
• Like seawall made of rocks
• Take a lot of budget to construct
• Labor intensive
• Beach is allowed
• Absorb energy of waves effciently

195. Offshore breakwaters
• Large stone structures that intercept
waves
• Causing them to break before reaching
shores
• Can lead to accretion of sediments
offshore

196. Rock Strong Points
• Like groynes rocks dumped to create
artificial headlands – reduce longshore
drifts
• Cheap to build
• Easily repaired
• Disrupt downdrift

197. Cliff-face strategies
• Cliff drainage: Reduce possibilities of
slope becoming saturated
• Increases sheer strengths
• Cliff grading: Reducing possibilities of
failures by angle

198. Soft-Engineering

199. Offshore Reefs
• Coral reefs act as natural breakwater
• Slows down wave and make them break
offshore
• Reduces coastal erosion
• But natural and may not directly disrupt
system

200. Beach Nourishment
• Using sand to fill up beaches
• May be expensive due to the need to
transport and purchase sand
• Does not disrupt natural system
• Disrupt natural system
• Short term solution as sand will be eroded
still

201. Managed Retreats
• Solves the problem in reducing human
costs
• However repaid with economic costs
• Cannot fully apply with the lower economic
classes who cannot afford land inshore
• Take away livelihoods of fishermen

202. Acceptance
• Letting nature takes its course
• Adapting to the situation
• Political unappealing
• May induce migration to other areas
• Does not solve the problem

203. Red-lining
• Planning permissions for certain areas
closer to coasts not allowed
• This is not full use of lands – politically and
economically unsound
• However conservation-wise, highly
effective
• Very cost effective